united states proceedings of the iufro technical session on · 2014. 10. 29. · the proceedings...

United States Department of Agriculture Proceedings of the IUFRO Pacific Southwest Research Station Technical Session on General Technical Report PSW-130

Geomorphic Hazards in Managed Forests August 5-1 1, 1990 Montreal, Canada

Rice. Ravmond M.. technical coordinator. 1991. Proeeedlncs of the IUFRO technical session - on geomorphic hazards in managed forests: 5-1 I August 1990: Montreal, Canada. Gcn. Tech. Rep. PSW-GTR-130, Berkeley, CA: Pacilic Saulhwest Research Slslion, Form Service, U.S. Department of Agriculture; 82 p.

The proceedings contains I I of the 17 papers presented at the technical session on reamorehic hazards in manaeed forests at the XIX World Conmss. International Union ol - - " Foreslry Research Organizations, August 5-11, 1990, Montreal, Cmuda, plus o m paper no1 presented orally. Two papers report research on lorrents, two are about snow, three concern landslides, and five discuss watershed management problems.

Relrieval Temrs: natural disasters, torrent control, watershed management, landslides, snow, avalanches, floods, erosion

Technical Coordinator:

RAYMOND M. RICE was, before his retirement, chief hydralogisl in the Effects of Forest Management on Hillslope Processes, Fishery Resources, and Stream Environmenls Research Work Unit, at the Slation's Redwood Scicnces Labomtary, 1700 Bnyview Drive, Arcata, CA 95521-6098.

Authors assumed full responsibility for the submission ol camera-ready manuscripts. Views expressed in each paper are those of the authors and not necessarily those of the sponsoring organizations. Trade names and commercial enterprises are mentmed solely for inlamation and do not imply endorsement of the sponsoring organizations.

Publisher:

Pacific Southwest Research Station P.O. Box 245 Berkeley, California 94701

December 1991

Proceedings of the IUFRO Technical Session on Geomorphic Hazards in Managed Forests August 5-1 1, 1990, Montreal, Canada

Raymond M. Rice, Technical Coordinator

Contents

... ...................................................................................................................................................................................... Foreword 111

Invited Papers .............................................................................................................................................................................. 1

. . .............................................................................................................. Severe Snow Loads on Mountain Afforestation In Japan 1

Ryazo Nifln, Yoslzio Ozeki, mid Slioichi Nibvnno

Priority Setting for Government Investment in Fosestly Conservation Schemes- An Example f1-0111 New Zealand .................... 6 Colin L. O'Louglilin

Voluntary Papers ....................................................................................................................................................................... 11

.................................................................................................................... Effect of Tree Roots on Shallow-Seated Landslides 1 L

Ka7rttokiAbe m ~ d Robert R. Zie~ner

...................................................................... Watershed Concerns and Recent Policy Formulat~ons in Sri Lanka and Australia 2 I

Rohan Ekannyake

Sul~ounding the Consequences of Watershed Disasters in the Periphety of the Indian TI-iangle ................................................. 28

Roha~i Eknnnyake

High-speed High-Stress Ring Shex Tests on Granular Sods and Clayey Soils .......................................................................... 33 Hiroshi Fukuokn mid Kyoji Snssa

............................. .................................................... Morphological Study on the Prediction of the Site of Surface Slides ... 42

Hiromasa Hiurct

........................................................................................ Experimental Study ou Impact Load on a Dam Due to Debris Flow 48

hvno Miyoslii

..................... .............................................. Sediment Dynamics of a High Gradient Stream in the Oi River Basin of Japan .. 56

Hideji Maita

USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991.

Contents

. ...................... .......................... Snow-Cover Condition in Japan and Damage of the Sugi (C~yptomeria Jnponica D Don) ... 65

Taira Hidenki

. ................... ............................... Study on Shearing Force and Impact Force of a Volcanic Mud Flow on Mt Sakurajimn ... 72

Yoshinobu Taniguclzi

Research of Wind Erosion lnlensity in the Region of Subotica-Horgos Sands ......................................................................... 79 Velizm Velasevic and Lj~honzir Lefic

USDA Forest Service Gm . Tech . Rep . PSW.GTR.130 . 1991 .

Foreword

The Technical Session of the Subject Group on Natusal Disasters was held on the afternoon of August 7, 1990 as part of the XIX World Congress of the lnlernational Union of Forestry Research Organizations in Montreal, Canada. About 35 scie~i- lists representing 10 nations were in attendance. Seventeen papers were presented, addressing the topics of all four Working Pxties in the Group. Two papers reported research on torrents, three were about snow, five concerned landslides, and seven

USDA Forest Service Gcn. Tech. Rep. PSW-GTR-130. 1991.

discussed watershed management problems. Four of the invited papers can be found in Volume 1 of the Proceedings of Division I , and two are in this volume. The remainder of this volume includes nine of the contributed papers presented at the technical session plus one that was not orally presented. 11 is hoped that this volume, together with others supported by the Subject Group in recent years, will foster increased understanding of natural disasters in forested environments.

Raymond M. R~ce, Leader I W R O Subject Group S1.04 Proceedings Technical Coord~nator

Severe Snow Loads on Mountain Afforestation in Japan1 Ryuzo Nitta, Yoshio Ozeki, and Shoichi Niwano2

Abstract: A s i m p l e d e v i c e f o r e s t i m a t i n g snow s e t t l i n g f o r c e on t r e e b ranches was used t o d e t e r m i n e t h e d i s t r i b u t i o n of snow s e t t l i n g f o r c e a t v a r i o u s h e i g h t s i n a snowy mountainous r e g i o n i n Japan . A t r a p e z o i d a l d i s t r i b u t i o n o f snow s e t t l i n g f o r c e was found t o e x i s t a t a l l s i t e s t e s t e d . It i s t h o u g h t t h a t a zoning scheme based on t h e damaging p o t e n t i a l o f snow on young man-made f o r e s t s would become p o s s i b l e , wi th t h e a c q u i s i t i o n of

One o f t h e l a r g e s t problems i n Japanese f o r e s t r y l i e s i n t h e low s u r v i v a l r a t e o f young man-made f o r e s t s i n t h e heavy snow a r e a s . I t i s r a r e t o s e e a b e a u t i f u l c o n i f e r p l a n t a t i o n where snow r e a c h e s o v e r 4 m i n d e p t h because of mechanical damage caused by l a r g e snow p r e s s u r e . Both on f l a t l o c a t i o n s and g e n t l e s l o p e s , snow s e t t l e m e n t c a u s e s b ranch and s tem deformat ion which o f t e n b r i n g s f a t a l b reakage . To d e c r e a s e such u n s u c c e s s f u l p l a n t i n g s much b a s i c d a t a f o r f o r e s t zoning a r e i n d i s p e n s a b l e . Out of such n e c e s s i t y t h e a u t h o r s have d e v i s e d and s e t new snow p o l e s i n mountains t o o b t a i n t r ee -deforming f a c t o r s s u c h as maximal snow d e p t h and snow s e t t l i n g f o r c e wi thou t b a t t e r i e s o r power Supply. The d a t a from t h e new snow p o l e s e x p l a i n t o u s how s e v e r e l y snow l o a d s work on young t r e e s .

DAMAGES TO CRYPTOMERIA I N SNOW REGIONS

The F o r e s t r y and F o r e s t P r o d u c t s Research I n s t i t u t e h a s a l o n g e s t a b l i s h e d snow exper iment s t a t i o n a t Tokamachi C i t y i n N i i g a t a P r e f e c t u r e , C e n t r a l Honshu. The Tokamachi S t a t i o n i s e n c i r c l e d by t h e snowy Naeba Mountains i n which t h e a u t h o r s have surveyed many c o n i f e r p l a n t a t i o n s of

l p r e s e n t e d a t t h e S u b j e c t Group 51.04 T e c h n i c a l S e s s i o n on Geomorphic Hazards i n Managed F o r e s t s , X I X World F o r e s t r y Congress , I n t e r n a t i o n a l Union of F o r e s t r y Research O r g a n i z a t i o n s , August 5-11, 1990, Montreal , Canada.

2 ~ o r e s t r y and F o r e s t P r o d u c t s Research I n s t i t u t e , Tsqkuba Nohrin, I b a r a k i , Japan .

CrvDtomeria D . Don. ( Japanese c e d a r ) F i g . 1 . The t y p e s o f snow damage t o Cryptomeria [ Iwatsubo and N i t t a 19871 a r e shown i n F i g . 2 . S t r a i g h t stems have much h i g h e r market v a l u e t h a n crooked s t e m s . T h e r e f o r e i n f i e l d su rvey , t h e a u r h o r s c l a s s i f y e v e r y c r y p t o m e r i a t r e e t o

The Japan Sea

7DOm

A

F i g . l--The s i t e s su rveyed . C i rc le : Snow s e t t l e m e n t r e c o r d e r T r i a n g l e : P l o t of Cryptomeria

F i g . 2--Damage t o Cryptomeria caused by snow l o a d s .

USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991

Table 1 C l a s s d i s t r i b u t i o n of Cryptomeria a t p l o t s of v a r i o u s a l t i t u d e s .

Altitude Age Share Height Max. snow Altitude m a .s .1 . yr A+B(pct) of B m depth m m a . s .1 .

*Mean of unsusceptible t r e e height (meter)

t h e f o l l o w i n g f o u r t y p e s : A : Middle and upper s tems i s s t r a i g h t .

Normal v a l u e . B : Middle and upper s tems a r e crooked,

o r t h e y have t r a c e s of recovery from s tem t o p b reakage . Lower v a l u e .

C : T i l t e d and crooked s tem w i t h lower t r e e h e i g h t . NO v a l u e .

D : Stem w i t h b reakage o r l a r g e bending, t o t a l l y s u p p r e s s e d o r dead i n n e a r f u t u r e . NO v a l u e .

Unless t h e p r o p o r t i o n o f t r e e s i n c l a s s e s A and B r e a c h e s 50 p e r c e n t i n a su rveyed p l o t (20 m by 20 m) when t h e t r e e h e i g h t r e a c h e s t w i c e t h e mean of maximal snow d e p t h , t h e p l a n t i n g would end i n f a i l u r e [ S h i d e i 19541.

Table 1 shows t h e r e s u l t of p l o t s u r v e y s o f Cryptomeria s t a n d s on f l a t s i t e s a t s e v e r a l a l t i t u d e s . The t r e e s a t t h e 1250 m l e v e l would r e c e i v e much more snow damage i n t h e f u t u r e because t h e i r crowns c o u l d n o t p r o j e c t o v e r t h e snow s u r f a c e f o r t h e n e x t f i v e - y e a r p e r i o d , though t h e y show a l a r g e r s h a r e o f A + B a t t h e age o f 15 . I n s h o r t , a l l o f t h e man-made f o r e s t s surveyed would b r i n g no wood market v a l u e i n t h e f u t u r e .

INDICATIONS OF SNOW SETTLEMENT

Lower b ranches a r e o f t e n b e n t down due t o p a r t i a l d e s t r u c t i o n of t h e i r b a s e s by heavy snow pack ing and s e t t l i n g ( F i g . 3 ) . The h e i g h t above ground o f t h e h i g h e s t ben t b ranches i n d i c a t e s t h e maximal snow d e p t h . T h i s de format ion i s b e i n g reproduced by a n i n e x p e n s i v e r e c o r d e r f o r maximal snow d e p t h i n Japan . The r e c o r d e r c o n s i s t s o f a p o l e w i t h h o r i z o n t a l "branches" made o f s o f t m e t a l f i x e d a t e v e r y 10 cm h e i g h t increment [Takahashi K . 19681 .

Long t e r m snow s e t t l i n g c a u s e s t h e bend ing n o t o n l y of t h e h i g h e s t b ranches ,

F i g . 3--Snow damage t o a Cryptomeria s t a n d .

b u t a l s o o f t h e lower b r a n c h e s . I f t h e b e n t a n g l e s of t h e b ranches from t h e h o r i z o n t a l d i r e c t i o n show g r e a t v a r i e t y a c c o r d i n g t o above-ground h e i g h t , t h e a n g l e s would i n d i c a t e t h e d i f f e r e n c e o f snow s e t t l i n g power o f t h e l a y e r s which c a t c h and deform t h e b r a n c h e s .

To o b t a i n more i n f o r m a t i o n on snow l a y e r s e t t l i n g , 20-cm long g a l v a n i z e d i r o n w i r e s o f r e g u l a t i o n q u a l i t y were f i x e d h o r i z o n t a l l y t o a 5-m t a l l p o l e a t e v e r y 20-cm h e i g h t i n c r e m e n t . L a t e each f a l l , t h e s e p o l e s w i t h h o r i z o n t a l w i r e s were s e t and, a f t e r t h e snow mel ted , t h e a n g l e s t h a t t h e w i r e s had been b e n t down by snow s e t t l i n g were measured ( F i g . 4 ) .

F i g . 4--Snow s e t t l i n g r e c o r d e r .

USDA Forest ServiceGcn. Tech. Rep. PSW-GTR-130. 1991

Table 2 Average t e m p e r a t u r e d u r i n g snow season a t Tokamachi Expt . S t n .

~ e a s o n Dec Jan Feb Mar AD r Mean

The w i r e was c a l i b r a t e d by l o a d i n g i n t h e basement of Tokamachi S t a t i o n where room t e m p e r a t u r e s t a y s a t around O°C d u r i n g t h e whole w i n t e r (Tab. 2 ) . P o i n t l o a d s w e r e a p p l i e d a t t h e f r e e ends of 20-cm long c a n t i l e v e r s f o r 150 days c o n t i n u o u s l y d u r i n g w i n t e r , and a f t e r t h a t t h e b e n t down a n g l e s were measured ( F i g . 5 ) . The c a l i b r a t i o n c u r v e i n r e l a t i o n t o wire d i a m e t e r , a n g l e and p o i n t l o a d , shown i n F i g . 6 , p r o v i d e s u s a good i n d i c a t i o n o f d i s t r i b u t i o n of snow s e t t l i n g f o r c e a l o n g t h e v e r t i c a l p r o f i l e o f t h e snowpack.

The d a t a o f t h o s e a n g l e s i n w i n t e r 1982/83 i n d i c a t e a f e a t u r e common t o t h e f i v e p r o f i l e s , t h a t i s , a t r a p e z o i d a l d i s t r i b u t i o n o f t h e a n g l e s ( F i g . 7) . The w i r e s p l a n t e d a t between +60 c m above ground and -40 cm from t h e h i g h e s t snow s u r f a c e of t h e season were b e n t a t a l a r g e b u t a lmos t c o n s t a n t a n g l e i n each c a s e .

0 I 2 3 4 5 6 P O I N T L O A D ( k g )

F i g . 6--The c a l i b r a t i o n c u r v e i n r e l a t i o n t o w i r e d i a m e t e r , bent-down a n g l e and p o i n t l o a d ( a p p l i e d a t t h e f r e e end o f 20-cm long c a n t i l e v e r s ) .

t h a t t h e a n g l e i n t h e middle l a y e r s of t h e former i s abou t 5 d e g r e e s g r e a t e r t h a n t h a t of t h e l a t t e r .

By p i c k i n g s i t e s where t h e average b e n t a n g l e i n t h e middle l a y e r s exceeded 60 d e g r e e s , and s i t e s where t h e maximum snow h e i g h t exceeds 4 m, T a b l e 3 i s o b t a i n e d . I t i s c l e a r from t h i s t a b l e t h a t ex t remely s e v e r e c o n d i t i o n s p r e v a i l a t a l t i t u d e s o v e r 700 m .

Cons ider ing Tab les 1 and 3, it i s p o s s i b l e t o a p p l y a zoning i n t h i s r e g i o n , a c c o r d i n g t o which a l t i t u d e s of 700 m and o v e r a r e u n s u i t e d t o economical f o r e s t p l a n n i n g .

F i g u r e 8 i n d i c a t e s t h a t maximum snow d e p t h a t t h e 1360 m a l t i t u d e s i t e i s about 1 m d e e p e r t h a n t h a t a t 500 m a l t i t u d e and

Although l i t t l e d a t a i s a v a i l a b l e a t t h e p r e s e n t , a zoning scheme b a s e d on damaging p o t e n t i a l s h o u l d become p o s s i b l e i n t h e f u t u r e by c o l l e c t i n g l a r g e amounts of d a t a on damaging p o t e n t i a l index w i t h

Tab le 3 S e v e r i t y of f o r e s t r y environment b a s e d on max. snow d e p t h and b e n t a n g l e .

F i g . 5 - - C a l i b r a t i o n o f t h e wires by l o a d i n g .

Winter 200 500 700 900 1100 136Q

1982/83 A+B A ava A+B 83/84 A A+B A+B A+B A+B A+B 84/85 A+B A A

A : Angle more than 60 degrees Diameter o f wire: 3 . 2 mm

B : Max. snow depth more than 4 m ava: Snow p o l e l o s t by avalanches.


3 m

TOKAMACHI KOSHlCHlGAWA YAHABUSHIYAMA MYOHO KOMATSUBARA 1

Fig. 7--Distribution of the wire angle along the vertical profile. Data for winter 1982/83 at five altitudes.

Wire diameter: 3.2 mm x : S-side of snow pole

- - : N-side of snow pole

1360m a.s.1. (Komatsubara)

351 86

X X

x * L li

X

X * X Y I X X x X * X I

* X

f - 60 90 deg.

30

500m a d . (Koshichigawa)

U-w.J-4

10 60 90 deg.

Fig. 8--Distribution of the wire angle along the vertical snow profile. Four season data at the sites on 1360 m and 500 m a.s.1.

Wire diameters: x x : 4.0 mm 0-0: 3 . 2 mm

USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130.1991

t h e s i m p l i f i e d method s t a t e d above. I n such b e l i e f , d a t a i s p r e s e n t l y b e i n g a c q u i r e d i n s e v e r a l r e g i o n s i n Japan [Takashino and Wakabayashi 1975; N i t t a e t a l . 1982 and 19841.

REFERENCES

Iwatsubo, G . and N i t t a , R . 1987. Snow. I n [ S h i d e i , T. e d i t e d : F o r e s t P r o t e c t i o n . 48,Asakura Shoten, Tokyo.]

N i t t a , R . , Ozeki, Y . and Niwano, S . 1982. Development of s i m p l e snow s e t t l i n g r e c o r d e r . Trans , Jpn . Soc. Snow and I c e . 147.

N i t t a , R . , Ozeki, Y . and Niwano, S . 1984. Height i n d i c a t o r o f b ranches s u s c e p t i b l e t o s e t t l i n g snow. Proc . 95th J p n . F o r . Soc . 313-314.

S h i d e i , T. 1954. On t h e snow damages o f f o r e s t t r e e s by snow p r e s s u r e . Res . B u l l e t i n Government F o r e s t Exp. S t n . 73. 1-89.

Takahashi . K . 1968. On t h e snow s c a l e f o r measur ing maximum snow d e p t h . Seppyo 30. 1 1 1 - 1 1 4 .

Takashino, K . and Wakabayashi, R . 1975. Wire ( b r a n c h model) de format ion by snow s e t t l i n g . Trans , J p n . Soc. Snow and I c e . 105.

( A l l p a p e r s w r i t t e n i n Japanese)

USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991

Priority Setting for Government Investment in Forestry Conservation Schemes-An Example from New Zealand1 Colin L. 0'Loughlin2

Abstract: In New Zealand responsibility for funding flood protection and erosion prevention and control projects rests largely with local regional authorities. However, in 1988 Central Government decided to provide direct funding for a major forestry conservation scheme in the erosion-susceptible East Coast region. Government's investment decision was influenced by a number of factors, the most important being the extent and severity of erosion in the East Coast region and its negative impact on the region's social and economic development.

A large part of New Zealand's wealth depends on pastoral farming. Pastoral land occupies 7.5 million hectares or 28 percent of the country's land surface, much of it steep hill country, and supports about 67 million sheep, 8 million dairy and beef cattle and 1 million deer and goats (New Zealand Department of Statistics 1989). Most of the pastoral land was carved out of indigenous forest between 1840 and 1970. It has been publically acknowledged since the beginning of the present century that high soil erosion rates cause pastoralism to be an unsuitable land use over large tracts of New Zealand's steeplands. Over the last 15 years several studies (Trustrum 1983, New Zealand Ministry of Works and Development 1980) have shown that pastoralism on erosion-susceptible hill country is not a sustainable land use. Pastoral farming continues to be a major land use on some of New Zealand's most unstable hill country which, to some, may seem to be an enigma considering New Zealand's international reputation for its technically advanced approaches to conservation and protection of soil and water values. Over the last 5 decades a number of soil conservation schemes have been initiated to stabilise soil on eroding pastoral land.

119th IUFRO World Congress August 5-11 1990, Montreal, Canada.

2~ssistant Secretary (Research), Ministry of Forestry, Wellington, New Zealand.

It is not the intention of this paper to unravel the reasons why unsuitable pastoral land use practices are widespread in New Zealand but rather the paper will endeavour to examine the way in which conservation schemes on eroding land are initiated and funded and how priorities are set. The role of Central Government will be examined. To this end the paper will concentrate on a forestry conservation scheme known as the East Coast Forestry Project located in the North Eastem part of New Zealand.

In New Zealand, forestry conservation schemes generally involve the blanket planting of eroding land with fast growing exotics, usually Pinus radiata but other species of conifers, or Populus are also often used. Open plantings of poplars are a commonly used soil stabilisation technique in poorly-drained gullies and other localised areas of instability.

POLICIES TO ENCOURAGE EROSION AND FLOOD CONTROL

There exist a number of Government policies that aim to provide protection against or control of erosion and flooding in New Zealand.

(i) Land use Controls

There exists legislation known as "the Soil Conservation and Rivers Control Amendment Act 1959" which was again amended in 1988, which provides catchment authorities with the power to control land use to prevent erosion. For instance catchment authorities can require land owners to plant trees on eroding land. However, this legislation is rarely used to enforce tree planting.


Catchment Grants

The Government contributes to flood protection and erosion control schemes through grants for specific works administered by regional catchment authorities. Nationwide catchment grants have averaged about $90 million per year over the last 20 years. It is planned to replace grants for specific works with a block subsidy system in the near future.

District Planning Schemes

These schemes can be used under the Town and Country Planning Acts (1954 and 1977) to designate areas of land for particular ultimate land uses (for example forestry). District planning schemes have not been effective in changing land use.

Disaster Relief

The Government has in the past contributed substantial amounts of money to disaster relief from flooding and siltation. For instance between 1968 and 1981 there were 7 major floods which cost the Government $2.9 billion or $223 million per year. Some of this money has been used for tree planting to stabilise soils and for retiring land from grazing.

Other Subsidies and Grants

In the past the Government provided for encouragement of farm scale forestry and agriculture conservation schemes through a variety of grants and subsidies. However, the present Government has introduced a market-led development strategy for New Zealand which has involved the removal of agricultural and forestry grants and subsidies. This has discouraged private afforestation and other conservation measures by private land holders.

Since 1984 the New Zealand Government has reshaped and reformed local (Regional) Government. The end result has been the amalgamation of more than 600 separate public agencies into 94 new district and regional

bodies. New legislation is presently being introduced under the general title "Resource Management Law Reform". Essentially the new legislation will consolidate a large number of existing pieces of legislation covered by a variety of Acts and replace them with a single Resource Management Act. Some of the policies outlined above will probably disappear with the introduction of the new Act which aims to provide Regional Governments (Councils) with greatly increased responsibility for managing natural resources and funding conservation schemes. Central Government is already playing a much reduced role in funding land use proiects and conservation/erosion control/floodcontrol schemes compared to the recent past.

EAST COAST FORESTRY PROJECT

established

f' Priority area for ,' new East Coast 1 forestry scheme 'L-.

Wairoa

HAWKE BAY

Figure 1: Map showing East Coast region and general area of the East Coast forestry scheme

A major economic appraisal of land use and development options for about 6,500 kilometres2 of severely eroding pastoral steeplands of the Raukumara Peninsula led to the initiation of a large scale forestry conservation scheme in 1969. The ori inal aim was to 3 plant approximately 1,000 kilometres of fast growing exotics, mainly radiata pine, at a rate of about


2,500 hectares per year. By 1987 when the scheme was halted, 36,100 hectares of dual purpose protection/production forest had been established at a total cost of $229 million. In addition to afforestation a large number of on-farm conservation schemes covering 28,200 hectares of sensitive terrain, had been implemented by 1987. Government contributed 64 percent of the total cost of $14.3 million for these schemes.

The on site benefits of afforestation include substantially reduced earthflow movement rates, cessation of gullying processes and a marked reduction in shallow landsliding (Pearce et 1987). To date the downstream benefits have not been quantified although in several upper catchment tributaries there are strong indications that a reduction in sediment supply from afforested slopes to stream channels is resulting in stream channel degradation.

Other benefits resulting from the East Coast forestry project are the commercial retums from the production of logs after the forest is 25 years old. Recent projections by the Ministry of ~ o r e s b y ~ suggest both existing plantings and future plantings are commercially viable in most areas except the areas to the far north and west of the East Coast region. The project also provided social benefits as it helped to prevent mral depopulation and unemployment in this rather isolated and economically depressed region.

EFFECTS OF CYCLONE BOLA AND SUBSEQUENT GOVERNMENT DECISIONS

When a subtropical cyclone, Cyclone Bola, moved across northern New Zealand between 6 and 9 March 1988 the torrential rainfall that fell on the East Coast region caused severe landsliding, erosion, flooding and siltation. Pastoral land was particularly damaged. Some pasture slopes lost 70 percent or more of their grass cover to shallow landslides. However, on hillslopes protected by mature native forest and older pine forests, landslides were less frequent. Damage to farms, forests, horticulture, roads, bridges and houses exceeded $120 million. The Central Government contributed approximately $80 million to the East Coast region as disaster relief to help defray the cost of damages resulting from Cyclone Bola.

%npublished data, Ministry of Forestry, Wellington, New Zealand.

8

The impacts of Cyclone Bola extended into the socio-economic area. The East Coast is presently one of the most depressed regions in New Zealand. The region is charactensed by a declining total population, falling property prices, a high economic and social dependency on agriculture and forestry which account for 23 percent of the total employment, and a high Maori population which comprises 37 percent of total East Coast population (New Zealand Officials Committee Report 1988). The severe impacts of the cyclone on the agriculture/forestry industries and the inability of the region to cope with the damage from a financial point of view were important factors in subsequent Government decision making. The results of the storm reinforced the fact that the East Coast was New Zealand's most susceptible region to widespread erosion and flooding damage and that erosion and flooding negatively influences the regional economy more than in other parts of New Zealand. The cyclone also highlighted the need for better land use on much of the unstable hill country in the region.

The severe damages caused by the cyclone (the largest of five severe storms to influence the East Coast in 20 years) was a major factor in the setting up of a Government Officials Committee to examine the original East Coast Project and an earlier review of this project. Among other things, the Committee was required to make recommendations to the Government on the future of the project and the Government's involvement in it. In its recommendations the Committee was split between those who recommended no Central Government funding should be provided for restarting the East Coast forestry project and those who strongly recommended that Central Government should intervene and provide additional funding for conservation plantings.

GOVERNMENT DECISIONS

In 1988 Government agreed to provide $8 million to directly subsidise a new East Coast Forestry Conservation Scheme on the East Coast pastoral forelands. The funding was to be spread over a 5 year period; 1989 to 1994; and was aimed at establishing about 3,000 hectares of protection forests per year. The scheme was to be targetted at erosion control on unstable pastoral hill country upstream of Gisborne City, Poverty Bay flats and Tologa Bay where the greatest assets at risk are located. The Government also agreed that the funding would be


provided as a subsidy covering two thuds of the cost of establishment and that the remaining one thud of the costs should be met by the region through the East Cape Catchment Board.

The Government also insisted that all protection forests would come under covenants which precluded logging for at least 25 years after planting and then only with the permission of the local catchment authority.

The main factors influencing Central Government to invest in such a scheme included:

. The real extent of severe erosion which is much greater than elsewhere in the country and has substantial negative impacts on the region's social and economic development.

. The need to cany out erosion control quickly and comprehensively to reduce future costs of erosion and flood damage, both to the region and to the Central Government.

. The lack of money and resources within the region for carrying out a comprehensive erosion control scheme.

Under the existing economic environment in New Zealand and the Government's intentions to devolve all responsibility for resource management to regional authorities, it is most unlikely that other regions in New Zealand will qualify for Central Government funding for major forestry conservation schemes in the future.

PROGRESS TO DATE

Despite the generous subsidies available for establishing conservation forests on unstable East Coast hill country, the East Cape Catchment Board who administer the Scheme, have found it difficult to obtain agreement from landowners to provide land for planting. After two planting seasons only about 4,500 hectares have been afforested. Farmers' reluctance to provide erosion prone pastoral land for afforestation stems from several factors:

. Concern that afforestation of sizeable portions of farmland will result in a decline in the stock carrying capacity of farms. The Department of Lands and

Survey (1977) concluded that forest planting of poorer grade land within a farm unit generally has little or no impact on stock numbers. However, in the case of a few farm units more than 50 percent of the farm area needed afforestation. Naturally, farmers were reluctant to yield up large parts of their farms for forestry and substantially reduce stock numbers.

A perception that tree plantations would not yield any return to the land holder in the foreseeable future but rather, would result in additional silvicultural and fencing costs.

The low profitability of many pastoral farms and low farm incomes which prevents landholders from being attracted by the long term benefits resulting from conservation forestry.

If unstable farmland is not relinquished for conservation forestry at the rate required by the East Coast Forestry Project, then the local regional authorities (the East Cape Catchment Board) may have to enforce afforestation in the priority areas requiring protection. The five year scheme aims at afforesting 15,000 hectares. However, this represents only 20 percent of the total area of severely eroding pastoral hill country in the East Coast region. There is clearly a need for a long term land use rationalisation scheme which will lead to the close integration of exotic and native forests, pastoral farming, horticulture and viticulture. Carefully located forests on the steeper unstable slopes and along riparian areas would provide improved protection to fertile valley bottoms and river plans where horticulture and other types of intensive farming are concentrated. Government Officials and East Cape Catchment Board staff agree that such a scheme would substantially increase farm productivity and reduce the costs of sustaining farming and horticulture on the better classes of land by reducing recurrent storm damage. In addition, recent Ministry of Forestry analyses of the economic viability of exotic forestry on the East Coast indicate that radiata pine forestry on the pastoral forelands has potential internal rates of return exceeding

4 7 percent .

4~npublished data, Ministry of Forestry, Wellington, New Zealand.


REFERENCES

Department of Land and Survey (New Zealand) 1977. King Country land use study. Wellington, New Zealand.

Department of Statistics (New Zeaiand) 1989. New Zealand Official Yearbook 1988-89. 93rd Annual Edition. 884p.

Ministry of Works and Development (New Zealand) 1980. Proceedings of a workshop on the influence of soil slip erosion on hill country pastoral productivity. Aokautere Science Centre Internal Report 21.

Officials Committee Report on East Coast Project Review (1988). A report to the Cabinet Development and Marketing Committee (unpublished), July 1988. 38p.

Pearce, A.J., O'Loughlin, C.L., Jackson, R.J., Zhang, X.B. 1987. Reforestation: on site effects on hydrology and erosion, eastern Raukumara Range, New Zealand. International Association of Hydrological Sciences Publication 167. 489-497.


Effect of Tree oots on Shallow-Seate Kazutoki Abe and Robert R. Ziemer2

Abstract: F o r e s t v e g e t a t i o n , e s p e c i a l l y t r e e r o o t s , h e l p s s t a b i l i z e h i l l s l o p e s by r e i n f o r c i n g s o i l s h e a r s t r e n g t h . To e v a l u a t e t h e e f f e c t of t r e e r o o t s on s l o p e s t a b i l i t y , i n f o r m a t i o n a b o u t t h e amount o f r o o t s and t h e i r s t r e n g t h s h o u l d b e known. A s i m u l a t i o n m o d e l f o r t h e r o o t d i s t r i b u t i o n o f Grvwtomer ia i a w o n i c a was proposed where t h e number of r o o t s i n each 0.5-cm d i a m e t e r c l a s s can be c a l c u l a t e d a t a r b i t r a r y d e p t h s . The p u l l - o u t s t r e n g t h of r o o t s was u s e d t o a n a l y z e t h e s t a b i l i t y o f f o u r d i f f e r e n t t y p e s of f o r e s t e d s l o p e s . Root r e i n f o r c e m e n t i s i m p o r t a n t on s l o p e s where r o o t s c a n e x t e n d i n t o j o i n t s and f r a c t u r e s i n bedrock o r i n t o a w e a t h e r e d t r a n s i t i o n a l l a y e r between t h e s o i l a n d b e d r o c k . Root r e i n f o r c e m e n t o f s o i l i n c r e a s e s q u i c k l y a f t e r a f f o r e s t a t i o n f o r a b o u t t h e f i r s t 20 y e a r s , t h e n r e m a i n s &out c o n s t a n t t h e r e a f t e r .

Sediment d i s a s t e r s by d e b r i s f l o w s , mud f l o w s , and l a n d s l i d e s o c c u r a l m o s t e v e r y y e a r d u r i n g t h e r a i n y J u l y t o O c t o b e r Typhoon s e a s o n i n J a p a n . I n J u l y 1982, a heavy r a i n f a l l of 488 nun i n a day, w i t h a maximum i n t e n s i t y o f 1 2 7 . 5 mm p e r h o u r , c a u s e d 4300 d e b r i s f l o w s i n N a g a s a k i p r e f e c t u r e , Kyushu I s l a n d . T h i s s t o r m d e s t r o y e d 2200 h o u s e s a n d k i l l e d 299 p e o p l e . D u r i n g J u l y 1983 , i n t e n s i v e r a i n f a l l i n i t i a t e d many d e b r i s f l o w s and 1 9 9 p e o p l e w e r e k i l l e d i n S h i m a n e p r e f e c t u r e , a l o n g J a p a n Sea on w e s t e r n Honshu I s l a n d .

l p r e s e n t e d a t t h e S u b j e c t Group S1 .04 T e c h n i c a l S e s s i o n on Geomorphic Hazards i n Manaqed F o r e s t s , X I X World C o n q r e s s , I n c e r n a r l o n a l Union o f F o r e s c r y R e s e a r c h O r s a n l z a c l o n s , Aususc 5-11, 1990, Clonereal,

2 ~ e s e a r c h S c i e n t i s t , F o r e s t r y and F o r e s t P r o d u c t s R e s e a r c h I n s t i t u t e , T s u k u b a , I b a r a k i , 305 Japan; and P r i n c i p a l Research H y d r o l o g i s t , P a c i f i c S o u t h w e s t R e s e a r c h S t a t i o n , F o r e s t S e r v i c e , U n i t e d S t a t e s ~ e ~ a r t m e n t o f A g r i c u l t u r e , A r c a t a , C A . U.S.A. 95521

The c a u s e o f s o much d e s t r u c t i o n and d e a t h m i g h t b e u n p r e c e d e n t e d i n t e n s i v e r a i n f a l l . I n a d d i t i o n , e x p a n s i o n o f c i t i e s , r e s o r t s , and r o a d s o n t o h i l l s l o p e s and mountain areas h a s been a l s o thought t o be a p r i m a r y c a u s e . I n response , n a t i o n a l a n d l o c a l g o v e r n m e n t s h a v e a d o p t e d a program of a g g r e s s i v e l y c o n s t r u c t i n g many e r o s i o n c o n t r o l works a t g r e a t e x p e n s e . But , even s o , it i s i m p o s s i b l e f o r s u c h c o n s t r u c t i o n t o p r o t e c t a l l m o u n t a i n h i l l s l o p e s from d e b r i s f l o w s .

An i m p o r t a n t c a u s e o f i n c r e a s e d f requency o f d e b r i s f lows i s t h e removal of f o r e s t s t o accommodate u r b a n i z a t i o n and r o a d c o n s t r u c t i o n i n mountainous a r e a s . I n monsoon a r e a s , l i k e J a p a n , where s t e e p mounta ins a r e c o v e r e d w i t h f o r e s t s , mass w a s t i n g i s t h e p r e v a i l i n g t y p e o f e r o s i o n . There i s a f r a g i l e b a l a n c e of s t a b i l i t y on s u c h s t e e p h i l l s l o p e s where t h e f o r e s t c o v e r i n t e r a c t s w i t h s o i l m o i s t u r e , s o i l s t r e n g t h , g e o l o g i c a l c o n d i t i o n , h i s t o r i c a l r a i n f a l l , and o t h e r f a c t o r s t o s t a b i l i z e t h e r e g o l i t h on a s l o p e . From a v iewpoin t o f s o i l mechanics , on many h i l l s l o p e s t h e f a c t o r of s a f e t y of a s l o p e (FS) approaches 1 . 0 d u r i n g a r a i n f a l l e v e n t t h a t o c c u r s once e v e r y s e v e r a l y e a r s . Under c o n d i t i o n s of s u c h d e l i c a t e b a l a n c e , removal of t h e t r e e s by l o g g i n g may r e s u l t i n a r e d u c t i o n i n s o i l s t r e n g t h s u f f i c i e n t t o c a u s e l a n d s l i d e s .

