ththe role of geosynthetics in erosion and sedimente role of geosynthetics in erosion and sediment
TRANSCRIPT
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
1/16
Geotextiles and Geom embranes
I I (1992) 535-550
T h e R o l e o f G e o s y n t h e t i c s i n E r o s i o n a n d S e d i m e n t
C o n t r o l A n O v e r v ie w
M . S . T h e i s e n
Erosion C ontrol M aterials, Synthetic Industries, Con struction Products D ivision,
4019 Industry Drive, Chattanooga, Ten nessee 37416, USA
A B S T R A C T
Th e u se o fgeosynthetic erosion an d sed im ent materials continues to ex pa nd at
a rap id pace. F ro m their early beginnings in the late 1950s geosynthetic
materials today are the bac kbo ne o f the erosion an d sedim ent control
industry. Geosynthetic com ponents are an integral par t o f erosion and
sedim ent materials ranging fr om temporary pro ducts such as hydraulic
m ulc h geofibers plastic erosion control mesh es an d nettings erosion control
blanke ts a nd si l t fence s to high perform ance tur f reinforcement mats
geocellular con finem ent systems erosion control geotexti les and abr ic or m ed
revetments. Th is pa pe r provides a b rie f overview of these materials an d
concepts.
I N T R O D U C T I O N
H o p e f u l l y w e a r e e n t e r in g a n e w e n v i r o n m e n t a l e r a w h e r e c o n c e r n f o r
t h e p r o t e c t i o n o f o u r p l a n e t 's n a t u r a l r e s o u r c e s w il l r e a c h g l o b a l
p r o p o r t i o n s . C o n t i n u e d t e c h n o l o g i c a l a d v a n c e s h a v e l ed to i m p r o v e d
m o n i t o r i n g o f E a r t h 's v i t al s ig n s. A s s u c h , p r i o r t h e o r e t i c a l m o d e l i n g o f
e n v i r o n m e n t a l c o n c e r n s s u c h a s t h e g r e e n h o u s e e ff ec t, o z o n e d e p l e t i o n ,
r i s i n g s e a l e v e l s , d e f o r e s t a t i o n , d r o u g h t , a c c e l e r a t e d e r o s i o n , s e d i m e n t
l o a d i n g o f w a t e r w a y s , sp e c ie s e x t in c t i o n a n d t h e e v e n t u a l d o w n f a l l o f
m a n k i n d a p p e a r c h i l l in g l y r ea li st ic .
535
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
2/16
536 M S The i sen
Slogans such as 'Think globally, act locally', 'Love your mother' and
'Someone always lives downstream' are spearheading the efforts of
numerous preservation groups. With the continued demise of oppressive
governments, optimism for world peace and an unprecedented feeling
of global unity, a spirit of environmental cooperation is beginning to
prevail.
The term 'non-point pollution' hopefully is heading toward obsolescence
with groups such as Stream Watch sloshing their way up muddy creeks to
pinpoint sources of unchecked sediment. Improved methods to detect
and monitor rates of erosion and sedimentation via high tech satellite
imagery or even the actions of the Stream Watchers of the world lends
credence to the old saying 'you can run but you can't hide'. Generators of
sediment and other pollutants can and will be identified.
Cumulative research suggests excessive sediment in our waterways is
the planet's most prevalent contaminant. Increscent economic and
social losses from reductions in arable farmland, timber production,
fishery yields, species diversity and navigable waterways exceed those
caused by pollutants in the public eye such as nuclear and hazardous
wastes, smog or ground water contamination. Worse yet, the problem is
exasperated as one moves downstream toward our coastlines and
population centers.
Recently a number of laws have been manda ted in the United States to
combat excessive erosion. Such legislation ranges from local erosion and
sediment control ordinances to numerous state and federal agricultural,
waste containment and surface mining acts, to the broadly encompassing
Environmental Protection Agency's Clean Water Act and The Farm Bill
administered by the Department of Agriculture. These actions are only
the tip of the iceberg as more and more government agencies and entities
get with the program.
Just what is erosion control? To control erosion is to curb or restrain
(not completely stop) the gradual or sudden wearing away of soils. One
has seen extreme examples of excessive erosion such as gullied hill
slopes or stream channels choked with debris, but often erosion goes
unchecked on fiat to moderately sloping terrain. Soil loss is a continually
occurring process in natural ecosystems as well as successfully reclaimed
sites--without it our scenery would be very boring. The goal of any
revegetation or erosion control project should be to stabilize soils and
manage erosion in an economical manner (Theisen, 1988).
In this era of shrinking budgets, decision makers are hard pressed to
reclaim disturbed sites at minimu m costs. Given site conditions such as
slope angles, climate, runoff, soil profile and ultimate land use, a
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
3/16
eosynthetics in erosion an d sed im ent control 537
specifier must select with confidence a technique he (she) feels will
perform up to expectations at the lowest cost. Over the past 25 years the
erosion control industry has experienced rapid growth and is becoming
more sophisticated. Materials developed for erosion and sediment
control (E & SC) are becoming increasingly effective. Improved design
and installation guidelines are directing the use of E & SC products
toward more specific and cost effective applications. The industry has
evolved from the seed drills, straw blowers, hydroseeders, excelsior, jute,
concrete channe l liners and rip rap of the sixties into a diverse hierarchy
of techniques and materials. It seems as if every month a new product is
introduced to control erosion and sediment in more specific situations.
Numerous materials have come and gone in the survival of the fittest,
most cost competitive products.
i s tor ical perspect ive
Many of us perceive the use of geosynthetic materials for erosion and
sediment control as a new horizon. However, geosynthetics have played
a major role in the E & SC industry for over 30 years, particularly in the
case of rolled goods. In 1958 a geosynthetic component was incorporated
into an erosion control system which has changed the course of slope,
channel and embankmen t protection. A'plastic cloth' was used in lieu of
a granular filter to prevent sand from washing out behind concrete
blocks used for shoreline protection (Richardson & Koerner, 1990). The
significant cost savings realized when a 0.4-mm thick plastic filter cloth
could replace up to a meter of soil peaked the interest of the US Army
Corps of Engineers. Subsequent successful installations of woven plastic
cloth filters in coastal Structures led to the birth of the geotextile industry
as is practiced today. Through the years millions of square yards of
woven and non woven geotextiles have been installed as part of hard
armor systems.
