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FEDERAL EMERGENCY MANAGEMENT AGENCY
Landslide Loss Reduction:A Guide for State and LocalGovernment Planning
EARTHQUAKE HAZARDS REDUCTION SERIES 52
Issued by FEMA in furtherance of the Decade for Natural Disaster Reduction.
FEMA 182/August 198&9
A % A ~ A A A A A A A A A A A A 'A
I I I I I I I I I I .: A A. A A AAIA AAAAAAAA SAAA .A A A A A A A A A A A A A A A A A ~~~~~~~, A A A AAAAAz
DISCLAIMERThis document has been reviewed by the Federal Emergency
Management Agency and approved for publication. Thecontents do not necessarily reflect the views and policies of
the Federal Emergency Management Agency.
FEDERAL EMERGENCY MANAGEMENT AGENCY
Landslide Loss Reduction:A Guide for State and LocalGovernment Planning
by:,Robert L. Wold, Jr.Colorado Division of Disaster Emergency ServicesandCandace L. JochimColorado Geological Survey
ii
II
Contents
FOREWORD .n............................... 7iACKNOWLEDGIMENTS ............................... vii
Advisory Committee ................................ viiCHAPTER 1-Introduction .......................... 1
Purpose of this Guidebook ........................... 3CHAPTER 2-Landslide Losses andthe Benefits of Mitigation ............................. 4
The Landslide Hazard ................................. 4Econoamic and Social Impacts ofLandsliding ................................. 4
Costs of Landslidling ............................... 4Impacts and 'Consequences ofLandsliding ................................. 4
Long-Term Benefits of Mitigation ..........- 5The Cincinnati, Ohio Study ................... 6The Benefits of Mitigation in Japan ..... 6 6
Pla nning as a Means of Loss Reduetion.....6Local Government Roles ........................ 7
CHAPTER 3-Causes and Types ofLandslides ................................. 9
What Is a Landslide7 ................................. 9Why Do Landslides Occur7 .......................... 9
Human Activities ................................. 9Natural Factors ................................ .9
Climate ................................ . 9Erosion ................................ 10Weathering ................................ 10Earthquakes ................................ 11Rapid Sedimentation ...................... 11Wind-Generated Waves ................... 11Tidal or River Drawdown ............... 11
Types of Landslides ................................ 11Falls ................................ 11Toopple ................................ 11Slides ................................ 11
Rotational Slide .............................. 12Translational Slide ......................... 12
Block Slide ................................ 13Lateral Spreads ................................ 13Flows ................................ 13
Creep ................................ 13Debris Flow ................................ 13Debris Avalanche ........................... 13Earthflow ................................ 14Mudflow ................................ 14
Lahar .............................. 14Subaqueous Landslide .......................... 15
Interrelationship of Landsliding WithOther Natural Hazards (The MultipleHazard Concept) ............................... 15
Landsliding and lDam Safety ............... 15Landsliding and Flooding .................... 17Landsliding and Seismic Activity ....... 18Landsliding and Volcanic Activity ....... 19
CHAPTER 4-Hazard Identification,Assessment, and Mapping .......................... 20
Hazard Analysis .............................. 20Map Analysis ............................... 20Analysis of Aerial Photographyand Imagery ............................... 20Analysis of Acoustic Imageryand Profiles ............................... 20Field Reconnaissance ........................... 20Aerial Reconnaissance ......................... 20Drilling .............................. 20Geophysical Studies ............................. 21Computerized Landslide TerrainAnalysis .............................. 21Instrumentation .............................. 21
Anticipating the Landslide Hazard .......... 21Tlranslation of Technical Informationto Users .............................. 21
Regional Mapping .............................. 22Commrunity-Level Mapping ................. 22Site-Specifie Mapping .......................... 22Types of Maps .............................. 22
Landslide Inventories .................... 22Landslide Susceptibility Maps ...... 23Landslide Hazard Maps ................. 25
CHAPTER 5-Transferring andEncouraging the Use of Information ....... 26
Information Transfer ............................... 26Users of Landslide HazardInformation ............................... 27
Developing an Information Base:Sources of Landslide HazardInformation .............................. 28
CHAPTER 6-Landslide Loss-Reduc-tionTechniques .............................. 30
Preventing or Minimizing Exposure
fli
Contents Continued
to Landslides ................................ 30Land-Use Regulations ......................... 30
Reducing the Occurrence of Landslidesand Managing Landslide Events .............. 30
Building and Grading Codes ............... 30Emergency Management ..................... 31
Controlling Landslide-Prone Slopesand Protecting Existing Structures .......... 31
Precautions Concerning Relianceon Physical Methods ............................ 32Design Considerations and PhysicalMitigation Methods .............................. 33
CHAPTER 7-Plan Preparation ................ 35Determining the Need for a State Plan ... . 35