The i n f l u e n c e o f f o r e s t s on s l o p e s t a b i l i t y h a s b e e n o n e o f t h e most i m p o r t a n t s u b j e c t s of s t u d y - - e s p e c i a l l y , t h e r o l e of t r e e r o o t s on r e i n f o r c i n g s o i l s h e a r s t r e n g t h . To e v a l u a t e t h e mechanical e f f e c t o f r o o t s i n s t r e n g t h e n i n g s o i l , however, t h e q u a n t i t y and d i s t r i b u t i o n o f r o o t s i n s u b s u r f a c e s o i l l a y e r s must b e q u a n t i f i e d .

I n t h i s p a p e r , a s i m u l a t i o n model f o r t h e d i s t r i b u t i o n and s t a b i l i z i n g e f f e c t o f r o o t s i s i n v e s t i g a t e d u s i n g a n i n f i n i t e s l o p e s t a b i l i t y a n a l y s i s model.

ROOT DISTRIBUTION

A s t a b i l i t y a n a l y s i s o f f o r e s t s l o p e s c a n b e made b y a d d i n g t h e s o i l s h e a r


s t r e n g t h a n d a r e i n f o r c i n g component p rov ided by t h e s t r e n g t h of r o o t s (Endo and T s u r u t a 1969; Gray and Ohashi 1 9 8 3 ) . Th i s r e i n f o r c i n g s t r e n g t h i s g e n e r a l l y shown by equa t i on [ I ] (Waldron 1977; Wu 1 9 7 6 ) .

C r = xtri ( s i n 8 + cos 8 * t a n a ) , [ I ]

where C r : Rein fo rc ing s t r e n g t h p rov ided by r o o t s

t r i : Root t e n s i l e stress gene ra t ed i n r o o t i a t t h e l a n d s l i d e s h e a r p l ane

8 : Slope g r a d i e n t

a : Angle o f i n t e r n a l f r i c t i o n of t h e s o i l .

The t e n s i l e stress f o r v a r i o u s s p e c i e s h a s been r e p o r t e d t o be a f u n c t i o n o f r o o t d i a m e t e r ( Z i e m e r a n d Swans ton 1977 ; Burroughs and Thomas 1977; O'Loughl in and Ziemer 1982; Abe and Iwamoto 1 9 8 6 ) . Thus, t o model t h e i n f l u e n c e of t r e e s on s l o p e s t a b i l i t y , t h e number and d iamete r o f r o o t s a t s p e c i f i c d e p t h s must be o b t a i n e d .

To d e v e l o p t h e r o o t model a n d t o u n d e r s t a n d t h e i n f l u e n c e o f d i f f e r e n t e n v i r o n m e n t a l c o n d i t i o n s on r o o t d i s t r i b u t i o n , r o o t s o f abou t 16 t r e e s o f

iaoonica, t h e most p o p u l a r s p e c i e s p l a n t e d i n Japan, were sampled i n f i v e d i f f e r e n t f i e l d s . The sampl ing was done a s f o l l o w s :

3 . The d i a m e t e r a t b o t h e n d s a n d t h e l e n g t h o f c u t r o o t s l a r g e r t h a n 0 . 5 mm i n d i a m e t e r were measured i n e ach 10- cm-thick l a y e r .

4 . The number, volume, and t o t a l l e n g t h of r o o t s were t h e n c a l c u l a t e d f o r e a c h l a y e r .

o f t h e Root Dlstrlhutlon

Root volume i n 10-cm-thick l a y e r s (V(z))

About 85 t o 90 p e r c e n t o f t h e t o t a l r o o t volume of a t r e e w a s found i n t h e uppe r h a l f o f t h e r o o t i n g d e p t h . Root volume d e c r e a s e s e x p o n e n t i a l l y wi th dep th .

To i n v e s t i g a t e t h e p a t t e r n o f r o o t d i s t r i b u t i o n b y d e p t h , V ( z ) , t h e accumula ted r o o t volume r a t i o , F ( z ) , was c a l c u l a t e d ( e q . [21) .

Zmax V r = C V ( Z )

z=o

where, V r : e n t i r e r o o t volume of one t r e e CV(z) : accumulated r o o t volume from t h e

ground s u r f a c e t o t h e dep th "z" Zmax: maximum dep th o f r o o t growth.

The s t u d y t r ee was c u t down and i t s The r e l a t i o n s h i p between F ( z ) and dep th "2"

e n t i r e r o o t s y s t e m was c a r e f u l l y c o u l d be auurox imated bv t h e u r o b a b i l i t v - - excava t ed . f u n c t i o n o f t h e w e i d u l l - d < s t r i b u t i o n A l l r o o t s were c u t a l o n g p l a n e s a t 10- ( f i c r . 21. The s o l i d l i n e i n f i s u r e 2 i s cm dep th i n t e r v a l s below t h e ground and t h e - We ibu l l p r o b a b i l i t y f u n c t i o n , f ( z ) , p a r a l l e l t o t h e s u r f a c e ( f i g . 1 ) . c a l c u l a t e d from equa t i on I31 (Makabe 1966 ) .

There a r e t h r e e p a r a m e t e r s t h a t must be e s t i m a t e d : a, y, and m. "y" i s a l o c a t i o n paramete r t h a t de te rmines a beg inn ing p o i n t

5 of t h e c u r v e . I n t h e r o o t d i s t r i b u t i o n % ca se , "y" i s 0, because t h e ground s u r f a c e

(z=0) i s t h e i n i t i a l p o i n t . "m" i s a shape paramete r . It can be r e a d o f f t h e Weibull- g raph a s a g r a d i e n t of t h e l i n e , and a l s o c a l c u l a t e d by e q u a t i o n [ 4 1 wi th "ZmaXu and "Xo"

F i g . 1 . M e t h o d o f s a m p l i n g f o r r o o t d i s t r i b u t i o n . A l l r o o t s were c u t a l o n g p l a n e s a t 10-cm i n t e r v a l s b e l o w t h e g r o u n d s u r f a c e a n d d i a m e t e r s o f b o t h e n d s and t h e l e n g t h s o f c u t r o o t s were measured i n e ach 10-cm t h i c k l a y e r . Zmax i s a maximum r o o t p e n e t r a t i n g dep th .

p o i n t where d i ame te r i s measured.

XO i s an i n t e r s e c t i n g p o i n t o f Fn(z)=O and t h e s o l i d l i n e ( f i g . 2 ) .

From o u r d a t a , it appeared t h a t i f Zmax i s deepe r , t h e g r a d i e n t o f "m" may be s t e e p e r . ( f i g . 2 ) . A r e g r e s s i o n between Zmax and XO r e s u l t e d i n equa t i on [51.

XO = 0.3522*Zmax - 10.799 [51

USDAForest ServiceGen. Tech. Rep. PSW-GTR-130.1991

S u b s t i t u t i n g e q u a t i o n [51 i n t o e q u a t i o n [ 4 ] , "m" can be e s t i m a t e d by e q u a t i o n [ 6 ] .

" a " i s a s c a l e p a r a m e t e r a n d c a n b e d e f i n e d as a dependent v a r i a b l e of Zmax by e q u a t i o n (71 .

A c c o r d i n g l y , t h e r o o t volume i n e a c h 10-cm- th ick l a y e r V ( z ) i s o b t a i n e d b y e q u a t i o n [81 .

z+10 V ( z ) = { f ( z ) d z l * V r

Z [ e l

Root Number

I n g e n e r a l , t h e most r o o t s a r e found 20 t o 50 c m d e e p . The number o f r o o t s t h e n g r a d u a l l y d e c r e a s e s w i t h d e p t h . S i x t y t o 85 p e r c e n t o f t h e r o o t s a r e s m a l l e r t h a n

F i g . 2 . R e l a t i o n s h i p between d e p t h ( z ) and a c c u m u l a t e d r o o t volume r a t i o ( F ( z ) ) i n t h e W e i b u l l g r a p h . W e i b u l l c o e f f i c i e n t "mu i s t h e g r a d i e n t o f a r e g r e s s i o n l i n e , o b t a i n e d by "b /a , "a" , and "b".

:Tree 1 i n Minakami, 0 :Tree 3 i n Minakami,

:Tree 5 i n Komatubara, + : T r e e 9 i n Misugi, +:Tree 10 i n Ksukuba.

S i t e T a p zone Middle zone Bottom Z<

Minakami 7.91 i-1.47 4.91 i-*'ll 5.95 i-l'

0 . 5 cm i n d i a m e t e r

To compare r o o t d i s t r i b u t i o n between e a c h f i e l d s i t e , t h e t o t a l r o o t i n g d e p t h was d i v i d e d i n t o t h r e e zones : t o p , middle , and bo t tom. I n t h e t o p zone, t h e r e a r e many l a t e r a l r o o t s t h a t v a r y w i d e l y i n d i a m e t e r . I n t h e bot tom zone, most r o o t s grow v e r t i c a l l y and t h e r e a r e few r o o t s g r e a t e r t h a n 1 . 0 cm i n d i a m e t e r . I n t h e middle zone, many r o o t s d e v e l o p v e r t i c a l l y and d i a g o n a l l y , b u t t h e r e a r e few l a t e r a l r o o t s . Even though t h e d e p t h zones do n o t c o i n c i d e w i t h s o i l h o r i z o n s a n d t h e t h i c k n e s s o f t h e z o n e s v a r i e s be tween s i t e s , e a c h r e s p e c t i v e d e p t h zone h a s s i m i l a r r o o t d i s t r i b u t i o n s . R o o t d i s t r i b u t i o n was e s t i m a t e d a s t h e r o o t number r a t i o , o b t a i n e d b y r e g r e s s i o n between t h e p r o p o r t i o n o f t h e number of r o o t s i n each 0.5-cm d i a m e t e r c l a s s , Y ( i) , and t h e d i a m e t e r c l a s s , i ( t a b l e 1 ) .

Mean volume of a r o o t i n each d i a m e t e r c l a s s (Vm ( i ) )

T h e r e was no d i f f e r e n c e i n t h e mean volume o f a r o o t i n e a c h d i a m e t e r c l a s s , V r n ( i ) , among t h e t h r e e d e p t h z o n e s . Consequen t ly , r e g r e s s i o n s were c a l c u l a t e d f o r each f i e l d s i te ( t a b l e 2 ) .

Maximum r o o t dep th (Zmax)

I t i s i m p o r t a n t t o n o t e t h e d e p t h o f r o o t p e n e t r a t i o n when e s t i m a t i n g t h e e f f e c t o f r o o t s i n s t a b i l i z i n g s l o p e s . The more r o o t s t h a t p e n e t r a t e a p o t e n t i a l s h e a r p l a n e , t h e g r e a t e r i s t h e c h a n c e t h a t v e g e t a t i o n w i l l i n c r e a s e s l o p e s t a b i l i t y . Some o f t h e f a c t o r s r e s t r i c t i n g Zmax a r e e x i s t e n c e of bedrock , s o i l p o r o s i t y , s o i l m o i s t u r e , s o i l s t r u c t u r e , s o i l c o n s i s t e n c y , and s o i l f e r t i l i t y . Morimoto (1982) and Ikemoto and T a k e s h i t a (1987) r e p o r t e d t h a t Zmax c o u l d b e e s t i m a t e d a s t h e d e p t h where t h e s o i l h a r d n e s s , u s i n g a c o n e p e n e t r o m e t e r , i s 27 mm, o r t h e N v a l u e (number Of f a l l s p e r 10-cm p e n e t r a t i o n ) i n

t h e sounding tes t i s 5 . However, much more d a t a on t h i s s u b j e c t i s needed.


Tab le 2--Mean r o o t volume, V m ( i ) , o f t h e f o u r f i e l d s i t e s

Site Mean root Coefficient of Sample volume determination number

Minakami 7 . 6 2 i2'" 0 . 9 6 5 1

Komatsubara 7 . 8 4 j,2.32 0.94 2 4

Tsukuba 7.81 i2.l4 0.97 53

YODEL

F i g u r e 3 i s a f low c h a r t o f t h e r o o t d i s t r i b u t i o n s i m u l a t i o n model. The i n p u t f a c t o r s a re f i e l d measurements o f h e i g h t ( H ) , d i ame te r ( D B H ) , and Zmax of t h e o b j e c t t r e e . The model o u t p u t i s t h e number o f r o o t s i n e a c h 10-cm l a y e r and each r o o t d i ame te r c l a s s . Y t ( i ) , Y m ( i ) , Y b ( i ) , and V m ( i ) a r e used i n t h e model a s v a r i a b l e s , s o t h e y must be measured f o r e ach r e g i o n

hav ing d i f f e r e n t environmental c o n d i t i o n s .

The model was composed a s f o l l ows :

(1) Inpu t DBH, H, and Z m a x .

( 2 ) C a l c u l a t e whole r o o t weight , W r , i n g .

W r can be c a l c u l a t e d by an a l l o m e t r i c formula, equa t i on 191 (Karizumi 1977 ) .

l o g W r = 0 . 8 2 1 6 * 1 0 ~ ( ~ ~ ~ ~ * ~ ) - 0 . 3 0 8 5 [91

(3) C a l c u l a t e whole r o o t volume, V r , i n 3 cm .

V r = W r / G s 1101

( 4 ) C a l c u l a t e r o o t volume i n each 10-cm l a y e r , V ( z ) .

V(z ) can be c a l c u l a t e d by equa t i on 181, where f ( z ) i s o b t a i n e d from e q u a t i o n 131 by s u b s t i t u t i n g Zma, i n t o equa t i ons

M)OB APPLIED PRINCIPLES

Aiiometric formula

10-cm-thick layer

Whole root volume (Vr )

in each diameter class and root diameter class each to-cm-thick layer

in each diameter class

Weibull distribution

Temporary volume of roots in each 10-cm.thick layer

diameter class and each to-cm-thick layer (N(i .2))

k

F i g . 3 . Flow c h a r t o f t h e r o o t d i s t r i b u t i o n s i m u l a t i o n model.

probability function


[61 and 171.

(5 ) S e t up t h e t emporary r o o t number i n each d i a m e t e r c l a s s and each 10-cm- t h i c k s o i l l a y e r , f ? ( i , z ) .

The maximum r o o t d i a m e t e r ( imax) s h o u l d b e d e t e r m i n e d , a n d f i ( i , z ) i n e a c h d i a m e t e r c l a s s (0.5-cm i n t e r v a l s i n t h i s p a p e r ) up t o imax i n each zone i s s e t up i n p r o p o r t i o n t o t h e r o o t number r a t i o s Y t ( i ) , Y m ( i ) , and Y b ( i ) . A l l 10-cm l a y e r s t h a t b e l o n g t o one zone have t h e same i n i t i a l v a l u e o f fi (i, z ) .

( 6 ) C a l c u l a t e t emporary r o o t volume i n 10-cm l a y e r , v ( z ) .

(7 ) C a l c u l a t e t h e r a t i o between V(z) and V ( z ) , k .

(8 ) D e t e r m i n e t h e number of r o o t s i n e a c h r o o t d i a m e t e r c l a s s and e a c h 10-cm l a y e r , N ( i , z ) .

Even f i n e r o o t s have a s t r o n g i n f l u e n c e i n p r e v e n t i n g l a n d s l i d e s (Bur roughs a n d Thomas 1977; Abe and Iwamoto 1 9 8 6 ) . Thus, t h e model must b e a b l e t o e s t i m a t e t h e number o f s u c h f i n e r o o t s . A l s o , t h e l a n d s l i d e s h e a r p l a n e h a s a t e n d e n c y t o o c c u r n e a r t h e l i m i t of r o o t i n g d e p t h where t h e r e a r e few r o o t s on t h e s h e a r p l a n e (Abe and o t h e r s 1 9 8 5 ) . T h i s model can e s t i m a t e t h e number o f r o o t s i n each d i a m e t e r class i n t h e d e e p e r l a y e r s . Fur thermore, it i s i m p o r t a n t t h a t r o o t d i s t r i b u t i o n u n d e r d i f f e r e n t c o n d i t i o n s can b e e x p r e s s e d b y one model.

ROOT BTRENGTE

The c o n t r i b u t i o n o f r o o t s t o i n c r e a s i n g s o i l s h e a r s t r e n g t h h a s b e e n m a i n l y e s t i m a t e d b y f o u r k i n d s o f e x p e r i m e n t s : t e n s i l e t e s t , p u l l - o u t t e s t , - ' s h e a r tes t , and l a b o r a t o r y s h e a r t es t .

Many t e n s i l e s t r e n g t h t e s t s o f r o o t s have been per fo rmed . A segment o f a r o o t specimen i s u s u a l l y l o a d e d i n t e n s i o n and t h e maximum v a l u e a t f a i l u r e i s measured ( O ' L o u g h l i n 1 9 7 4 ; B u r r o u g h s a n d Thomas 1977; Ziemer and Swanston 1977; Nakane and o t h e r s 1983; Abe and o t h e r s 1986) . From t h e s e t e s t s , t h e t e n s i l e s t r e n g t h o f l i v e r o o t s and i t s d e c l i n e a f t e r t h e r o o t s d i e h a v e b e e n m e a s u r e d f o r many o f t h e i m p o r t a n t t r e e s p e c i e s .

The p u l l - o u t t e s t measures t h e maximum

r e s i s t a n c e when a r o o t i s p u l l e d o u t o f t h e s o i l ( f i g . 4 ) . Tsukamoto (1987) and Abe a n d Iwamoto ( 1 9 8 6 ) r e p o r t e d p u l l - o u t s t r e n g t h c o u l d b e p r e d i c t e d b y r o o t d i a m e t e r a n d was i n d e p e n d e n t o f s l o p e c o n d i t i o n s and r o o t t y p e , such a s l a t e r a l , t a p , o r s i n k e r r o o t . P u l l - o u t s t r e n g t h was composed o f t a n g e n t i a l f r i c t i o n be tween s o i l and r o o t s , and was i n f l u e n c e d by r o o t b e n d i n g , b r a n c h i n g , r o o t h a i r s , and t h e t e n s i l e s t r e n g t h a t b r e a k a g e s .

Data from in-situ s h e a r tes ts (Endo and T s u r u t a 1969; Ziemer 1981; O'Loughl in and o t h e r s 1982; Abe a n d Iwamoto 1987) a r e i m p o r t a n t f o r e v a l u a t i n g t h e a p p r o p r i a t e n e s s o f t h e o r e t i c a l c o n c e p t s . But, it i s d i f f i c u l t t o per fo rm s u c h tes ts on s t e e p rocky h i l l s l o p e s .

L a b o r a t o r y s h e a r t e s t s h a v e b e e n p e r f o r m e d t o r e v e a l t h e mechanism o f t h e r o o t r e i n f o r c i n g e f f e c t (Waldron 1977; Wu 1976; Waldron and Dakess ian 1981; Gray and O h a s h i 1 9 8 3 ; S h e w b r i d g e 1 9 8 5 ) . We c o n d u c t e d d i rec t s h e a r t e s t s u s i n g s a n d t h a t c o n t a i n e d r o o t s a n d m o d i f i e d t h e r e i n f o r c e m e n t model p r o p o s e d by Waldron (1977) and Wu (1976) :

AS= [ { ( l c ~ ~ b ~ e - ' ~ ~ ) '/*-I) *E*arl ( c o s 8 t a n @ t s i n 8) + E * I * ~ ~ * B [I41

where, E : Young modulus a r : c r o s s s e c t i o n a l a r e a o f t h e

r o o t s B: one h a l f of a s h e a r d i sp lacement I : modulus of s e c t i o n 8: r o o t a n g l e a t t h e o r i g i n

: i n t e r n a l f r i c t i o n a n g l e of sand .

From o b s e r v a t i o n s o f s h a l l o w l a n d s l i d e s i t e s , t h e r e were o n l y a few f i n e r o o t s on t h e b o t t o m s h e a r p l a n e s (Abe and o t h e r s 1 9 8 5 ) . And, f o r f a l l e n trees, most of t h e r o o t s were broken n e a r t h e i r t i p s where t h e

Recorder

F i g . 4 . Diagram o f t h e r o o t p u l l - o u t t e s t

USDA Forest Sewice Gen. Tech. Rep. PSW-GTR-130. 1991

d i a m e t e r was l e s s t h a n 1 t o 2 cm. T h i s s u g g e s t s t h a t most r o o t s were p u l l e d o u t . Burroughs and Thomas (1977) r e p o r t e d t h a t t h e wid th o f t h e s h e a r zone ranged from 7 t o 25 cm and t h e m a j o r i t y o f t r e e r o o t s had f a i l e d i n t e n s i o n . S t u d i e s o f s l o p e f a i l u r e i n s o i l o v e r g l a c i a l till i n Alaska i n d i c a t e d t h a t t h e e x p e c t e d w i d t h o f t h e s o i l s h e a r zone ranged from 7 . 5 t o 30 c m , and t h a t t h e e x p e c t e d mode of r o o t f a i l u r e i s i n t e n s i o n (Wu, 1 9 7 6 ) . We assume t h a t t h e r o o t s c r o s s i n g a s h e a r zone g e n e r a t e t e n s i l e s t r e n g t h , a r e e l o n g a t e d i n t e n s i o n , and b r e a k a t t h e t i p s , n o t i n t h e s h e a r z o n e . Thus, t h e mode of r o o t f a i l u r e i s s i m i l a r t o t h a t d u r i n g a p u l l - o u t t e s t . Abe and Iwamoto (1986) conduc ted t e s t s on CrvDtomeria iaDonica and measured b o t h t h e p u l l - o u t r e s i s t a n c e a n d t h e t e n s i l e s t r e n g t h a t t h e p o i n t of b reakage ( f i g . 4 ) . The r e s u l t s were q u i t e d i f f e r e n t . The p u l l - o u t r e s i s t a n c e i n c l u d e s t h e t e n s i l e s t r e n g t h a t b r e a k a g e , p l u s t h e t a n g e n t i a l f r i c t i o n between r o o t s and s o i l a n d t h e mechan ica l s t r e n g t h caused by p u l l i n g b e n t p a r t s o f t h e r o o t t h r o u g h t h e s o i l . Consequen t ly , it i s n o t a p p r o p r i a t e t o u s e t h e maximum t e n s i l e s t r e n g t h t o r e p r e s e n t r o o t r e i n f o r c i n g s t r e n g t h . Al though t h e r e l a t i o n s h i p between p u l l - o u t r e s i s t a n c e a n d t h e t h e o r e t i c a l r e i n f o r c e d s o i l s t r e n g t h i s n o t f u l l y u n d e r s t o o d , we p o s t u l a t e t h a t b o t h a r e abou t e q u a l .

S t a b i l i t y o f a f o r e s t e d s l o p e w a s s i m u l a t e d u s i n g t h e p u l l - o u t r e s i s t a n c e (PO) , o b t a i n e d b y a r e g r e s s i o n a n a l y s i s ( e q . [151) of t h e r o o t d i a m e t e r ( D ) a t p u l l

p o i n t s ( f i g . 4 ) .

SLOPE STABILITY ANALYSIS

G e o l o g y , s o i l m e c h a n i c s , a n d s o i l m o i s t u r e a f f e c t s l o p e s t a b i l i t y and a l s o a f fec t t h e d i s t r i b u t i o n o f t r e e r o o t s , e s p e c i a l l y t a p r o o t s . Tsukamoto (1987) c l a s s i f i e d s l o p e s i n t o f o u r t y p e s .

A t y p e - - R e g o l i t h i s t h i n and u n d e r l a i n by bedrock w i t h few c r a c k s and j o i n t s . The r o o t s cannot p e n e t r a t e t h e bedrock and a r e d e n s e l y d i s t r i b u t e d i n t h e r e g o l i t h . Tap r o o t s a r e n o t i m p o r t a n t . S o i l w a t e r cannot p e r m e a t e t h e b e d r o c k , a n d p o r e w a t e r p r e s s u r e i s e a s i l y g e n e r a t e d on t h e bedrock s u r f a c e . Thus , t h i s t y p e o f s l o p e i s r a t h e r u n s t a b l e and mos t ly found on d i p p i n g s l o p e s i n t e r t i a r y p a r e n t m a t e r i a l s .

B type- -Regol i th i s t h i n and u n d e r l a i n by b e d r o c k h a v i n g many j o i n t s a n d c r a c k s . Roots a r e a b l e t o p e n e t r a t e i n t o bedrock and c o n t r i b u t e t o s t a b i l i t y . P o r e w a t e r

p r e s s u r e i s seldom g e n e r a t e d b e c a u s e o f h i g h p e r m e a b i l i t y . Accordingly , t h i s t y p e of s l o p e i s q u i t e s t a b l e and i s found i n a r e a s w i t h mesozo ic and p a l e o z o i c p a r e n t m a t e r i a l .

C t y p e - - R e g o l i t h i s t h i n and t h e r e i s a t r a n s i t i o n a l (wea thered) l a y e r between t h e r e g o l i t h and bedrock . Root growth may be a f f e c t e d by s o i l d e n s i t y and h a r d n e s s o f t h i s t r a n s i t i o n a l l a y e r . S o i l m o i s t u r e does n o t e a s i l y pe rmea te t h e t r a n s i t i o n a l l a y e r , b e c a u s e o f i t s h i g h d e n s i t y , and p o r e w a t e r p r e s s u r e i s e a s i l y g e n e r a t e d . Roots a r e most e f f e c t i v e on t h i s t y p e of s l o p e . A s r o o t s t r e n g t h d e c l i n e s a f t e r l o g g i n g , many d e b r i s f l o w s would b e e x p e c t e d . T h i s t y p e i s f r e q u e n t l y found i n g r a n i t e mountains .

D t y p e - - R e g o l i t h i s t h i c k a n d r o o t s can grow w i t h o u t r e s t r i c t i o n by s o i l l a y e r s . T h i s t y p e of s l o p e i s u s u a l l y found a t t h e b a s e o f h i l l s l o p e s and have a g e n t l e a n g l e . D e b r i s f l o w s n e v e r o c c u r on t h i s t y p e of s l o p e .

The s t a b i l i t y o f t h e s e f o u r t y p e s o f s l o p e was i n v e s t i g a t e d b y a s s u m i n g r e a s o n a b l e v a l u e s o f i m p o r t a n t s o i l and s l o p e c h a r a c t e r i s t i c s ( t a b l e 3 ) .

The A-type s l o p e h a s 80 cm o f r e g o l i t h t h i c k n e s s u n d e r l a i n b y b e d r o c k w i t h o u t c r a c k s and t h e r o o t s can n o t p e n e t r a t e more t h a n 80 c m deep . The B-type s l o p e a l s o h a s 80 c m of r e g o l i t h , b u t bedrock i s f r a c t u r e d a n d r o o t s c a n i n v a d e t h e c r a c k s up t o 100 cm d e e p . The C-type s l o p e a l s o h a s 80 c m o f r e g o l i t h , p l u s a 40-cm-thick t r a n s i t i o n a l l a y e r u n d e r l a i n b y b e d r o c k . The D-type s l o p e h a s 150 c m of r e g o l i t h and a 40-cm-thick t r a n s i t i o n a l l a y e r u n d e r l a i n by b e d r o c k . The s t a b i l i t y c a l c u l a t i o n s assumed t h a t t h e ground w a t e r r e a c h e d t h e g round s u r f a c e . F o r e s t s o f w t o m e r h i a ~ o n i c a aged 10, 20, 30, and 40 y e a r s were assumed t o b e growing on each s l o p e . The

T a b l e 3 - - C h a r a c t e r i s t i c s o f t h e f o u r s l o p e s - - - - - - - Slope type-------

A B C D

Slope a n g l e ( O ) 32 32 32 1 5 Thickness of r e g o l i t h (cm) 80 80 80 1 5 0 T r a n s i t i o n a l zone (cm) 0 0 40 40 Cohesion of s o i l ( ton/m2) 0 .2 0 .2 0 . 2 0.2

I n t e r n a l a n g l e of s o i l ( o ) 30 30 3 0 3 0 C o h e s i c n o f b e d r o c k ( t o n / m 2 ) 20 20 20 20 I n t e r n a l a n g l e of bedrock(O) 40 40 40 40 Ground water t a b l e dep th (cm) 0 0 0 0 Dens i ty of s o i l (g / cc ) 1 . 3 1 . 3 1 . 3 1 . 3 Dens i ty of bedrock (g /cc ) 2 . 5 2 . 5 2 . 5 2 . 5 zmax (cm) 80 1 0 0 100 170


s i z e of t r e e s i n each f o r e s t was obta ined from y i e l d t a b l e s . Root d i s t r i b u t i o n s (number of r o o t s i n each 10-cm-thick s o i l l a y e r f o r each 0.5-cm diameter c l a s s ) were s imula ted us ing t h e model ( f i g . 3 ) . The r e i n f o r c i n g s t r e n g t h (AS) i n each 10-cm- t h i c k l a y e r was c a l c u l a t e d using equation [ 1 6 1 .

where, AS ( 2 ) : r e i n f o r c i n g s t r e n g t h a t depth z cm

N ( 2 , i) : number of roo t s of diameter i cm a t depth z cm

P O ( i ) : pul l -out s t r e n g t h of a root with diameter i cm.

The s i m u l a t i o n r e s u l t s of t h e f o u r s lope types a r e shown i n f i g u r e 5 . S o i l s h e a r s t r e n g t h , S s , shows an a b r u p t inc rease a t t h e boundary between s o i l and bedrock of t h e A-type and B-type s lopes , b u t on t h e C-type s l o p e t h a t has a t r a n s i t i o n a l s o i l l a y e r , s o i l s h e a r

SO IL-STRENGTH lk f / m a I 1 3 4

:Soil shear strength - - - - - - - :Promoting sliding ~tren th i' a:Rooted oil of a fore~t aged 0

o:Rooted soi 1 of a forest aged 20 -:Rooted soil of a forest aged 30 +:Rooted soi l of a forest aged 40

s t r e n g t h g r a d u a l l y i n c r e a s e s . Shear s t r e s s , P s , exceeds t h e s o i l shear s t r eng th a t a depth of 40 t o 80 cm on type A, B, and C s lopes . This ind ica tes a p o t e n t i a l shear zone a t t h e s e d e p t h s l e a d i n g t o t h e p o s s i b i l i t y of a l a n d s l i d e . The r e i n f o r c i n g s t r e n g t h by r o o t s (AS) was c a l c u l a t e d by equation [I61 and added t o Ss ( f i g . 5 ) .

On t h e A-type s lope , t h e growth of t a p roo t s i s r e s t r i c t e d by t h e bedrock so the re i s no r e i n f o r c i n g e f f e c t a t t h e boundary ( p o t e n t i a l shea r zone) . AS i s increased by t h e growing f o r e s t only t o a depth of 70 cm. In o the r words, although t h e number of roo t s i s increased a s t h e f o r e s t becomes o lde r , root reinforcement of t h e s o i l never develops a t t h e boundary and P s w i l l exceed Ss a t t h i s depth when t h e ground water su r face r i s e s . This condit ion can lead t o a d e b r i s flow.

On t h e B-type s l o p e , however, r o o t s p e n e t r a t e t h e c racks i n t h e bedrock, and roo t reinforcement develops a t t h e s o i l - bedrock boundary. When t h e f o r e s t i s o lde r

SO I L-STRENGTH (k f/n' 1 1 03 134 105

Fig . 5. Simulated rooted s o i l shear s t r e n g t h of f o r e s t s having four d i f f e r e n t ages on A, B, C, and D type of s lopes

USDA Forest Service Gem Tech. Rep. PSW-GTR-130.1991

than 20 years , AS becomes s t r o n g e r than Ss, and P s never exceeds shear s t r eng th of t h e rooted s o i l , Sr ( f i g . 5 ) . But, f o r t h e 10-yea r -o ld f o r e s t , AS i s no t s t r o n g enough t o prevent a d e b r i s flow on t h e s lope .

The C-type s lope i s s i m i l a r t o t h e B- t y p e . Roots invade and r e i n f o r c e t h e t r a n s i t i o n a l zone, and t h e p r o b a b i l i t y of l ands l ides decreases a s t h e f o r e s t becomes o l d e r .

The D-type s lope i s always s t a b l e with o r without a f o r e s t .

The f a c t o r of s a f e t y (FS) a t t h e p o t e n t i a l shear zone inc reases f o r type B and C s l o p e s a s t h e age of a f o r e s t inc reases , up t o an age of 20 t o 25 years , a f t e r which it remains about cons tant a t about 2.0 ( f i g . 6 ) . For these slope types, t h e FS of 10-year-old f o r e s t s i s under 1 .0 , i n d i c a t i n g a h i g h p r o b a b i l i t y of l a n d s l i d e s . The FS values were ca lcu la ted f o r a c o n d i t i o n where t h e ground water reaches t h e ground s u r f a c e . For A-type s lopes , FS does not change with increas ing f o r e s t age because r o o t s cannot r e in fo rce t h e s o i l and bedrock i n t e r f a c e . Type-D s lopes remain s t a b l e a t a l l ages of f o r e s t .

DISCUSSION

A s f o r e s t s grow, r o o t systems develop t o provide s t r u c t u r a l support t o t h e t r e e s and t o absorb water and n u t r i e n t s . Roots a r e important i n s t a b i l i z i n g h i l l s l o p e s . To q u a n t i f y t h e amount of r o o t r e in fo rcement A S , it i s necessary t o

Forest age o:A type of slope o:B type of slope A:C type of slope +:D type of slope

Fig . 6. Change i n t h e f a c t o r of s a f e t y a s t h e f o r e s t ages .

understand t h e r e l a t i o n s h i p between roo t growth, s l o p e s t r u c t u r e , and dep th of s l i d i n g s u r f a c e . In t h i s paper , r o o t reinforcement was modelled f o r f o u r types of s l o p e s . Previous r e sea rch has shown t h a t t h e r e a r e high s lope f a i l u r e r a t e s on g r a n i t e , s h a t t e r e d paleozoic and mesozoic, and t e r t i a r y s lopes a s soc ia ted with young f o r e s t s (Tsukamoto 1987) . I t i s expected t h a t t h e r e a r e d i f f e r e n c e s i n AS r e l a t e d t o d i f f e r e n c e s i n g e o l o g i c a l l y r e l a t e d s lope s t r u c t u r e . Thus, it i s important t o i d e n t i f y those f a c t o r s t h a t r e s t r i c t t h e growth of roo t s and t o quan t i fy t h e number and s i z e of r o o t s t h a t can pene t ra te i n t o j o i n t s of bedrock o r t r a n s i t i o n a l s o i l l a y e r s and r e i n f o r c e t h e p o t e n t i a l shear zone.

Logging can cause a l a r g e decrease i n AS. A s t h e roo t s decay, a f t e r a 40-year- o l d f o r e s t h a s been c u t , t h e s h e a r r e s i s t a n c e of rooted s o i l i n t h e p o t e n t i a l shea r zone w i l l decrease t o one t h i r d of t h a t i n t h e uncut f o r e s t ( f i g . 5 ) , and t h e p r o b a b i l i t y of s lope f a i l u r e w i l l increase . Kitamura and Namba (1981) noted t h a t t h e r e s i s t a n c e of t r e e stumps t o uproo t ing decreases r ap id ly a s the root systems decay fol lowing timber h a r v e s t . They concluded, when cons ide r ing t h e combined e f f e c t of root decay of t h e cut t r e e s and root growth of t h e p lan ted t r e e s , t h a t t h e f o r e s t s o i l would reach a minimum s t r e n g t h between 5 and 10 years a f t e r c u t t i n g and rep lan t ing . Ziemer and Swanston (1977) measured t h e changes i n s t r e n g t h of r o o t s remaining i n t h e s o i l a f t e r logging and noted t h a t even t h e l a r g e s t r o o t s l o s t a p p r e c i a b l e s t r e n a t h .