Another geosynthetic breakthrough was initiated about 10 years later.
In the mid 1960s only one type of erosion control blanket existed. A state
soil conservationist discovered the material used for wrapping cotton
bales could be used to prevent soil erosion. The material was jute, a
woven mesh of thick natural yarns, when applied on the soil surface
provided thousands of tiny check dams to help keep soil from washing
away. Jute blankets allow vegetation to become establ ished on steeper
slopes and in higher flowing swales than traditional straw and hay
mulches. A similar material remains in use today.
However, jute has its drawbacks: its open weave construction leaves
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
4/16
538 M S Theisen
s o il e x p o s e d , th e o r g a n i c m a t e r i a l te n d s t o s h r i n k a n d s w e l l u n d e r f ie l d
c o n d i t i o n s , a n d it is e x tr e m e l y f l a m m a b l e . T o a c h i e v e o p t i m u m r es u lt s
s t ra w o r h a y m u l c h s ti ll m u s t b e p l a c e d b e n e a t h t h e j u te .
W h a t w a s n e e d e d w a s a o n e s te p , r o ll o u t m u l c h b l a n k e t . T h e f ir st
a t te m p t s i n v o l v e d a v e r y d e n s e m a t o f c u r le d , b a r b e d a s p e n w o o d
( e x c e ls i o r) f ib e rs . T h e m a t e r i a l s t a y e d t o g e t h e r b u t w a s t o o d e n s e t o a l l o w
v e g e t a ti v e g r o w t h . N e x t , a t w i s te d k r a ft p a p e r n e t w a s p l a c e d a b o v e a
t h i n n e r m a t o f e x c e ls i o r f ib er s. V e g e ta t io n g re w t h r o u g h t h e b l a n k e t b u t
p e r f o r m a n c e o f th e p a p e r n e t t in g w a s v e ry i n c o n s i st e n t; o ft e n b r e a k i n g
d o w n t o o q u i c k l y a n d b e i n g l i ft ed b y t h e v e g e t a t i o n or , w o r s e ye t, a l l o w i n g
t h e b l a n k e t t o b e w a s h e d a w a y b e f o re v e g e t at iv e e s t a b l i s h m e n t . A
s t ro n g e r , n o n - m o i s t u r e s e ns i ti v e , m o r e d u r a b l e n e t t i n g w a s n e e d e d .
P o l y p r o p y l e n e n e t t i n g w a s t h e a n s w e r .
C o m b i n i n g a d e n s e m a t o f e x c e ls i o r w i t h a p l a s ti c n e t l e a d t o th e f ir st
s u c c e s s f u l e x c e l s i o r e r o s i o n c o n t r o l b l a n k e t s . F i e l d tr ia l s w i t h v a r i o u s
n e ts , fi b e r le n g t h s a n d g l u e p a t t e r n s r e s u l t e d i n e s s e n t i a l ly t h e s a m e
b l a n k e t s w e s ee to d a y. T h e k e y to t h e i m p r o v e d p e r f o r m a n c e o f ex c e l si o r
o v e r j u t e b l a n k e t s is th e p l a s t ic n e t b a c k b o n e o f t h e p r o d u c t .
i a x i a l l y o r i e n t e d p r o c e s s n e t s
B i a x i a ll y o r i e n t e d p r o c e s s ( B O P ) n e t s a r e ty p i c a l ly m a n u f a c t u r e d f r o m
p o l y p r o p y l e n e o r p o l y e t h y l e n e re s in s . B O P n e t s a re e x t r e m e l y v e r s a ti l e
i n t h a t c o m p o s i t i o n , s t re n g t h , e l o n g a t i o n , a p e r t u r e s i ze a n d s h a p e , c o l o r
a n d u l t r a v i o l e t s t a b i l i t y c a n e a s i l y b e d e s i g n e d i n t o t h e p r o d u c t f o r
s p e c if i c s it e r e q u i r e m e n t s . S i n c e t h e y d o n o t a b s o r b m o i s t u re , th e s e n e t s
d o n o t s h r i n k a n d s w e ll l ik e k ra ft p a p e r n e ts a n d j u t e b la n k e t s. B O P n e t s
h a v e p r o v e n t o b e s o a d a p t a b l e t h e y a r e b e i n g u s e d t o c r e a t e m o r e
c o m p l e x p r o d u c ts a n d a re e v e n u s e d a lo n e t o a n c h o r l o o se f ib e r m u l c h e s
s u c h a s s t ra w , h a y a n d w o o d c h i p s. T h e l i g h t w e i g h t n e t t i n g s p l a c e d o v e r
m u l c h e s c o m e i n r o ll s w h i c h a r e 3 - 4. 5 m i n w i d th , w e i g h o n l y a b o u t
5 5 k g a n d w i l l c o v e r 0 .4 h (1 a c r e ) o r m o r e . I n s t a l l a t i o n o f t h e s e p r o d u c t s
is le ss l a b o r i n t e n s i v e t h a n t r a d i t i o n a l n e t t i n g p r o d u c t s .
E r o s i o n c o n t r o l m e s h e s
A s te p u p f r o m B O P n e t ti n g s a r e w o v e n p o l y p r o p y l e n e g e o te x ti le e r o s i o n
c o n t r o l m e s h e s . I n f ac t, t h e n e w e r t w i s t ed f ib e r e r o s i o n c o n t r o l m e s h e s
c a n p r o v i d e c o m p a r a b l e p e r f o r m a n c e t o e r o s io n c o n t r o l b l a n k e ts . T h e s e
p h o t o b i o d e g r a d a b l e , n a tu r a l l o o k in g , h i g h s t r en g t h p o l y p r o p y l e n e
m e s h e s p r o t e c t t h e s o i l s u r f a c e f r o m w a t e r a n d w i n d e r o s i o n w h i l e
a c c e l e r a t i n g v e g e ta t iv e d e v e l o p m e n t . F o u r m e t e r , l ig h t w e i g h t r o ll s
f a c i l i t a t e i n s t a l l a t i o n o n s l o p e s a n d c h a n n e l s . E r o s i o n c o n t r o l m e s h e s
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
5/16
eosynthetics in erosion an d sedim ent control 539
m a y b e u s e d a l o n e , w i t h d r y m u l c h e s o r a s a s t a b i li z in g u n d e r l a y f or so d
r e i n f o r c e m e n t . T h e y a l s o s h o w p r o m i s e a s a n o p e n w e a v e g e o t e x t i l e
f a c i n g f o r fo s t e r in g v e g e t a t io n o n g e o s y n t h e t i c a l l y r e i n f o r c e d s t e e p e n e d
s l o p e s o r b i o e n g i n e e r i n g i n s t a l l a t i o n s .
E r o s i o n c o n tr o l b l a n k e t s E C B s )
B O P n e t ti n g s o r w o v e n m e s h e s o f v a r y i n g c h a ra c t er is t ic s a r e n o w p l a c e d
o n o n e o r b o t h s id e s o f f in e l y t u n e d e r o s io n c o n t ro l b l a n k e t s a d a p t e d t o
a n t i c i p a t e d s i t e c o n d i t i o n s . T h e s e 1 - 2 - m w i d e b i o d e g r a d a b l e f i b e r
e r o s i o n c o n t r o l b l a n k e t s ( E C B s ) a r e c o m p o s e d o f s tr aw , e x c e ls io r , c o t to n ,
c o c o n u t , p o l y p r o p y l e n e o r b l e n d s t h e r e o f . N e t t i n g s o r m e s h e s m a y
c o n t a i n U V s t a b i l i z e r s f o r c o n t r o l l e d d e g r a d a t i o n o r l o n g c h a i n
i n t e r ru p t e r s to a c c e l e r a te p h o t o d e g r a d a t i o n . C o l o r s v a r y f ro m c l ea r , t a n ,
g r e e n t o b l a c k . M e t h o d s o f h o l d i n g t h e f i be r s in p l a c e r a n g e f r o m g l u es
a n d g l u e s tr ip s t o m o r e s u p e r i o r p a r a l l e l l o c k s t it c h i n g w i t h c o t t o n ,
p o l y e s t e r o r p o l y o l e f i n t h r e a d s . A p p l i c a t i o n s f o r t h e w i d e v a r i e t y o f
b l a n k e t s r a n g e f r o m p r o t e c t i o n o f g r a d u a l t o s te e p s lo p e s to l o w o r
m o d e r a t e ly f l o w i n g c h a n n e l s . T h e s e b l a n k e t s m a y p r o v i d e te m p o r a r y
re s i s t ance t o f l ow ve loc i t i e s o f up t o nea r l y t h r ee me t e r s pe r s econd .
F i n a l l y a n d p e r h a p s o f m o s t c o n c e r n t o t h e e n v i r o n m e n t , t h e se
m e s h e s a n d n e t ti n g s m a y u l t i m a t e l y b e c o m e b i o d e g r a d a b le . A s p h o t o -
d e g r a d a t i o n p r o g r e s s e s th e p l a s t ic c h a i n s a r e c u t i n t o s h o r t e r a n d s h o r t e r
s e g m e n t s d o w n t o a p l a s t ic ' s a n d ' w h i c h b e c o m e s p a r t o f t h e s o il . T h e s e
s h o r t s e g m e n t s b e c o m e b i o l o g i c a l ly d e g r a d a b l e a n d a r e a tt a c k e d b y s o il
m i c r o o r g a n i s m s a n d c o n v e r t e d t o c a r b o n d i o x i d e a n d w a t e r ( G u i l l e t ,
1 97 4). I t is u n f o r t u n a t e t h a t e m o t i o n a l , u n i n f o r m e d a n t i - p l a s ti c s t ig m a s
s o m e t i m e s p r e c l u d e t h e u s e o f t h e s e e x t r e m e l y c o s t ef fe c ti v e t e m p o r a r y
ma te r i a l s .
T E R M s v er su s P E R M s
A t t h is p o i n t a n i m p o r t a n t d i s t in c t i o n m u s t b e p r e s e n t e d r e g a r d i n g t h e
i n t e n d e d u s e o f E & S C m a t e r ia l s. F o r m a n y i n s t a l l a t io n s v e g et a ti o n
a l o n e w i ll p r o v i d e a d e q u a t e l o n g t e rm e r o s i o n p r o t e c ti o n . H o w e v e r ,
g e t t in g v e g e t a ti o n e s t a b l i s h e d r e q u i r e s a v a r i e t y o f t e c h n i q u e s . M a t e r i a l s
o f a t e m p o r a r y n a t u r e w h i c h f a c i l i t a t e v e g e t a t i v e e s t a b l i s h m e n t , t h e n
d e g r a d e , m a y b e t e r m e d T E R M s ( t e m p o r a r y e r o s i o n a n d r e v e g e t a t i o n
mater ia l s ) .
B a s i c a l ly T E R M s c o n s i s t o f d e g r a d a b l e n a t u r a l a n d / o r s y n t h e t i c
c o m p o n e n t s w h i c h p r o v i d e t e m p o r a r y e r o s i o n c o n t r o l a n d f a c i l t a t e
v e g e t a t i v e e s t a b l i s h m e n t . T h e s e s h o r t t e r m m a t e r i a l s d e g r a d e l e a v i n g
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
6/16
540 M S The i sen
TABLE 1
General TERM Techniques
Straw, hay and hydraulic mulches
Tackifiers and soil stabilizers
Hydraulic mulch geofibers
Erosion control meshes and nets (ECMNs)
Erosion control blankets (ECBs)
Fiber roving systems (FRSs)
o n l y v e g e t a ti o n f o r lo n g t e r m l o w t o m e d i u m f lo w r e si s ta n c e . Ta b l e 1 l is ts
v a r i o u s T E R M t e c h n i q u e s .
S it e c o n d i t i o n s r e q u i r i n g r e i n f o r c e d v e g e t a t i o n o r r e v e t m e n t sy st e m s
w i ll re q u i re P E R M s ( p e r m a n e n t e r o s i o n a n d r e v e g et a ti o n m a t e ri al s) .