In g e n e r a l , t h e i n f l u e n c e of f o r e s t logging on d e b r i s flows a r e g r e a t e s t i n g r a n i t i c and t e r t i a r y s l o p e s (C-type) . P a l e o z o i c and mesozoic s l o p e s (8- type) g e n e r a l l y do n o t have an i n c r e a s e d i n c i d e n c e of d e b r i s f low a f t e r f o r e s t removal. Tsukamoto (1987) explained t h a t t h e r eason f o r t h i s i s t h a t t h e h igh p e r m e a b i l i t y of t h e f r a c t u r e d bedrock p r e v e n t s t h e b u i l d - u p of l a t e r a l groundwater flow along t h e bedrock. Ohta (1986) sugges ted t h a t roughness of t h e bedrock a l s o makes t h i s t y p e of s l o p e s t a b l e .

AS t e n d s t o i n c r e a s e a s t h e f o r e s t becomes o l d e r , up t o an age of about 20 y e a r s , a f t e r which AS remains abou t c o n s t a n t . The c o n t r i b u t i o n of a s i n g l e t r e e t o AS cont inues t o i n c r e a s e a s t h e t r e e becomes o l d e r . However, t h e number of t r e e s i n t h e f o r e s t decreases with f o r e s t age ( t a b l e 4 ) and t h e n e t e f f e c t i s a cons tan t AS a f t e r about 20 yea r s . Forty- . . year-old s t ands of Uygwtomerla laxmica

USDA Forest Service Gem Tech. Rep. PSW-GTR-130. 1991

Table 4--Sizes o f CrvDtomeria iaDonjca

---------- Tree aqe (yr) ----------

DBH (cm) 5.0 13.8 20.0 24.3 Height (m) 5.4 12.1 15.8 18.1 Number (ha-l) 3430 2265 1345 1030

2 Area (m ) 2.9 4.4 7.4 9.7

have a h i g h d e n s i t y - - o n e t r e e p e r 3 . 1 x 3 . 1 m . F o r t h i s s t a n d d e n s i t y , it i s a c c e p t a b l e t o e s t i m a t e AS on a u n i t a r e a b a s i s . However , f o r o l d - g r o w t h a n d s c a t t e r e d trees, it may n o t b e p r o p e r t o e s t i m a t e t h e r e i n f o r c e d s t r e n g t h b y u n i t a r e a , because t a p r o o t s t e n d t o c o n c e n t r a t e below t h e widely-spaced tree t r u n k s .

Most r o o t s i n t h e p o t e n t i a l s h e a r zone a r e l e s s t h a n 1 . 0 c m i n d i a m e t e r . I n t h i s p a p e r , o n l y t h e e f f e c t o f r o o t s w i t h i n t h e s h e a r zone were c o n s i d e r e d . However, s o i l r e i n f o r c e m e n t by l a t e r a l r o o t s s h o u l d a l s o be c o n s i d e r e d . Burroughs and Thomas (1977) r e p o r t e d t h a t zones o f weakness deve loped be tween s tumps t h a t c o u l d l e a d t o t h e i n i t i a t i o n o f s l o p e f a i l u r e .

CONCLUSIONS

Using a model o f t r e e r o o t d i s t r i b u t i o n a n d t h e p u l l - o u t s t r e n g t h o f r o o t s t o e s t i m a t e t h e e f f e c t o f r o o t s upon s l o p e s t a b i l i t y , we conc lude t h a t : (1) Root re in forcement c o u l d be expec ted on

s l o p e s where r o o t s grow i n t o j o i n t s o f b e d r o c k o r w e a t h e r e d t r a n s i t i o n a l l a y e r s . DS i n a p o t e n t i a l s h e a r zone o n s u c h s l o p e s h a d t w i c e t h e s h e a r s t r e n g t h o f s o i l wi thou t r o o t s .

( 2 ) Most r o o t s d i r e c t l y a f f e c t i n g s l o p e s t a b i l i t y a r e a b o u t 1 . 0 cm o r l e s s i n d i a m e t e r .

( 3 ) A f t e r a f f o r e s t a t i o n , DS would i n c r e a s e q u i c k l y f o r abou t 20 y e a r s , t h e n remain n e a r l y c o n s t a n t .

REFERENCES

Abe, K . ; Iwamoto, M . ; Y o s h i n o , S . ; I s h i g a k i , I . ; Tarumi, H . 1 9 8 5 . Tree - r o o t d i s t r i b u t i o n on a l a n d s l i d e s u r f a c e . T r a n . 9 6 t h . Ann. Mtg. J p n . F o r . Soc . : 639-642.

Abe, K . ; Iwamoto, M . 1986. An e v a l u a t i o n o f t r e e - r o o t e f f e c t on s l o p e s t a b i l i t y by t r e e - r o o t s t r e n g t h . J . J p n . F o r . Soc . 68: 505-510.

Abe, K . ; Iwamoto, M . ; Sammori, T. 1986 . S t r e n q t h o f b i n d i n q s o i l by t r e e r o o t . Trans ; 3 8 t h . Ann. M t g . an to J p n . F o r . SOC. : 217-220.

Abe, K . ; Iwamoto, M . 1987 . S o i l mechan ica l r o l e o f t r e e r o o t s i n p r e v e n t i n g l a n d s l i d e s . P r o c . 5 t h I n t e r n a t i o n a l C o n f e r e n c e a n d F i e l d Workshop o n L a n d s l i d e s ; 1987; C h r i s t c h u r c h , N Z ; 1- 9 .

Burroughs, E. J . J r . ; Thomas, B . R . 1977. D e c l i n i n g r o o t s t r e n g t h i n D o u g l a s - f i r a f t e r f e l l i n g a s a f a c t o r i n s l o p e s t a b i l i t y . R e s e a r c h P a p e r INT-190. O g d e n , UT: U.S . D e p a r t m e n t o f A g r i c u l t u r e , F o r e s t S e r v i c e . 27 p .

Endo, T . ; T s u r u t a , T. 1969. The e f f e c t o f t h e t r e e ' s r o o t upon t h e s h e a r s t r e n g t h of s o i l . 68 Ann. Rep. Hokkaido B r . , F o r . Experiment S t a t i o n : 167-182.

Gray, D . H . ; Ohashi , H . 1983. Mechanics of f i b e r r e i n f o r c e m e n t s i n s a n d . J . Geotech. Div. ASCE lOE(GT3): 335-353.

Ikemoto, W . ; T a k e s h i t a , K . 1987. E f f e c t o f t r e e r o o t on s l o p e s s t a b i l i t y . T r a n s . of Sabo R e s e a r c h P r e s e n t a t i o n Meet ing: 262-265.

K a r i z u m i , N . 1977 . Root b i o m a s s . JIBPO S y n t h e s i s ( S h i d e i , T . ; K i r a , T. , e d . ) . U n i v e r s i t y o f Tokyo P r e s s , Tokyo. 1 6 : 45-52.

Ki tamura, Y . ; Namba, S . 1981. The f u n c t i o n of tree r o o t s upon l a n d s l i d e p r e v e n t i o n Dresumed t h r o u s h t h e u D r o o t i n a t e s t . B u l l . of F o r . and F o r . ~ L o d . ~e ; . I n s t . 313: 175-208.

Makabe, H . 1 9 6 6 . Usage o f W e i b u l l p r o b a b i l i t y g r a p h . N i p p o n K i k a k u Kyoukai. 81 p .

Morimoto, Y . 1982 . Syamen Ryokka Kashima Syuppankai, Tokyo: 94-120.

Nakane, K.; Nakagawa, K . ; T a k a h a s h i , F . 1983 . Change i n t e n s i l e s t r e n g t h o f J a p a n e s e r e d p i n e r o o t s a f t e r d e a t h by f i r e . J . J p n . F o r . Soc . 65: 155-165.

Ohta , T. 1986. F o r e s t e f f e c t on p r e v e n t i o n o f sed iment d i s a s t e r . Repor t of F o r e s t Management R e s e a r c h Meet ing . 298: 17- 1 C L " .

O ' L o u g h l i n , C . L. 1974 . A s t u d y o f t r e e r o o t s t r e n g t h d e t e r i o r a t i o n f o l l o w i n g c l e a r f e l l i n g . C a n a d i a n J . o f F o r . Research 4 (1) : 107-113.

O'Loughl in , C . L . ; Rowe, L . K . ; P e a r c e , A . J . 1982 . E x c e p t i o n a l s t o r m i n f l u e n c e s on s l o p e e r o s i o n and sediment y i e l d s i n s m a l l f o r e s t c a t c h m e n t s , n o r t h W e s t l a n d , New Z e a l a n d . P r o c . o f N a t i o n a l Symposium o f F o r . Hydrology, Melbourne, A u s t r a l i a .

O ' L o u g h l i n , C . L . ; Ziemer , R . R . 1982 . I m p o r t a n c e o f r o o t s t r e n g t h a n d d e t e r i o r a t i o n r a t e s upon e d a p h i c s t a b i l i t y o f s t e e p l a n d f o r e s t s . P r o c e e d i n g s o f IUFRO Workshop P.1 .07-00 Eco logy o f S u b a l p i n e Ecosystems a s a Key t o Management. 1982 August 2-3, C o r v a l l i s , O R . C o r v a l l i s , O R : Oregon S t a t e U n i v e r s i t y ; 70-78.


S h e w b r i d g e , S . 1 9 8 5 . The i n f l u e n c e o f r e i n f o r c e m e n t p r o p e r t i e s o n t h e s t r e n g t h a n d d e f o r m a t i o n c h a r a c t e r i s t i c s o f a r e i n f o r c e d s a n d . Berke ley , CA: U n i v e r s i t y of C a l i f o r n i a ; D i s s e r t a t i o n

Tsukamoto, Y . 1 9 8 7 . E v a l u a t i o n o f t h e e f f e c t o f t r e e r o o t s on s l o p e s t a b i l i t y . B u l l . o f t h e E x p e r i m e n t F o r e s t s . Tokyo Univ . o f A g r i c . a n d Technol . N O . 23: 65-124.

Waldron, L . J . 1977. The s h e a r r e s i s t a n c e o f r o o t - p e r m e a t e d homogeneous a n d s t r a t i f i e d s o i l . S o i l S c i e n c e Soc . o f America J. 4 1 : 843-849.

Waldron, L . J . ; D a k e s s i a n , S . 1981. S o i l r e i n f o r c e m e n t b y r o o t : c a l c u l a t i o n o f i n c r e a s e d s o i l s h e a r r e s i s t a n c e f rom r o o t p r o p e r t i e s . S o i l S c i e n c e 1 3 6 ( 6 ) : 427-435,

Wu, T . H . 1 9 7 6 . I n v e s t i g a t i o n s o f l a n d s l i d e s on P r i n c e o f Wales I s l a n d , A l a s k a . Geotech. Eng. Rep. 5 , Columbus, O H : D e p t . C i v . Eng . , Ohio S t a t e Univ. 94 p .

Z i e m e r , R . R . 1981. Roots and t h e s t a b i l i t y o f f o r e s t e d s l o p e s . I n : D a v i e s , T. R. H . ; P e a r c e , A . J . , e d s . E r o s i o n and S e d i m e n t T r a n s p o r t i n P a c i f i c Rim S t e e p l a n d s ; 1981 January ; C h r i s t c h u r c h , N Z . IAHS/AISH P u b l . No.132 Wal l ingford , U K : I n t e r n a t i o n a l A s s o c i a t i o n o f H y d r o l o g i c a l S c i e n c e s ; 343-361.

Z i e m e r , R . R . ; Swanston, D . N . 1977. Root s t r e n g t h c h a n g e s a f t e r l o g g i n g i n s o u t h e a s t A l a s k a . R e s e a r c h Note PNW- 3 0 6 . P o r t l a n d , OR: U.S. Depar tment o f A g r i c u l t u r e , F o r e s t S e r v i c e . 10 p .

USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130. 1991

Watershed Concerns and Recent Policy Formulations in Sri Lanka and Australia1 Rohan Ekanayake2

A b s t r a c t : A d d r e s s i n g t h e p r o b l e m s a s s o c i a t e d w i t h w a t e r s h e d s i n b o t h c o u n t r i e s i s t h e aim o f t h i s p a p e r a s w e l l a s a s s e s s i n g t h e r e s p e c t i v e w a t e r s h e d p o l i c i e s . A t t e n t i o n h a s been drawn t o s p e c i f i c economic, env i ronmenta l and s o c i o c u l t u r a l c o n s i d e r a t i o n s i n t h e r e c e n t p a s t . An i n t e r e s t i n g f e a t u r e of t h e most r e c e n t p o l i c y deve lopments i s t h e t e n d e n c y t o f o l l o w a b a l a n c e d approach t o w a t e r r e s o u r c e development i n e i t h e r s i t u a t i o n . I n A u s t r a l i a , it i s e n v i s a g e d t o f o l l o w a c o - o r d i n a t e d and s u s t a i n a b l e u s e and management o f l a n d w a t e r , a n d v e g e t a t i o n r e s o u r c e s on a w a t e r c a t c h m e n t b a s i s . I n S r i Lanka however, a f t e r a p ro longed l u l l i n p o l i c y a p p r o a c h e s i t i s o n l y b e g i n n i n g t o p r e p a r e t h e framework towards a b e a r a b l e

e .

W h i l e a c c o m m o d a t i n g a s i m i l a r p o p u l a t i o n t o A u s t r a l i a , S r i Lanka i n i t s t i n y 270 m i l e s s t r e t c h , h a s i t s p e o p l e c l u s t e r e d on t h e m o i s t sou thwes te rn t h i r d o f t h e i s l a n d known a s t h e 'wet zone ' . I n A u s t r a l i a , where t h e main c o n c e n t r a t i o n i s i n t h e e a s t e r n p a r t o f t h e c o n t i n e n t , t h e r e i s heavy r e l i a n c e on ca tchments o f t h e Great D i v i d i n g Range a n d t h e a s s o c i a t e d r u n - o f f f o r a g r i c u l t u r e and h y d r o e l e c t r i c i t y . I n S r i Lanka, t h e c a t c h m e n t s f o r n e a r l y a l l i t s m a j o r r i v e r s r e s t i n t h e c e n t r a l h i g h l a n d s where most o f i t s h y d r o e l e c t r i c i t y i s

P r e s e n t e d a t t h e S u b j e c t Group S1.04 T e c h n i c a l S e s s i o n on Geomorphic Hazards on Managed F o r e s t s , X I X World Congress I n t e r n a t i o n a l Union of F o r e s t r y Research O r g a n i s a t i o n s , A u g u s t 5 - 1 1 , 1 9 9 0 , Montreal , Canada.

R e s e a r c h E c o n o m i s t , Wate r a n d Land Resources D i v i s i o n , Department o f Pr imary I n d u s t r i e s a n d E n e r g y , a n d f o r m e r l y R e s e a r c h S c h o o l o f S o c i a l S c i e n c e s , A u s t r a l i a n N a t i o n a l U n i v e r s i t y , Canber ra .

g e n e r a t e d a n d w a t e r d i v e r t e d f o r d o w n s t r e a m p u r p o s e s . C o m p a r e d t o A u s t r a l i a , S r i L a n k a r e c e i v e s a r e l a t i v e l y h i g h e r r a i n f a l l m a i n l y f rom t h e monsoonal r a i n s .

WATERSHED MANAGEMENT

S r i Lanka

I r r i g a t i o n s t r u c t u r e s i n t h e d r y zone o f S r i Lanka h a s a h i s t o r y o f 2000 y e a r s , a n d t h u s , i t s f i r s t w a t e r management p r a c t i c e s can b e r e l a t e d t o t h a t t i m e . However, i n modern S r i Lanka, s o i l e r o s i o n and wate r shed problems were f i r s t r e c o g n i s e d and a d d r e s s e d i n t h e l e g i s l a t u r e i n t h e e a r l y 1 9 4 0 ' s . But p o l i c y f o r m u l a t i o n d i d n o t t a k e p l a c e t i l l r e c e n t t i m e s b e f o r e a major r i v e r b a s i n development programme was i n i t i a t e d s u r r o u n d i n g t h e Mahaweli r i v e r . Large ly , towards t h e s u s t e n a n c e o f t h i s programme, it was i n e v i t a b l e some p o l i c y b e i n t r o d u c e d t o manage t h e n a t u r a l r e s o u r c e s s u r r o u n d i n g i t s c a t c h m e n t s . T h i s m a t e r i a l i z e d o n l y i n t h e l a t e 1989 when a n i n t e r i m r e p o r t on w a t e r s h e d management was c o n s i d e r e d by p o l i c y makers i n S r i Lanka.

The r e l e v a n t l e g i s l a t i o n were f i r s t i n t r o d u c e d i n A u s t r a l i a i n 1915, and i t s m a i d e n w a t e r r e s o u r c e a s s e s s m e n t programme began i n 1963. A u s t r a l i a ' s main w a t e r management programme i n v o l v e s t h e Murray-Darl ing r i v e r b a s i n t h a t s p r e a d s o v e r f o u r of i t s major s t a t e s .

More r e c e n t l y , a B i l l was t a b l e d i n t h e New S o u t h Wales L e g i s l a t u r e t o implement t o t a l ca tchment management o f t h e S t a t e ' s n a t u r a l r e s o u r c e s , namely, t h e c o - o r d i n a t e d and s u s t a i n a b l e u s e and management of l a n d , wa te r , and v e g e t a t i o n r e s o u r c e s on a c a t c h m e n t b a s i s . Such p o l i c y deve lopments f o l l o w e d t h e r e c e n t F e d e r a l c o n c e r n s o v e r a b a l a n c e d approach t o n a t u r a l r e s o u r c e s management i n A u s t r a l i a .


CONCERNS FOCUS

While d e f o r e s t a t i o n i n t h e catchment v e g e t a t i o n i s common i n b o t h c o u n t r i e s a n d e x c e s s i v e p r e s s u r e o n w a t e r r e s o u r c e s , i s t h e r e g e n u i n e c o n c e r n i n S r i Lanka and i n A u s t r a l i a t o a m e l i o r a t e t h e s i t u a t i o n and a c h i e v e a b a l a n c e ? The e x t e n t o f t r e e c l e a r i n g i n A u s t r a l i a i n t h e main catchment (Grea t D i v i d i n g Range) o f t h e Murray-Dar l ing B a s i n a l o n g t h e e a s t e r n c o a s t i s shown i n t h e map. S r i Lanka , h a v i n g c a r r i e d o u t i t s l a s t p a r t i a l f o r e s t i n v e n t o r y i n 1956, f a c e s s i m i l a r e x c e s s i v e d e f o r e s t a t i o n i n t h e main ca tchment of t h e Mahaweli and it i s e s t i m a t e d t h a t i t s f o r e s t c o v e r h a s d w i n d l e d f rom 56 p e r c e n t i n 1956 t o a mere 15 p e r c e n t i n t h e p r e s e n t t i m e s .

ienl ot Tree Clearing in Australia Since European Setllernent

I n b o t h s i t u a t i o n s , e n v i r o n m e n t a l f l o w management a n d f l o o d m i t i g a t i o n remain u n r e s o l v e d p o l i c y i s s u e s m a i n l y b e c a u s e o f l a c k o f i n f o r m a t i o n and t h e a s s o c i a t e d s o c i a l and economic f a c t o r s . I t i s i n t h e same i n t e r e s t t h a t it h a s become a p p a r e n t t h o s e i s s u e s b e a d d r e s s e d i n a c o h e r e n t p o l i c y f rame f o r b r o a d i n t e r - t e m p o r a l r e a s o n s . The s u s t a i n a b l e f rame s t i l l remains t h e same- t h e T r i n i t y o f S o i l , T r e e s and Water (diagram 1).

I n t h i s p a p e r , a n a s s e s s m e n t o f t h e w a t e r s h e d p o l i c i e s o f b o t h c o u n t r i e s h a s b e e n c a r r i e d o u t d r a w i n g a t t e n t i o n t o s p e c i f i c e c o n o m i c , e n v i r o n m e n t a l a n d s o c i o c u l t u r a l c o n s i d e r a t i o n s i n t h e r e c e n t p a s t .

INSTITUTIONS and p o l i c y

Government p o l i c y i n t e r v e n t i o n i s two-pronged i n wa te r shed c o n c e r n s . D i r e c t and i n d i r e c t . D i r e c t p o l i c i e s a r e o f t e n r e g u l a t i n g m e a s u r e s t h a t a f f e c t a wa te r shed .

I n d i r e c t p o l i c i e s c o n v e r g e on t h e i n t e g r a t e d l a n d - u s e s i n a n o v e r a l l w a t e r s h e d r e g i o n . U s u a l l y t h e s e measures d o n o t f a l l w i t h i n t h e s c o p e o f a p a r t i c u l a r p o l i c y c o n s i d e r a t i o n . I t would b e f a i r t o s a y t h a t i n e f f e c t , i n d i r e c t p o l i c y once a p p l i e d h a s i n d i r e c t e f f e c t s on t h e w a t e r s h e d . These i n d i r e c t e f f e c t s a r e t h e n moulded i n t o e x p l i c i t p o l i c y i n t h e n e x t a p p l i c a t i o n .

Indirect Policy I

( a t y p i c a l t h e o r e t i c a l e x p l a n a t i o n of an e f f e c t on a wa te r shed)

I i n t r o d u c t i o n ......p r i c e s u b s i d y f o r

a g r i c u l t u r a l p r o d u c t i o n /

i n t e n s i v e and ...... e f f e c t s from t h e e x t e n s i v e l a n d v e s e t a t i o n cover r e d u c t i o n - u s e / i n c r e a s e d s o i l ...... i n c r e a s e d s e d i m e n t a t i o n e r o s i o n

/ r e s e r v o i r ...... power c u t s , o i l impor t s w a t e r l e v e l s t o f u e l e x t r a t u r b i n e s d i m i n i s h i n g I

o v e r a l l ... economic, r e s o u r c e and env i ronmenta l e f f e c t s on s o c i e t y

The p o l i t i c a l economy w i t h i n which p o l i c i e s a r e formed, reshaped and a p p l i e d i s a r t i c u l a t e d u n i q u e l y a c c o r d i n g t o t h e s p e c i f i c s p a t i a l c o n d i t i o n i n S r i Lanka and A u s t r a l i a . Trees and Soil Conservolion A .led,.,,b

I n S r i Lanka, it i s more c e n t r a l l y c o n t r o l l e d a n d r e g i o n a l l y a p p l i e d . I n A u s t r a l i a however, it i s more r e g i o n a l l y c o n t r o l l e d a n d r e g i o n a l l y a p p l i e d . F o r i n s t a n c e , t h e r o l e o f t h e C e n t r a l Government i n i n s t i t u t i o n a l m a t t e r s i n S r i Lanka i s a u t h o r i t a t i v e i n n a t u r e , whereas i n A u s t r a l i a t h e r o l e o f t h e F e d e r a l Government i n w a t e r a f f a i r s i s more o r i e n t e d t o w a r d s a p r o - a c t i v e p a r t i c i p a t i o n .

USDA Forest SelviceGen. Tech. Rep. PSW-GTR-130. 1991

I n managed and unmanaged w a t e r and w a t e r s h e d a f f a i r s , S r i Lanka 's c e n t r a l l y d o m i n a t e d a n d d i r e c t e d p o l i c y i s e s s e n t i a l l y a l i n e f u n c t i o n a l sys tem ( n o t n e c e s s a r i l y though t h e y a r e e f f i c i e n t ) . I n A u s t r a l i a , s e v e r a l r e g i o n a l ( S t a t e s ) g o v e r n m e n t s h a v e d i f f e r e n t p o l i c y a p p r o a c h e s , i n s t i t u t i o n a l s t r u c t u r e s i n p l a c e , and l e g a l frameworks i n w a t e r s h e d s e t t i n g s ( n o t n e c e s s a r i l y though t h e y a r e i n e f f i c i e n t ) .

C o n s i d e r t h e t w o - n a t i o n ' s main w a t e r s h e d r e g i o n s . The f o c u s i s on t h e more n a t u r a l l y i m p o r t a n t a s w e l l a s s o c i a l l y d e s i r e d p r o d u c t i v e r e g i o n s ( i . e . B a s i n s ) .

T h e s e B a s i n s s e r v e a s t h e i r r e s p e c t i v e economic and e c o l o g i c a l n e r v e s where most s o c i a l t r a n s f o r m a t i o n s o c c u r , v a l u a b l e c u r r e n c y exchange e a r n e d , more i m p o r t a n t l y f o o d p r o d u c e d , t h e p e o p l e p r o d u c t i v e l y employed a n d s c a r c e a n d b e a r a b l e w a t e r managed.

The r e c e n t phenomenon i s n o t s o much a n o p t i m i s t i c and p rob lem s o l v i n g w a t e r f r o n t t o b o t h c o u n t r i e s , b u t c o n s i s t o f overwhelming problem s o l v i n g h o r i z o n s . It i s i n f a c t i n h e r i t a n c e i n b o t h s i t u a t i o n s . The g r e a t e s t t a s k s t h a t b o t h c o u n t r i e s have a s p i r e d a r e t h e c h a l l e n g e s f a c e d w i t h the a c c e n t u a t e d env i ronmenta l consequences from t h e c o n t i n u e d r e s o u r c e d e g r a d a t i o n .

A t c r o s s r o a d s a r e t h e f a v o u r i t e c o n c e p t s f o r p o l i c y m a n i p u l a t i o n i n f l o o d m i t i g a t i o n , e n e r g y s u s t e n a n c e , w a t e r q u a l i t y m a i n t e n a n c e , t o t a l a p p r o a c h t o b a l a n c e d r e s o u r c e u s e a n d o f c o u r s e s u s t a i n a b i l i t y .

D e s p i t e t h e optimism, t h i s b r i n g s u s t o a t h i r d s e t o f p o l i c y a p p l i c a t i o n . N a t u r a l R e s o u r c e s Management S t r a t e g y (NRMS) f o r o v e r a l l r e s o u r c e p l a n n i n g and

management f o r a B a s i n wide s y s t e m . The i n i t i a t i v e s a r e ( f o l l o w i n g t h e maps) ;

S r i Lanka- Mahaweli A c c e l e r a t e d Program

A u s t r a l i a - Murray-Darling Basin N a t u r a l Resources Management S t r a t e g y and Program.

S r i Lanka:

Optimum c o n s e r v a t i o n o f c a t c h m e n t s i s i n pursuance .

Land Development Ordinance 1935.

S o i l c o n s e r v a t i o n A c t f o l l o w s a f t e r u p r i v a t e member B i l l i n t h e L e g i s l a t u r e i n 1940.

A c o n s i d e r a b l e l u l l i n t h e 1 9 5 0 ' s th rough t o 1 9 6 0 ' s .

Absence o f i n t e g r a t e d B a s i n wide watershed a n a l y s i s .

Lack o f i n d e p t h s t u d y on d e t a i l e d catchment hydro logy .

D e f f i c i e n c y i n r e s o u r c e s and h i g h l e v e l o f r e s o u r c e d e g r a d a t i o n w i t h p l a n t a t i o n a g r i c u l t u r e and p r i v a t e f e l l i n g i n t h e main ca tchment .

A l l Bas ins :

R i v e r s 1 0 3 , t o t a l c a t c h m e n t a r e a 59,217 s q km and number of s t r e a m gauging s t a t i o n s (River Gauging S t a t i o n s ) ; 68.

The Mahaweli B a s i n catchment 10,443 s q km a n d 1 8 RGS, number o f r u n - o f f s t a t i o n s : on a d a i l y b a s i s - n i l , monthly- 7 .

Recent on wate r shed developments :

F i r s t I n t e r i m Report on Land 1985.

Second I n t e r i m Report on Land 1989


Basin developments: 1 The Murray-Darling Basin \

In the Mahaweli Accelerated Program total run-off in the project at lowest points of diversion is 10,000 cu m or 25 percent of the total run-off.

A Forestry Master Plan (1986) to circumvent the acute deforestation has been introduced

1/7th of Australia's surface catchment falls within the purview of Murray-Darling Basin.

20 major rivers off the Great Dividing Range.

40,000 years history of the Basin associated Aboriginal Culture.

The length of the River is 3780 km

Australia:

First Legislation in 1915 on Murray- Darling Basin Agreement between New South Wales, Victoria and South Australia.and River Murray Waters Amendment Act 1987.

Catchment management and water management follows.

Federal level New directions of Water Management 1987 and Instream Uses of Water.

Recently, NSW State Legislation on Total Catchment Management, 1989 (see community participation as per media publicity) .

Basin wide:

135 RGS and 10 within the Murray- Darling Basin.

River Murray Waters Act 1987.

30 to 40 percent of Australia's total natural resource based production occurs in the Basin.

7000 wetlands within the Murray waters.

Murray yields 12,000 gigalitres and the Darling carries 12 percent of the run- off over 50 percent of the Basin area.

CONSTRAINTS

Conflicts in the institutional arrangements create external diseconomies and in turn have created duplication and overlapping of institutions in both situations.

These impediments have caused disincentives to achieve efficiency and there is a large resource value depletion in both watersheds. This is largely reflected in undercharging for water and lack of appreciation of the resource has been aggravated by the absence of a rent which is the key to secure the resource for intergenerational purposes.


The way t h e p o l i t i c s i n t e r p r e t p r i o r i t i e s , i g n o r a n c e , pos tponement o f a c t i o n s and u n d i s c l o s e d d e f i n e d r e g i m e s p a r t i c u l a r l y i n t h e s u s t a i n a b i l i t y i s s u e s h a v e c a u s e d t h e g r e a t e s t i n e q u i t y i n watershed concerns i n t h e s e s i t u a t i o n s .

I n A u s t r a l i a , i n t e r - g o v e r n m e n t a l quangos such a s t h e River Murray Agreement p r e s e n t bona f i d e commitment by t h e S t a t e s t o c o - o r d i n a t e d , comprehens ive r e g i o n a l approach t o i n t e r s t a t e wa te r and r e s o u r c e i s s u e s .

T h e r e i s l e g a l o p i n i o n t h a t a r a t i o n a l scheme f o r b a l a n c i n g c o n f l i c t i n g i n t e r e s t s w i t h i n t h e Murray-Darling Basin a n d f o r a d m i n i s t e r i n g t h e s y s t e m i s u n l i k e l y t o s p r i n g up, a l o n e and unaided, a s a v o l u n t a r y p r o d u c t of S t a t e c o n s e n t .

I n S r i Lanka, t h e i n f a n t s t a g e o f i t s h a n d l i n g o f n a t u r a l r e s o u r c e s a n d i n i t i a t i v e s , and t h e s l o w p r o g r e s s and c a u t i o u s a p p r o a c h v i n d i c a t e t h e whole o b j e c t i v e of wa te r shed p r o t e c t i o n f o r good economic and e n v i r o n m e n t a l r e a s o n s . The e x p e c t a t i o n t h a t f o r e i g n h e l p would always be fo r thcoming t o s a l v a g e t h i n g s t h a t have gone wrong f o r d e c a d e s due t o p o l i t i c a l m i s h a n d l i n g o f i m p o r t a n t i s s u e s i s i n i t s e l f a summation of t h e i d e o l o g y b e h i n d t h e s c e n e .

I n A u s t r a l i a , a major problem t h a t t h e M u r r a y - D a r l i n g B a s i n w a t e r s h e d p l a n n i n g c o n f r o n t s i s t h e v o l u n t a r y non- p a r t i c i p a t i o n of t h e Queens land s t a t e i n t h e S t r a t e g y t o manage t o t a l w a t e r , v e g e t a t i o n a n d e n v i r o n m e n t a l f l o w s . I n t e r m s o f key t r i b u t a r i e s , t h e S t a t e ' s p a r t o f t h e catchment i s c r i t i c a l t o a c h i e v e a b e a r a b l e l e v e l o f w a t e r f l o w s i n t h e downstream. They a r e a l s o t h e u n d e r l y i n g c a u s e s f o r most o f t h e f l o o d i n g i n t h e a d j o i n i n g S t a t e o f NSW ( d u r i n g t h e p r e p a r a t i o n o f t h i s m a n u s c r i p t t h e i r h a s b e e n a p o s i t i v e d e v e l o p m e n t t o c o n g l o m e r a t e Q u e e n s l a n d t o t h e R i v e r Murray Waters Agreement) .

CONCLUSION

N a t u r a l r e s o u r c e management i s t a k e n up by a b r o a d l y mode l led t o t a l ca tchment concep t which h a s impor tan t pa ramete rs and i m p l i c a t i o n s . However, it i s a b r a n d new phenomena. Only t i m e can d e t e r m i n e t h e s i g n i f i c a n c e o f t h e s t r a t e g y a s w e l l a s t h e a c c e l e r a t e d i n i t i a t i v e s .

T o t a l ca tchment management h a s scope f o r f l o o d m i t i g a t i o n , s o i l c o n s e r v a t i o n a n d s e d i m e n t a t i o n p r o b l e m s i n e i t h e r s i t u a t i o n . The concep t i s i n harmony w i t h a n o v e r a l l s u p p l y o f v e g e t a t i o n r e s o u r c e s

and s u s t a i n e d p r o d u c t i v e r e s o u r c e f o r t h e r e s p e c t i v e r e g i o n s .

I n t e r g e n e r a t i o n a l i s s u e i s a n o t h e r i m p o r t a n t p o l i c y d e b a t e t h a t looms g i v i n g p e r t i n e n t a t t e n t i o n t o i n t e r t e m p o r a l e q u i t y v a l u e o f t o t a l r e s o u r c e s i n a w a t e r s h e d . A t t h i s p o i n t i n t i m e t h e b e s t c o u l d b e a c h i e v e d i s t o l e a r n from t h e p a s t m i s t a k e s a n d a c c o m m o d a t e comprehensive s e t s of o b j e c t i v e s n o t o n l y t o c i rcumvent p r e v i o u s impediments b u t t o g u a r d a g a i n s t r e o c c u r r e n c e o f d e g r a d a t i o n s a n d d e n u d a t i o n s . Because s i n g l e i s s u e o r i e n t e d s o l u t i o n s i n a w a t e r s h e d r e g i o n d o e s n o t c a r r y t h a t much o f we igh t i n p o l i c y j u s t i f i c a t i o n anymore.

However, t h e d e t e r m i n i n g f o r c e i s n o t t h e way t h a t p o l i c y i s forwarded i n a p a c k a g e , b u t t h e t r a d e - o f f s d e s i r e d p o l i t i c a l l y and implemented c o n c e r n i n g w h e t h e r e q u i t y o r e f f i c i e n c y i s t h e c r i t e r i o n o f t h e d a y . I t i s paramount b e c a u s e n e i t h e r w i l l b e a c h i e v e d i f b o t h c r i t e r i a a r e pursued .

A conceptual model of watershed

policy

I Level of p o l i c y s u b s t i t u t i o n = l e v e l of

program/NRMS p o l i c y

I Take NRMS f o r i n s t a n c e a s a f u n c t i o n of

T o t a l Catchment

I Management [NRMS f (TCM) I

I TCM f ( s o i l , v e g e t a t i o n , wa te r shed)

I T h e r e f o r e , t h e s i g n i f i c a n c e f o r wa te r

p o l i c y

I a s t h e i n s t i t u t i o n f o r watershed concerns

n o t e :

NRMS= N a t u r a l Resources Management S t r a t e g y

TCM= T o t a l Catchment Management


REFERENCES COMMUNITY REPRESENTATIVES CATCHMENT MANAGEMENT

COMMITTEE for the Lower Murray-Darling Region

CATCHMENT MANAGEMENT ACT, 1989 The N S W Government is erlablirhing Calchment Managcmenl Cammillecr, under the Catchment Management Ac l 1989. to implement Tola1 Catchmen! Manrgcmenl ( T C M ) objcctiver. T C M k a community-based approach 10 natural resource management. I1 is the co-ordinated and ~ustainable urc and management of land. water, veaclalion. fauna and other natural resources. Its aim is in balvncc r&ouicc use and canrcivation To allow various and d i k i n g Wcslern N S W land use management lssucs to be adequately and effectively addressed i t is proposed to divide the Wcstcrn R c ~ i o n into two reeionr:

The boundary between these regions follows the Sydney-Broken Hill Railway line until Menindee Lakes. The Menindee Lake System. Broken Hill and the enlirc Lake Viclaria catchment lies within the Lower Mur ray -Dar l i n~ Region. Thc eartcrn boundary of ihc Lowcr Murray-Darling region iollows ihc catchmen1 boundary wi lh the Lachlan and Murrumbidgce, being the boundary t o the Lachlan and Muriumbidgee T C M regions. The southern and western boundaries follow the Murray RivcrjVictorian border and South Australian border rerncclivelv. Pcrsun, who ace landhuldcir, laodu&% or who ham an intercst i n environmenval mal ien in the Lawer Murray-Darl ing are invited to apply lo be represenlalives o i i h c region on the T C M Cornmillee. Members o i lhe exisling WWern Calchment Management Cammiltcc wi l l becamo members o i (he Cammiltee within which they reside and do not nced to reapply. Applicanu rhould Dossesr the followine oualities: - .

coirm tmw: io su.!din~b e dc.cl~pmcn1. kns~lcagc. lntererl ~r ckpcrien:e n nalur2l rcrodrce mmlgemml . 3bd 1) 10 rcprejcn! commun t y ,cur. moucdgc o i m t . r i rcromcc I r r x r .n the catcnmcm and hou thcsc tisuer 3ifc:t 1 k pc.ap.c. rnd r x r 8 ::lpml.r, 75 P I I ~ ~ ~ C W L U 1b.ni n~ ~ n d thc %bll.t, lo uork wc. . .... F - - r . - .

Further iniormation is available from M r . Brenda" Diacono, T C M Comdinatoi: (Ohill RR 0 2 5 5 ~

~ ..,.. Wril lcn applications providing details in terms o f the above ualitics should bc with M r . Diacono (c/- N S W Soil Conservation %,,vice. 32 Sulphidc Slrccl, Brakcn H i l l 2880) by 11 August. 1990.

1. Western

2. Lower Murray-Darling

THE NEW SOUTH WALES GOVERNMENT q Putting people first by managing better Bo

Australia Murray-Darling Basin by Murray- Darling Basin Ministerial Council. 1990. Natural Resources Management Strategy Towards a Sustainable Future; ii.

Clark, S.D.; 1983. Intergovernmental Quangos: The River Murray Commission. Australian Journal of Public Administration XLII (1) : 155- 171.

Commonwealth of Australia; 19897. River Murrav Waters Amendment Act. No. 154

Day,

of 1987. Australia; Commonwealth Government Printer.

Diana G.; 1988. River Mismanagement: Policy, Practice or Nature?; Centre for Resource and Environmental Studies Working Paper 1988/1; Australian National University; 1- 42.

Democratic Socialist Republic of Sri Lanka; 1985. First Interim Report of the Land Commission; Sessional Paper No.1- 1986. Department of Government Printing Sri Lanka.

Democratic Socialist Republic of Sri Lanka; 1989. Second Interim Report of the Land Commission- 1985. Department of Government Printing Sri Lanka.

Department of Primary Industries and Energy; 1988. Instream Use of Australia's Water Resources; Australian Water Resources Council Water Management Series No.11. Australian Government Printing Press; 1-13.

de Silva, Chandrananda R.K. 1982. Sri Lanka Country Paper. In: Water and Soil Miscellaneous Publication No. 45; Catchment management for optimum use of land and water resources: Documents from an ESCAP seminar; 1982 Wellington; 191-202.

Extent of Tree Clearing in Australia Since European Settlement by Ive and Cock. 1989. Rural Land Degradation in Australia: The Australian Conservation Farmer; 1 (3) .

ACKNOWLEDGEMENTS Murray-Darling Basin Ministerial Council;

I thank my friend S. Gunatunqa, Sri Lanka; 1990. Natural Resources Management

for sending research material. This paper Strategy Murray-Darling Basin:

was supported by the Scientist Assistance Towards a Sustainable Future;

Program of Canada. August, 1990.

26 USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991

Murray-Darling Basin Ministerial Council; 1987. Murray-Darling Basin Environmental Resources Study; july 1987; State Pollution Control Commission, Sydney. 27-113; 251-281.

NEDECO; 1979. Mahaweli Ganga Development Program Implementation Strategy; Netherlands Engineering Consultants; The Hague September 1979; Volume 1 Main Report; 17-21.

New South Wales Government. Community Representatives Catchment Management Committee. The LAND. 1990 July 26. 2 (col.1) . New South Wales.

New South Wales (NSW) State Parliament; 1989. Catchment Management Bill. First Print.

Soil Conservation Service of New South wales; 1990. Total Catchment Management: A State Policy Including State Soils Policy, State Trees Policy.

Sri Lanka Mahaweli Basin and Accelerated Program b.y IIM1.1986.; 19.

Sri Lanka Mahaweli Basin and Mahaweli River Catchment appeared in a paper presented by Rohan Ekanayake; Economics of Multiple Use of Production Forests in Sri Lanka. 1986. 30th Annual Conference of the Australian Agricultural Economics Society; February 3-5, 1986; 20.

The Global Water Runoff Data Project. 1989. World Climatic Programme Research, Workshop on the Global Runoff Data Set and Grid Estimation, WCRP - 22 and WMO/TD - No. 302, 1988 November 10-15; Klobenz, FRG; 6-12.

Trinity of Soil, Trees and Water based on a diagram in a publication of the NSW Soil Conservation Service.

USDA Forest SewiceGen. Tech. Rep. PSW-GTR-130.1991

Surrounding the Consequences of Watershed Disasters in the Periphery of the Indian Triangle1 Rohan Ekanayake2

A b s t r a c t : The w a t e r s h e d o f t h e ' I n d i a n T r i a n g l e ' i s formed by t h e f l o w o f two m i g h t y r i v e r s which e m a n a t e f rom t h e H i m a l a y a . The Ganges a n d B r a h m a p u t r a embrace t h e l a n d s a n d t h e p e o p l e s o f Nepa l* , I n d i a * a n d B a n g l a d e s h * b e f o r e emptying i n t o t h e Bay o f Benga l . A r e c e n t monsoon submerged two t h i r d s o f t h e low- l y i n g B a n g l a d e s h r e n d e r i n g 25 m i l l i o n p e o p l e homeless . Can t h e f u t u r e of t h e s e p e o p l e b e s e c u r e d by l o w e r i n g t h e w a t e r l e v e l s downstream? A r e t h e r e a l t e r n a t i v e s t r u c t u r a l p r o p o s i t i o n s a n d a r e t h e y e c o n o m i c a l l y and p o l i t i c a l l y f e a s i b l e ? What e f f e c t w i l l t h e e x c e s s i v e removal o f n a t u r a l b a r r i e r s t o r a i n i n t h e u p p e r ca tchments have on p o l i c y ?

A major i s s u e a d d r e s s e d i n t h i s p a p e r i s t h e s u s t a i n a b l e development and e c o l o g i c a l s t a b i l i t y i n t h e s e w a t e r s h e d r e g i o n s . A m a j o r i t y o f t h e e n v i r o n m e n t a l problems i n t h e r e g i o n ' s w a t e r s h e d s i n t h e p a s t have o c c u r r e d main ly due t o u n d e s i r a b l e human i n t e r f e r e n c e i n r e g i o n a l e n v i r o n m e n t a l f l o w s and v e g e t a t i o n r e s o u r c e s . P l a u s i b l e s o l u t i o n s t o o n - g o i n g a n d f u t u r e e n v i r o n m e n t a l c r i s i s w i l l l a r g e l y depend o n how b r o a d t h e r e g i o n a l c o n s e n s u s i s s u r r o u n d i n g t h e c o n f l i c t i n g wate r . r e source i s s u e s . Depending on how t h e dominan t r u r a l s o c i a l b a s e a d j u s t t o i m p o r t a n t d y n a m i c s o f t h e p r o b l e m , t h e p a p e r c o n c l u d e s t h a t s u s t a i n a b i l i t y w i l l be a n i s s u e v u l n e r a b l e t o p o l i t i c a l interDretation.

P r e s e n t e d a t t h e S u b j e c t Group 5 1 . 0 4 T e c h n i c a l S e s s i o n on Geomorphic Hazards on Managed F o r e s t s , X I X World C o n g r e s s I n t e r n a t i o n a l Union o f F o r e s t r y R e s e a r c h O r g a n i s a t i o n s , A u g u s t 5 - 1 1 , 1 9 9 0 , Montreal , Canada.

R e s e a r c h Economist working i n t h e Water Branch o f t h e Land Resources D i v i s i o n i n t h e Depar tment o f P r i m a r y I n d u s t r i e s and Energy a n d f o r m e r l y R e s e a r c h S c h o o l o f S o c i a l S c i e n c e s , A u s t r a l i a n N a t i o n a l U n i v e r s i t y , Canber ra .

L i k e most w a t e r s h e d r e g i o n s i n t h e world, t h e wa te r shed r e g i o n o f t h e ' I n d i a n t r i a n g l e ' i s on i t s h i s t o r y ' s r a p i d growth t r a c k . A sudden p r o g r e s s o f e v e n t s on s e v e r a l i n t e r r e l a t e d f r o n t s - t h e economic, t h e e c o l o g i c a l a n d t h e p o l i t i c a l h a s combined t o s p u r s i g n i f i c a n t changes b o t h i n t h e r e l a t i o n s h i p s be tween p e o p l e s , po l i cy-makers and governments and i n t h e way t h e s e f o r c e s i n t e r a c t i n t h e management-use a n d c o n s e r v a t i o n - o f t h e w a t e r and v e g e t a t i o n r e s o u r c e s a s a whole.

THE PEOPLE

The s i g n i f i c a n c e ( p e r c e n t ) o f r u r a l p o p u l a t i o n t o t h e r e l e v a n t S o u t h A s i a n n a t i o n s i s shown from t h e U n i t e d N a t i o n s P o p u l a t i o n S t u d i e s ( 1 9 8 9 ) .

Year Nation 1955 1965 1975 1985

I n d i a 82.4 81.2 78 .5 7 4 . 5

B 'desh 95 .3 93.8 90.9 88.1

Nepal 9 7 . 3 96.5 95.2 9 2 . 3

The compos i t ion of t h e p o p u l a t i o n i n t h e t r i a n g l e i s n o t d i f f e r e n t from t h e r e s p e c t i v e n a t i o n a l a g g r e g a t e s and t h u s it i s b a s e d s i g n i f i c a n t l y i n t h e r u r a l a r e a s . A g r i c u l t u r e i s p r e d o m i n a n t a n d a l a r g e dependence on n a t u r a l r e s o u r c e s i s common i n t h e r e g i o n . The i m p o r t a n c e o f w a t e r r e s o u r c e t o t h e peop le i n t h e watershed i s immense f o r t h e i r l i v e l i h o o d and s o d o e s t h e f o r e s t r y r e s o u r c e (Ekanayake 1 9 9 0 ) .

THE PROBLEM

It i s a r e g u l a r f e a t u r e i n Bangladesh l i f e t o e x p e r i e n c e f l o o d s e v e r y y e a r and i t i s n o t s u r p r i s i n g t o e x p e c t f l o o d i n g w i t h a lmos t e v e r y monsoon fo l lowed up by a d r o u g h t . A r e c e n t monsoon submerged two t h i r d s o f t h e l o w - l y i n g a r e a s o f B a n g l a d e s h r e n d e r i n g 25 m i l l i o n p e o p l e h o m e l e s s . D e s t r u c t i o n s t o c r o p s a n d economic l o s s e s a r e i n s u r m o u n t a b l e . The September 1988 f l o o d s i n u n d a t e d 2 m i l l i c n h a of farmland (FEER 1989) .


Like t h e r i v e r d i s p u t e i n v o l v i n g t h e Euph ra t e s -T ig r i s and S h a t t a 1 Arab i n t h e M e d i t e r r a n e a n , t h e l ong - runn ing d i s p u t e between I n d i a , Bangladesh and Nepal on t h e c o n t r o l o f wa t e rways o f Ganges a n d Brahmaput ra h a s l e d t o a s equence o f u n c o n t r o l l e d f l o o d s and d r o u g h t s i n t h e r e g i o n of t h e t r i a n g l e .

Occurrence of heavy f loods3 i n t h e t r i a n g l e i n t h e p a s t have been;

Decade 1950 1960 1970 1980

AS s am - 2 2 4 ( I n d i a )

Bangladesh 3 3 3 4

I t i s c l a i m e d t h a t i n c r e a s i n g p o p u l a t i o n have added impe tu s on t h e w a t e r s h e d d i s a s t e r s by way o f e x t r a dimensions of human and economlc c o s t s .

popu l a t i on4 ( t o t h e c l o s e s t m i l l i o n )

1955 1967 1977 1987 Inc r ea se '77-'87 (pet)

I n d i a 386 504 626 781 25

B'desh 83 103 24

Nepal 9 11 13 18 3 8

Consumer P r i c e s Index ( C P I ) 1980=100 Averaga

1964 1972 1980 1987

I n d i a 31 .5 51.8 100.0 184.4

Bangladesh 1 2 . 6 24.9 100.0 212.7

Nepal 33 .0 51 .3 100.0 204.3

The e x t r a burden o f CPI i n c r e a s e on t h e economy a s a r e s u l t o f popu l a t i on i n c r e a s e f o r t h e n a t i o n s i s e v i d e n t from t h e above d a t a a s w e l l a s t h e r u r a l dimension of t h e problem.

A g r i c u l t u r e a ccoun t s f o r n e a r l y h a l f o f t h e n a t i o n a l income of I n d i a and it s u p p o r t s about 70 p e r c e n t of t h e c o u n t r y ' s

I n fo rma t ion on f l o o d occu r r ence i n t h e r e g i o n i s from C e n t r e f o r S c i e n c e and Environment of I n d i a .

P o p u l a t i o n and economic i n d i c a t o r s a r e from I n t e r n a t i o n a l F i n a n c i a l S t a t i s t i c s ( 1988 ) .

p o p u l a t i o n . But l a r g e p a r t s of c u l t i v a t e d l a n d u s u a l l y e x p e r i e n c e t h e p rob lem of i n s u f f i c i e n t r a i n f a l l f o r c r o p g rowth e i t h e r i n t e rms o f p r e c i p i t a t i o n o r i t s d i s t r i b u t i o n t o match w i t h c r o p w a t e r r e q u i r e m e n t s . N a t i o n a l Commission on A g r i c u l t u r e e s t i m a t e s I n d i a ' s u t i l i s a t i o n of a n n u a l p r e c i p i t a t i o n would improve i n t h e e a r l y p a r t o f t h e n e x t c e n t u r y from i t s c u r r e n t l e v e l of 2 5 p e r c e n t .

B a n g l a d e s h h a s a n a r e a o f 1 4 . 4 m i l l i o n ha l y i n g i n t h e d e l t a o f t h e r e g i o n ' s t h r e e g r e a t r i v e r s ; t h e Ganges, t h e Brahmaputra and t h e Meghna of which 9 . 1 m i l l i o n h a ( 6 4 p e r c e n t ) a r e c u l t i v a t e d . About 80 p e r c e n t o f t h e popu l a t i on a r e engaged i n a g r i c u l t u r e (Map i n d i c a t i n g B a n g l a d e s h and s u r r o u n d i n g c o u n t r i e s wi th p r i n c i p a l r i v e r s ) .

The mean a n n u a l r a i n f a l l i n Bangladesh v a r i e s from abou t 1 ,300 mm i n t h e wes te rn p a r t t o a lmost 5,000 mm i n t h e n o r t h e a s t o f t h e c o u n t r y a n d i s c h a r a c t e r i s e d b y w i d e s e a s o n a l f l u c t u a t i o n s w i th about 90 p e r c e n t of t h e r a i n f a l l o c c u r r i n g i n t h e f i v e month p e r i o d of t h e monsoon (May t o Sep tember ) . I n s p i t e o f a n o v e r a l l abundance of r a i n f a l l , s e r i o u s d rough t s do occu r .

Nepal h a s an a r e a o f 141,000 s q km l i e s p a r a l l e l t o t h e main Himalaya range of moun ta in s . About two t h i r d s o f l a n d a r e a i s t a k e n up by h igh mountains and t h e lower s l o p e s , t h e remain ing one t h i r d , a na r row s t r i p t o t h e s o u t h c a l l e d t h e T e r a i , i s t h e b o r d e r - l i n e o f t h e Indo- Gange t i c p l a i n s . About 10 p e r c e n t o f t h e p o p u l a t i o n l i v e s i n t h e Himalaya r e g i o n , 50 p e r c e n t i n t h e h i l l s o f t h e l ower s l o p e s and t h e remainder i n t h e T e r a i .


THEORY AND EMPIRICS

The t r i a n g l e r e g i o n l i k e many r e g i o n s i n d e v e l o p i n g economies r e l y h e a v i l y on w a t e r r e s o u r c e d e v e l o p m e n t t o f o s t e r economic growth. The n a t i o n s i n t h e r e g i o n a l s o have t h e p o t e n t i a l t o d e v e l o p hydro power t o e a s e burden of h i g h import b i l l s on f u e l . I n a d d i t i o n , f l o o d m i t i g a t i o n i s c r u c i a l f o r enhanc ing t h e p r o d u c t i v i t y o f low-lying l a n d s .

Even w i t h modern mechanisms of w a t e r r e s o u r c e management, it h a s n o t been a b l e t o c o n t r o l f l o o d s i n t h e low l y i n g a r e a s o f t h e t r i a n g l e . None o f t h e c o u n t r i e s i n t h e r e g i o n have r e a l i s e d even h a l f o f t h e i r hydro power p o t e n t i a l .

To s u s t a i n p r o d u c t i o n , wa te r and l a n d u s e p o l i c i e s must be i n t e g r a t e d . T h i s i s t h e o r y . I n p r a c t i c e , t h e c o u n t r i e s i n t h e r e g i o n l a c k o v e r a l l w a t e r r e s o u r c e and v e g e t a t i o n m a n a g e m e n t s t r a t e g i e s . D e f o r e s t a t i o n i n t h e c a t c h m e n t s a n d e x c e s s i v e removal o f n a t u r a l b a r r i e r s t o r a i n i n t h e r e g i o n ' s h i g h l a n d s h a v e f u r t h e r d i s t u r b e d t h e e c o l o g i c a l b a l a n c e .

I n summary , i t i s shown b y e n v i r o n m e n t a l s c i e n c e t h a t d e f o r e s t a t i o n i n h i g h l a n d s r e d u c e s t h e a b s o r p t i v e c a p a c i t y o f i t s w a t e r s h e d s . When t h i s i s r e l a t e d t o t h e c u r r e n t t o p i c , monsoonal r a i n s r u n i n h i b i t e d o f f t h e d e n u d e d s l o p e s , c a u s i n g e r o s i o n i n t h e f e r t i l e s o i l . The s e d i m e n t a t i o n i n downstreams c a u s e s f l o o d s . The t a r n i s h e d g roundwate r r e t e n t i o n l e v e l s c a l i b r a t e d r o u g h t s f u r t h e r i n g t h e i m b a l a n c e i n a g r i c u l t u r a l p r o d u c t i o n ( s e e I v e s and M e s s e r l i 1989 . ' T h e H i m a l a y a n d i l e m m a : r e c o n c i l i n g d e v e l o p m e n t a n d c o n s e r v a t i o n ' f o r a c o n t r a s t i n g b u t s u b t l e H i m a 1 a y a n Environmental Degrada t ion Theory) .

POLICY

Water h a s become a d i p l o m a t i c i s s u e i n t h e r e g i o n . Bangladesh b e i n g a low- l y i n g s t a t e i s a t a d i s a d v a n t a g e i n n e g o t i a t i o n s r e c e i v i n g n e a r l y 90 p e r c e n t of w a t e r from a c r o s s t h e b o r d e r . Nepal h a s a n enormous c a p a c i t y t o deve lop i t s hydro e n e r g y h a v i n g h a r n e s s e d o n l y 0 . 5 p e r c e n t of i t s p o t e n t i a l s o f a r . Being a upst ream s t a t e i s t o i t s a d v a n t a g e i n w a t e r n e g o t i a t i o n s . I n d i a , a c c o r d i n g t o F a r E a s t e r n Economic Review, by w i t h h o l d i n g h y d r o l o g i c a l a n d c l i m a t o l o g i c a l i n f o r m a t i o n c a n e f f e c t i v e l y i n f l u e n c e s t r u c t u r a l u n d e r t a k i n g s i n t h e t r i a n g l e r e g i o n . Some o f t h e most e l e m e n t a r y d a t a on hydro logy and power g e n e r a t i n g c a p a c i t y o f N o r t h I n d i a r e m a i n c l a s s i f i e d a s m i l i t a r y s e c r e t s ( i b i d ) .

So f a r , t h e e f f o r t s t o s e c u r e wider e c o n o m i c b e n e f i t s f o r t h e r e g i o n by p r o v i d i n g f o r d r o u g h t s i n Ganges d e l t a have f a i l e d . S i m i l a r l y , f i n d i n g a s o l u t i o n t o a n n u a l f l o o d i n g h a s been a n e q u a l l y i n t r a c t a b l e impasse .

W h i l e r e s e r v o i r s i n N e p a l would r e l i e v e f l o o d i n g i n t h e Ganges, most o f i n u n d a t i o n i s c a u s e d by t h e Brahmaputra- Meghna waterway, which c a r r i e s t w i c e t h e G a n g e s ' s volume of w a t e r (Asiaweek Map) . I n d i a n s t r o n g view i s t h a t t h e p r o p o s e d G a n g e s - B r a h m a p u t r a l i n k c a n a l would g r e a t l y c o n t a i n f l o o d i n g i n t h e d e l t a . T h i s i s c o n t r a s t e d by Bangladesh on t h e l a c k o f a p p r e c i a b l e e f f e c t o f l o w e r i n g w a t e r l e v e l s downstream.

C o n s t r u c t i n s s t o r a s e dams i n t h e ~ ~

I n d i a n t e r r i t o r y - w i t h e x c l u s i v e b e n e f i t s t o B a n g l a d e s h ' s downstream i s n o t favoured b y t h e c o s t b e a r i n g s i d e . However, c o n s i d e r i n g t h e n o r t h e r n I n d i a n s i t u a t i o n , where t h e w o r l d ' s h i g h e s t mountains meet some o f t h e w o r l d ' s f l a t t e s t p l a i n s and t h e r a i n f a l l i s c o n c e n t r a t e d i n 90 s h o r t - d a y s , it a p p e a r s t h a t t h e u n r i v a l l e d t r u s t f o r w a t e r r e s o u r c e management i s c o n t a i n e d i n up land s t o r a g e .


Some a r g u e s u c h p o l i c y a s p u r e l y i s s u e c e n t r e d a n d b r a n d t h e m a s ' m a k e s h i f t s ' . The c o n f l i c t between energy a n d i r r i g a t i o n p r i o r i t i e s becomes most a c u t e d u r i n g t h e d r y s e a s o n when t h e r e i s more demand f o r w a t e r a t f a rm- leve l w h i l e t u r b i n e s need t o m a i n t a i n s p i l l l e v e l s f o r e n e r g y g e n e r a t i o n . . T h e q u e s t i o n i s , who can s u g g e s t e q u i t y by d i s p l a c i n g h i g h l a n d p e o p l e i n c a t e r i n g t o e n e r g y needs of t h e c i t y - d w e l l e r s ?

L a c k o f p o l i t i c a l w i l l i n i m p l e m e n t i n g f a r - r e a c h i n g f o r e s t r y o r i e n t e d f l o o d c o n t r o l measures i n t h e t r i a n g l e r e g i o n have been t h e c a s u a l t y o f o p t i n g t o more l o c a l l y b e n e f i c i a l a c t i v i t y . I g n o r i n g t h e b e s t p o s s i b l e p a t h - t h e l e s s p a i n f u l n a t u r a l ways, and wi thou t a n y g l i m p s e a t s e i s m i c b r e a c h i n g a n d e x c e s s i v e m e l t i n g o f snow, t h e more l o c a l i s e d s u g g e s t i o n s are c a r v e d i n s m a l l t o medium s c a l e i n t e r v e n t i o n t o p r e v e n t s a t u r a t i o n of water- f lows.

v A c c o r d i n g t o Myres ( 1 9 8 9 ) , i n t h e

c a u s e o f s u s t a i n a b l e d e v e l o p m e n t e n v i r o n m e n t a l r e s o u r c e b a s e makes a c r i t i c a l c o n t r i b u t i o n a s t h e u l t i m a t e s u p p o r t o f much e c o n o m i c a c t i v i t y . Expanding on t h a t , o t h e r s have added t h a t s u s t a i n a b i l i t y c o n c e p t h a s m a j o r i m p l i c a t i o n s f o r i n t e r g e n e r a t i o n a l r e s p o n s i b i l i t y . T h i s means, i n s t i t u t i o n a l a r r a n g e m e n t s s h o u l d t a k e i n t o a c c o u n t o f s o c i a l l y u n j u s t i f i e d e n v i r o n m e n t a l d e g r a d a t i o n a s s o c i a t e d w i t h i n t r a g e n e r a t i o n a l a c t i v i t y .

Economic j u s t i f i c a t i o n o f s u s t a i n e d w a t e r p r o v i s i o n t o any s i t u a t i o n must t a k e i n t o account of c l i m a t i c v a r i a b i l i t y . T h i s h a s i m p o r t a n t i m p l i c a t i o n s f o r b o t h d r y l a n d w a t e r p r e s e r v a t i o n a s w e l l a s monsoona l - f lush s i t u a t i o n s . The e v i d e n c e from t e m p e r a t e r e g i o n a l w a t e r management i n i t i a t i v e s a s w e l l a s sub- tempera te and monsoon r e g i o n s a r e i m p o r t a n t i n t h i s r e s p e c t .

A s ment ioned i n F r e d e r i c k and G l e i c k 1 9 8 8 , i t i s c r u c i a l t o i d e n t i f y shor tcomings i n t h e c a p a c i t y of t h e w a t e r r e s o u r c e r e g i o n t o a d a p t t o l a r g e changes i n w a t e r - f l o w s i n t h e a b s e n c e o f new i n f r a s t r u c t u r e o r i n s t i t u t i o n a l changes o r t e c h n o l o g i c a l developments .

T h i s i n v e s t i g a t i v e a p p r o a c h w i t h l i t t l e economic o r s o c i a l s t r a i n w i l l b e proven u s e f u l t o t h e r e g i o n g i v e n f u t u r e changes i n water-flow p a t t e r n s .

THE OUTCOME

G i v e n t h e e q u i t y q u e s t i o n s a n d s e n s i t i v e d e c i s i o n making h o r i z o n s i n t h e r e g i o n ' s p o l i t y , t h e r e i s no g u a r a n t e e t o s u g g e s t t h a t s u s t a i n a b l e g u i d e - l i n e s w i l l b e e a s i l y c o n s t i t u t e d h e r e . I n t h e v a s t m a j o r i t y o f t h e s e s o c i e t i e s , s u b s i s t e n c e i s t h e main f o r c e t h a t d r i v e s l i v i n g b e i n g s f u r t h e r . L i k e w i s e , t h e p o l i c y m a k e r s a r e o v e r w h e l m e d b y d o m e s t i c p r i o r i t i e s and a r e u n a b l e t o s u g g e s t any b e t t e r s u s t e n a n c e . For example, even under a r e a s o n a b l e e d u c a t i o n system, a m a j o r i t y of t h e p o p u l a t i o n would be u n i n t e r e s t e d i n e n v i r o n m e n t a l p rob lems a s economics b i t e h a r d . S r i Lanka, w i t h i t s v e r y h i g h e d u c a t i o n a l a t t a i n m e n t l e v e l s , i s u n a b l e t o respond t o any env i ronmenta l c r i s i s and t h i s i s wide ly e v i d e n t i n i t s h a n d l i n g o f h i g h o c c u r r e n c e i n p e s t i c i d e con tamina ted d e a t h s .

T h e r e f o r e , even a t t h e p e r i l o f a r e g i o n ' s l o n g - t e r m economic v i a b i l i t y , p o l i c y may n o t i n t e r v e n e f o r r e m e d i a l a c t i o n n o t m e r e l y b e c a u s e o f t h e i r e d u c a t i o n a l b a c k g r o u n d a n d s p e c i f i c e x p e r i e n c e . Most e n v i r o n m e n t a l c r i s i s , a r e r e g i o n a l l y b a s e d and need t o be hand led a t r e g i o n a l l e v e l s .

The approach i s t o f i n d t r a d e o f f s t o o f f s e t g a i n s and l o s s e s u n t i l no one i s worse o f f ( o r b e t t e r o f f ) . U n t i l such t i m e t h a t t h e p o l i c y makers a r e non- ignoran t , t h e n a p o s s i b i l i t y e x i s t s f o r c o o p e r a t i o n . However, e v e n a t r e g i o n a l l e v e l s , s u b r e g i o n a l b i a s e n g u l f s t h e i s s u e t a b l e s . A t t h o s e l e v e l s , d e c i s i o n s b a s e d on househo ld s e n s i t i v i t i e s h a v e p r i o r i t y o v e r t h e i n t e r g e n e r a t i o n a l i s s u e s . The p a i n o f t h o s e d e c i s i o n s though i s p a s s e d on t o t h e s o c i e t y o r p o s s i b l y t o t h e n e x t g e n e r a t i o n f o r a b s o r p t i o n . T h i s i s a resemblance o f t h e c u r r e n t i s s u e s u r r o u n d i n g i t s eco logy and f u t u r e economic wel l -being.

USDAForest Service Gen. Tech. Rep. PSW-GTR-130.1991

CONCLUSION

T h e f u t u r e o f a h a r m o n i o u s r e l a t i o n s h i p t h a t t h e p e o p l e s o f t h i s r e g i o n a s p i r e , w i l l l a r g e l y h i n g e on t h e d e c i s i o n - m a k e r s ' a b i l i t y t o g r a p p l e w i t h r e a l i s s u e s a f f e c t i n g t h e w a t e r s a n d f o r e s t s o f t h e r e g i o n a n d t h e i r p r o d u c t i v i t y . However , t h e r e i s n o g u a r a n t e e t h a t t h e y w i l l b e s e n s i t i v e t o g e n e r a t i o n a l i s s u e s o r w i d e r b e n e f i t s o u t s i d e t h e i r h o r i z o n s . N e i t h e r , t h e y can b e e n t r u s t e d w i t h t h e f u l l e s t c o n f i d e n c e t o h a n d l e dynamic i s s u e s t h a t we a r e d i s c u s s i n g i n a way c o m p a t i b l e w i t h n a t u r a l l i m i t a t i o n s . A t t h e end of t h e day, t h e most r e s p e c t e d n o t i o n s w e d e b a t e f o r p o l i c y may show v u l n e r a b i l i t y t o t h e e x p e d i e n c y a n d i n t e r p r e t a t i o n o f t h e p o l i t i c i a n .

ACKNOWLEDGEMENT

T h i s p a p e r was s u p p o r t e d by t h e S c i e n t i s t A s s i s t a n c e Program o f Canada.

REFERENCES

Asiaweek map on Regional- f lows T e r r a i n s and Locat i o n s

Asiaweek; Number 4 1988 Defence p l a n s a f t e r t h e d e l u g e ; 34-35.

Bangladesh and Sur rounding C o u n t r i e s , wi th P r i n c i p a l R i v e r s ; A u s t r a l i a n N a t i o n a l U n i v e r s i t y

E a s t e r , Wil1iam.K.; Dixon, John A . ; and Hufschmidt, Maynard M . 1989 e d . Watershed Resource Management: An I n t e g r a t e d Framework w i t h S t u d i e s from As ia and t h e P a c i f i c . S t u d i e s i n Water P o l i c y a n d Management, No. 1 0 . Boulder : Westview P r e s s ; 3-15

Ekanayake, Rohan. 1990. Women and a c c e s s t o s o u r c e s of househo ld energy : v a l u e o f l a b o u r and r e s o u r c e s c a r c i t i e s i n p e a s a n t economies of South A s i a . C o n t r i b u t e d Paper t o t h e 3 4 t h Annual Confe rence o f A u s t r a l i a n A g r i c u l t u r a l Economics S o c i e t y , 1990 February 12- 16; B r i s b a n e A u s t r a l i a

F a r E a s t e r n Economic Review 2 February 1989. The Wasted Waters, Himalayan Blunder and Resource and R i g h t s ; 16- 2 2 .

F r e d e r i c k , Kenneth D . ; G le ick , P e t e r H . 1988. Water Resource and C l i m a t e Change. I n : Rosenberg, Norman J . ; E a s t e r l i n g , Wil l iam E . ; Crosson, P i e r r e R . ; Darmstad te r , J o e l . e d Proceed ings o f a Workshop on Greenhouse Warming: Abatement and Adapta t ion h e l d i n Washington, D . C . 1988 June 14-15; 133-143

MacNeill , J i m . 1989. The Greening of I n t e r n a t i o n a l R e l a t i o n s . I n t e r n a t i o n a l J o u r n a l l (1) Winte r : 1- 3 5

Myers, Norman ; 1989. The Environmental B a s i s o f S u s t a i n a b l e Development. I n : Schramm, Gunte r and Jeremy W.Warford e d . P u b l i s h e d f o r t h e World Bank, The John Hopkins U n i v e r s i t y P r e s s , Ba l t imore : 57-68.


High-speed High-Stress Ring Shear Tests on Granular Soils and Clayey Soils1 Hiroshi Fukuoka and Kyoji Sassa2

Abstract : The purposes of this study is to obtain exact knowledge of the influences on friction angle during shear by shearing speeds. Ring shear tests on sandy and clayey materials have been carried out with a newly developed High-speed High-Stress Ring Shear Apparatus to examine if there are some changes in the frictional behaviors of these materials at high shearing speeds of O.OIcm/sec-100cm/sec and high normal stress of 0-3.8k$/cm2. Samples used for tests were glass beads, tennis court sands in the university campus, the Toyoura standard sands (uniform beach sands) and bentonite clays. All tested samples were dry.

Although result on the glass beads showed that the friction angle during shear was independent of shear speed under the normal stress up to 3.8kgf/cm2, 2 N 5 degrees of change in friction angle were observed on the tennis court sands, the Toyoura standard sands and the bentonite clays. In the tests on the Toyoura standard sands and the bentonite clays, friction angle increased as the shear speed increased. On the contrary, friction angle during shear of the tennis court sands decreased a t a shearing speed of lOOcm/sec.

Change in grain size distribution implies that heavy crushing or grinding of particles occurred during shear. The grain size distribution become wider during shear by grain crushing in samples except glass beads. It could result in the increase of density and accordingly increase of the friction angle. Crushing or grinding of grains during shear can change the shape of grains. The Toyoura standard sands have round shape, because they are beach sands, it may become angular by crushing during shear. On the contrary, the tennis court sands have angular shape because they are taken from mountain slopes, it may become round by grinding during shear. Round grains have a small friction angle. It may be interpreted that the tennis court sands had a smaller friction angle during shear because of the change of angular grains to round grains by grindings. Hence, i t can be said that the friction angle is affected by crushing or grinding of grains during shear, which appears in a higher normal stress and a greater shear speed (shear distance).

To know the frictional characteristics of soils during high speed shearing is very important for the research on motion of landslides.

lPaper presented at the XIX World Congress of the Interna- tional Union 01 Forestry Research Organizations, 5-11 August, 1990, MontrCal, Canada.

2Post Graduate Student and Associate Profesor, respectively, Disaster Prevention Research Institute, Kyoto University, Uji, Ky- oto, Japan

To measure the friction angle during shear, it is most appropriate to use ring shear apparatus because landslide motion usually causes long distance shearing of about several meters t o some hundred meters. Bishop, 1961, developed a ring shear apparatus and carried out ring shear tests on samples of several kinds of clays in order to examine residual strength of clays which is a steady strength appearing after the peak strength. In reactivation of old landslides, the mobilized shear strength is not the peak strength in the virginal shear of the soil, but the residual strength which is a small steady state strength appearing after the peak strength. Bishop's ring shear apparatus had a sample box of which diameter was about 15cm (outside) and lOcm (inside). The maximum normal stress is 2.5k$/cm2. The shear speed in his experiment was 1.3~lO-~crn/sec and the maximum shear displacement was 132cm. But it is not enough for research of the motion of landslide, it needs a faster shear speed up to some meters per a second, and longer shear displacement up t o some meters.

Sassa, 1984, developed a Low-Stress High-speed Ring Shear Apparatus in 1984 for the research of motion of debris flow. The diameter of the sample box is 30cm (inside)- 48cm (outside). The maximum normal stress is 0.4kgf/cm2. The shear speed is 0.001 to 150cm/sec.

In order to know whether the shear friction during shear depends on shear speed or not, Sassa carried out ring shear tests on glass beads, the Toyoura standard sands. The results of ring shear test on glass beads of 2.0mm diameter are shown in Figure 1. Measured data on normal stress versus shear resistance which has a stress dimension are plotted. The tests were carried out under the normal stress up to 0.3kgf/cm2. The normal stress was continuously increased under the constant shear speed. Such tests were repeated of same sample on different shear speeds of 0.001, 0.1, 1, 90cm/sec. Almost all data are on a straight line inclined 19" and there are little scatters among the data. So, this

2 Normal Stress (kqflcrn )

Figure 1-Result of low-stress high-speed ring shear tests on dry glass beads of 2.0mm diameter. Void ratio e=0.65- 0.67 (Kaibori, 1986).