P E R M s m a y b e s u b d iv i d e d i n to
b io techn ic l compos i te s
w h e n v e g e t a t io n
i s r e i n f o r c e d o r r m o r s y st e m s w h e n n o n - v e g e t a te d i n e r t m a t e r ia l s a r e
ins ta l l ed .
B i o t e c h n i ca l c o m p o s i t e s ar e c o m p o se d o f n o n - d e g r a d a b l e c o m p o n e n t s
w h i c h f u r n i sh t e m p o r a r y e r o s i o n p r o t e c t i o n , a c c e l e r a t e v e g e t a t i v e
g r o w t h a n d u l t im a t e l y b e c o m e s y n e r g is t ic a l lye n t a n g l e d w i t h l i v in g p l a n t
t is su e t o e x t e n d t h e p e r f o r m a n c e l i m i t s o f v e g e ta t io n . Th i s r e i n f o r c e d
v e g e t a ti o n p r o v i d e s 'p e r m a n e n t ' m e d i u m t o h i g h f lo w re s i st a n ce s o l o n g
a s b i o t e c h n i c a l c o m p o s i t es a r e p r o t e ct e d f r o m s u n l i g h t v i a s h a d i n g a n d
so i l c o ve r. Ta b l e 2 o u t l i n e s e x a m p l e s o f b i o t e c h n i c a l c o m p o s i t e s . H a r d
a r m o r s y st em s g e n e r a l l y e m p l o y i n e r t m a t e r i a ls u s e d t o p r o v i d e h i g h t o
m a x i m u m f lo w re s is t a n ce w h e r e c o n d i t i o n s e x ce e d p e r f o r m a n c e l i m i t s
o f r e i n f o r c e d v e g e t a t i o n sy s t e m s . S u m m a r i z e d i n Ta b l e 3 a r e sy s t e m s
u s e d t o p r o v i d e p e r m a n e n t e r o s i o n p r o t e c t io n o f a re a s s u b j e c t to h i g h
f lows , waves and /o r scour a t t ack .
Fiber roving systems FR Ss)
A n o t h e r g e o s y n t h e t i c c o n c e p t p r o v i d i n g m o d e r a t e e r o s i o n p r o t e c t i o n
a re f ibe r rov in g sys tems (FRSs) . D eve lope d in the l a t e 1960s rov ings a re
a p p l i e d i n a c o n t i n u o u s s t r a n d f o r p r o t e c t io n o f d r a in a g e s w a le s a n d
slopes .
F i b e r g l a ss r o v i n g is a m a t e r i a l f o r m e d f r o m f i b e rs d r a w n f r o m m o l t e n
g l a ss a n d g a t h e r e d i n t o s t r a n d s t o f o r m a s i n g le r i b b o n . P o l y p r o p y l e n e
r o v in g is f o r m e d f r o m c o n t i n u o u s s t ra n d s o f f ib r i ll a te d y a r n s w o u n d
o n t o c y l i n d r ic a l p a c k a g es s o t h a t t h e m a t e r i a l c a n b e f ed c o n t i n u o u s l y
f r o m t h e o u t s i d e o f th e p a c k a g e . U se o f fi b e rg l a ss r o v i n g h a s b e e n
d e c l i n i n g d u e t o it s c a r c i n o g e n i c p r o p e r t i e s a n d is b e i n g d i sp l a c e d b y
e n v i r o n m e n t a l l y f r ie n d l y p o l y p r o p y l e n e r o vi ng .
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
7/16
Geosynthetics in erosion an d sediment control 541
T A B L E
Types of BiotechnicalComposites(PERMs)
UV stabilized fiber roving systems (FRSs)
Erosion control revegetationmats (ECRMs)
Tuff reinforcementmats fiRMs)
Sports turf geofibers
Vegetatedgeocellularcontainmentsystems(GCSs)
Vegetatedconcreteblock systems
T A B L E 3
Types of Armor Systems (PERMs)
Geocellular containmentsystems (GCSs)
Fabric formed revetments(FFRs)
Concrete block systems
Gabions
i p r a p
Composites and hybrids
Erosion control roving is unique because of the flexibility of
application, allowing for any width or thickness of material to be applied
(Agnew, 1991). Other erosion control materials, such as blankets or mats
require the user to apply the width or thickness of material supplied.
Fiber rovings may be viewed as an in-situ erosion control geosynthetic
with reduced labor and material costs over traditional blanket materials.
Using compressed air, roving is applied through a nozzle and then
anchored in place using emulsified asphalt or other natural or synthetic
soil stabilizers. The biodegradable polypropylene roving may be used for
temporary applications (TERM) or when UV stabilized is appropriate
for extended use situations (PERM).
T R M v e r s u s E C R M
Turf reinforcement is a me thod or system by which the natural ability of
plants to protect soil from erosion is enhanced through the use of
geosynthetic materials. A flexible three dimensional matrix retains seeds
and soil, stimulates seed germination, accelerates seedling development
and most importantly, synergistically meshes with developing plant
roots and shoots. In laboratory and field analyses, biotechnically
reinforced systems have resisted flow rates in excess of four meters per
second for durations of up to two days, providing twice the erosion
protection of unreinforced vegetation (Carroll e t a l . 1991). Such
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
8/16
542
M S Theisen
performance has resulted in the widespread practice of turf reinforce-
ment as an alternative to concrete, rip rap and other armor systems in the
protection of open channels, drainage ditches, detention basins and
steepened slopes.
Permanent geosynthetic mattings are composed of durable synthetic
materials stabilized against ultraviolet degradation and inert to chemicals
normally encountered in a natural soil environment. These mattings
consist of a lofty web of mechanical ly or melt bonded polymer nettings,
monofilaments or fibers which are entangled to form a strong and
dimensionally stable matrix. Polymers include polypropylene, poly-
ethylene, nylon and polyvinyl chloride.
Geosynthetic mattings generally fall into two categories: tu r f r e in force -
m e n t m a t s T R M s )
or
eros ion con t ro l r evegetat ion m a ts EC RM s) .
Higher
strength TRMs provide sufficient thickness and void space to permit soil
filling/retention and the development of vegetation within the matrix.
TRMs are installed first, then seeded and filled with soil. Seeded prior to
installation, ECRMs are denser, lower profile mats designed to provide
long term ground cover and erosion protection, By their nature of
installation TRMs can be expected to provide more vegetative entangle-
ment and long term performance than ECRMs. However, denser ECRMs
may provide superior temporary erosion protection.
Geoceilular containm ent system s G C Ss)
Geocellular containment systems work in a unique fashion in that
strength or stabilization by confinement is achieved by a series of three-
dimensional cells up to 20 cm deep. When expanded into position, the
polyethyleneor polyester cells have the appearance of a large honeycomb,
one of nature's most efficient structures. The cells are then backfilled
with soil, sand or gravel depending upon application. For revegetation,
the soil-backfilled cells are seeded, fertilized and covered with a variety
of TERM or PERM techniques. The mulches provide surface protection
while the cells greatly reduce the chances of subsurface failure and act as
a deeper rooted biotechnical composite. Vegetated GCSs are limited to
flow velocities of two to three meters/second because of the tendency of
the nearly impermeable cells to sustain scouring under high flow
velocities (Chen & Anderson, 1986).
For higher flow condit ions GCSs may be also filled with concrete or
gravel to create a hard armor system. Typically a geotextile will be placed
beneath the expanded web to provide separation and/or filtration.
Erosion control applications for GCSs are many including steep slope
revegetation, channel liners, shoreline revetments, retaining walls, boat
ramps, and low flow stream crossings.
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
9/16
eosynthetics in erosion an d sedim ent control 543
F a b r ic f o r m e d r e v e tm e n t s
Fabric forming systems are mattresses typically constructed of water
permeable, double layer woven geotextiles which are posit ioned on the
area to be protected and filled with a structural grout. The two layers of
geotextile are joined at discrete points to create a form which when filled
with grout will conform to most subsoil conditions. Thickness and
geometry are determined by internal spacer threads woven into the
upper and lower sheets of fabric. In many cases the mattresses may be
installed for less cost than conventional armor systems since all
construction is conducted in place (Richardson & Koerner, 1990).
o n c r e t e b l o c k s y st e m s
Concrete block systems consist of prefabricated concrete panels of
various geometries which may be attached to and laid upon a woven
monofilament or non-woven geotextile. Bending and torsion are
accommodated by having the concrete blocks articulated with joints,
weaving patterns or connection devices. Concrete block systems may be
subdivided into three groups: non-tied interlocking blocks, cable-tied
blocks, or in-situ concrete (Hewlett
e t a l .
1987). In some cases the entire
erosion control section may be manufactured, trucked to the job site and
placed as a unit.
G a b i o n s
Gabions are compar tmented rectangular containers made of galvanized
steel hexagonal wire mesh and filled with hand-sized stone. Cells of
equal capacity are formed by factory-inserted wire netting diaphragms or
partitions which add strength to the container and help maintain its
shape during the placement of stone. In highly corrosive conditions a
polyvinyl chloride coating is used over the galvanized wire.
Advantages of gabions include flexibility, durability, strength, per-
meability and economy versus rigid structures. The growth of native
plants is promoted as gabions collect sediment in the stone fill. A high
percentage of installations are under lain by woven monofilament and
nonwoven geotextiles to facilitate sediment capture and prevent wash
out from behind the structure.
R i p r a p
Rip rap consists of stone dumped in place on a filter blanket or prepared
slope to form a well graded mass with a minimum of voids. Stone used for
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
10/16
544 M S The i sen
r i p r a p i s h a r d , d u r a b l e , a n g u l a r i n sh a p e ; r e s i s ta n t to w e a t h e r i n g a n d t o
w a t e r a c t i o n ; a n d f r e e f r o m o v e r b u r d e n , s p o i l , s h a l e a n d o r g a n i c
m a t e r i a l . Th e r i p r a p m a t e r i a l is g e n e r a l l y p l a c e d o n a g r a v e l b e d d i n g
l a y e r a n d / o r a w o v e n m o n o f i l a m e n t o r n o n w o v e n g e ot ex ti le fa b ri c.
e r f o r m a n c e o f e r o s i o n c o n t ro l m a t e r ia l s
S e v e ra l t es t p r o c e d u r e s h a v e b e e n p r o p o s e d t o q u a n t i f y p e r f o r m a n c e o f
e r o s i o n c o n t r o l m a t e r i a l s . I n i t i a l c o n c e r n f o r v e g e t a t e d sy s t e m s i s
t e m p o r a r y e r o s io n p r o t e c ti o n p r io r t o a n d d u r i n g s e ed g e r m i n a t i o n a n d
se e d l i n g d e v e l o p m e n t . Ty p i c a l ly , t h i s l e v e l o f p e r f o r m a n c e i s m e a su r e d
b y t h e m a t e r i a l 's a b i l i t y t o m i n i m i z e so i l l o ss w h e n su b j e c t e d t o v a r i o u s
f l o w r a t e s a n d / o r r a i n f a l l a m o u n t s . T e m p o r a r y e r o s i o n p r o t e c t i o n i s
i m p o r t a n t b u t t h e l o n g t e r m g o a l o f a n y e r o s i o n c o n t r o l m a t r i x i s t o
p r o v id e p e r m a n e n t e r o s i o n p r o t e ct io n v i a p e r m a n e n t v e g e ta t io n a n d / o r
s u b s e q u e n t r o o t r e in f o r c e m e n t . T h e m o r e r a p i d l y v e g e t a ti o n b e c o m e s
e s t a b l i s h e d t h e m o r e r a p i d l y l o n g t e r m e r o s i o n c o n t r o l m a y b e
a c c o m p l i sh e d . Th u s , t h e m a t e r i a l' s a b i l i t y to f a c i li t a te v e g e ta t iv e
e s t a b l i s h m e n t is e q u a l l y i m p o r t a n t . T o o m u c h e m p h a s i s o n a n e r o s i o n
c o n t r o l p r o d u c t' s t e m p o r a r y p r o t e c t i o n m a y i n h i b i t t h e g r o w th o f n e w l y
e m e r g i n g s e e d li n g s .