2 Normal Stress (kgflcm )

Figure 2-Result of low-stress high-speed ring shear tests on Toyoura standard sands. Void ratio e=0.88-0.91 (Kaibori, 1986).

result means that the shear friction of the glass beads is independent of shear speed in the range of shear speed and the normal stress as mentioned above.

Results of ring shear tests on Toyoura standard sands are shown in Figure 2. Procedure of the tests are almost same with the tests on the glass beads. Shear tests are carried out under the normal stress up to 0.15kgf/cm2. Shear speeds of these tests are 0.01, 0.1, 1 and 90 cm/sec. The friction angle of all shear speed is 33.5".

Hungr and Morgenstern, 1984, developed a high velocity ring shear apparatus in 1984. The diameter of the sample box was 15cm (outside) and l l cm (inside). The maximum normal stress is about 2kgf/cm2 and the maximum shear speed is 2m/sec. In use of the apparatus, they carried out ring shear tests on polystyrene beads and the Ottawa quartz sands of various grain sizes under two shear speeds of 0.025cm/sec and 98cm/sec. Results of the tests showed that the friction angle was almost independent of shear speed.

Sassa, 1988, developed a High-Stress High-speed Ring Shear Apparatus in 1988 for the research of landslide. It attained high normal stress up to 3.8kgf/cm2 and it corresponds to the depth of about 19w23m of landslide mass, hence research on the motion of real landslides has become possible. The diameter of the sample box is 33cm (outside) and 2lcm (inside). The maximum shear speed is i50cm/Sec.

With the apparatus, Vibert, Sassa and Fukuoka, 1989, carried out the ring shear tests on torrent deposit of the Denjo river and soils of the Jizukiyama landslide in order to examine whether the shear friction depends on shear speed or not. Result of the tests on dry torrent deposits of the Denjo river showed that the friction angle during shear under the shear speed up to lOcm/sec is 35.0" but the friction angle at 100cm/sec under the normal stress up to 1.2kgf/cm2 is 36.5" (Figure 3).

Result of the tests on unsaturated (degree of saturation was 20%) Jizukiyama landslide soil showed that the friction angle during shear was 32.8" a t O.Olcm/sec, 35.0" at O.lcm/sec, and 38.5" at lcm/sec and lOcm/sec (Figure 4). The magnitude of the variation is about 6", larger than the result on the sample of the Denjo river. The friction angle during shear of both sample tended to increase as the shear

F

3 i? 1 -

E ;; $ 0

8 0 1 2 Norma l Stress 0 kgf l3 cm2

Figure 3-Result of high-stress high-speed ring shear tests on dry torrent deposit of the Denjo river. Void ratio e=0.50-0.57 (Vibert et al., 1989).

I , I

1 2 3 4 Norma l Stress 0 k g f / c m 2

Figure 4-Result of high-stress high-speed ring shear tests on unsaturated Jizukiyama soil. De ree of saturation S, = 20%. Void ratio e=0.50~0.57 f ~ i b e r t et al., 1989).

speed increased. Examination of both sheared samples after the tests

showed that so much fine ground grains were found on the shear plane. It seemed that this grinding of soil particles relates to the variation of friction angle during shear, and the magnitude of the variation relates to the grain size.

So using the High-speed High-stress Ring Shear Appa- ratus, we have done ring shear tests of various samples at various shear speed to examine what causes the variation of friction angle.

SAMPLES AND APPARATUS

Samples for tests

Samples of different material and different grain size were chosen. Tested samples are glass beads of 0.2mm diameter, tennis court sands, Toyoura standard sands (uni-


beach sands) and the bentonite clay. Because pore pressure of the sample is not measured during shear test, effective stress can not be measured. So when dry or not-saturated sample were used, no excess pore water pressure would be generated and total stress would be equal to effective stress. So all of the samples tested by the apparatus were dry.

Glass Beads

Glass beads are of 0.2mm uniform diameter. The specific gravity of the glass beads is 2.50.

Tennis Court Sands

Tennis court sands are taken iron1 the tennis court in the university campus. They are taken from mountain slope and consist of angular grains. The specific gravity is 2.60. They are dried before the tests.

Toyoura Standard Sands

Toyoura standard sands is Japanese uniform beach sands sold by a Japanese company and used as a standard sands for calibration of test apparatus for soils by Japanese soil mechanics researchers. It is a uniform, clean fine quartz sands with round grains. The grain size is 0.05 - 0.5mm. The specific gravity is 2.49.

Bentonite Clays

Bentonite clays used in the tests is a dry clay powder sold in Japan and usually used for civil engineering works. It is well ground and with grain size smaller thau 0.3mm. The specific gravity is 2.58. Permeability of the clays is always very small and it takes so much time lor dissipation of excess pore water pressure, so the sample used for shear test was completely dry to prevent generation of pore water pressure.

Structure of the Apparatus

Figure 5 is the schematic diagram of High-speed High- Stress Ring Shear Apparatus. The sample box is shaped circular channel. The diameter of the sample box is 33cm (outside) and 21cm (inside). It is made of transparent acrylic resin, retained by metal f ran~e and the outside of the sample can be observed during test. Section of the sample boxis 6cm wide and about 6-8cm high. The width of the section is constant. The loading plate can move ver- tically, so only the height of the sample can change. The sample box is separated horizontally a t about midheight (Figure 6). The lower one is rotated by servo-control motor for shear. Several non-skid needle assemblies are fixed on the base and the ceiling (loading plate) of the sample box and they prevent the sample from slipping on either side. So, rotation of the lower sample box causes shear of sample. After the shear test, horizontal shear plane is usually formed between the upper and the lower part of the sample box. There is a rubber edges at the inside and outside gaps between the upper and the lower part of the sample box and they are bound on the upper part of the sample box to seal the gap, and preventing leak of sample from the sample box.

Counter Weight

Figure 5-Schematic diagram oi the High-speed High-Stress Ring S h e a Apparatus. A: servo-control motor lor shear, B: servo-control motor for gap control, C: servo-control air regulator, D: load cell for normal stress, E: load cell for shear stress, F: dial gauge for volume change, G: shear displacement detector, H: dial gauge for gap.

The electric servo-control motor (marked as A in the Figure 5) can rotate the lower part of the sample box at constant speed, so i t enables constant shear s eed shear test. Available shear speed is from 0.001cm$ec to 150 cm/sec with use of four different gears in the gear box (also in A in the Figure 5).

The normal stress to the sample is given by an air compressor. The compressed air is put into six air pistons through an servo-control air regulator. The air pistons push down the loading plate (ceiling of the sample box) and the normal stress is loaded on the sample uniformly. The maximum normal stress is 3.8kgf/cm2.

The gap distance between the upper and the lower part of the sample box should be constant throughout the test procedures, because too much narrowing of gap distance or contact of the upper and the lower part of the sample box may increase the measured value of the normal stress. While, too much widening of gap distance may lead to leak of sample from the sample box during shear test.

So, the apparatus has a servo-control motor for gap control (marked as B in Figure 5) and a electric distance meter for gap distance measurement on the order of 1/1000 mm. With them, gap distance is kept constant during a test as the same value at which shearing of the sample starts.


LOAD

stainless steel L f rarne

A

Figure 6-Section of sample box of the High-speed High-Stress Ring Shear Apparatus.

Monitoring System

Normal load on the sample is measured with a load cell set beneath the axis (marked as D in Figure 5). The compressed air which produces the normal load on the sample push up the air pistons and axis, then normal load is measured as tension force.

Shear resistance of the sample is measured with a load cell (marked as E on Figure 5). The upper part of the sample box and the upper unit (including air pistons) are fixed and restricted not to rotate with the lower part of the sample box, (marked E in Figure 5) with load cell for shear resistance. So, shear resistance is measured as tension force. As the shear resistance is supposed to originate uniformly on the shear plane, the shear resistance is easily calculated from the equation of shear torque. Above mentioned two load cells are electrically connected to dynamic strain meters with cables, and tension forces are measured with them.

Vertical displacement of the sample is measured with the dial gauge (marked as F on Figure 5). As the sample box cannot deform sideways, the measured vertical displacement multiplied by the area of loading plate is variation of volume of the sample.

Shear displacement is measured with rotary encoder which contact with the lower part of the sample box which rotates during test. The shear speed is calculated from the rate of rotation and it is displayed at each result of the tests shown below as the shear speed at the center of the sample.

All these measured parameters (normal load, shear resistance, sample height and shear displacement) are output as electric voltage through the amplifier unit. All values are recorded on the sheet of a pen-recorder and also put

Figure 7-The High-speed High-Stress Ring Shear Apparatus.

sample box

load cell

Figure 8-Calculation of shear resistance and shear torque of the High-Stress High-speed Ring Shear Apparatus.

Figure 9-Screen copy of real-time monitoring system of the apparatus, assisted by personal computer. Displaying normal stress and shear resistance relation.


into personal computer through A/D converter board in it , then the data are saved on magnetic floppy disk and the normal stress (u)-shear resistance (r,) relation are plotted on the computer display at real time. Figure 9 is the screen copy of the computer display of the real-time moni- torinn system plotting stress conditions (normal stress and shea;reiistance). -

Pore Dressure is not measured because it is difficult to measure pore pressure at the shear plane. Only total stress on the sample can be measured. Thereiore, tests were carried out under dry conditions.

Calculation

Normal stress a (kgf/cm2) is calculated from:

Here, W: Normal load acting on the sample through loading plate measured by the load cell, TI: diameter of the sam le box (inside), r2: diameter of the sample box (outside! yt: total unit weight of the sample, h,,: sample height above shear plane (about 3-4cm). yt. hWp is at most 0.008kgf/cm2. The normal stress loaded on the sample during the ring shear tests are between 0.5-3.8kgf/cm2, so this term is almost negligible. So, this term was not calculated during

Shear resistance r from the equation of rotational

Here, R: distance from the axis to the load cell for shear resistance, F: shear load measured a t load cell which retains the upper part of the sample box from rotation.

PROCEDURE OF TESTS

Sample Preparation

The soils for the sample was compacted inside the sample box up to about 6cm high with steel bar. Compaction is carefully executed to make homogeneous sample.

Then set the upper unit including loading plate and air pistons, connect electric cables of measuring device to amplifiers and strain meters and connect air tubes of air pistons to the air regulator. The air compressor start,s to run and supply pressure to air regulator.

Consolidation

Before shear test begins, sample is consolidated with normal stress of 3.8kgf/cm2. Progress of consolidation is monitored by the dial gauge for measurement of sample height on pen-recorder. All soils for sample except bentonite were sandy soil and dry, consolidation completed quickly within about several seconds. Bentonite clay sam-

ple, which was dry powder, also completed consolidation quickly.

Ring shear test

After the sample is consolidated, normal stress is decreased to 0.5kgf/cm2. Then slowest gear is connected to the servecontrol motor, corresponding signal voltage for O.Olcm/sec is set on servo-control unit, and then servo- control motor starts. Confirming that the sample reaches residual condition, increase normal stress gradually up to 3.8kgf/cm2 at constant rate and decrease to 0.5kgf/cm2 again, then stop the servo-control motor. During shear test, stress path (relation between normal stress and shear resistance) is drawn continuously on computer display at real time.

Ring shear tests a t shear speed of 0.1, 1, 10, 100 cm/sec follow after the test at O.Olcm/sec step by step. At each test, appropriate gear is selected and test is executed in same way except test at 100cm/sec. As it takes about some minutes to complete one cycle of a test, during which servo-control air regulator increases and decrease the normal stress, at the test of 100cm/sec sample sometimes leaks outside through the gap between the upper and the lower part of the sample box. I t is difficult to keep running for long time at 100cm/sec. Then the test a t 100cm/sec is done in different way, that for about only three or ten seconds the sample box is rotated for the discrete normal stresses of 0.5, 1.5, 2.5 and 3.5kgf/cm2.

After shear test on each sample is completed, the upper unit, the upper part of the sample box and also the sample above the shear plane is removed and shearing plane of the sample is closely examined.

RESULT OF TESTS

Glass beads

Dry glass beads were tested under the normal stress up to 3.8kgf/cm2. Figure 10 is the result of uniform dry glass beads of 0.2mm diameter. Ring shear test was executed at constant shear speed of O.Olcm/sec as the normal stress was increased gradually. Then, another test a t faster shear speed (0.1, 1, 10, 100cm/sec, step by step) followed it in

, 2 0 m 1 2 3 4 .c (0

2 Normal stress (kgf/cm

Figure 10-Result of high-stress high-speed ring shear tests on the 0.2mm glass beads. Void ratio during shear test: e=0.87-0.88.


the same procedure. So continuous normal stressshear resistance relation was gained at each test. Plotted points in the figures of normal stress v.s. shear resistance in this paper are picked up from the recorded data at the normal stresses of every 0.5kgf/cma between 0.5 and 3.5kgf/cm2.

The friction angle scattered little, mean friction angle is 23.0°, being independent of shear speed of O.Olcm/sec to lOcm/sec. Test at 100cm/sec was carried out, but some sample leaked out of the sample box and the test was ter- minated. From the examination of sample after shear test, no grinding or crushing of the glass beads occurred.

Tennis court sands

Results of high stress ring shear test on dry tennis court sands are shown on Figure 11. It displays the relation between normal stress and shear resistance. The friction angle at the shear speed slower than lOcm/sec is 35.1°, hut it decreases to 31.9' at 100cm/sec. After the test, removing the upper unit and the upper part of the sample box and cross section of the sample was closely examined. So much fine ground grains were observed on and near the shearing plane (Figure 13 (a) and (b) ). Variation of grain size distribution between before and after the shear test are shown in Figure 12. Curve of after the test is that of

1 2 3 4 2 Normal Stress (kgffcm )

Figure 11-Result of high-stress high-speed ring shear tests on the dry tennis court sands in the university campus. Void ratio during shear test: e=0.51~0.68.

- L, 0 G r a i n S i z e l m m l e,

Figure 12-Grain size distribution of the tennis court sands. - 0 : before the test, 0 - 0 : after the test

Figure 13 (a) The campus soils after test. (b) Well ground soil particles of the shear zone on the fingers.

the sample taken from fine ground grains around the shear plane. It shows dearly that shearing causes grinding of grains.

Toyoura Standard Sands

Figure 14 is the test results of the dry Toyoura standard sands at shear speed of 0.01-100 cm/sec. The test was done from the slowest speed of O.Olcm/sec to the highest speed of 100cm/sec step by step. The friction angle during shear increased from 31.7" to 33.8" under the respective shear speed. Thereafter, tests were continued at slower speeds; lcm/sec, O.lcm/sec, O.Olcm/sec step by step. These tests at reducing shear speeds were carried in


order to examine whether shear friction depends only on the shear speed or not. Results of the tests were shown on Figure 15. Change of the sample height which means change of the sample volume and friction coeficient which is tan$, (tangent of friction angle) versus shear speed is plotted. Plots with number of 1-5 are the same data of Figure 14. Plots with number of 6-8 are the results of suc- cessive tests following Figure 14. Sample height increased until1 the test of No. 3 and then continued to decrease during tests of No. 4-7. Increasing process was maybe di- latancy of the sample. The decreasing process seemed to

1, be owing to crushing of the sample. I t is proved by the comparison of grain size distribution between before and aiter the test, shown in Figure 16. Smaller grains finer

I than 0.05mnm which was not included in the sample before

a, 14 Grain S i z e l m m )

Figure 16. Grain size distribution of the Toyoura standard sands. 0 - 0 : before the test, 0 - 0 : after the test

Figure 14-Result of high-stress high-speed ring shear tests on the dry Toyoura standard sands. Void ratio during shear test: e=0.65~0.83.

Shear Speed (cmlsec)

Figure 15-Shear speed v.s. sample height and frictiond coefficient relationship for the dry Toyoura standard sands.

the ring shear test appear in the distribution curve of the sample after the test. Although Figure 16 is not comparison of the sample of shear plane, but of total sample, it is obvious that grain crushing occurred in the sample. Fric- tion coefficient tends to increase during the tests of No. 1-5 and almost keep constant (or slightly decreased) during the tests of No. 6-8.

Bentonite Clay

Test result of ring shear tests on the bentonite clays is shown in Figure 17. It showed the greatest difference of friction angle with the change of shear speed. The friction an le was 28.6" a t the first test with shear speed of O.Olcm/sec. And then i t varied as 34.1" at O.lcm/sec, and 34.8" at 1 and lOcm/sec. In this test, test a t the speed of O.Olcm/sec was executed again after the test at lOcm/sec. But the friction angle remained almost same with that at lOcm/sec speed.

Figure 18 shows the entire process of shear test at shear speed of O.lcm/sec. The normal stress increased up to 3.5kgf/cm2 and decreased again. Shear resistance also changed in proportion with the normal stress. The most important is the behavior of the friction coefficient, namely tangent of friction angle (tan$,). It increased with increase of normal stress (during the shear displacement of 0-20cm)

Normal S t r e s s ( k g f / c m 2 )

Figure 17-Result of high-stress high-speed ring shear tests on the dry bentonite. Void ratio during shear test: e=1.74-2.04.


2 z I

E .ri ! f ~ r i c t ~ o n ' a l ...... .......... 0

C o e f f l c e i e n t

T i -.A?- !

UJ Sample Heigl

1

0 10 20 30 40 50

Shear Displacement (cn)

Figure 18-Variation of frictional coefficient, sample height, shear resistance during a cycle of test. (shear velocity:0.lcm/sec)

Figure 19-Grain size distribution of the dry bentonite. 0 - : before the test, 0 - 0 : after the test

and also while the normal stress kept constant peak (shear displacement of 2 0 ~ 3 0 c m While the normal stress is decreasing, the friction coe k cient . remained constant (shear diplacement of 30~45cm) . The sample height decreased during shear and didn't recover the initial height at the end of the test.

Figure 19 is the comparison of grain size distribution of bentonite sample between before and after the test. This is from the sample of shear zone. It still clearly exhibited the effects of grain crushing through shearing.

Influence of Grain-crushing on the Friction Angle during Shear

The results shown above by the High-speed High-Stress Ring Shear Apparatus suggest that friction coefficient may be affected by crushing (grinding) of grains a t increasing

Figure 20-Bentonite sample after ring shear tests, showing polished and striated slip surface (upper portion of the sample is removed).

process of normal stress. And high speed shearing may have worked for a rapid crushing. We observed heavily crushed grains in shear zones after the tests of each sample except the glass beads. Glass beads are enough strong not to be crushed under the normal stress of the apparatus and the friction angle does not change with shear speed.

Here, we suppose two factors influencing the variation of friction angle during shear caused by grain crushing. One is the variation of grain size distribution and another is the variation of grain shape, i.e. round or angular.

As for the variation of grain size distribution, crushing of grains during shear, especially in the material of uniform grains makes a lot of finer grains and the sample becomes wider in grain size distribution. It should increase the density of the sample and the interlocking between grain particles. Increase of density of soils usually causes increase of internal friction angle. This seems to be the reason why the friction angle increased in the test of Toyoura standard sands and bentonite clays.

However, in the test on the tennis court sands, the friction angle at a high speed shearing decreased in spite of occurring of grain crushing. What can be the cause of this is not clear at present, but one possibility is the shape of grains. The initial shape of Toyourasands which were from beach was round, so crushing can make them angular. So the variation of grain shape in the Toyoura standard sands didn't act for decreasing of the friction angle and so the factor of variation of density had to be dominant. We could not observe the initial and sheared grain shape of bentonite clays by eyes, then the influence of the variation of grain shape on the friction angle of bentonite clays was unknown.

On the contrary, the tennis court sands were mountain sands, the initial shape was rather angular, so crushing


could increase the roundness of grains. Because sample of round grains usually have smaller friction angle than that of angular grains, crushing of grains during shear can reduce the friction angle. It can be one interpretation.

ACKNOWLEDGMENTS

We thank Professor Michiyasu Shima, Disaster Preven- tion Research Institute, Kyoto University, for his super- vision and cooperation to our research. We acknowledge Dr. Christophe Vibert from &ole des Mines, Paris for his cooperation to the high-speed ring shear tests.

REFERENCES

Bishop, A. W.; Green, G. E.; Garga, V. K.; Andresen, A,; Browns, J. D. 1961. A new ring shear apparatus and its application to the measurement of residual strength. G6otechnique 21(4): 273-328.

Hungr, 0.; Morgenstern, N. R. 1984. High velocity ring shear tests on sand. G6otechnique 34(3): 415-421.

Kaibori, M. 1986. Study on the movement of the slope failure materials. Doctor thesis for the Faculty of Agriculture, Kyoto University.; 99 p.

Sassa, K. Computer simulation of landslide motion. 1990. In: Proceedings, XIX World Congress of the Inter- national Union of Forestry Research Organizations, volume 1; 351-362.

Sassa, K. and others. 1984. Development of ring shear type debris flow apparatus: Report of Grant-in-Aid for Scientific Research by Japanese Ministry of Edu- cation, Science and Culture (No.57860028). 30p.

Sassa, K. 1988. (Special Lecture) Geotechnical Model for the Motion of Landslides. In: Proceedings, 5th international symposium on landslides, volume 1; 1988 July 10-15; 37-55. also In: Bonnard C., editor. Landslides. Rotterdam: A.A. Balkema Co., Inc.; 37-55.

Vibert C.; Sassa, K.; Fukuoka, H. 1989. Friction characteristics of granular soils subjected to high speed shearing. In: Proceedings of the Japan-China symposium on landslides and debris flows, volume 1; 1989 October 3 and 5; Niigata and Tokyo: The Japan Landslide Soc. and The Japan Sac. of Erosion Con- trol Engineering.; 295-299.

USDA Forest Service Gen. Tech. Rep. PSWIGTR-130. 1991

Morphological Study on the Prediction of the Site of Surface Sli Hiromasa Hiura2

Abstract: The annual continual occurrence of surface slides in the basin was estimated by modifying the estimation formula of Yoshimatsu. The Weibull Distribution Function revealed to be usefull for presenting the state and the transition of surface slides in the basin. Three parameters of the Weibull Function are recognized to be the linear function of the area ratio a/A. The mapping of the hazardous zones could be successfully done using the stream line distribution map and the relief map.

Sediment yield produced by frequent surface slides on the mountain slopes of granitic rocks become as dangerous as those produced by gigantic landslides or large scale slope failures, because of the high frequency of occerrence in a basin in spite of the dimension.

It is recognized that surface slides will occur on the mountain slopes of every geology. As for the investigations on surface slides, almost all papers in Japan deal with surface slides which occur on the mountain of granitic rocks which are often severely weathered and distribute widely in the soutb-western district of Japan and disasters due to this geology occur frequently on the occasion of heavy rain which will he brought about by the typhoon or the frontal storm.

ESTIMATION FORMULA OF SURFACE SLIDES

In order to express the condition of the occurrence of surface slides in a basin, usually the parameter a/A; the ratio of the total area of surface slides to the area of a basin (the termi- nology "area ratio" is used hereafter)is used. In most of the studies concerning the occurrence of surface slides, efforts were made to express the area ratio as the function of the precipitation and formulas by Uchiogi(1) and Yoshimatsu(2) are the presentative ones. Here, the formula below by Yoshimatsu is taken to be discussed.

a/A = K x Rr x (~-r)l.5 ------ (1 )

~XIX l!orld Congress of IUFRO, August 5-1 1 , 1990 Montral, Canada

2~ssociate Professor of Forestry, Kohchi Univ. Nangoku City, Kohchi Prefecture (before October 1990; Research Associate of ICyoto Prefectural Univ. )

where, "R" is the amount of precipitation of one continual rain which has led to the disaster occurrence of surface slides, "r" is the invalid limited precipitation being of no effect on the occurrence of surface slides, Rr is the relief ratio and K is the coefficient.

In Table 1, values concerning the above formula by Yoshimatsu are indicated;area of the basin, total area of surface slides in the basin, area ratio and relief ratio and Figure 1 shows the relation between the area ratio and the amounts of continual precipitation both for measured and calculated are shown, and both values show good conformity. Table l--States of the occurrence of surface

slides due to heavy rain(by Yoshimatsu(2)) (i)R.Kamanashi basin ................................................. Precipi- Area of Total area Area Relief tation(mm)basin of slides ratio ratio

................................................ (ii)R.Tenryuu basin ................................................. Precipi- Area of Total area Area Relief tation(mm) basin of slides ratio ratio .................................................

(iii)R.Kizu basin ------------- ~

Precipi- Area of Total area Area Relief tation(mrn) basin of sli.des ratio rxtio

USDA Forest SelviceGen. Tech. Rep. PSW-GTR-130.1991

(iv)R.Arita basin

Precipi- Area of Total area Area Relief tation(mm) basin of slides ratio ratio

The values of the relief ratio could be considered to have constant value when we think of it for a fixed basin. The value of the coefficient K can be the presentative constant of a basin and when the value of K is bigger, sediment yield due to surface slides or other mass movements seem rather vivid in the basin than others.

l o 0 - 0 Measured

One continual rain (mm)

Figure I--Relation between the area ratio and precipitation of one continual rain

As a result, this formula represents only the state of the occurrence of surface slide and only

represents that the more the the amount of precipitation augments, the bigger the value of the area ratio becomes. In other words, the temporal increase of the number of surface slides in a fixed basin can not be estimated.

As for the value of the invalid precipitation; r of these formula are determined by the data in order to reduce the formula and subsequently the precipitation of one continual rain which would lead to the occurrence of surface slides is not necessarily bigger than the derived "r" value. So, in the following part, in order to predict the amount of surface slides which will occur repeatedly in the same basin, derived value of "r" are not used, and treating "ru as a variable, determined it to suit the real state of the temporal increase of surface slides.

TRANSITION OF THE AREA RATIO IN A BASIN

Before discussing about the transitionsin of the value of area ratio, it is necessary to know the upper limited value of the area ratio. Figure 2 shows the relation between the total area of surface s1ides;a and the area of the basin;A. The oblique line in the Figure is the line when a/A = 1.0 and in this case, all part of the mountain of a basin is bare due to surface slides, consequently, the total area of surface slides should be plotted beneath the oblique line.

When the area of two basin are decided arbitrary and if there are no surface slides, the initial states are plotted on the abscissa as shown in Figure 2 by 0 and e, and these two points move directly upwards as the total area of the surface slides increases. Even when the values of "a" are same for two different basins, the values of a/A differ to each other because of the value of the area of the basin are not the same. In this condition, the larger the area of the basin becomes, the less the value of a/A becomes. Subsequently, in the case of discussing exactly about the area ratio, the value of the area of basins should be made uniform. But, to discuss about it here is not the aim of this paper, the author only point out the importance of this subdect.

1 +

1 V

A: Area of The basin -

Figure 2--Relation between the total area of surface slides and the area of the basin


Figure 3 and 4 show the relation between the total area of surface slides and the area of the basin by the author and Yoshimatsu respectively. As shown in both figures, common envelope curves are drawn and in this case, the value of the area ratio is 1.5 and this value can be the upper limited value of the area ratio. This value coin- cides with that of the R.Kamanashi basin which is given by Yoshimatsu, though the conditions of the occurrence of surface slides seems extremely ruined condition.

Figure 3--Relation between the total area of surface slides and the area of the basin by Riura

A t!"')

Figure &--Relation between the total area of surface slides and the area of the basin by Yoshimatsu

Transition of the number of surface slides

Figure 5 shows the yearly fluctuation of surface slides of the Tsuchiyabara district(R.Kizu). As seen in Figure 5, the values of the area ratio tends to increase and converge to a final value. The values of the area ratio in 1971 and 1976 are indicated below;

Year Area ratio

and the maximum precipitation of a year during 1971 and 1976 are as follows; .................................................. Year 1971 1972 1973 1974 1975 1976 Precp.(mm)l66.3 203.0 133.1 144.0 157.5 240.0

0 L 1966. 1971 1976 Year

Figure 5--The yearly fluctuation of the area ratio of R.Kiau basin

These values do not exceed the invalid precipitation 325mm which is presented by Yoshimatsu. Thus, it is clear that the formula can not be used for the estimation of the yearly increment of the area ratio. So, as mentioned above, taking the invalid precipitation as a variable, and dividing precipitation into two groups;R>200mm and R<200mm and assuming the value of the area ratio to be a/A =0.0012 and 0.0006 correspondingly to the precipitation respectively. The results of the estimation of the invalid precipitation are indicated in Table 2 as well as the maximum precipitation, the difference of both precipitations;the valid precpitation;(R-r) and the area ratio. As the mean value of the area of the basin is approximately ten km from Table 1 , then annually fifty slides when R>200mm and twenty-five slides when R<2OOmm will occur accoding to the estimation of this paragraph and these values seem reasonable.

Table 2--Maximum continual precipitation;R, area ratio; a/A, invalid precipitation;r and valid precipitation; (R-r) for Tuchiyabara district(R.Kizu basin)

Year Maximum conti- Invalid Valid Area nual precip. precip. precip ratio


PRESENTATION OF THE STATE OF SURFACE SLIDES IN USE OF THE WEIBULL DISTRIBUTION FUNCTION

It was recognized above that the state of the occurrence of surface slides in a basin at an arbitrary state can be expressed by the area ratio which is the function of the precipitation. On the other hand, the Weibull Distribution Function which the author has employed has successfully presented the state of the yearly fluctuation of surface slides(3). Here, by combining both method, the hazard mapping of surface slides is presented.

Firstly, the foregoing results are summarized and then the method for mapping is presented. It is natural that the value of area ratio of a basin differs to each other according to the difference of the state and history of the occurrence of surface slides in a basin. The Weibull Distri- bution Function is one of the statistic density functions and originally adopted for the treatment of the experimental data and because of its easi- ness and conformity, it has come to be used frequently. The formula of this function is expressed below;

Three parameters included are the location parameter: y , the scale parameter:a and the shape parameter:m respectively. Thus, the state of the distribution of surface slides of a basin at an arbitrary time can be expressed by these three parameters. The author has already recognized that when the number of surface slides increase yearly in a basin, a and m increase, but y decreases, and confirmed that the values of three parameters fluctuate in accordance with the transition of the slide numbers.

Area ratio and Weibull parameters

Table 3 indicates the number of slides, the area ratio a/A and values of three parameters of five survey basins(Figure 6). These basisns have different situations concerning the occurrences of surface s1ides;for exemp1e:numerous slides have just occurred, the number of slides is increasing or decreasing and so on. Figure 7 shows the relation between Weibull parameters and area ratio . The scale parameter a and the shape parameter m increase with the increase of a/A, and location parameter Y decreases inversely. So, the conditions of the occurrences of surface slides could be presented by a set of Weibull parameter values at an arbitrary value of a/A and in that case, the scale parameter is the most effective one. Following formulas to calculate Weibull parameters using the value of the area ratio were derived using data in Table 3.

a = 37.5091 (a/~)-0.1272 --------- (3) m = 18.2635(a/~)+0.4645 --------- (4) y = -10.5580(a/A)-0.0614 --------- (5)

Sumiyoshi district

0 0

\ R.Inubuse basin

district (R.Kizu basin)

Figure 6--The location map of the survey areas

Table ?--Yearly fluctuation of Weibull parameters (i)Tsuchiyabara district ................................................ Year Total number Area Parameter

of slides ratio a m Y

1966 1109 0.0282 1.011 0.994 -0.353 1971 1768 0.0450 1.573 1.155-0.441 1976 1936 0.0492 1.802 1.240 -0.528 ................................................ (ii)Minamiyamashiro district ................................................ Year Total number Area Parameter

of slides ratio a m Y ................................................

................................................ (iii)Sumiyoshi district ................................................ Year Total number Area Parameter

of slides ratio a m Y

I966 937 0.0196 0.685 0.801 -0.316 1967 1296 0.0403 1.587 1.215-0.544 1971 623 0.0130 0.448 0.771 -0.216 ................................................ (iv)Misumi district


(v)R.Inubuse basin

Year Total number Area Parameter of slides ratio a m Y

................................................ 1964 1321 0.0049 0.067 0.000 0.116 1972 4054 0.0151 0.626 0.934 -0.291

SIMULATION OF THE FUTURE SLIDE DISTRIBUTION AND MAPPING

Of five districts investigated hitherto, in the case of Tsuchiyabara district(R.Kizu basin), the number of surface slides continues to increase . So, the author tried to simulate the plane distribution of slides and to draw them on the map . The simulation was done according to the flow chart shown in Figure 8 and following procedures;

1) As a basis, the distribution map of surface slides existing in 1971 was used and the area ratio was a/A = 0.0450(Table 3). 2) Establish maximum precipitation of each year and calculate annual value of area ratio. 3) In five years from 1971 to 1976, the increment of surface slides is a/A = 0.0042. 4) Substituting a/A = 0.0450 into formulas; (3), (4) and (5), the values of parameters were calculated as follows: a = 1.718, m = 1.363 and Y = -0.581. 5) Calculate by the equation (2) , the ratio of each mesh(75mx75m) containing zero to nine slides, and multiplying them by the total number of meshes of the basin(1678 for Tsuchiya- bara district), the real number of each mesh is estimated. Table 4 indicates the values of real and estimated number of meshes. 5) Draw the distribution map indicating hazardous mesh suffering from the occurrence of surface slides by the number of slides in 1976.

Table 4--The estimated and real number of each mesh containing slides in 1976 (Tsuchiyabara district:R.Kizu basin)

Number of slides Real Estimated in each mesh Number Ratio Number Ratio

................................................ 0 719 42.8 682 40.6 1 416 24.8 530 31.6 2 286 17.0 280 16.7 3 156 9.3 120 7.2 4 55 3.3 45 2.6 5 28 1.7 15 0.9 6 10 0.6 5 0.3 7 5 0.3 1 0.1 8 2 0.1 0 0.0 9 1 0.1 0 0.0

................................................ Total number of slides:1936 1742 Total number of meshe: 1678 1678

Morphlogical analysis

46

Area ratio

Figure 7--Relation between the Weibull parameter and the area ratio

Fix the value of area ratio

Estimation of Weibull parameters 1

I Calculate the ratio of 1 I each mesh in use of Weibull Distribution Function I

Decide the number of each mesh containing

I Draw the distribution map indicating hazardous mesh suffering from surface slides bs the number of slides

Figure 8--Flow chart to map the hazardous zone of surface slides

Before drawing the map, subsequent morphlogical analysis was done.

In general, a knick point in the longitudinal profile of a stream is recognized as the place

USDA Forest Sewice Gen. Tech. Rep. PSW-GTR-130.1991

where mass movement occurs vividly and many slides also occur at this point. The knick point is located at the uppermost point of a river where a stream line disappear on the topographical map. A point of abrupt change of the inclination seen in the longitudinal profile of a slope can be the point of the occurrence of surface slides and this point can be distinguishes as where the relief of a mesh suddenly diminishes, in other words, the inclnation of the slope turns from steep to gentle when going upstream or going upwards on the slope on the relief map. In the first meaning, the stream line distribution map and in the second meaning, the relief map were used.

The mesh on which the knick point is found and the mesh whose relief indicates the steep inclination are not always the same. So, both when two conditions are overlapped and when either condition is satisfied, the increase of number of slides in the mesh is decided, the former prefe- rentially. As the total number of the meshes is limited, the meshes which are to be increased were selected carefully considering the topographical conditions surrounding them.

Figure 9-Simulated distribution map of surface slides

Distribution map of the future slides

As for the total number of the surface slides, the real number exceeds the estimated value by 194 . This is due to the difference of the number of meshes containing more than three slides in them. The estimated number of meshes containing one slide in them is fairly large. The ratio of the estimated value to the real value is 1.3, so this value could be considered as the safty factor and to prepare for the dangerousness of the disaster using hazard map, this value never seem to indicate the excess value.

Figure 9 shows the numerical map of simulated plane distribution of slides. The circled numerals in Figure 9 are those who make good guesses. There are 600 meshes among 1687 meshes, of which the place of the occurrences of slides were guessed and the ratio of the guess is about 35.8pct. Of meshes containg zero slide, there are 350 meshes among 682 meshes could be guessed and in this case, the ratio is 51.3pct. Consequently, the simulation could be considered to be done successfully, considering the complexity of the process of the mass movement on the mountain slopes.

ACKNOWLEDGEMENTS

The author greatfully acknowledge the contribution given by M. Ken Ashida, Master of Agriculture of Kyoto Prefectural University, for his contribution to discussion and drawing figures.

REFERENCES

(1) UCHIOGI Tamao 1971. Landslide due to One Continual Rainfall. Journal of Japan Soc. of Erosion Control Eng.: No.79, 21-34

(2) YOSHIMATSU Hiroyuki 1977. The Estimation of Expression on Landslides. Journal of Japan Soc. of Erosion Control Eng.: No.102, 1-9

(3 ) HIURA Hiromasa 1988. Hazard M a ~ ~ i n e in Use .. . of Surface ~1ide'Transition ~ohk1.-1988 International Symposion "INTERPRAEVENT 1988 - GRAZ"; 297-313


Experimental Study on Impact Load on a Dam Due to Debris Flow1 lwao Miyoshi2

ABSTRACT

When a dam is struck by mud or debris flow, it is put under a great impact load and sometimes is destroyed. To prevent such destruction, it is important to perform basic research about the impact load on a dam due to debris flow.

Thus, we have made an experimental study and tried to establish a method to estimate such a impact load on the dam. The experiment was performed with glass beads of 5mm in diameter as bulk solid, in an open channel which is 7m in length, and 15cm in both width and depth. In these experiments, the load on the dam was measured by a dam-type load measuring device, and simultaneously the behavior of the debris flow was observed by a high speed video (200 frames per second). In the high velocity area, the load consist- ed of the dynamic pressure on the flow, and most agree at each point in time with the one assessed from the flow's momentum variation. However there is no method to estimate debris flow's momentum variation on an obstructed object. Consequently, a model is proposed to estimate quantitatively the deformation of the flow and the load on the dam. The results from the computer simulation of this model agree well with the experimental results.

INTRODUCTION

Debris flow is one of the most disastrous phenomena in mountain.area. This is a flow of the mixture of soil, cobble, boulder, and water, that run down with great energy. The debris flow has given

1. Paper presented at the XIX World Congress of the International Union of Forestry Research Organizations, Montreal, Canada, August 5-11, 1990.

2. Department of Forestry, Kyoto University, Japan.

huge damage to our life. To prevent this kind of disaster, we have made great efforts, and have built a great number of dams, as one of these efforts. Dams have a certain effect on the control of sediment transportation, and usually the energy of the debris flow is attenuated or completely dissipated by the time it reaches a dam or by a dam itself. Re- cently in Japan, where steep mountains are close to cities, the debris flow is stopped by a dam directly. However, when such a flow strikes a dam, it generates a great impact load, sometimes destroying the dam. In such a case, the debris flow increases its energy by taking up the sediment and water on the dam and the situation becomes more dangerous. To prevent such accident, it is important to establish a method to estimate the impact load on a dam, when the debris flow strike it.

The impact load of debris flow can be roughly categorized in two groups by means of the generating mechanism (Mi- zuyama,1979). One is the load generated when boulders or floodwood in the flow hit the dams (solid impact load), and the other one is the load when the hydraulic bore of the debris as a fluid hits the dam (fluid impact load). The former tends to cause partial break of the concrete dam and the latter tends to cause large scale destruction of the dam. Therefore, from the stand point of disaster prevention, it is rather important to be able to estimate the fluid impact load.

In Japan, the dynamic fluid load of the debris flow that decides the design strength of the concrete dam is accounted for from the dynamic pressure of debris flow as the steady jet flow as seen in follow equation.

2 F = Dqv = DAv (1)

where F is the load, D is the bulk densi-


ty of the fluid, q is the discharge, v is the velocity, and A is the cross sectional area of the fluid. The dynamic pressure of the steady jet flow is the pressure on the wall during the steady jet flow changes its direction on the wall.

Several previous works on the impact load on fluid theory can be seen. But if the behavior of the debris flows different from that of regular jet flow, then reconsideration is required.

Hirao et a1.(1970) made an experimental study on impulsive force on the bank due to hydraulic bore. In their experiment, the pressure on the wall, which was fixed in the channel in right angle, was measured, when it was hit by hydraulic bore of a few kind of fluid running down the channel. They reported that the measured load on the wall was 1.0-4.5 times lager than the load that calculated from the dynamic pressure of the flow as the steady jet flow. But the mechanism of load generation was not referred in this report. Miyamoto and Daido(1983) also studied on the impact load of mud- debris bore on the bank. In this work, the load was discussed theoretically and some experiments had be made. But some simplifications in their theory make it hard to apply to actual phenomena directly. Some more previous works on similar themes can be seen, but those are not enough to estimate the impact load of the debris flow yet.

In this paper, both the load and the behavior of the head part of debris flow is made clear on the basis of results of

experiments ..and the load is discussed with the deformation of the flow head.

EXPERIMENT

A diagram of experimental apparatus is shown in Fig.1. The flow channel was made of steel and transparent acrylic board so that the side view of the flow can be observed. The size of the channel is 7m in length, 150mm in both width and depth. The channel bed was roughened by gluing glass beads (5mm in diameter) onto it. The channel's angle of inclination was 16 degree. Bulk solid were spherical glass beads with a diameter of 5mm and a specific gravity of 2.53. A t the upper end of the channel, main and sub water supply device were attached, and at the bottom, dam-type load measuring instrument was set. The front face of the dam was at a right angle to the channel direction and the size of loading board is 120mm height and 150mm width. The load on the dam-type measuring instrument was measured by a dynamic skrain meter and recorded by a oscillograph. As the same time, the side view of the flow on the dam was recorded by a high speed video recorder (200 frames per second).

The glass beads were put on the channel bed on the upper side of the dam making a movable bed 4m in length with 50mm depth. The glassbeads were saturated entirely by water from the sub water supply device, and then, the pre-deter- minded volume of water from the main water supply device was released all at once, and this forced the glassbeads from

Main water supply device Sub water supply device High speed video Movable bed Dam type load measuring instrument

Fig. 1 Diagram of experimental apparatus

USDA Forest ServiceGen. Tech. Rep. PSW-GTR-130. 1991

the movable bed to move downstream as a debris flow. The velocity of the debris flow could be controlled by the volume of water in the main water supply device. The debris flow was checked by the dam at the bottom of the channel; the load on the dam was measured and the behavior of the flow was recorded from the channel side by the high speed video recorder. The record of both the load and the behavior of the flow were to be analyzed on the same axis of time. For this purpose, a pilotlamp was turn on in the site of the video recorder, and simultaneously in common circuit, a signal was sent to the oscilograph.

velocities and the measured maximum loads are shown in Fig.3. The measured maximum loads increased with the velocities and each type of the load has its velocity range. The morphology of the flow on the dam, when maximum load generated, varied with the velocity or/and type of the load. Fig.4 shows the side views of the each type's typical flow, when the maximum load was recorded. In the case of type C , when the maximum load generated, the dam was filled with debris. In this case, the load is relatively small and can be explained as the static load of debris. On the other hand, in the case of type A and B, in spite of rather larger maximum load, the static load is much smaller than that of type C. This means that, in the case of type A and B, the maximum load mainly consists of dynamic load. Consequently, it is important to estimate this dynamic load so as to estimate the impact load on the dam.

The flow's velocities were in the range of 0.4m/s to 2 4 s . In all cases, distinct hydraulic bores could be observed and the flow could be considered as a steady flow at the dam point. The load on the dam measured in the experiment was recorded by the oscirograph. The measured loads can be classified in three types by the variation in time as shown in Fig.2. The load in type A has a clear peak in a very short time (from 0.01 to 0.07second) after impact; t,he load in type B also become maximum in very short time, but doesn't have a clear peak; the load in type C increases rather slowly. The relations hi^ between the

In general, the dynamic load of debris flow has been discussed in comparison with the dynamic load of the steady jet flow in the same profile. Fig.5 shows the relationships between the velocities and the maximum measured load per cross section of the bore. The broken line "P" in Fig.5 is the dynamic pressure of the steady jet flow, calcu-

Time Time Time

Fig.2 Type of load

I: Type A O : Type B

I

0 50 1 DO 150 200 250

velocity (cm/s)

Fig.3 Relation between velocity and measured load

Fig.4 Flow morphology when maximum load generated

USDA Forest SelviceGen. Tech. Rep. PSW-GTR-130. 1991

lated in the relationship of eq.(2). 2

P = DV (2)

The bulk density was determined to be 3

1.4gf/cm from results of preliminary experiments. This figure shows that the maximum load is larger than the one due to the dynamic pressure of steady jet flow at each velocity.

Fig.6 and Table 1 shows the variation of the form of flow's head part and the measured load. After impact, the debris flow change its direction along the dam- front surface just like the behavior of the jet flow. From 0.05 to 0.06 second after impact, the head part jumps up above the dam, and makes overflow. The maximum load measured at this point. Then the debris begins to stop and makes sedimentation from the corner between the channel bed and the dam face, and static part grows to the final sedimentation. The sedimentation makes the impact angle larger between the flow and the dam face and the load on the dam becomes smaller.

Fig.7 shows the relationship between the velocity and timelag (the difference of time between the moment at which flow's head touch the dam face and at which the load become maximum). The

timelag seems to be in inverse proportion to the velocity. In other words, the length of the head part of the flow, that reach the dam until maximum load arises, is constant (about lOcm in this experiment), in spite of the difference in velocity. This means that the shape of the flow's head has an important role in the mechanism of load generation and that this part's properties should be adopted in estimating the impact load.

e A A %A@ a: Type A

e: Type B / A: Type C

x ffl d 0 50 100 150 200 250 Z

Velocity ( cm/s)

Fig.5 Relation between velocity and maximum load per cross secsion area of flow

Movable bed I I I

/ / f / , , Channel bed 1'0 c m / /

Fig.6 Morphological variation of debris flow's head at intervals of 0.01 second

Tine Load bet) (Kpf)

Table 1 Variation of impact load with time

- 1agXVelocity u a,

= lOcm "I -

- 0 50 100 150 200 250

Velocity (cm/s )

Fig.? Relation between velocity and time lag


A DISCUSSION OF THE LOAD ON THE BASIS OF MOMENTUM VARIATION OF THE FLOW HEAD

In this chapter, the mechanism of load generation will be discussed in the relation with the variation of the load and the deforming process of the flow head.

If the flow is in a fully steady state before the impact point, the debris flow' head, that include enough part concerning the generation of the impact load, can be treated as a series of momentum points. On the assumption that the flow depth of this part is equal in each section, the discussion can be made in two dimension. Then, this part is expressed as a plane with some mass on X-Y two dimensional axis, as shown in Fig.8, and the surEace line is described as a function h(x,t). At the time t, this fluid part exists in O<x<xe, and the center of gravity on X axis xg is in the relation of

The center of gravity given by this equation varies with the deformation of the flow head, and is defined as a function of time xg(t). Then, the acceleration of the gravity center is also defined as a function of time ag(t) as

dt'

It is the dam that gives the force which makes this acceleration, thus the load on the dam is described as follow.

Fig.8 Model of flow head as a system of material points

where, B is the width of channel. As a consequence, the load on the dam is regulated by the function h(x,t) that express the surface line of the flow head.

These way of analysis was applied in results of the experiment. In this analysis, the head part of the flow, that include enough part concerning the generation of the impact load, is considered to be cut off and be independent from the following flow, as shown by the broken line in Fig.S(a). Fig.S(a) shows the morphology of the flow head at each 0.01 second interval after impact on the dam, that was observed in the experiment by the high speed video. The variation of the flow' gravity center is calculated from this morphological variation and the average loads that should be generated on the dam during each 0.01 second are

Fig.g(a) Behavior of the system of X material points in flow's head at interval of 0.01 second

w

3 0: Observed - 0: Calculated

a a 0 A

Time (sec

Fig.S(b) Relation between measured and calculated load

USDA Forest SelviceGen. Tech. Rep. PSW-GTR-130.1991

calculated from this and the bulk density. It is determined that the bulk density used in the calculation is to be

3 1.4g/cm . The comparison between the measured and the calculated load is shown in Fig.S(b). The two loads are in good agreement until the maximum point, and this means that the impact load of the debris flow is regulated by the deformation of the debris flow head. After the maximum point, the measured load becomes lager than the calculated one. This difference may be caused by the static load due to sediment of the debris.

FLOW MODELING AND COMPUTER SIMULATION

The impact load of the debris flow is regulated by the deformation of the debris flow head, as described in previous chapter. Therefore, the best method to roughly calculate the impact load is by estimating the deformation process of the flow head quantitatively using the initial conditions (flow velocity, flow depth, bulk density). Although h(x,t) may have complex form affected by many factors, here a simple model is proposed that is analogous to the behavior of a jet flow checked by a perpendicular wall.

In this model, some functions are prepared. The original flow depth is to be described as a function of the distance from the flow front H(x). The bulk density in each part of the flow is also to be described as a function of the distance from the flow front too, to take up the effect of the density distribution in x direction. As shown in Fig.10, the debris flow flows from x direction to y axis which represent the dam face with keeping initial velocity. The flow come to y axis and shift its position on the surface of original flow at each time in order from the front and, as a result of

Hd x

Fig . 1 0 Flow deformation model

a series of this behavior, the fluid goes up to y direction along y axis. when the fluid shifts its position, each part of the flow changes its flow depth from H to Hd. Hd at each time is decided by R which is the ratio of Hd and H (R=Hd/H). R is also a function of the distance from the flow front. These functions of the distance from the flow front can be transformed to the functions of the time by means of velocity. Therefore the load on the dam and the morphology of the flow head at each time can be obtained by completing these functions of time as Ht(t), Dt(t), Rt(t). The load can be described as a function of time as

2 B v d

2 Ft(t)=Dt(t)llt(t)Bv t 7. -(Dt(t)Ht(t) Rt(t))

d t (6)

(cml k, - Calculated

Fig.ll(a) Comparison between observed and calculated morphology of debris flow head. (Each line indicates 0,0.1,0.3,0.5,0.7 second after impact )

- Calculated ----. Observed

0.05 0.1 Time ( sec)

Fig.ll(b) Simulated result of impact load on high velocity(l.70m/s).


After some transformations are made on this equation, the maximum load can be expressed by giving each value of composing functions Dt, Ht, Rt and their time differential functions (Dm, Hm, Rm, D'm, H'm and R'm respectively) at that time.

HmR'm K = l t - RmH'm

t - D'm

t - 2~ v aomv

Where K is a coefficient that mean the ratio between the maximum load and the load by dynamic pressure of a steady jet flow in same profile.

Now this modeling is applied to the experiment. The composing functions are decided as follow.

H(x), the function that represents the flow depth, is to be described in a simple form that suits the morphology of the flow head in each experimental run, as follow

where, H10 is the flow depth at lOcm from the front; a and b are the parameters that are decided in each run for better suitabilities, which have the range of 0.5-0.7 and 0.6-0.7 respectably. This function is applied to about 20cm length in the flow front. D(x), the function that represents the bulk density in each part of the flow, is decided on the basis of the preliminary experiment, as a empirical equation.

R(x) is the function that represents the deforming property of the flow, and also considered to express the ratio between the velocity components rise along the dam face and these which turn back to upstream after impact. This function is also decided so as to suit the experimental result.

Fig.11 is the comparison between the observed and the calculated morphology of the flow's head and the load on the dam. The velocity of this flow is 170cm/s a 1 the flow depth at lOcm from the front is 4.8cm and parameter a and b in equation (9) are 0.5 and 0.6 respectively. The function R(x) used in this calculation is

In this function, the x is given in cm unit. This function of the distance is

- Calculated .---_. Observed

Fig.l2(a) Com~arison between observed andcalcuiated morphology of debris flow head. (Each line indicates 0,0.1,0.3,0.5,0.7 second after impact. )

Calculated Observed

Time (sec)

Fig.lZ(b) Simulated result of impact load on low velocity.

0 1 2 3 4 5 Load by dynamic pressure (Kgf)

of steady jet flow

Fig.13 Relation between load by dynamic pressure of steady jet flow and measured load.


transformed to function of the time with the velocity (170cm/s) as

Both the deforming process of the flow and the load on the dam are well simulated. Fig.12 is the simulated result of another experimental run, by same R(x). The velocity of this flow is 108cm/s, and the flow depth at lOcm from the front is 6.3cm, and the parameters of the flow depth function a, b are 0.7 and 0.7. The calculated results can be said to agree well with the observed one in spite that function R(x) is decided to suit for other experimental run. The difference of the load between the calculated and the observed after the maximum point is most likely caused by the effect of overflow above the dam, which is ignored in this model.

The estimation of the maximum load is one of the most important problem in the practical aspect. The maximum load can be estimated with the model and the functions above. With these functions and the condition that the maximum load arises when vt=lOcm in this experiment (see Fig.7), eq.(9) is transformed to

(13 Since Hm is in the range of 4.1-6.3 and parameter a is 0.5-0.7, b is 0.6-0.7 as the results of the experiments, K should be in the range of 1.47-2.70. Fig.13 is the relationship between the load by the dynamic pressure of steady jet flow and the maximum measured load. The calculated value of K expresses the entire tendency of the experimental results.

CONCLUSION

The impact load on the dam when debris flow strikes it was measured and the behavior of the flow was observed in

the experiment. In the low velocity area, the measured load could be explained as the static load by the sediment of debris. On the other hand, in the high velocity area, the measured load was rather great and corresponded to the momentum variation ~f the debris flow head. Then a model was proposed that estimate the characteristic momentum variation of the debris flow. Both the load on the dam and the deformation process of the flow could be well simulated by means of this model. The measured maximum load was 1.47-2.70 times larger than the load by the dynamic pressure of the steady jet flow in same profile of each debris flow.

In this way, the impact load on the dam due to debris flow has been made clear and, although more investigation will be required to apply this model to practical situations, the impact load can be estimated at least on an experimental level.

REFERENCES

Hirao,K. et a1 1970. An Experimental Study on Impulsive Force due to Hydraulic Bore. Journal of Japan Society of Erosion Control Engineer- ing No.76 : pp.11-16.

Miyamoto,K. and Daido,A. 1983. Study on the Impact load of Mud-Debris Bore on the Bank. Memoirs of the Re- search Institute of Science and Encineerinc. Ritumeikan Univ. No.42. - - . : pp.61-79.

Miyoshi,I. and Suzuki,M. 1990. Experi- mental Study on Impact Load on a Dam Due to ~ e b r i s Flow: Journal of the Japan Society of Erosion Control Engineering No.169. : pp.11-19.

Mizuyama,T. 1979. Estimation of impact force on dam due to debris flow and its problems. Journal of the Japan Society of Erosion Control Engineer- ing No.112 : pp.40-43.


Sediment Dynamics of a High Gradient Stream in the Oi River Basin of Japan1 Hideji Maita2

Abstract: This paper discusses the effects of the valley width for discontinuities of sediment transport in natural stream channels.

The results may be summarized as follows: 1)ln torrential rivers. deposition or erosion depend mostly on the sediment supply. not on the magnitude of the flow discharge. 2lWide valley floors of streams are depositional spaces where the excess sediment from the upper stream area is temporarily deposited. In the erosional process that follows, the sediment runs off down stream in a way that can be explained by an exponent i a1 process.

Numerous researches in the area of sediment control work in mountainous areas have been carried out. However, our Understanding of the effect of discontinuities in the history of sediment transport is still insufficient. In order to gain a fuller Understanding, it is first necessary to examine the morphology of streams in their natural state without sediment control structures. With this in mind we selected the Higashigochi basin of a small tributary of the Oi river as our study area. During 1982 the basin was subjected to a period of intense rainfall of more than 900mm This released abundant sediment, about 150,000m3 in the observed reach. As a result the morphology of the stream changed. Taking this opportunity, we were able to study and come to a greater understanding of the dynamics of sediment transport. This paper analyzes a series of changes in the mor~holos~ of a high gradient gravel-bed stream that resulted from nine floods.

'presented at the Subject Group 51.04 Technical Session on Geomorphic Hazards in Managed Forests, XIX World Congress, International Union of Forestry Research Organizations, August 5-1 1,1990, Montreal, Canada.

'~ssistant Professor of the Institute of Agricultural and Forest Engineering. University of Tsukuba, Ibaraki, Japan

STUDY AREA

Topoqraphy and Geoloqy

The Higashigochi river basin, with a drainage area of about 28 km2, is a small tributary of the Oi river system emptying into the Pacific side of Honshu Island. A 2406 meter peak, located at the north corner of the basin is the highest point,

Figure I--The study area.


while the elevation of the confluence with the main river, about 770 meters, is the lowest point in the study area. This gives a relief of about 1640 meters over a linear distance of 7.5 km. Reflecting this high relief, slopes are in general very steep with an average of about 38' (Fig. I).

The bedrock is mainly composed of shale and sandstone from the Cretaceous period. The rock is generally fractured because the basin is situated in the high, uplifting zone of the Japanese Southern Alps.

As a result of these topographical and geological conditions, the ratio of landslide scars to the area of the basin is 2.9 percent and this figure reaches 7.6 percent in the upper basin.

Stream ChmUi!!22

The longitudinal profile of the Higashigochi river is shown in Figure 2. This figure shows that the stream is steep and the profile can be divided into three parts in terms of it5 gradient. The lower part, with a gradient of about 1/30, the middle part with a sradient of about 1/20 and the upper section the sradient of which is more than 1/10. The observed reach was located in the upper section. As to the planar shape of the stream, the meander and the variation of channel width is remarkable.

Climate

According to the climatic records at the Sannosawa station (Fig. I ) , the average rainfall between the months of April and November from 1970 to 1981 was about 2,500 mm. Consequently, the mean annual precipitation may reach about 3,000 mm, but it is very variable.

The mean annual temperature is 9.E°C, with the highest temperature occurring in August and the lowest in January. Temperature records of daily maxima and minima suggest that freeze/thaw processes are normally active from the latter half of November to the first half of April (Fig. 3).

Veqetation

Vegetation is predominantly deciduous below the 1,500-1.800 meter zone and conifers dominate at higher elevations. Below the 1.500-1,800 meter zone, Japanese cedar (Chryptomeria japonica D. Don), Japanese cypress (Chamaecyparis obutusa S. et Z.) and Japanese larch (Larix leptolepis Gordon) have been planted.

Observed reach

The observed reach extended about 1 km, where the stream, coming through the V-shaped narrow valley first meets a wide floor of about 40 to 130 meters. Then the stream again enters a narrow valley section at the end of the observed reach (Fig. 4). The gradient of the stream bed in the observed reach ranges from 1/8 to 1/15.

Because no modification of the channel of the reach by sediment control structures had been undertaken, we were able to examine the morphology of the channel in its natural state.

METHOD

In this research we regarded the actual stream channel itself as the place for the field experiments. As a result, various measurements

- 0 5 10

DISTANCE FRON THE CONFLUENCE(km)

Figure 2--The longitudinal profile of the Higashigochi river.

F MONTH

Figure 3--The climate of the study area.


Figure 4--The observed reach after the 8209 flood and the location of the cross sections

were carried out in the study area. In order to record a sequence of changes in the channel morphology of the observed reach, whenever a river bed fluctuation occurred over the period 1979 to 1985, the leveling of 22 cross sections of the observed reach at intervals of about 50 meters was carried out(Fig. 4). Plane surveying was mostly carried out at the same time. The vertical and horizontal distribution of the grain size of the stream bed was investigated after the river bed fluctuations in September 1980 and September 1982. In order to measure the volume of the deposits on the bedrock of the observed reach, seismic prospecting was carried out after the river bed fluctuation in August 1981.

Rainfall was measured by several rain gauges placed around the basin (Fig. I ) and the flood discharge was calculated by a storage function run-off model below (Maita et al. 19841.

P Sl=KQ . Pz0.6, K=8.6~~'~*. TI=2.5A 0. I4,,-O. 4

Here. SI is the hypothetical storage depth of rainwater over a basin considering the time lag TI between rainfall excess re and flood discharge Q, and A is the area of a basin.

SHAPE CHANGES OF THE STREAM CHANNEL

Threshold Rainfall

Nine river bed fluctuations were confirmed in the observed reach from 1979 to 1985. Table I shows the largest values recorded for the continuous rainfall and hourly rainfall measured at several precipitation stations. It also shows the maximum calculated peak discharge at the end of the observed reach for each of the rainfall events and when a river bed fluctuation occurred.

Table I--The magnitude of rainfall and discharge for each flood .

flood continuous max. hourly peak name rai nfal 1 rainfal l discharge

(mm) (mm/h) (m3/s)


8506 Q SCALE

Figure 5--The changes in t he lowest lon9i tudinal stream bed p r o f i l e i n t h e observed reach.

E BED PROFILE OF THE n DEPOSlTlONAL PEOK IN E w = 0 - C 4 =rim -1 W

DISTANCE FROM THE CONFLUENCE(km)

Figure &-The changes in t he longitudinal bed p r o f i l e of t h e 3.3 km of stream between a check dam and the observed reach before and a f t e r t he 8208 flood.

From the f igu res in Table 1, i t seems tha t a continuous r a i n f a l l level of about 200 mm o r a maximum hourly r a i n f a l l of about 30 mm is the threshold r a i n f a l l fo r a r i ve r bed f luc tua t ion in the Higashigochi r i ve r basin. Such f i9ureS occurred about once every 1.3 t o 1.5 years.

Chanses of Channel Shape

Figure 5 shows the lowest longitudinal Stream bed p r o f i l e in t he observed reach. The p ro f i l e , formed by the 8208 flood ( t h e flood in August 19821, is divided into two s tages . One. shown as 82081 in Figure 5, i s t h e bed p r o f i l e of the depositional peak. The o ther , shown as 8208I1 , i s t h e p r o f i l e a f t e r t he recession flow of t he 8208 flood p a r t i a l l y eroded the buried bed. Because of t he c l a r i t y of t he p r o f i l e changes, each p r o f i l e is compared t o the p r o f i l e a f t e r t he 8009 flood ( t h e flood in September 19801. Other floods were named in t h i s manner.

Figure 6 shows the longitudinal stream bed P ro f i l e of t he approximately 3.3 km of stream between a check dam and the observed reach before and a f t e r t he 8208 flood. As shown in Figure 4 and 5, t he l a rge deposition of t he 8208 flood was caused by a continuous r a i n f a l l of 933 mm and an hourly r a i n f a l l of 69.5 mm ( a recurrence in terva l of more than 30 yea r s ) , which Typhoon no. 10 produced between August 1 and 3, 1982 (Fig. 7) . This event ra i sed the stream bed from 3 meters t o 8 meters. Subsequently, rapid erosion ensured tha t the bed p r o f i l e regained its former shape very rapidly. As shown in Figure 6, t he check dam had no influence on the deposition in the observed reach caused by the 8208 flood. Besides i t was noted tha t t he re was almost no d r i f t wood debris in the observed reach in s p i t e of such a l a r s e flood.

Figure 8 shows the changes in the cross sec t ional channel p ro f i l e s i n t h e observed reach. The black shaded pa r t s of t h e diagram represent deposition. Erosion i s shown by the unshaded area between the l i nes describing the cross sec t ion . The la rge deposition almost f la t tened the bed in the observed reach. After the f lood, incision of t he stream hed meant t ha t these p ro f i l e s nearly recovered t h e i r former shape. The recovery was more rapid in t he narrow par t of t he val ley than in the wide pa r t .

Figure 9 shows the changes in t he planar shape of t he stream bed in the observed reach. The la rge deposi t ion not only caused la rge changes in t he planar shape but a l s o the locat ion of t he thalwegs. The erosional process of t he stream bed meant t h a t t he shape of t he bed returned t o its former shape and the thalwegs returned t o t h e i r former posi t ions.

Thus, la rge depositions have a marked e f f ec t on the stream bed but these changes a r e not permanent and the erosional process causes the channel shape t o r eve r t to i t s former one.


toy

Figure 8--Some examples of the changes in the cross sectional profiles in the observed reach.

Figure 9--The changes in the planar shape of the stream bed in the observed reach. The black shaded parts of the diagrams represent the low water flows.


Figure 7--The observed hyetograph in the study area and the calculated hydrograph at the end of the observed reach in the 8208 flood.

7+ LINE(LEFT BANK) unit: cm

,, "ean ,:grain diameter O

range locm

Fisure 10--The structure of the deposit formed by the 8208 flood at 7t line.

Structure of Deposits Formed by the 8208 Flood

Fisure 10 shows the structure of the deposit formed by the 8208 flood at 7+ line shown in Fisure 4. Although the deposition was formed by one flood there are several parts with laminar structures. As Iseya et a1.(1990) described, it is thought that this structure was formed when a shallow and high velocity flow transported heterogeneous sediment, raising the bed at a high rate. Because of the large deposition, the grain size of the stream bed became smaller. On the

other hand, erosion caused the grain size to become larger as the smaller sediment was removed from the stream bed.

WANT I TAT I VE CHANGES OF RIVER BED FLUCTUATION

Changes of the Volume of Deposit -

Figure I 1 shows the changes of the volume of the deposits on the bedrock in the observed reach. This was found by using the volume of the river bed fluctuation and cross sectional bedrock Profiles measured by seismic prospectins in October 1981. The volume of the river bed fluctuation can be obtained by the following steps. First, as shown in Fisure 12, the volume of the river bed fluctuation of the segment is calculated by the equation below.

Here, V is the volume of the river bed fluctuation of the segment, L is the distance between two adjacent cross sections, El 1 ,E12,. .etc, and Dl 1 ,D12,. .etc, are the areas surrounded by the two cross sectional profiles before and after a flood at the Al cross section. EIl,E12,..etc, represents the area eroded and is negative, DIl,D12,..etc, represents the deposited area and is positive. E21,E22, ..etc, and 021,D22,..etc, represent the same variables measured at the A2 cross section. The volume of the river bed fluctuation of the observed reach can be obtained by taking the sum of the volumes of each segment. Thus, the overall volume may be positive or negative in sign.

As can be seen from Figure 1 1 , the volume of the depo3its was decreased gradually to about 120,000 m by the process of erosion between 1980 and 1981. But the 8208 flood jn 1982 deposited sediment of more than 150,000 m and the total volume 05 sediment on the bedrock increased to 270,000 m . Af5er that, it decreased rapidly to about 130,000 m . As the changes between 1982 and 1985 show, the erosional process continued in the observed reach after the 8208 flood despite the fact that there were some large rainfalls in this period. This means that there was little sediment in the upper basin of the observed reach because unstable debris had been mostly swept from the stream beds and the slopes of the upper basin by the heavy rainfall associated with the 8208 flood.

ANALYSIS AND DISCUSSION

Figure 13 shows the relation between the absolute value of the river bed fluctuation in the observed reach and the peak flow discharge. This peak flow discharge was adopted as an index of the magnitude of discharge. As the graph shows, the volume of the river bed fluctuation is not always large in comparison with the increase of flow discharge and it seems probable that the ordering of the floods is an important factor. To attempt to unravel this complicated


W u ( er 4 e

51 - n

3 f: 101 k( ma/: r u w n.

( X IOS mS u, 201 C E - U V1 u 0 Y n. PC w n n

w w > e PC

IOC k m 0 0

w w = = 2 * -1 0 1 > - 0

ORDER OF FLOOD OCCURRENCE

Figure 11--The changes of the volume of the deposits on the bedrock in the observed reach.

Figure 13--The relation between the absolute value of the river bed fluctuation in the observed reach and the peak flow discharge.

I\*' betore a flood A

Figure 12--The schematic diagram to obtain the volume of the river bed fluctuation.

relationship, the idea of the specific volume of the river bed fluctuation was introduced. The specific volume was obtained by dividing the volume of the river bed fluctuation by the peak discharse adopted as an index of the flood discharse.

Figure 14 shows the specific volume of the river bed fluctuation in the observed reach arranged in the order in which the floods occurred. As this graph shows, a regularity is apparent . The specific volume decreases exponentially in the erosional process following the large deposition of the 8208 flood. As shown in Figure 15, this regularity of the erosional process in the observed reach can be expressed by the following exponential equation.

Here S is the specific volume of the river bed fluctuation per unit distance, t is the occurrent order expressed as 1 2 etc, during the erosional process. In the case of the series of events in the observed reach a is 3.3 and ,8

Figure 16 shows the different ways in which the specific volume decreases during the erosional process, depending on the width of the valley . This difference can be expressed in terms of the parameters of the exponential equation above. In the wider parts of the valley in the observed reach (average width 72 meters), n is 3.3 and ,3 is 0.8. In the narrower parts in the observed reach (average width 50 meters), n is5.0and p is 1.4. Thus, as thevalley becomes wider p decreases. It is believed that ,3 can be used as an index to shown how the valley floor width influences the volume of the river bed fluctuation.


ORDER OF F L O O D OCCURRENCE

( 8209X6305X8308X830SX8506 ) t : ORDER OF FLOOD OCCURRENCE

Fiqure i6--The different ways in which the specific volume decreases during the erosional process, depending on the width of the valley.

Figure 14--The specific volume of the river bed fluctuation in the observed reach arranged in the order in which the floods occurred.

CONCLUSION

t : ORDER OF FLOOD OCCURRENCE

Figure 15--The exponential relation between the specific volume in the observed reach and the order of the flood occurrence during the erosional process.

The magnitudes of the flow discharge and the river bed fluctuation did not exhibit a one to one correspondence. We were able to find a regularity in the quantitative changes by arranging the river bed fluctuations in the order of the occurrence of the floods. This implies that the history of sediment transport plays an important role. That is to say, when little unstable debris remains in the upper reaches and slopes of the basin, a trend towards the erosion of the river bed continues even if a larger flood occurs. Thus, in torrential streams in headwater regions, deposition or erosion depend mostly on the sediment supply, not on the magnitude of the flow discharge.

The valley floor width is closely related to the dynamics of sediment transport. In the erosional process, the specific volume of the river bed fluctuation decreases rapidly in narrow valley floors, but only decreases slowly in wide floors. On the other hand, in the depositional Process, the wider the valley floors are, the more sediment from the upper reach they can retain. Therefore, the wide valley floors of a stream are depositional spaces where the excess sediment from the upper stream area is temporari IY deposited. In the erosional process that follows, sediment runs off down stream in a


way that can be explained by an exponential process. In other words, wide valley floors represent spaces that retard sediment transport.

I thank Michio Kaijo, Motoyuki Sunasaka, Teruo Otsubo, Toru Endo, Akira Takinami, Masanori Wade and Kunihiro Segawa, Agricultural and Forestry Research Center, University of Tsukuba, for their assistance to the field work.

REFERENCES

Iseya, Fujiko; lkeda Hiroshi; Maita Hideji. 1990. Fluvial deposits in a torrential gravel-bed stream by extreme sediment supply: sediment structure and depositional mechanism. The 3rd International Workshop on Gravel-Bed Rivers, Florence,ltaly, September 25-29.1990.

Maita, Hideji; Otsuho,Teruo; Kaijo, Michio. 1984. Hydraulic geometry in a natural torrent. Transactions, the 95th Meeting of the Japanese Forestry Society: 641-643 (in Japanese).


Snow-Cover Condition in Japan and Damage of the Sugi (Cryptomeria Japonica D. Don)' Hideaki Taira2

Abstract: Japan is one of the most snowiest regions in the world. Particularly the mountainous area of Honshu (the main island), along the Japan Sea has heavy snow in winter. In some places, snow piles up more than four meters and the ground is coverd with snow about one hundred and forty days a year. The sugi tree is widely planted in snowy regions, and snow-pressure damages, such as basal bending, occure in juvenile stands, and after that crown snow-damage, such as stem breakage, happen in younger stands about 10-30 years-old. Basal bending is formed by the difference in recovery rate between the upper part and the lower part of the stem during growing season. Root damage occurs when the stem is prostrated, and the compression wood is formed in the process of the reelection of the fallen stem. Crown snow-damage happens during the condition of comparative warm air temparatures ranged from three degrees below zero to three degrees above zero. The strength of the stem against crown snow-damage depends on the diameter of the tree, tree taper,constunt rr for the root, and the modulus of elasticity. Pulling up the fallen stem, and controlling the tree density are important in preventing these snow damage.

Introduction: It is said that Japan is the snowiest region in the world. The Japan sea area of Honshu has a lot of snow every year. Though the snow protects plants from severe coldness in winter and is an important source of water, it also is the cause of damages such as basal bending and stem breakage. The sugi is an important spicese for reforestation in Japan and the total area of sugi reforestation exceeds 4.15 million ha., making it about 48 percent of the total artifical forest in Japan. The sugi is widely planted. in snowy regions, but suffer many kinds of snow damages every year. Basal bending, stem breakage,stem bending and uprooting are recognized problems in the sugi reforestation, and these snow damages are classified in to two types; one is snow-pressure damage which occurs in younger aged

trees until1 they are about ten-years-old and the other is crown snow-damages which occur in trees over ten years old. But the types of snow damage depends on the snow-cover condition. The author will talk about the relationship between the snow-cover condition in Japan and the type of snow damage, the mechanism of main snow damage and its control.