P e r h a p s t h e m o s t c r it ic a l p a r a m e t e r i n a n e n g i n e e r i n g d e s ig n i s fl o w
r e s i s ta n c e b e f o r e , d u r i n g a n d l o n g a f t e r v e g et a ti v e e s t a b l i sh m e n t . S o m e
e r o s i o n c o n t r o l m a t e r i a l s m a y b e w a s h e d a w a y b e f o r e t h e v e g e t a t i o n
t a k e s h o l d w h i l e o t h e r s m a y t e m p o r a r i l y e x h i b i t e x c e l l e n t f lo w r e s is t a n c e
o n l y t o lo se t h e i r e f fe c ti v e n es s a s t h e y d e g r a d e o r d e c o m p o se o v e r t im e .
S p e c i f i e r s m u s t t a k e i n t o a c c o u n t i m m e d i a t e a n d l o n g t e r m f l o w
r e s is t a n ce b a s e d u p o n l o n g e v it y o f t h e m a t e r ia l w h e n d e s i g n i n g g ra s s ed
s l o p e s a n d w a t e rw a y s .
T w o b a s ic d e s i g n c o n c e p t s a re u s e d t o e v a lu a t e a n d d e f i n e a c h a n n e l
c o n f i g u r a t i o n t h a t w i l l p e r f o r m w i t h i n a c c e p t e d l i m i t s o f s ta b i li ty . Th e se
m e t h o d s a r e d e f i n e d a s th e p e r m i s s ib l e v e l o ci ty a p p r o a c h a n d t h e
p e r m i s s i b l e tr a c ti v e f o r ce ( sh e a r s tr es s ) a p p r o a c h . U n d e r t h e p e r m i s s i b l e
v e l o c it y a p p r o a c h t h e c h a n n e l is a s s u m e d s t ab l e i f t h e a d o p t e d v e l o c it y is
l o w e r t h a n t h e m a x i m u m p e r m i s s i b l e v e lo c it y . Th e t r a c ti v e f o rc e
( b o u n d a r y sh e a r s t r e s s ) a p p r o a c h f o c u se s o n s t r e s se s d e v e l o p e d a t t h e
i n te r f ac e b e tw e e n f lo w i n g w a t e r a n d t h e m a t e r ia l s f o r m i n g t h e c h a n n e l
b o u n d a r y ( C h e n & C o t to n , 1 988).
T h e p e r m i s s i b le v el o c it y a p p r o a c h u s es M a n n i n g ' s e q u a t i o n w h e r e
w i t h g i v e n d e p t h o f flo w , D , t h e m e a n v e l o c i ty m a y b e c a l c u l a t e d a s :
V = R 2 3 S l 2 n
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
11/16
eosynthetics in erosion an d sediment co ntrol 5 4 5
w h e r e
V =
n - -
R
a v e r a g e v e l o c i t y i n t h e c r o ss s e c t i o n
M a n n i n g ' s r o u g h n e s s c o e f f ic i en t
h y d r a u l i c r a d iu s , e q u a l t o t h e c r o s s - se c t io n a l a r e a ,A , d i v i d e d b y
t h e w e t te d p e r i m e t e r , P
S = f r ic t io n s l o pe o f t h e c h a n n e l , a p p r o x i m a t e d b y t h e a v e ra g e b e d
s l o p e f o r u n i f o r m f lo w c o n d i t i o n s
Th e t r a c t iv e f o rc e a p p r o a c h u se s a s i m p l i f i e d sh e a r s tr es s a n a l y s i s
w h i c h i s e q u a l t o :
w h e r e
=
y =
D
S
yDS
t rac t ive force
u n i t w e i g h t o f w a t e r
m a x i m u m d e p th o f f lo w
a v e r a g e b e d s l o p e o r e n e r g y s lo p e
D e s i g n c r it e ri a b a s e d o n f lo w v e lo c i ty m a y b e l i m i t e d b e c a u s e
m a x i m u m v e lo c it ie s v a r y w i d e ly w i th c h a n n e l l e n g t h ( L), s h a p e (R ), a n d
rou ghn ess coe f f i c i en t s (n ). In rea l i ty i t i s the fo rce deve lo ped by the f low,
n o t t h e f lo w v e l o c it y i ts e lf , t h a t c h a l l e n g e s t h e p e r f o r m a n c e o f e r o s i o n
c o n t r o l sy s te m s . T r a c t iv e f o r ce s c a u se d b y f l o w i n g w a t e r o v e r t h e g r o u n d
su r f a c e c r e a t e sh e a r s t r e s se s w h i c h c a n b e u se d a s a d e s i g n p a r a m e t e r
i n d e p e n d e n t o f c h a n n e l s h a p e a n d r o u g hn e s s. M o r eo v e r, th e h i g h e r
s tr es se s d e v e lo p e d i n c h a n n e l b e n d s o r o t h e r c h a n g e s i n s t r e a m c h a n n e l
g e o m e t r y c a n b e q u a n t i f i e d b y s i m p l i f i e d sh e a r s t r e s s c a l c u l a t i o n s ,
p r o v i d i n g a h i g h e r l e v el o f d e s i g n c o n f i d e n c e t h a n o t h e rw i s e p o s s ib l e
(Chen & Cot ton , 1988) .
C r i t ic a l s h e a r s t re ss d e t e r m i n a t i o n s a r e m e a n t t o b e u s e d w i t h v e lo c i ty
c a l c u l a t i o n s f o r p r e s c r e e n i n g o f c h a n n e l l i n i n g d e s i g n s . M a n n i n g ' s
e q u a t i o n r e m a i n s t h e p r i m a r y h y d r a u l i c r e s e a r c h a n d d e s i g n t o o l .
H o w e v e r , a s e v e r y d a y p r a c t i c e h a s d e t e r m i n e d , a s i m p l i f i e d s c r e e n i n g
c r it e ri a s u c h a s m a x i m u m s h e a r s tr es s i s n e c e s s a r y t o e n s u r e p r o p e r l y
e n g i n e e r e d d e s i g n o f c h a n n e l l i n i n g e r o s i o n c o n t r o l sy s te m s . F i g u r e 1
c o m b i n e s c u m u l a t i v e re s e a r c h f o r s e ve r al e r o s i o n c o n t r o l m a t e r ia l s a n d
a t t e m p t s t o g r o u p c a t e g o ri e s o f e r o s i o n c o n t r o l m a t e r i a l s in t o t h e i r c o s t
e f fec tive des ig n n iches .