THE SNOW COVER CONDITION IN JAPAN AND SNOW DAMAGE

The mean annual maximun snow depth of Japan is shown in Fig-1. A high percentage of snowy areas are distributed along the Japan Sea, and in some areas, snow depth exceedes four meters.ln contrast there is only about 10-50 centimeters in the area along the Pacific Ocean, and the mountainous area of Shikoku and Kyushu island, and most areas of Shikoku, Kyushu and the southern part of the main island have less than 10 centimeters.

The Pacific Ocean

Fig.-1. Distribution map of annual maxmun snow depth


crn

C 0..

0 LO 80 120 160 200 c rn

Basal bending

Fig.- 2. The relation between annual maxmun

snow depth and basal bending

Quality of snow also varies. There is dry snow in Hokkaido, and the northern and mountainous areas of Honshu, but in the area along the Japan Sea there is wet snow which sticks easily on trees. Snow pails up on the tree crown, and causes stem breakage, which is called crown snow-damage. Also in the Pacific Ocean area of Honshu, crown snow-damage occurs when tropical low pressure passes by the Pacific Ocean and brings wet snow in early spring.

The relationship between basal bending and the mean annual snow depth are shown in Fig-2. Basal bending is about 20 centimeters in the areas where snow depth is below 1 meter. As the snow depth reaches 2 meters, basal bending increase over 60 centimeters, and at depths over 2.5 meters, basal bending increase to 178 centimeters. Basal bending increases as the snow depth increases.

Fig: 3 Basal bending of cryptomeria

Fig.- 4. Crown snow-damage of cryptomeria


Tree height 2-3 m Tree height more than 10. Leaning stem rree height 6-7 . Crown snov-damage occur Damage of roots begin Turn over, stem breakage,

crack of stem occur under - - - - _ _ _ - - - - _ _ _ ---.__ much snow - - - _ _ _ - - - _ _ _ Heavy snowy region

- - - - - - _ _ - - - _ _ (more than 2.5 m )

- - - .____ Less snowy region --..- - - - _ _ - - - - - - _ _ _ (less than 1.0 m ) - . - - - - - - _ _ _ _ _

.... Tree height less than 1.5 n

*-

Stem is Pressed on the ground Damage of roots begin. Roots Tree is buried by snow come out under the stem Turn over,stem breakag, Stem is stabilized by developed

crack of stem occur. Under roots, so the tree is unburied Part of stem is transformed into root

- - - _ _

Fig.- 5. Variation of snow damage of cryptomeria by relation between snow depth and tree height

Stem is Pressed on the ground Less damage Tree height 4-5 m 1

Tree is unburied by snow -*-

The extent of tree damage varies according from the pulling out of roots to the cracking to the snow depth and tree height(Fig-5). In areas of the basal stem and stem brakage. In areas with

with snow depths of less than 1.0 meters, only depths of over 2.5 meters of snow, the ratio of

trees less than 2.0-2.5 meters in height are dieing trees due to snow damage increases

prostrated in winter. Root damage is not serious drastically, and it is difficult to forest the

and stem breakage which becomes fatal seldom sugi in this area.

occurs. As the tree reaches more than 2.0-2.5 meters in height, the stem does not prostrate with average snow fall depth. However, in heavy

THE MECHANISUM OF MAIN SNOW DAMAGE

snow the po&~b~l~ty of stem breakage and cracklng at the bottom of the stem Increases and many trees

Snow Pressure Damage

fall and pull out their roots. Snow damage on The stem of the sugi leans with the initial trees varies from the pulling out of roots to stem breakage (als ocalled crown snow-damage). Crown

snow fall and is buried by subsequent snow falls.

snow-damage occurs in trees more than 10 meters in The snow-covered stem is pressed down by the

height because the stem becomes stiff (and hence, weight of the accumulated snow and subsequent

resistant to bending ) and the roots are large sedimentation of snow, and is subjected to elastic

enough to resist stem prostration. In regions of strain, elastic after-strain and permanent deformation.

heavy snow, the young stem repeatedly prostrates and the uprooting of the trees is common. The new roots develop under the part of stem still

In younger trees ( one to two years ) where

touching the ground, and the tree then develops stems are soft and thin, the stress is mainly put

resistance against futher prostration. The effects on the stem and the stem does not lean from the

of snow damage during the growing stages rangs base when the snow press it down on the ground. But,for trees more than three-years-old (height :

USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991 67

1.5-2.0 nmeters), the stem leans from the base because of the increase in its bending stiffness.

In early spring after the release of snow pressure,the stem begins its straightening process with rapid, simple elastic recovery, then elastic after-strain follows. The -stem completes its recovery through elastic after-strain until the end of April or early May at which time the stem resumes its recovery with growth and the formation of compression wood. For one-and two-year old trees, stem straigthening is completed by the middle of June or early July ; after that, some of the trees increase in weight with tree growth, and this also contributes to the basal bend formation (Fig-6).

Since straightening of the stem with growth is great in one-, two-and three-year-old trees, there is less basal bending on these trees. On the other hand, since straightening of the leaning stem decreases with age, there is greater basal bending in older trees.

The recovery rate observed at each stem positions varies in relationship to the stem's distance from the base. The nearer the stem is to the base, the slower the recovery rate. This difference in recovery rate at various stem positions causes basal bending (Fig-7).

The basal bending of the sugi increases every year. During the early stages of growth, snow depth has no effect on the basal bending of the sugi, but, when the tree attains a height of more than 1.5 meters, increase in snow depth greatly affects stem prostration resulting in greater basal bending. In addition to the two factors mentioned, the slope of the site also affects basal bending. if the snow depth and the

height of tree are the same, the amount of stem prostration is affected by the degree of slope. As the slope steepens, the amount of stem prostration increases resulting in greater basal bending.

When the stem is prostrated by snow, the roots suffer damage at the upper part by stretch, at the lower part by pressure, and at the left and right sides by twist. The left and right twisting of the roots, however, does not badly injure them so that they can develop well on both side of the slope. Roots on the down slope side are only slightly damaged due to an increase on the compression force. But roots on the upper slope side are the ones that are severely damaged. They are pulled out,resulting in poor root development.

Therefore, mature bent trees have deformed roots and large side roots (Fig-8 ). In areas with snow depths of less than 1.0 meters, most of the trees more than 2.5 meters in height are not easily prostrated and the amount of stem prostration is small. Hcnce, the damage on roots is not so severe and the roots develop normally. In areas of heavy snow, beside root damage and deformation, the lower part of the stem is transformed into roots. When this stem touches the ground due to the weight of snow, roots start to develop from it and the part touching the ground is transformed into a main root.

Roots on both the side and the lower part of the slope are not easily damaged and hence, can develop well. The transformation of the lower part of the stem into a main root increases the resistance of tree against prostration by snow. Morever, the tree is not readily buried in the snow because the transformed main roots effectively prevent stem prostration.

Horizmlal deuiafion(cm)

Fig.- 6. Process of straightening of t h e prostrated stem of a typical 2-year-old tree

Fig.- 7. Relationship between the deviation from former position ( f ) and rates of straightening of prostrate s t e m s ((rlf) x 100) at each position during a growing season


Fig: 8 Deformation of roots

After basal bending is stabilized, surface roots on the down slope develop and the diameter of the lower stem increases towards the down slope. Therefore, the curve of the lower part of the stem is apparently corrected.

Crown Snow-Damage

Snow damage after basal bending has stabilized is called crown snow- damage. It is the phenomena in which the stems are broken by an accelerating snow load on the tree crown. This is roughly classfied into breakage of the stem, breakage of the tip of the stem, and uprooting. Uprooting is the predominant damage among trees less than twenty-years-old, and is sometimes difficult to distinguish from snow pressure damage. Breakage of stem is common in twenty-to thirty-years old stands, and this stand is most sensitive to snow crown damage. In stands More than thirty-years-old, the breakage of the tip of the stem is common, but it is not serious. Also trees with larger stems are more resistant to crown snow-damage than those with smaller stems. But it is difficult to evaluate tree strength against snow crown damage by the shape factor of stem. It is only a comparative standard and it dose not become an absolute one. As mentioned before, crown snow-damages is the phenomena in which the stem is broken by an unendurable snow load, so crown snow-damages can look as if the broken stem is a failure of the tapered column receiving an eccentric compressive load of snow, i .e. the buckeling load (PC,) of stem can be estimated by the following equation.

PC, = u 2 * rS2 -E*I./L2 r ,' : satisties following the equation tan r/r=-I /81a-u r 2 *L2-IoIL 6 : ratio of taper the stem 8:I - S E :Mudulus in elasticity L : Height of gravity of a snow-laded crown I,: Second moment of cross cection base at the

stem

It is understood from the equation that the strengthen against snow crown damage is determined by the diameter of the stem, the taper of the stem, the height of gravity of a snowload, modulus in elasticity in bending, the u-index whose value was obtained from the regression coefficient between the turning angle of the tree stem and the turning moment at the stem base. The estimated breaking load is 200-500 kilogram of trees about 20 centimeters at diameter breast height and is agreed with the experimental load which is gotten from broken trees receiving vertical loads as shown Fig-11 .

CONTROL METHODS OF MAIN SNOW DAMAGE

Many methods of controlling snow damage have been adapted in the past.0f these control methods, the author will mentioned the most useful ones in this paper.

Snow Pressure Damage

As the cause of basal bending of young trees is stem prostration by snow, pulling up the fallen stem is the most effective method of


. ..

~ i ~ . 11. ~ i ~ ~ ~ ~ . of snow-loaded trcc and vertical loading test procedure for resistance of tree stem (Hakntani and othcrs.l981). Legend: G : lhc ccntcr of grrvily of r m o w l a d m crown. a : hor i zml r l dirptjlccment of the cenlcr oigrav. i ly o i the snow.iadcn crown l rom the rlem axis. P: snow lord. 8: lurning rndc ~t the stem bate. L: hcighl of the cenlcr o i gravity 01 the mowladen crown lrom lhc ground. 6 : delicction at the height L. D.: dismeler 11 the r i m bare, A: dirmclcr nl the hcighl L.

control. In regions of heavy snow, slant planting which deforms the roots is adaptable because the deformed roots is unsusceptible to stem prostration. Fertizetion increases tree growth, but basal bending also increases at the same time. The degree of basal bending is different largely among the cultivares, so planting of small bend cullivares is an effective way to reduce basal bending. But, it is hard to lean with initial snow, so cultivares with a small degree of basal bending were less frequent in stems leaning under snow, but many stem breakage were observed in heavy snow regions (with snow depths over 1.5 meters).

Crown Snow-Damage

One of the most effective methods for controlling crown snow-damage is to decreas the height/diameter ratio by control 1 ing stand density. The most desirable stand density is 800 -1200/per hectare at planting, and repeated thinnings are requied when the competition occurs in the stand as the tree grow. Also, as modulus in elasticity in bending is different in the cultivarer, it is important to choose cultivar with large modulus in elasticity in bending for forest owners in the area of much crown snow-damage.

LITERATURE CITED

Fujimori, T. ; Matsuda, and Kiyono, Y. 1987. Stand

cul tivars. B G ~ letin of the Toyama prefectual forest experiment station 11: 7-17.

Kato, A. ; Nakatani, H. ; Taira, H. and Aiura, H. 1988. Estimation snow-load required to cause stem failure in Boka-sugi stand. Journal of the Toyama forestry and forest products research center 1: 1-6.

Katsuta, M. and Matsuda, K. 1984. Differences in the damage from snow crowning among Cryptomeria japonica cultivars (1). Rinboku no ikusyu ( Forest tree breeding ) 131: 12-17.

Kitamura, M. 1981. Uber die Schneeshaden des Sugi- Bestandes in Schneereichen Gebiet Japans. Beitrage zur Wildbacherosions Lawinenforschung (4). FBVA. Wine: 257-262.

Maeda, T.; Miyakawa, K. and Tanimoto, T. 1985. Vegitation and regeneration of beech forest in Gomisawa (Niigata Prefecture).- Performance of Sugi planted in beech forest zone and a proposaI for natural regeneration in the zone -. Bulletin of the government forest experiment station 333: 123-171.

Nakatani, H. ; Kato, A. ; Taira, H. ; Iijima, Y. and Sawada, M. 1984. Deflection and resistance performance of tree stems subjected to snowload in sugi stands, Journal of the Japan wood research society 30(11): 886-893.

Nitta, R. 1983. The variety of heavy-snowfall conditions causing disastrous forest damage during the winter of 1980181, Trans. 94th meeting of Japan forest society: 727-728.

Shidei, T. 1954. Studies on the damages on forest tree by snow pressures. Bulletin of the government forest experiment stastion 73 : . --

structure and snow damage in relation to stand 1-68.

age -Sugi plantations in Fukui prefecture in Taira, H. 1982. The influence of differences in the 1981 heavy-snowfall-. Journal of Japan the degreeof initial snow throw effected forest society fiR(3): 96-106 by early winter snow on basal bending in - - - - - ~. ...., .-

Kato, A.; Taira, H. and Nakatani, H. 1986. young sugi( Cryptomeria japonica D. Don ). J. Differences of snow damage and resistive Jap. For. soc. 64: 453-460. performance of tree stem in three Sugi -. 1984. The process of bend forming and

70 USDA Forest Service Gen. Tech. Rep. PSW-GTR-130.1991

reerecting of the lower part in the stem due to the snow pressure and the tree weight increase in Tateyama sugi ( Cryptomeria japoni ca D.Don). Bei trage zur Wi ldbacherosions -und Lawinen-forschung(5) .FBVA. WI EN: 139-147.

----. 1985. Basal-bend formation in young sugi ( Cryptomeria japonica D.Don ). J. Jap. For. soc. 67:. 11-19.

-. 1986. Eeffects of inclined planting, fertilization and tying up the stem with rope on characters in young sugi ( Cryptomeria japonica D,Don ).J. Jpn. For. soc. 68:333-337.

-----. 1987. The study of mechanism of Sugi . basal bending and its control methods,

Bulletin of the Toyama prefectual forest

experiment station. 12: 80. ----. 1988. The role of snow in coniferous stem

bend formation Beilrage zur Wildbacherosions -und Lawenenforschung(7). FBVA. WIEN. 275-283.

Takahashi, K. and Nitta. R. 1984. Wind' s role in snow damage distribution at two man-made forests, Trans. 95th meeting of Japan forestsciety: 309-310.

Tsukahara, H. ; Ohtani, H. and Suto. S. 1975. The bending of root sides of the forest trees planted by Cryptomeria seed1 ings on the steep stands in the heavy snowrr region. Jurnal of Yamagata agriculture and forestry sociaty. 32: 21-30.


Study on Shearing Force and Impact Force of a Volcanic -

Mud Flow on Mt. Sakurajimai Yoshinobu Taniguchi2

Abstract: Two k i n d s o f s h e a r i n g stress m e t e r s ( t y p e A and t y p e B ) were s e t on t h e channe l bot tom i n t h e Arimura R i v e r and t h e Mochiki R i v e r on M t . Sakura j ima . Volcan ic mud f lows t a k e p l a c e t h e r e about 100 t i m e s a y e a r . The r e s u l t s o f t h e s u r v e y s demons t ra ted t h a t t h e a c t u a l s h e a r i n g f o r c e o f a v o l c a n i c mud f low on M t . Sakura j ima was from 0 .46 t o 2 .50 kgf/cm2. The a c t u a l impact f o r c e c a u s e d by c o l l i s i o n s of b i g s t o n e s , which were c o n t a i n e d i n a mud flow, w i t h t h e channe l bot tom was c a l c u l a t e d t h e o r e t i c a l l y a t abou t 1 5 times g r e a t e r t h a n t h e dead l o a d s o f t h e s t o n e s . The c o l l i s i o n o f s t o n e s i n a mud f low caused g r e a t a b r a s i o n of c o n c r e t e ,

A g r e a t number of v o l c a n i c mud f lows t a k e p l a c e e v e r y y e a r on M t . Sakuraj ima i n s p i t e of l i t t l e r a i n f a l l . They o f t e n damage b o t h dams and channe l s , and a l s o t h r e a t e n t h e i n h a b i t a n t s of Sakura j ima . I n t h i s s t u d y , t h e magnitude of t h e a c t u a l s h e a r i n g f o r c e o f a v o l c a n i c mud f low was r e s e a r c h e d i n o r d e r t o make c l e a r t h e mechanism o f t h e d e s t r u c t i o n and t h e a b r a s i o n of a dam o r a c o n c r e t e channe l i n t o r r e n t s o f M t . Sakura j ima . The d a t a were a n a l y z e d by t h e t h e o r i e s of h y d r a u l i c s and t h e c o l l i s i o n o f an e l a s t i c body. The c a u s e o f d e s t r u c t i o n and t h e a b r a s i o n o f a dam o r a c o n c r e t e channe l by mud f lows c o u l d be c l a r i f i e d t o some e x t e n t from t h e r e s u l t s o f t h e s e s u r v e y s .

SEDIMENT YIELD ON MT. SAKURAJIMA

M t . Sakura j ima , which l i es i n t h e s o u t h e r n p a r t o f Japan ( F i g . l ) , i s one of t h e most a c t i v e vo lcanoes i n J a p a n . I t i s

-

l p r e s e n t e d a t t h e S u b j e c t Group S1.04 T e c h n i c a l S e s s i o n on Geomorphic Hazards i n Managed F o r e s t s , X I X World F o r e s t r y Congress, I n t e r n a t i o n a l Union of F o r e s t r y Research O r g a n i z a t i o n s , August 5-11, 1990, Montreal , Canada.

2 ~ o s h i n o b u Tan iguch i : (1985) 58-2811. P r o f e s s o r o f A g r i c u l t u r e and F o r e s t S c i e n c e . F a c u l t y of A g r i c u l t u r e , Miyazaki U n i v e r s i t y , Miyazaki 889-21, Japan

TOKYO

F i g . 1 Map o f Japan

l o c a t e d i n Kagoshima Bay and h a s an a r e a of 80 km2 and c i r c u m f e r e n c e of 52 k i l o m e t e r s . There a r e t h r e e c r a t e r s on M t . Sakura j ima: Ki tadake C r a t e r (1117 m e t e r s above s e a l e v e l ) , Nakahake C r a t e r (1060 m e t e r s ) , and Minamidake C r a t e r (1040 meters). Minamidake C r a t e r i s c u r r e n t l y e r u p t i n g v i g o r o u s l y . Tab le 1 shows t h e v o l c a n i c a c t i v i t i e s o f M t . Sakuraj ima f o r t h e p a s t 20 y e a r s (Osumi P u b l i c Works O f f i c e , 1 9 8 6 ) .

L a t e l y t h e b a r i n g of mountain s l o p e s h a s been making conspicuous p r o g r e s s on M t . Sakura j ima i n l i n e w i t h t h e v i g o r o u s v o l c a n i c a c t i v i t i e s . The b a r i n g o f t h e s l o p e s h a s been caused by b o t h t h e e f f e c t of f a l l from t h e e r u p t i o n s and t h e a c t i o n o f s u l p h u r g a s from smoke e m i s s i o n s o f t h e Minamidake C r a t e r . The r e c e d i n g o f v e g e t a t i o n on t h e s l o p e s i n t h e upper r e a c h e s o f e a c h t o r r e n t h a s c o n t i n u e d on M t . Sakuraj ima, and t h e b a r i n g of t h e g downwards y e a r by y e a r . A number of g u l l i e s have formed on t h e s l o p e s . These s l o p e s have been s u f f e r i n g from r a p i d e r o s i o n , and t h e y have been p roduc ing a g r e a t amount of sediment f o r t h e l a s t 20 y e a r s . F i g . 2 shows a p i c t u r e o f t h e s l o p e s around t h e Ki tadake C r a t e r . There i s no v e g e t a t i o n i n t h i s a r e a , and many r i l l s and s m a l l g u l l i e s have a l r e a d y formed on t h e s l o p e .

Some of t h e geomorphological f a c t o r s i n r e f e r e n c e t o mud f lows were a n a l y z e d by


Table 1 Volcan ic a c t i v i t i e s o f M t . Sakuraj ima

number o f occurances smoke . .

YSaZ erupt- e a r t h q u a k e s

u s i n g b o t h a s e r i e s of s e r i a l pho tographs from 1947 t o 1984 and t h e r e p o r t on t h e sediment y i e l d on t h e s l o p e s of M t . Sakura j ima (Osumi P u b l i c Works O f f i c e , 1 9 8 8 ) . These r e s u l t s a r e shown i n F i g s . 3-6.

F i g . 3 shows t h e expansion o f t h e t o t a l a r e a of t h e s e g u l l i e s i n t h e 38 y e a r s from 1947 t o 1984. The i n c r e a s e i n t h e i r t o t a l a r e a i n t h e 26 y e a r s from 1947 t o 1972 i s l e s s t h a n t h a t i n t h e p e r i o d s i n c e 1974. Volcan ic a c t i v i t y became v e r y v i g o r o u s a f t e r 1974. T h i s f a c t shows t h a t t h e r e s h o u l d b e a r e l a t i o n s h i p between t h e number of mud f l o w s and t h e v o l c a n i c a c t i v i t y s i n c e 1974. The same tendency a l s o e x i s t s i n t h e l e n g t h o f g u l l i e s ( F i g . 4 ) . T h i s p r o v e s t h a t t h e g u l l i e s have been c o n s i d e r a b l y ex tended , and t h e y have a l s o expanded i n wid th by t h e f a i l u r e of

F i g . 2 G u l l i e s on t h e s l o p e of M t . Sakura j ima

1940 1960 1980 year 0 1

1940 1980 year

F i g . 3 Expansion of F i g . 4 I n c r e a s e of g u l l i e s t o t a l l e n g t h

of g u l l i e s

O + 1940 1980 year 1940 1960 1y"@

F i g . 5 Change of g u l l y F i g . 6 I n c r e a s e i n width number of

g u l l i e s

s i d e w a l l s o v e r t h e l a s t 10 y e a r s ( F i g . 5 ) . An a v e r a g e r a t e of t h e expansion of t h e g u l l i e s i n t h e 20 y e a r s from 1947 was Only 0 .13 m/yr . On t h e o t h e r hand, it i n c r e a s e d t o 0 .76 m/yr i n t h e 8 y e a r s from 1966. The l a t t e r i s 5 .9 t i m e s g r e a t e r t h a n t h e fo rmer . However, it h a s d e c r e a s e d s i n c e 1980, because f r e s h g u l l i e s began t o form on t h e s l o p e s . F i g . 4 shows t h e g r e a t e x t e n s i o n of g u l l i e s . The number of g u l l i e s i n c r e a s e d consp icuous ly i n t h e 20 y e a r s from 1947 t o 1966 ( F i g . 6 ) . T h i s means t h a t t h e f o r m a t i o n o f g u l l i e s had a l r e a d y ended d u r i n g t h e s e y e a r s . Most of t h e sediment y i e l d on M t . Sakuraj ima i s c a u s e d by t h e e x t e n s i o n and t h e expansion o f g u l l i e s . The v o l u m e t r i c r a t e of t h e sediment y i e l d by t h e e x t e n s i o n of g u l l i e s i s 4 1 p e r c e n t o f t h e whole, and t h e expans ion o f them i s 59 p e r c e n t .

SURVEYING METHOD

A s u r v e y of t h e s h e a r i n g f o r c e of a v o l c a n i c mud f low a c t i n g on a channe l

USDA Forest Service Gem Tech. Rep. PSW-GTR-130.1991

{ SENSOR MOVABLE PLATE PLATE

F i g . 7 S h e a r i n g stress mete r ( t y p e A )

DIRECTION OF

~ i g . 8 S h e a r i n g stress mete r ( t y p e B )

bot tom h a s been go ing on i n t h e Mochiki R i v e r s i n c e 1987 u s i n g t h e two k i n d s o f s h e a r i n g stress m e t e r s shown i n F i g . 7 ( t y p e A) and F i g . 8 ( t y p e B ) . No d a t a have been o b t a i n e d from t h e t y p e A s u r v e y up t o t h e p r e s e n t , b u t some d a t a have been g o t t e n from t h e t y p e B . I n t h e t y p e B, p l a t e A i s t r a i l e d downstream by t h e s h e a r i n g f o r c e a c t i n g on i t s s u r f a c e , and p l a t e B i s b e n t by t h e s h e a r i n g f o r c e . A s a r e s u l t , a bend ing moment i s g e n e r a t e d i n p l a t e B . There shou ld , however, be a b a l a n c e between t h e s h e a r i n g f o r c e and t h e bending moment. Accordingly , t h e s h e a r i n g f o r c e a c t i n g on p l a t e A ( t h e channe l bottom) can be e a s i l y measured by t h e magnitude o f i t s d e f l e c t i o n b a s e d on t h e t h e o r y of t h e d e f l e c t i o n of a c a n t i l e v e r . The change i n s h e a r i n g f o r c e c a n n o t b e measured e v e r y t i m e by t h i s method, b u t t h e maximum s h e a r i n g f o r c e can b e e a s i l y measured u s i n g t h i s m e t e r .

When a dead l o a d o f 56 .8 k i lograms was a p p l i e d t o t h i s s h e a r i n g stress meter ( t y p e B) f o r t h e c a l i b r a t i o n of obse rved v a l u e s , t h e a v e r a g e d e f l e c t i o n o f p l a t e B was 8 m i l l i m e t e r s . T h i s mete r i s l i m i t e d by t h e f a c t t h a t p l a t e B can n o t r e c o v e r from i t s d e f l e c t i o n , because a space caused by t h e

bend ing moment forms between p l a t e B and t h e w a l l of c o n c r e t e t o which p l a t e B i s a t t a c h e d ( F i g . 8 ) . T h i s s p a c e i s i n e v i t a b l y f i l l e d up by s o i l and sand which a r e c o n t a i n e d i n a mud f low whenever one r u n s down on p l a t e A . On account of t h i s , p l a t e B o f t h i s meter cannot a v o i d i n c r e a s i n g i n d e f l e c t i o n , whenever a bending moment a c t s on t h e p l a t e . Of c o u r s e , t h i s happens on c o n d i t i o n t h a t t h e d e f l e c t i o n i s w i t h i n t h e p r o p o r t i o n a l l i m i t o f t h e s t r e n g t h o f t h e m a t e r i a l o f which t h e p l a t e i s made.

SURVEYING RESULTS

Table 2 shows t h e v o l u m e t r i c c o n c e n t r a t i o n o f t h e mud f low samples c o l l e c t e d by t h e a u t h o r i n t h e Arimura R i v e r on J u l y 18 , 1987 i n o r d e r t o i n v e s t i g a t e t h e change o f composi t ion o f a mud f low (Taniguchi and Takahashi , 1 9 8 9 ) .

The observed v a l u e s of t h e s h e a r i n g f o r c e s of s e v e r a l mud f lows a r e shown i n t a b l e 3 . Some v e l o c i t i e s o f t h e mud flow, and t h e d i a m e t e r s o f t h e s t o n e s i n it a r e shown i n t a b l e 4 . They were measured on a v i d e o t a p e r e c o r d e d by Osumi P u b l i c Works O f f i c e on September 24, 1988. One huge s t o n e i n t h e mud f low i s shown i n F i g . 9. These p i c t u r e s were t a k e n from t h a t v i d e o . F i g . 10 i s a p i c t u r e of t h e measurement o f t h e d e f l e c t i o n o f p l a t e B i n t h e Arimura R i v e r a f t e r t h e o c c u r r e n c e of t h e mud f low on October 6, 1988. No g r e a t number of huge s t o n e s g a t h e r e d t o g e t h e r a t t h e f r o n t of t h a t mud f low was observed .

Tab le 2 Gra in s i z e d i s t r i b u t i o n and c o n c e n t r a t i o n of mud f low on J u l y 18, 1987

C o l l e c t i o n Time LC min. 15 min. 30 min,

g r a i n d i a m e t e r d i s t r i b u t i o n r a t e - - - - - - - - ( P C ~ ) -------

o v e r 2000 $ 1 . 0 1 . 0 2 . 9 840 3 . 5 3 . 1 7 . 7 500 5 . 8 6 . 9 1 2 . 9 250 22.2 22.4 3 2 . 5

37 2 . 2 under 37 0 . 2

c o n c e n t r a - 1 5 . 6 32 .0 3 4 . 3 t i o n ( p c t ) d e n s i t y 1.11 1 . 2 5 1 .27 (g/cm3)


Table 3 Observed s h e a r i n g f o r c e s of mud f lows

d a t e observed s h e a r i n g f o r c e r i v e r

2 . 1 3 Arimura 0.462 Arimura 1 .402 Arimura 2.502 Mochiki

Tab le 4 S t o n e s ' d i a m e t e r s i n t h e mud f low on September 2 4 , 1988 and t h e i r v e l o c i t i e s .

S t M e d i a m e t e r veloc1t.v (cm) m/sec

F i g . 9 Huge s t o n e i n t h e mud f low on September 2 4

F i g . 10 Measurement of s h e a r i n g f o r c e o f a mud f low

DISCUSSION

The t y p e B s h e a r i n g s t r e s s meter i s s t r u c t u r a l l y a k i n d of c a n t i l e v e r . According t o t h e t h e o r y o f c a n t i l e v e r d e f l e c t i o n , t h e r e s h o u l d b e a l i n e a r i t y between t h e s h e a r i n g stress (2) and t h e

maximum d e f l e c t i o n 6 o f t h e p l a t e :

6 - 2 (1) If it i s supposed t h a t t h e magnitude of

t h e s h e a r i n g stress (Zo) a l r e a d y known a c t s on t h e s h e a r p l a n e ( p l a t e A ) , and t h a t t h e d e f l e c t i o n of p l a t e B i s 60, t h e r e s h o u l d

be t h e f o l l o w i n g r e l a t i o n between 2, 20 and

6 , 60, u s i n g e x p r e s s i o n (1) :

z /TO = 6 /60 ( 2 ) The s h e a r i n g s t r e s s meter was t e s t e d by a dead l o a d of 56 .8 k i l o g r a m s . A s a r e s u l t of t h a t , t h e mean v a l u e o f t h e d e f l e c t i o n s (60) was 8 m i l l i m e t e r s i n t h e l o a d t e s t . When t h e above v a l u e of 8 m i l l i m e t e r s i s s u b s t i t u t e d i n t o e q u a t i o n (21, t h e f o l l o w i n g i s o b t a i n e d :

T = 0.357 6 ( 3 )

Some d a t a (& 6 .0 c e n t i m e t e r s , 1 . 3 c e n t i m e t e r s and 4 .0 c e n t i m e t e r s i n t h e Arimura R i v e r mud f low which t o o k p l a c e on September 24, 1988, October 6, 1988, and February 17,1989, and 7 . 0 c e n t i m e t e r s i n t h e Mochiki R i v e r mud f low on February 17, 1989) were o b t a i n e d . When t h e s e v a l u e s were s u b s t i t u t e d i n t o e q u a t i o n ( 3 ) , t h e r e s u l t s o f computa t ions were shown i n t a b l e 3 above.

I t is , however, d o u b t f u l whether a l i n e a r i t y b e t w e e n . t h e s e s h e a r i n g f o r c e s and d e f l e c t i o n s of t h e p l a t e might s t r i c t l y e x i s t i n t h i s c a s e , because t h e s e observed d e f l e c t i o n s a r e consp icuous ly l a r g e .


However, see ing t h a t these de f l ec t ions began t o occur in t h e t e s t when t h e a c t i n g load had gone over 57 kilograms, it was evident t h a t a shear ing fo rce a t l e a s t g r e a t e r than 0.29 kgf/cm2 ac ted on t h e shear p lane .

The shear ing fo rce of a mud flow a c t i n g on a channel bottom can be expressed a s follows, taking t h e flow model of a mud flow shown i n Fig. 11 i n t o cons idera t ion:

2 = po g ~ s i n 8 ( 4 )

where po i s t h e dens i ty of a mud flow; H i s i ts water he ight ; and 8 i s t h e angle of t h e channel s lope . When t h e a c t u a l l y observed values of a dens i ty of 1.27 g/cm3 and a water height of 1 . 0 meters i n t h e mud flow of t h e Arimura River on Ju ly 18, 1987 a r e s u b s t i t u t e d i n t o equation ( 4 ) , t h e shear ing

Fig.11 Flow model of a mud flow

s t r e s s (2) becomes about 9 gf/cm2. The computed value from equation ( 4 ) cannot prove t h a t a l a r g e shear ing s t r e s s a s g rea t a s 0.5 - 2.5 kgf/cm2 should occur even i f t h e r e i s a very l a rge s c a l e of a mud flow. Judging from t h a t , it can be i n f e r r e d t h a t such a l a r g e shear ing s t r e s s must be caused by t h e f r i c t i o n between s tones and t h e channel bottom, because these s tones a r e dragged along t h e channel bottom a t a r a t h e r high speed.

Using t h e a c t u a l shearing fo rce a c t i n g on t h e channel bottom, t h e s i z e of a s tone contained i n t h e mud flow which took p lace i n t h e Arimura River on September 24, 1988 could be es t imated . When it was supposed t h a t t h e dens i ty of a s tone was 2.7 g/cm3 and i t s f r i c t i o n a l c o e f f i c i e n t was 0.7, t h e s i z e of a s tone corresponding t o t h e above shear ing fo rce of 2.13 kgf/cm2 was c a l c u l a t e d a t about 60 centimeters i n length f o r one s i d e of a cube, o r about 80 cent imeters i n t h e diameter of a sphere. Many s tones corresponding t o such s i z e s were observed on t h e video. Judging from t h a t , it can be seen t h a t t h e ca lcu la ted value of t h e s i z e of a s tone i s proper compared with t h e a c t u a l s i z e s . However, t h e maximum s i z e of a s tone i n t h e Arimura River mud flow on September 24 was 3.8 meters . This proves t h a t t h e concept of shear ing fo rce i n t h e case i n which a mud flow i s regarded a s only a f l u i d l i k e water cannot be used f o r t h e so lu t ion of an

a c t u a l problem l i k e t h e abrasion of a concrete channel bottom.

When a mud flow accompanied by many s tones flows on a channel bottom, i t s abrasion i s very conspicuous, because t h e s tones a r e dragged along t h e channel bottom. A grea t f r i c t i o n between t h e su r face of t h e channel bottom and s tones i s generated.

The hydraul ic drag fo rce of a s tone ( a pe r fec t cube o r sphere) i n f l u i d can be expressed a s fol lows:

F = (1/2) CoPo V2A ( 5 ) where F i s t h e drag force ; CD i s t h e c o e f f i c i e n t of t h e drag force; V i s t h e r e l a t i v e ve loc i ty between f l u i d and a s tone; and A i s the area of t h e appl ica t ion of t h e drag fo rce . The value Co became about 8 from t h e r e s u l t s of t h e computations on t h e mud flow which took p lace on Ju ly 16, 1987 i n t h e Arimura River.

Supposing t h a t CD was 8, t h e dens i ty of a mud flow was 1.27 g/cm3 ( t h e value in t a b l e 2 ) , t h e s t o n e ' s diameter was 3.8 meters ( t h e maximum diameter i n t h e mud flow on September 24, 1988 i n t h e Arimura R i v e r ) , and t h e r e l a t i v e ve loc i ty was 5 . 1 m/sec., t h e drag fo rce of t h e mud flow could be est imated a t 50 tons by equation ( 5 ) . On t h e o the r hand, t h e f r i c t i o n a l r e s i s t a n c e of a s tone on t h e channel bottom i s est imated a t 40 - 50 tons , using t h e value 0 . 7 6 a s t h e c o e f f i c i e n t of i t s f r i c t i o n . Judging from t h e above r e s u l t , it can be seen t h a t a mud flow with a water height of about 1 meter and a r e l a t i v e ve loc i ty of about 5 m/sec can e a s i l y ca r ry a huge s tone a s l a rge a s 3 meters i n diameter . The g rea t f r i c t i o n i s caused by many s tones dragged along a channel bottom by a mud flow. There i s another repor t t h a t t h e temperature rose about 0 .5 - 1.5012 i n t h e Mochiki River when a mud flow ran down i n t h e channel (Hirano, 1989). This shows t h a t t h e f r i c t i o n a l heat s t a t e d above might have a r e l a t i o n t o t h e f r i c t i o n which was generated between t h e concrete channel bottom and t h e s tones .