M axim um pe rmiss ib le ve loc it ie s fo r vege ta tive t echn ique s a re i l lu s t ra t ed
u n d e r v e g e t at e d a n d n o n - v e g e t a t ed c o n d i t io n s . T h u s a d e s i g n e r w i ll h a v e
p e r f o r m a n c e g u i d e l i n e s f r o m t h e t i m e a m a t e r i a l is i n s t a l le d to w h e n i t
b e c o m e s f u l l y v e g e ta t ed .
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
12/16
546 M S The i sen
6'0
E
~ , 4 . 5
.90
:>
r
. ~ 3 - 0
u~
1 0
1-5
17D
E
0
._ l
Hi g h v e l o c i t y b l a n k e ts
_ f i b e r r o v in g s y s t e m s h i g h
r a t e ? ~
M e d i u m v e l o c i t y b l a n k e t s a n d m e s h
f i b e r r o vi n g s y s t e m s l o w rate?X - ~
L o w
v ~o cit~ ; ~ l ; ~ ; P . . . . .
I I
2 5
F l o w d u r a t i o n , h
H a r d a r m o r s y s t e m s
~ t e d
TR
S o f t a r m o r z o n e
N n v e g e t a t e d T RM o r E CR M
1 0 0 1. C o v e r . . . . . . . . . .
L i m i ts o f n a t u r a l v e g e t a t i o n
Poor cover
are soil erosion
1 0 2 0 5 0
Fig. 1. Recommended maximum design velocities for various erosion control materials.
*No known published data for flows exceeding 0.5 h.
l o w d u r a t io n
Of key importance is the significance of duration of flow. Note from
Fig. 1 that allowable flow velocities decrease with flow duration. This is a
critical point. Manufacturers of both organic and synthetic erosion
control products often express the erosion resistance of their materials in
terms of maximum allowable flow velocity. Though unstated, these flow
limits are typically for very short durations (minutes rather than hours).
They do not reflect the potential for severe erosion damage that results
from moderate flow velocities over a period of several hours. Ironically,
many manufacturers, designers and users do not consider duration of
flow when evaluating and selecting erosion control measures (Theisen &
Carroll, 1990).
Typically, a major precipitation event will produce significant flow
velocities with durations lasting hours or days--not minutes. The two
day design duration was selected because in grass waterways, high
velocity flow events should be no longer than about two days in duration,
following which grass recovery and subsoil drainage should be able to
take place (Hewlett
e t a l .
1987). As Fig. 1 illustrates, duration of flow will
reduce the erosion resistance of a grassed surface. It is critical that design
of grassed waterways take this into account.
Flow values for the various temporary erosion control mulches,
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
13/16
eosynthetics in erosion an d sedim ent control 547
blankets, meshes and rovings have been truncated and placed into the
lower left area of the graph because extended flow duration trials for
these materials have not been reported. Their long term performances
may either go up or down as vegetation becomes established and
ultimately will fall into the niche for natural vegetation as the product
degrades.
The Soft Armor Zone begins just above the limits of natural
vegetation. Performance data for reinforcing mats ranges from un-
vegetated TRMs and ECRMs (which exceed performance of natural
vegetation) to the upper curve which delineates maximum recommended
design velocities obtained from field and laboratory evaluation of
vegetated TRMs (Western Canada Hydraulic Laboratories Ltd, 1979;
Hoffman & Adamsky, 1982; Hewlett e t a l . 1987; Theisen & Carroll, 1990;
Carroll
e t a l .
1991).
The upper end of the graph is comprised by the niche for hard armor
materials. The graph is not intended to establish upper performance
limits for these materials, but rather to define the upper limits of 'soft
armor' (reinforced vegetation). Performance for hard armor materials
will be considerably higher and upper limits are beyond the scope of this
paper.
ed i m ent contro l
Going hand in han d with aggressive erosion control measures should be
a well conceived sediment control plan. Erosion control measures are an
offensive strategy to attack potential sedimentation while sediment
control practices are a stop gap defensive strategy. In erosion and
sediment control planning, the old sports axiom that a strong offense is
the best defense is certainly apropos. Vegetation is clearly the finest
sediment control product on the planet
Geosynthetic silt fences have become a standard construction practice
over much of the United States replacing straw and hay bales, brush
layers and rock check dams. Silt fences are generally installed at the
beginning of the construction project and usually consist of woven slit
tape geotextiles mounted on a prefabricated fence.
A well designed silt fence must initially screen silt and sand particles
from runoff. A soil filter is formed adjacent to the silt fence and reduces
the ability of water to flow through the fence. This leads to the creation of
a pond behind the fence which serves as a sedimentat ion basin to collect
suspended soils from runoff water. To meet such needs, the geotextile
must have properly sized openings to form the soil filter and the storage
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
14/16
548 M S T h e i s en
c a p a c i t y o f t h e f e n c e m u s t b e a d e q u a t e t o c o n t a i n t h e v o l u m e o f w a t e r
a n d s e d i m e n t a n t i c i p a t e d d u r i n g a m a j o r s to r m ( R i c h a r d s o n & K o e r n er ,
1990).
P o r o u s s e d i m e n t c o n t r o l s t r u c t u r e s a r e t h e n e w e s t g e o s y n t h e t i c
a p p r o a c h t o s e d i m e n t c o n t r o l . A t h r e e - d i m e n s i o n a l m o l d a b l e m a s s o f
c r i m p e d p o l y p r o p y l e n e f i b e r s m a y b e p l a c e d i n f i ll s o r g u l l ie s t o p r o v i d e
p a s s i v e s e d i m e n t c o n t r o l . P l a c e d b y h a n d w i t h i t s s i z e a n d s h a p e
d e t e r m i n e d b y t h e i n s t a ll e r , a p p l i c a t i o n s i n c l u d e f il l a n d g u l l y r e p a i r,
d i t c h c h e c k s , s e d i m e n t t r a p s , a n d p e r i m e t e r b e r m i n g . M o r e o v e r t h e
f i b e r s m a y b e e n c a p s u l a t e d i n a p o l y p r o p y l e n e m e s h t o c r e a t e
p r e f a b r i c a t e d c h e c k d a m s f o r sw a l e a n d d i t c h p r o t e c ti o n . T a b l e 4 li s ts a
f e w s e d i m e n t c o n t r o l t e c h n i q u e s .
the r geosynthet ic opportun i ti e s
I d e a s f o r g e o s y n t h e t ic e r o s io n a n d s e d i m e n t c o n t r o l m a t e r i a ls a b o u n d .
C e r t a i n l y n e w i d e a s h a v e b e e n o m i t te d o r a r e b e i n g d e v e l o p e d a t t h e ti m e
o f th i s p u b l i c a ti o n . O d d s a r e h i g h t h a t g e o s y n t h e ti c s w i l l w o r k t h e i r w a y
d o w n t h e l a d d e r i n t o m o r e t r a d i t i o n a l a p p l i c a t i o n s s u c h a s h y d r a u l i c
m u l c h e s a n d e r o s i o n c o n t r o l b l a n k e t s . H y d r a u l i c m u l c h g e o f i b e r s
( w h i c h i m p r o v e t h e t e n a c i t y o f w o o d f ib e r a n d r e cy c le d p a p e r m u l c h e s )
a n d r e c y c le d p l a s t ic f ib e r b l a n k e t s a n d m a t s a re a l r e a d y e n t e r i n g t h e
m a r k e t . G e o f i b e r s a r e b e i n g u s e d a s p a r t o f s p o r ts t u r f s y s t e m s in m a j o r
a t h l e t i c s t a d i u m s p r o v i d i n g b o t h g r o u n d s t a b i l i z a t i o n a n d a r o o t
r e i n f o r c i n g m a t r i x .
T h e f u t u re o f g e o s y n t h e t i c s fo r E & S C l ie s p a r t l y i n t h e r e c y c l i n g O f
w a s t e p l a st ic s g e n e r a t e d f r o m o t h e r a p p l i c a t i o n s . P o l y m e r s p e c i fi c a t io n s
f o r E & S C a p p l i c a t i o n s a r e n o t a s s t r i n g e n t a s o t h e r g e o s y n t h e t i c
m a t e r i a l s s u c h a s g e o m e m b r a n e s , g e o g r i d s a n d g e o t e x t i l e s . I t i s a n
e n v i r o n m e n t a l l y f r ie n d l y g e s tu r e i n a n e n v i r o n m e n t a l l y f r ie n d l y in d u s t ry .
And r ecyc l ed p l a s t i c s a r e cos t e f f ec t i ve .
TABLE 4
Examples of Sediment Con trol Techniques
Vegetation
Straw and hay bales
Brush layers
Silt fences
Porous sediment control structures (PSCSs)
Rock check dams
Sediment traps, basins and ponds
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
15/16
Geosynthetics in erosion an d sediment control 549
More research on E & SC effectiveness of the myriad of materials is
mandatory. Questions regarding resistance to extended flow durations
and long term performance for all materials must be answered. Systems
must be developed for standardizing product descriptions, sanctioning
uniform test and evaluation procedures, and creating a market reporting
system to insure broad acceptance of E & SC industry. Organizations
such as the Internat ional Erosion Control Association (IECA), Erosion
Control Technology Council (ECTC), American Society for the Testing of
Materials (ASTM), Industrial Fabrics Association International (IFAI),
and the Geosynthetics Research Institute (GRI) must lead the way.
Another hurdle to overcome or trail to blaze, depending upon how one
looks at it, is the issue of biodegradable plastics for short term
applications. This is an area of very important research. Members of the
industry as well as the general public must be educated. The performance
advantages of man made fibers over natural fibers is recognized in many
sectors of the textile industry. The E & SC industry is quite possibly a
sleeping giant for man made fibers. Keep your ear to the ground and your
eyes wide open because 'you ain't seen nothin' yet'. The future of
geosynthetics in erosion and sediment control is bright
REFERENCES
Agnew, W. (1991). Erosion control product selection.Geo technical Fabrics Report
9 (3), 24-27.
Carroll, O. Jr, Rodencal, J. & Theisen, M. S. (1991). Evaluation of turf
reinforcement mats and erosion control and revegetation mats under high
velocity flows.Proceedings o f the X X II Ann ual Conference of the International
Erosion Control Association Orlando, FL.
Chen, Y. H. & Anderson, B. A. (1986). Development of a methodology for
estimating embankmentdamage due to flood overtopping. USDOT Federal
Highway Administration and USDA Forest Service, report number
DTFH61-82-C-00104, Ft Collins, CO.
Chen, Y. H. & Cotton, G. K. (1988). Design of roadside channels with flexible
linings. Federal Highway Administration report HEC-15/FHWA-1P-87-7,
McLean, VA.
Guillet, J. E. (1974). Plastics, energy and ecology--a harmonious triad. Plastics
Engineering 30 (8), 48-56.
Hewlett, H. W. M., Boorman, L. A. & Bramley, M. E. (1987). Design of re-
inforced grass waterways. Construction Industry Research and Information
Association, Report 116, London.
Hoffman, G. L. & Adamsky, R. (1982). Nylon erosion control mat. Presented at the
Transportation Research Board sixty-first annual meeting Washington DC.
Theisen, M. S. (1988). Cost-effective techniques for successful erosion control.
Proceedings High Altitude Revege tation Work shop No. 8 Ft Collins, CO.
Theisen, M. S. & Carroll, R. G. (1990). Turf reinforcement--the 'soft armor"
-
7/26/2019 ThThe Role of Geosynthetics in Erosion and Sedimente Role of Geosynthetics in Erosion and Sediment
16/16
550 M. S. Theisen
al ternat ive .
Proceedings of the XXI Annual Conference of the International
Erosion Control Association,
W a s h in g t o n D C .
R icha rds on , G . N . & Ko em er , R . M. (eds ) (1990).A Design Primer. Geotextiles and
Related Materials,
In d u s t r i a l F a b r i c s A sso c i a t i o n In t e rn a t i o n a l , S t P a u l, M N .
W e s t e rn C a n a d a H y d ra u l i c L a b o ra t o r i e s L t d (1 9 7 9 ) .
Cove Country Club:
Experimental Studies on Permissible Shear Stresses of Bermuda Grass.
P o r t
C o q u i l a m , B r it is h C o l u m b i a , C a n a d a .