A mud flow a l s o has t h e same c h a r a c t e r i s t i c a s a d e b r i s flow. It g r e a t l y v i b r a t e s t h e e a r t h around t h e stream when it flows a t a high speed. The v ib ra t ion i s caused by t h e c o l l i s i o n of s tones with t h e concrete channel bottom o r s idewal ls of t h e stream. There a r e some r e p o r t s t h a t t h e v ib ra t ions caused by c o l l i s i o n s between huge s tones and t h e channel bottom have acce le ra ted s lope f a i l u r e s along t o r r e n t s . This c o l l i s i o n i s a l s o another important f a c t o r i n t h e d e s t r u c t i v e damage of dams o r concrete channels i n t o r r e n t s . The v ibra t ion caused


by t h e c o l l i s i o n of a huge s tone i n a mud- debr i s flow was surveyed on t h e slopes of M t . Yake i n order t o es t imate t h e occurrence of a s lope f a i l u r e when t h e flow ran down i n a t o r r e n t . An acce le ra t ion of 0 . 1 g a l was observed a t a point 15 meters from t h e cen t re of t h e t o r r e n t i n cross sec t ion (Matsumoto Publ ic Sabo Works Office, 1975) . There might have been a g r e a t v ib ra t ion near t h e c e n t r e . This problem should be taken i n t o cons idera t ion t o prevent dams o r channels from being damaged i n t o r r e n t s .

The r e l a t i o n s h i p between t h e s t r eng th of t h e concrete of a channel and t h e abrasion caused by t h e c o l l i s i o n of s tones contained i n a mud flow i s unclear even now. The impact fo rce caused by t h e c o l l i s i o n of an e l a s t i c body with concrete can be expressed a s follows (Okubo, 1963):

(a2/ 2E)Al = Wo(S + h) ( 6 ) where a i s the impact s t r e s s per u n i t a rea ; E i s t h e c o e f f i c i e n t of t h e modulus of concrete; A i s t h e a rea of the app l i ca t ion of a fo rce ; L i s t h e length of a body; Wo is a dead load S i s t h e f a l l i n g height of a body from a l e v e l ; and h i s t h e compressed th ickness of concre te . By solving equation ( 6 ) , a i s obtained:

a = (2EWo (S + h) /A 1 ) ' I 2 (7)

On t h e o the r hand, a can a l s o be expressed a s fol lows:

a = E ( X / ~ ) (8) By s u b s t i t u t i n g equation (8 ) i n t o equation ( 6 ) , a can be solved:

a = (Wo/A) (1 + dl+ 2SEA/Wol ( 9 ) When it i s supposed t h a t ho i s t h e th ickness corresponding t o a dead load ( W o ) , ho can be expressed a s fol lows:

ha = W ~ L / A E (10) When equation (10) i s s u b s t i t u t e d i n t o equation ( 9 ) , a can be solved:

a = (w0/n) (1 + q x (11) The s t r a i n (h) caused by t h e impact fol of a s tone which i s contained i n a mud can be solved, using equations (8) and (10) :

h = X o ( l + . \ , I (12) The dead load corresponding t o t h e above s t r a i n can be est imated, using equations (8) and (12) :

w/w0 = 1 + ~~ (13) When it i s supposed t h a t Do i s t h e a c t u a l s t o n e ' s diameter, t h e converted diameter (D), def ined here a s t h e diameter of an imaginary s tone which i s assumed t o be equal t o t h e impact fo rce caused by an a c t u a l s tone with t h e diameter ( D o ) s t a t e d

above, can be ca lcu la ted a s follows, using equation (13) and both expressions of W =

~ p , ~ ~ / 6 , W = 7tpS~o3/6:

D / D o = (1 + ( 1 4 ) where D i s t h e converted diameter defined above; p, i s t h e dens i ty of a s tone . When

it i s supposed t h a t S i s 10 centimeters , ha i s 1 mil l imeter , and s t o n e ' s diameter i s 3 .8 meters ( t h e maximum diameter i n t h e Arimura River mud flow on September 24, 1988), t h e diameter ( D ) of an imaginary s tone ( t h e converted diameter corresponding t o t h e impact force caused by an a c t u a l s tone with a diameter of 3 .8 meters i s es t imated t o be about 9 . 4 meters. This means t h a t t h e impact fo rce has t h e same e f f e c t a s a huge s tone loaded on t h e channel bottom. I t shows t h a t channel works should be designed s a f e l y enough t o prevent a concrete channel from des t ruc t ion , because a channel may be a t t acked by a very high impact fo rce .

I f it i s supposed t h a t both areas of t h e app l i ca t ion of forces , t h e dead load ( W O ) and t h e impact load (W), a r e equal, Wo and W can be expressed a s follow:

Wv = AaO (15)

w = A a ( 1 6 ) When expressions (15) and (16) a r e subs t i - t u t e d i n t o equation ( 1 3 ) , t h e following equation can be obtained:

a/ao = 1 + ( 1 7 )

Do i n equation (17) i s t h e s t r e s s by t h e dead load derived from an a c t u a l impact s t r e s s ( a ) . The s t r e s s ((r) must be within t h e al lowable s t r e n g t h of t h e concre te . It i s genera l ly s a i d t h a t t h e l i m i t of t h e s t r e n g t h of concrete i s about 250 kgf/cm2. Accordingly, t h e maximum (a) must be about

250 kgf/cm2. I f t h e same values a s t h e above (hv = 1 mil l imeter and S = 10

cent imeters) a r e used here, Go can be derived from equation ( 1 7 ) :

250/00 = 15

:. av = 1 6 .kgf/cm2

When t h e a rea of t h e app l i ca t ion of a fo rce i s about 10 cm2, t h e whole force becomes 167 kilograms, and a s t o n e ' s diameter corresponding t o t h i s allowable fo rce i s ca lcu la ted a t 50 cent imeters . However, t h e a c t u a l compressed th ickness of t h e concrete of a channel must be l e s s than t h e 1 mil l imeter assumed above. Then t h e value of oo becomes smal ler than 1 6 . 7 kgf /cm2. Accordingly, t h e allowable diameter of a s tone i n a mud flow t o prevent t h e des t ruc t ion of a concrete channel must be l e s s than 50 cent imeters .


The above i s a d i s c u s s i o n from t h e p o i n t o f view of t h e compress ive s t r e n g t h o f c o n c r e t e . S h e a r i n g f o r c e i s a l s o a v e r y i m p o r t a n t f a c t o r i n t h e d e s t r u c t i o n o f a c o n c r e t e c h a n n e l . I t i s g e n e r a l l y s a i d t h a t t h e s h e a r i n g s t r e n g t h o f c o n c r e t e i s 1 / 4 - 1/7 o f i t s compress ive s t r e n g t h (Okada and Muguruma, 1989) . Accordingly , t h e a l l o w a b l e s i z e o f a s t o n e s h o u l d be even s m a l l e r t h a n 50 c e n t i m e t e r s i n d i a m e t e r . I t can be f o r e s e e n t h a t t h e d e s t r u c t i v e a c t i o n a g a i n s t a c o n c r e t e channe l w i l l i n c r e a s e even more by d i n t of t h e s h e a r i n g f o r c e caused by t h e f r i c t i o n of s t o n e s w i t h a channe l bottom, i n a d d i t i o n t o t h e compress ive f o r c e by t h e impac t . The Osumi P u b l i c Works O f f i c e began t o c a r r y o u t a s u r v e y of t h e a b r a s i o n o f t h e channe l c o n c r e t e i n t h e Mochiki R i v e r i n 1988. That c o n c r e t e channe l was c o n s t r u c t e d t o t h e s t r e n g t h of 160 kgf/cm2. The mixing p r o p o r t i o n of t h a t c o n c r e t e i s shown i n t h e f o l l o w i n g .

slump w a t e r a g g r e g a t e a d d i t i v e cement f i n e c o a r s e

A mud f low t o o k p l a c e on October 6, 1988, a week a f t e r t h e channe l works had been completed, and it abraded t h e c o n c r e t e i n t h e s u r v e y s e c t i o n . That mud f low c o u l d n o t be r e c o r d e d on v i d e o t a p e , because i t t o o k p l a c e a t n i g h t . The a b r a s i o n of t h e c o n c r e t e w a s 2 . 5 c e n t i m e t e r s i n d e p t h . The r e s u l t o f t h e s t r e n g t h tes t of t h e c o n c r e t e r e p o r t e d t h a t t h e s t r e n g t h on t h e 7 t h day a f t e r t h e mixing of t h a t c o n c r e t e was 110 kgf /cm2.

Taking i n t o c o n s i d e r a t i o n t h e f a c t t h a t t h e s h e a r i n g s t r e n g t h of c o n c r e t e i s about 1 /7 of t h e compress ive , t h e a l l o w a b l e compress ive s t r e n g t h o f 110/ kgf/cm2 c o r r e s p o n d s t o a n a l l o w a b l e s h e a r i n g s t r e n g t h of 1 5 . 7 kgf/cm2. The s h e a r i n g f o r c e o f t h e mud f low which took p l a c e on t h e Mochiki R i v e r on February 17, 1989, was 2 . 5 kgf/cm2. A s t h e mud f low on October 6, 1988, c o u l d n o t b e r e c o r d e d on v i d e o t a p e , i t s s c a l e was unknown, b u t t h e marks o f t h e w a t e r h e i g h t i n t h e channe l a f t e r t h i s f low n e a r l y e q u a l t o t h e marks o f t h e mud f low on February 17, 1989, i n t h e same r i v e r . A s b o t h s c a l e s were a lmos t e q u a l , t h e v a l u e of 2 . 5 kgf/cm2 was s u b s t i t u t e d f o r i t s s h e a r i n g f o r c e . It r e s u l t e d i n t h e c a l c u l a t e d v a l u e ( t h e a l l o w a b l e s h e a r i n g s t r e n g t h o f t h e m a t e r i a l , 1 5 . 7 kgf/cm2) b e i n g l a r g e r t h a n t h e observed ones . However, i n t h e c a s e i n which such s h e a r i n g f o r c e a c t s a c t u a l l y on a channe l bot tom a s a r e p e a t e d f o r c e , t h e s h e a r i n g f o r c e o f 2 . 5 kgf/cm2 i s n o t s m a l l a s compared w i t h t h e

a l l o w a b l e s h e a r i n g s t r e n g t h o f t h e c o n c r e t e (15 .7 kgf/cm2) s t a t e d above.

CONCLUSION

The r e s u l t s of s u r v e y s i n t h e Arimura R i v e r and t h e Mochiki R i v e r showed t h a t t h e a c t u a l s h e a r i n g f o r c e of a mud f low on t h e s u r f a c e o f a channe l bottom was about 0 . 5 - 2 . 5 kgf/cm2. According t o t h e t h e o r e t i c a l c a l c u l a t i o n s , t h e f r i c t i o n a l f o r c e which s h o u l d be caused by a s t o n e of abou t 80 c e n t i m e t e r s i n d i a m e t e r cor responded t o t h e f o r c e o f 2 .13 kgf/cm2 i n t h e Arimura R i v e r mud f low on September 24, 1988. Such s i z e s of s t o n e s c o u l d be observed on t h e v i d e o . The impact f o r c e caused by huge s t o n e s i n a mud f low was d e r i v e d from t h e t h e o r y o f t h e c o l l i s i o n o f a n e l a s t i c body, and it proved t h a t t h e impact .force o f a s t o n e was s e v e r a l t i m e s g r e a t e r t h a n t h e dead l o a d caused by t h a t s t o n e . When a s h e a r i n g s t r e s s o f abou t 2 . 5 kgf/cm2 a c t e d on a c o n c r e t e channe l wi th a compress ive s t r e n g t h o f 110 kgf/cm2, t h e a b r a s i o n o f t h a t c o n c r e t e was 2 . 5 c e n t i m e t e r s i n d e p t h .

REFERENCES

Hirano, M . 1989. Report o f r e s e a r c h p r o j e c t , Grant i n Aid f o r S c i e n t i f i c Research; 25 p . ( i n J a p a n e s e ) .

Matsumoto Sabo P u b l i c Works O f f i c e . 1975. P u b l i c a t i o n of s u r v e y s of M t . Yake 7 . M i n i s t r y of C o n s t r u c t i o n : 37 p . ( i n J a p a n e s e ) .

Okada, K . , and H . Muguruma. 1989. E n g i n e e r i n g handbook of c o n c r e t e . Tokyo: Heibon-sha Co., 404 p . ( i n J a p a n e s e ) .

Okubo, H . 1963. S t r e n g t h of m a t e r i a l . Tokyo: Shokoku-sha Co.; 40-41 ( i n J a p a n e s e ) .

Osumi P u b l i c Works O f f i c e . 1982. Report of t h e r e s e a r c h work on sediment y i e l d from t h e Kurokami R i v e r . M i n i s t r y of C o n s t r u c t i o n ; 1 3 p . ( i n J a p a n e s e ) .

Osumi P u b l i c Works O f f i c e . 1986. Sabo i n vo lcano Sakura j ima . M i n i s t r y of C o n s t r u c t i o n ; 8 p . ( i n Japanese) .

Osumi P u b l i c Works O f f i c e . 1988. Sabo i n vo lcano Sakura j ima . M i n i s t r y o f C o n s t r u c t i o n ; 5 p . ( i n Japanese) .

Taniguch i , Y . , and M . Takahash i . 1985. Exper imenta l s t u d y on sediment y i e l d and f l u i d i z a t i o n of s o i l mass i n a n a r e a o f a c t i v e v o l c a n o . P r s c e e d i n g of I n t e r n a t i o n a l symposium on Eros ion , D e b r i s Flow and D i s a s t e r Prevention-Tsukuba 1985: 133-138.

Tan iguch i , Y . , and M . Takahashi . 1989. P r e d i c t i o n f o r t h e escape from t h e s t r i k e of a v o l c a n i c mud f low i n a t o r r e n t and t h e c h a r a c t e r i s t i c o f i t s movement. J o u r n a l of t h e Japan S o c i e t y of E r o s i o n C o n t r o l 4 4 ( 4 ) :26 p . ( i n J a p a n e s e ) .


Research of Wind Erosion Intensity in the Region of Subotica-Horgos Sands1 Velizar Velasevic and Ljubornir Letic2

Abstract: Wind i s an i m p o r t a n t e r o s i o n a l p r o c e s s i n t h e a r e a s of s teppe-savanna c l i m a t e i n Europe a s t y p i f i e d by t h e Vojvodina p l a i n i n Yugoslavia . C u l t i v a t e d and f o r e s t e d p l o t s on t h e Subotica-Horgos Sands were used t o s t u d y a e o l i a n e r o s i o n p r o c e s s e s . Wind e r o s i o n on t h e c u l t i v a t e d p l o t was 3-29 t i m e s g r e a t e r t h a n t h a t o c c u r r i n g on a p l o t p l a n t e d t o f o r e s t t r e e s . That e r o s i o n r e s u l t s i n impor tan t l o s s e s of humus and n u t r i e n t s . A p r a c t i c a l e q u a t i o n e s t i m a t i n g wind e r o s i o n from wind -3

D e f l a t i o n p r o c e s s e s i n t h e zone o f s teppe-savanna c l i m a t e i n Europe a r e r e p r e s e n t e d i n t h e l a r g e p l a i n of Vojvodina, which i s a c o r n f i e l d and a r e g i o n of p a r t i c u l a r importance t o Yugos lav ia . The u s e o f contemporary a g r i c u l t u r a l e n g i n e e r i n g , t h e i n a p p r o p r i a t e o r g a n i z a t i o n o f t h e t e r r i t o r y , d e s t r u c t i o n o f p r o t e c t i v e g r e e n cover , and o t h e r u n f a v o r a b l e e f f e c t s l e a d t o t h e i n i t i a t i o n and development of d e f l a t i o n p r o c e s s e s of d i f f e r e n t i n t e n s i t i e s . T h i s a s p e c t o f s o i l d e s t r u c t i o n a f f e c t s , f i r s t of a l l , a g r i c u l t u r e , w a t e r r e s o u r c e s management, t r a f f i c , i n f r a s t r u c t u r e , environment , e t c . The r e g i o n of Vojvodina i s c h a r a c t e r i z e d by he te rogeneous s o i l t y p e s , r a n g i n g from sands , b l a c k s o i l , chernozem, and smoni tza t o g l e y e d s o i l which, i n g i v e n c l i m a t e c o n d i t i o n s , a r e d i f f e r e n t l y t h r e a t e n e d by t h e p r o c e s s o f wind e r o s i o n . I n t h i s paper w e s h a l l p o i n t o u t t h e r e s e a r c h on wind e r o s i o n ( s t a r t e d i n 1980) on t h e s o i l s of l i g h t mechan ica l compos i t ion ( p o t e n t i a l l y t h e most t h r e a t e n e d s o i l s ) , on t h e Subotica-Horgos Sands .

l p r e s e n t e d a t t h e S u b j e c t Group 51.04 T e c h n i c a l S e s s i o n on Geomorphic Hazards i n Managed F o r e s t s , X I X World F o r e s t r y Congress, I n t e r n a t i o n a l Union o f F o r e s t r y Research O r g a n i z a t i o n s , August 5-11, 1990, Montreal , Canada.

2 ~ a c u l t y o f F o r e s t r y , U n i v e r s i t y of Beograd, Beograd, Yugos lav ia .

3 ~ b s t r a c t s u p p l i e d by S e s s i o n Chairman.

The Subotica-Horgos Sands a r e s i t u a t e d i n t h e North-Northwest p a r t o f Vojvodina p l a i n between t h e Danube and T i s a r i v e r s . The a v e r a g e l e n g t h of t h e Sands i s 48 km and t h e a v e r a g e d i a m e t e r i s 5-11 km. The Sands cover an a r e a a b o u t of 240 km2. The Vojvodina p l a i n i s a well-known orchard-grape v i n e c o u n t r y , w i t h more t h a n 33 p e r c e n t under v i n e y a r d s and o r c h a r d s , a b o u t 20 p e r c e n t f o r e s t s and woodlands, and o v e r 34 p e r c e n t under g r a s s l a n d . I t i s c h a r a c t e r i z e d by m i l d l y u n d u l a t i n g dune r e l i e f o f n o r t h w e s t - s o u t h e a s t d i r e c t i o n , a s w e l l a s by a h i g h l e v e l of underground w a t e r s , 2 - 8 m . A s t h e s e Sands a r e i n t h e zone of a r i d c l i m a t e , a t t h e boundary o f s teppe-savanna and s l i g h t woodland c h a r a c t e r , under t h e i n f l u e n c e o f p e d o g e n e t i c f a c t o r s , t h e r e can b e d i s t i n g u i s h e d d i f f e r e n t t y p e s o f sand : grey-yel low, brown, b l a c k , b l a c k loamy, and s a l i n e s a n d s w i t h d i f f e r e n t p r o d u c t i o n c a p a c i t i e s .

METHOD OF RESEARCH

A compara t ive method of s t a t i o n a r y o b s e r v a t i o n by wind-gage s t a t i o n s has been a p p l i e d on s p e c i a l l y s e l e c t e d e r o s i o n p l o t s , o f which one, u s e d f o r a g r i c u l t u r a l p r o d u c t i o n , h a s n o t been p r o t e c t e d ( " U " ) , w h i l e t h e o t h e r ("P") has been p r o t e c t e d w i t h f o r e s t p l a n t i n g s , f i g u r e 1.

F i g u r e 1 - - ~ x p e r i m e n t a l wind-gage s t a t i o n r e c o r d s d e f l a t i o n p r o c e s s e s .


Table 1. Average monthly and annua l d e p o s i t i o n q u a n t i t i e s (En kg m - l ) Loc. "U" and l o c . "Pu

Months En J a n F e b Mar Apr May J u n e J u l y Rug S e p Oct Nov Dec En

Loc."U' (kg m-l) 0 . 2 7 2 0 . 7 6 5 0 .504 0 . 6 9 3 0 . 3 0 6 0 .350 0 . 5 0 7 0 .106 0 .136 0 . 1 1 6 0 .040 0 . 0 6 2 3 . 8 5 7 Loc.'P" ( k g m-l) 0 .017 0 .026 0 .028 0 . 0 4 7 0 . 0 5 3 0 .038 0 . 0 4 0 0 .039 0 . 0 2 5 0 . 0 1 9 0 .014 0 .010 0 .356 R e l a t i o n U/P 1 6 2 9 1 8 1 5 6 9 13 3 5 6 3 6 11

Table 2 . Average monthly v e l o c i t i e s (m s a t 0 .O5 m above ground f r e q u e n c i e s ( p c t ) and s torm winds (12 .3 m s-l) NW and N d i r e c t i o n s .

P a r a m e t e r s J a n F e b Mar Apr May

V e l o c i t y (m s-l) 8 . 1 0 8 . 4 9 8 .13 6 .24 7 . 8 9 4 .32 - 9 . 0 1 4 .90 7 . 1 3

F r e q u e n c y ( p c t ) 2 3 . 4 2 1 1 . 8 8 7 . 2 1 6 . 2 3 5 . 7 6 4 . 6 5 - 1 6 . 8 5 3 2 . 5 1 0 . 7 7

F o r c e IK) 3 . 0 8 2 . 4 8 3 . 0 0 2 . 8 2 3 . 5 1

Months

-

J u n e J u l y Auy S e p O c t Nov Dec Average

Exper imenta l s t a t i o n s r e c o r d : q u a n t i t y o f a e o l i a n d e p o s i t i o n , wind f requency and v e l o c i t y , a i r and s o i l t e m p e r a t u r e s , a i r and s o i l humid i ty , e t c . F i e l d d a t a a r e a n a l y z e d i n o r d e r t o q u a l i f y and q u a n t i f y t h e d e f l a t i o n p r o c e s s , a s w e l l a s t o d e f i n e t h e c o n d i t i o n s o f c l i m a t e and r e s i d u a l s o i l i n which t h e y o c c u r .

RESULTS OF RESEARCH

The a n a l y s i s of t h e d a t a o b t a i n e d a t e x p e r i m e n t a l s t a t i o n s "U" and "P" h a s p roved s i g n i f i c a n t d i f f e r e n c e s i n t h e d i s t r i b u t i o n and i n t e n s i t y o f d e f l a t o r y p r o c e s s e s , as w e l l a s i n t h e p a r a m e t e r s of c l i m a t e and r e s i d u a l s o i l which a f f e c t them.

The d a t a on t h e annua l i n t e n s i t y o f wind e r o s i o n , w i t h 2.127-5.490 t km-l p e r y e a r , emphasize t h a t u n p r o t e c t e d a r e a s ( l o c . "U") of t h e r e s e a r c h e d r e g i o n a r e t h r e a t e n e d by e r o s i o n , whereas t h e p r o t e c t e d a r e a s ( l o c . "P") a r e s u b j e c t e d t o d e f l a t i o n p r o c e s s e s o f abou t 11 t i m e s lower i n t e n s i t y , r a n g i n g from 0.247 t o 0.444 t km-l p e r y e a r , a v e r a g e 0.356 t km-l p e r y e a r ( t a b l e 1 ) . According t o t h e d a t a i n t a b l e 1, maximum v a l u e s o f wind e r o s i o n i n t e n s i t y o c c u r i n t h e f i r s t h a l f o f t h e y e a r between J a n u a r y and J u l y , amounting t o abou t 80 p e r c e n t t o t a l a n n u a l q u a n t i t y o f a e o l i a n d e p o s i t i o n , whereas t h e remain ing 12 p e r c e n t a r e d e p o s i t e d between August and December.

T h e r e f o r e i n t h e u n p r o t e c t e d a r e a s o f t h e Subotica-Horgos Sands, d e f l a t i o n p r o c e s s e s o s c i l l a t e w i t h i n c a t e g o r i e s I1 and 111, s t a r t i n g from medium i n t e n s i t y

e r o s i o n (2 .0 - 5 . 0 t km-l p e r y e a r ) t o i n t e n s i v e e r o s i o n ( 5 . 0 - 7 . 0 t km-l p e r y e a r ) . I n t h e p r o t e c t e d a r e a s o f t h e Sands, d e f l a t i o n p r o c e s s e s a r e reduced t o t h e l e v e l of normal e r o s i o n ( c a t e g o r y I o f e r o s i o n p r o c e s s e s ) w i t h t h e i n t e n s i t y lower t h a n 0 . 5 t km-l p e r y e a r .

The d e g r e e o f h a z a r d (comparison of p r o t e c t e d and u n p r o t e c t e d a r e a s of t h e Sands) i s i n c l u d e d i n t h e e x p r e s s i o n B =

IeeP / IeeS , and ranges between 11 f o r annua l and 171 f o r d i u r n a l i n t e n s i t i e s o f wind e r o s i o n . T h i s p o i n t s o u t t h e s i g n i f i c a n t d i f f e r e n c e s i n t h e d e g r e e of h a z a r d o f t h e compared l a n d s , which i s c o n d i t i o n e d by t h e b u f f e r i n g e f f e c t o f p r o t e c t i v e p l a n t i n g s on t h e d e f l a t o r y p r o c e s s e s i n t h e p r o t e c t e d e r o s i o n p l o t s .

The e s t a b l i s h m e n t of " e r o s i o n a c t i v e " winds h a s been performed by t h e c r i t e r i o n of c r i t i c a l ( i n i t i a l ) v e l o c i t i e s (Vs>Vkr) . Accordingly , t h e i n i t i a l v e l o c i t y n e c e s s a r y t o move t h e m i x t u r e of D . Tavankut sands Ds

= 0 . 1 8 mm, i s about 3 .0 m s - l a t t h e h e i g h t of 0.05 m above ground. T h i s d e n o t e s s tormy winds (>12 .3 m s-l) a s e r o s i o n a c t i v e winds.

I n t h e r e s e a r c h e d r e g i o n o f t h e Pannonian P l a i n , by t h e "Modified Method o f I n s t r u m e n t a l A n a l y s i s " , t h e f o l l o w i n g dominant winds have been d i s t i n g u i s h e d : NW ( 1 4 ) and N (16) w i t h t h e degree o f dominance r a n g i n g up t o 10 t i m e s . Average monthly v e l o c i t i e s ( a t 0.05 m) and wind f r e q u e n c i e s a r e p r e s e n t e d i n Tab le 2 .

Stormy winds i n t h e Subotica-Horgos Sands o c c u r 48.96 p e r c e n t i n t h e p e r i o d


Table 3 . Average monthly a i r temperatures ( S C ) , p r e c i p i t a t i o n (mm), r e l a t i v e a i r humidity ( p c t ) , and t o t a l s o i l moisture, l o c . "U" and "P"

Montlls Climatic Loc. Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Annual VP* NVP** Factors

Air nu,, - 0 . 8 7 - 0 . 5 4 6 . 0 7 1 0 . 0 1 1 5 . 5 8 1 7 . 6 3 2 0 . 1 6 1 9 . 8 1 1 6 . 6 4 1 0 . 8 8 3 . 9 1 0 . 4 1 9 . 9 8 1 6 . 6 4 3 . 2 5 Temp. OC "P" - 1 . 5 2 - 0 . 4 9 5 . 8 6 1 0 . 7 0 1 5 . 0 0 1 8 . 0 4 1 9 . 5 3 1 8 . 9 1 1 6 . 0 2 1 0 . 5 8 3 . 0 7 - 0 . 0 4 9 . 6 4 1 6 . 6 4 2 . 9 1

Precip. "Uv 2 8 . 7 8 2 1 . 4 8 3 5 . 4 2 3 2 . 1 6 5 4 . 9 2 9 0 . 3 0 3 5 . 2 2 3 0 . 7 4 4 3 . 1 8 3 9 . 8 4 4 0 . 2 0 4 7 . 3 6 499 .60 2 8 6 . 5 2 2 1 3 . 0 8 (llm) "P" 3 1 . 3 6 2 2 . 8 8 3 7 . 4 8 3 4 . 3 8 5 7 . 4 4 8 8 . 7 6 3 9 . 6 6 2 5 . 7 0 4 6 . 2 4 4 4 . 2 6 4 1 . 6 2 4 9 . 2 6 5 1 9 . 0 4 2 9 2 . 1 8 2 2 6 . 8 6

Relative "U" 8 1 . 4 5 7 8 . 2 4 6 8 . 9 2 6 4 . 1 9 6 5 . 4 0 6 6 . 7 7 6 7 . 4 9 6 7 . 8 9 7 1 . 8 8 7 2 . 7 6 7 7 . 5 9 8 3 . 0 1 7 2 . 1 3 6 7 . 2 7 7 7 . 0 0 Humidity "P" 8 8 . 6 6 8 1 . 0 6 7 2 . 5 7 6 8 . 3 1 6 7 . 3 2 7 0 . 4 4 6 9 . 3 4 7 2 . 2 7 7 5 . 7 0 7 7 . 7 3 8 2 . 9 6 8 6 . 5 4 7 5 . 9 1 7 0 . 5 6 8 1 . 2 5 of Air (pct) Total Soil "U" 3 . 8 2 6 . 5 2 2 . 6 8 3 . 3 6 3 . 3 2 2 . 3 0 2 . 4 2 2 .56 2 . 6 8 3 . 9 6 4 . 9 6 7 . 0 4 3 . 8 0 2 . 8 0 4 . 8 0 Moisture "P" 1 5 . 7 8 2 1 . 0 2 1 2 . 6 0 9 . 5 6 6 . 7 0 6 . 4 2 5 . 7 0 4 . 9 6 7 . 5 6 1 0 . 8 8 1 1 . 4 2 1 7 . 8 0 1 0 . 8 7 6 . 8 0 1 4 . 9 0 (PCt)

* VP denotes Vegetational Period ** NVP denotes Non-Vegetational Period

between 10 a.m. and 3 p.m. A s per t h e i r dura t ion , category I1 winds (60 - 360 min.) occur most f requent ly i n March and October. In add i t ion , it has been observed t h a t e ros iona l ly a c t i v e a i r cu r ren t s of NW d i r e c t i o n ( 1 4 ) a r e more favorable (warmer and d r i e r a i r ) t o t h e development of d e f l a t i o n , than t h e winds of N ( 1 6 ) d i r e c t i o n .

The degree of nonuniformness of a i r cu r ren t s expressed through t h e f a c t o r s of fo rce (K) and frequency (percent ) ranges between 1 . 0 and 9 . 6 . These values f o r NW ( 1 4 ) and N (16) winds o s c i l l a t e much l e s s , averaging 3.33 and 3.86 ( t a b l e 2) which i s very s i g n i f i c a n t f o r t h e evaluat ion of t h e aggressiveness of a i r c u r r e n t s .

The ana lys i s of da ta ( t a b l e 3) of t h e hydrometric regime of t h e researched eros ion p l o t s p o i n t s t o t h e s i g n i f i c a n t l y more humid regime on t h e protec ted erosion p l o t , which decreases t h e development of d e f l a t o r y processes .

The ana lys i s of aeol ian deposi t (En ) and r e s i d u a l s o i l (OZ) r e su l t ed i n severa l i n d i c a t o r s of condi t ions i n which d e f l a t i o n processes occur. The following a r e t h e most important ones :

P a r t i c l e - s i z e composition of t h e researched sands i n d i c a t e s a very "erodible s o i l " . The content of e rod ib le p a r t i c l e s smal ler than 1 mm ( t o t h e depth of 0.05 m ) amounts t o more than 9 9 percent , and t h e condit ion of e r o d i b i l i t y i s 40 percent of t h e s e p a r t i c l e s .

Sand moisture (rough dispers ion) i s a very s i g n i f i c a n t f a c t o r i n t h e group of s o i l phys ica l p r o p e r t i e s which condit ion t h e "pseudo cohesion" reducing t h e

development of t h e d e f l a t i o n process . The content of t o t a l sand moisture ( t o t h e depth of 0.05 m ) on t h e unprotected area ranges between 2.3 percent and 7.0 percent , and on t h e protec ted area it i s 4 . 9 percent t o 21 percent ( t a b l e 3 ) . The r e l a t i o n of moisture ( W Z ) and apparent cohesion ( c ) i s defined by t h e funct ion:

and it has been es tab l i shed f o r Wz = 1 - 21 percent , with t h e corresponding values of cohesion of up t o c = 6 . 7 9 kN x m-*. On t h i s occasion it has been observed t h a t d e f l a t i o n processes occur a t t h e s o i l moisture below 7 percent , which corresponds t o cohesion below c = 3.0 k N x m-2 .

The ana lys i s of t h e r e l a t i o n of chemical c h a r a c t e r i s t i c s of t h e aeol ian deposi t ion (En) and t h e r e s i d u a l s o i l ( O Z ) p o i n t s t o t h e very s i g n i f i c a n t ind ica t ion of s o i l f e r t i l i z a t i o n l o s s a f f e c t e d by d e f l a t i o n processes. It i s denoted by t h e "de f l a t ion c o e f f i c i e n t " presented i n t a b l e 4 .

Table 4 . The degree of t h e damaging e f f e c t of d e f l a t i o n process expressed a s d e f l a t i o n c o e f f i c i e n t mu=En x oZ-l

Number Nutrients mu = En x 0,-l

1 H u m u ~ 5 . 7 - 1 6 . 2 2 CaC03 1.1 - 1 . 3 3 Total Nit~ogen 3 . 2 - 1 4 . 0 4 Readily Available P 1 5 . 5 - 2 0 . 3 5 Readily Available K 6 . 4 - 1 4 . 3

USDA Forest Service Gen. Tech. Rep. PSW-GTR-130. 1991 81

By the research of correlation between aggressive factors of climate, resistances of soil particles, and the quantity of aeolian deposition in the conditions of the Pannonian Plain, the basic equation of wind erosion has been developed:

where:

En - Quantity of aeolian deposition in kg m-l;

A and B - coefficients of regression; e - base of natural logarithms; Qv - air flow in seconds through

the observed cross section in m3s-1;

T - duration of each aggressive wind in s.

The formula is practical, as it is incomparably easier (with the aid of analytical evaluations and graphs of input parameters) to evaluate the erosion process, which otherwise calls for a rather complicated procedure of measurements.

CONCLUSIONS

By the analysis of data presented in the paper, it can be concluded as follows:

- In steppe-savanna conditions of the Pannonian Plain deflation processes represent a significant factor of soil destruction. They are factors which have adverse effects on the quality of the environment and, in general, on human activities in the region.

- Light soils (sands) of the Subotica- Horgos Sands are very erodible (containing

more than 90 percent particles smaller than 1 mm) and they can be classified as category I11 wind erosion hazard (Chepil and Woodruff 1954) - soils not resistant to wind erosion, or as (III), category of intensive erosion (Letic, Lj. 1989) with 5.0 - 7.0 t km-1 per year of deflation.

- Deflation processes occur in the periods winter - spring (Jan - Apr) and summer (June - July) and they are caused by aggressive winds NW (14) and N (16), velocity above 3.0 m s-l (at 0 .O5 m above ground) .

- The researched soils are subject to the accelerated nutrient loss resulting in fertility loss.

- These researches have a practical value, as they widen and supplement the knowledge of the measures of struggle against the phenomena of deflation, i.e. the establishment of shelterbelt plantings (and other measures) in this part of the Pannonian Plain.

REFERENCES

Chepil, W.S. and N.P. Woodruff. 1954. Estimations of wind erodibility of field surfaces. Journal of Soil and Water Conservation 9:257-265, 285.

Letic, Lj. 1989. Istrazivanje intenziteta eoloske erozije na Suboticko-horgoskoj pescari, Disertaci ja, Beograd.

Svehlik, R. 1975. Vetrna eroze pudy na jinovychodni Morave, Sv. 20, C.S.R. ve ZH. Praha.

Velasevic, V. 1978. Zastita i unapredjenje suma Suboticko-horgoske pescare, Studi ja, Subotica.


The Forest Service, U.S. Department of Agriculture, is responsible for Federal leadenhip in forestry. It carries out this role through four main activities:

Protection and management of resources on 191 million acres oTNational Forest System lands Cooperation with State and local governments, forest industries, and private landowners to help protect and manage non-Federal forest and associated range and watershed lands

Participation with other agencies in human resource and communily assistance progmms to improve living conditions in rural areas Research on all aspects of forestry, rangeland management, and forest resources utilization.

The Pacific Southwest Research Station Represents the research branch o i the Forest Service in California, Hawaii, American Samoa and the western Pacific.

Persons of any race, color, national origin, sex, age, religion, or with any handicapping conditions are welcon~e to use and enjoy all racilities, programs, and services of the US. Department of Ag~iculture. Discrimination in any form is strictly against agency policy, and should be reported to the Secretary of Agriculture, WashingLon, DC 20250.

Proceedings of the IU

FRO

Technical Session on G

eomorphic H

azards in Managed Forests

On

-

August 5-1 1,1990, M

ontreal, Canada