Federal Disaster Relief andEmergency Assistance Act(Section 409) ................................ 35
The Planning Team ................................ 36The Planning Process ................................ 37
Step 1 - Hazard Analysis ..................... 37Step 2 - Identification of ImpactedSites ................................ 37Step 3 - Technical InformationTransfer ................................ 38Step 4 - Capability Assessment ........... 38Step 5 - Determination of Unmet
Local Needs ............................... 39Step 6 - Formulation of Goals andObjectives ............................... 40
Local Landslide HazardMitigation ............................... 40Development of MitigationProjects ............................... 40
Step 7 - Establishment of aPermanent State HazardMitigation Organization ...................... 41Step 8 - Review and Revision .............. 43
CHAPTER 8-Review and Revision ofthe Plan and the Planning Process .......... 44
Inventory of Landslide Costs ..................... 44Evaluation of Mitigation Projects andTechniques ............................... 44
Examples of Innovative MitigationApproaches ............................... 45
Analyses of Local Mitigation Programs .... 45CHAPTER 9-Approaches for Over-coming Anticipated Problems ................... 46
Organizational Problems ........................... 46Management Problems .............................. 46Financial Problems ............................... 46Coordination Problems .............................. 47
REFERENCES CITED ............................... 48
iv
Figures
la. Map showing relative potential ofdifferent parts of the conterminousUnited States to landsliding .................... 1
lb. Potential landslide hazard inMaine ............................. 2
2. Major damage from debris flow,Farmington,Utah ............................ 6 5
3. "Bucket brigade," Farmington, Utah ....... 54. Landslide losses in Japan 1938-1981 ...... 65. The relationship of people, landslides,
and disasters ............................ . 76. Aerial view of the Savage Island
landslide, Washington state .................. 107. Ruins of home destroyed in Kanawha
City, West Virginia ............................ 108a. Rockfall .118b. Rockfiall on U.S. Highway 6,
Colorado .119a. Topple .129b. Topple, western 'Colorado . 12lOa. Rotational slide .12lb. Rotational slide, Golden, Colorado . 1311. Translational slide .1312. Block slide .113a. Lateral spread .1413b. Lateral spread, Cortez, Colorado. 1414a. Creep .1414b. Creep, Mt. Vernon Canyon, Colorado .... 14
15. Debris fan formed by debris flows .......... 1516a. Earthiflow ................................. 1516b. Roan Creek Eartlilow, DeBeque,
Colorado ................................ 1517. Damage from Slide Mountain
landslide, Nevada ................................ 1618. Jackson Springs landslide,
Franklin D.Roosevelt Lake,Washington state ................................. 17
1L9. Aerial view of the Thistle landslide,Utah ................................ 18
20. Landslide inventory map, Durango,Colorado ................................. 23
21. Landslide inventory map, La Honda,California ................................. 24
22. Landslide susceptibility map, KingCounty, Washington ................................ 24
23. Earthquake landslide hazard map,San Mateo County, California ................ 25
24. Hazardous area warning sign ................ 3125. Warning system schematic ..................... 3226. Rudd Creek debris basin, Farmington,
Utah ................................ 3227. Retaining wall, Interstate 70,
Colorado ................................ 3328. Executive Order establishing
Colorado Natural Hazards MitigationCouncil .... 42
Tables
1. Estimates of minimum landslidedamage in the United States,1973-1983 ............................. 2
2. Techniques for reducing landslidehazards .............................. 8
3. Examples of resources available for-obtaining/transferring landslide
information ....................................... 26.4. Potential users of landslide hazard
information .............................. 275. Examples of producers and providers
of landslide hazard information ............... 296. Physical mitigation methods ..................... 337. Capability assessment checklist ............... 38
V
Foreword
There is a need for a comprehensive programto reduce landslide losses in the United Statesthat marshals the capability of all levels of gov-ernment and the private sector. Without such aprogram, the heavy and widespread losses tothe nation and to individuals from landslideswill increase greatly. Successful and cost-effec-tive landslide loss-reduction actions can andshould be taken in the many jurisdictions fac-ing landslide problems. The responsibility fordealing with landslides principally falls uponstate and local governments and the privatesector. The federal government can provide re-search, technical guidance, and limited fundingassistance, but to meet their responsibility formaintaining the public's health, safety andwelfare, state and local governments mustprevent and reduce landslide losses throughhazard mapping, land-use management, andbuilding and grading controls. In partnershipwith public interest groups and governments,the private sector must also increase its effortsto reduce landslide hazards.
Dramatic landslide loss reduction can beachieved. The effective use of landslide build-ing codes and grading ordinances by a few stateand local governments in the nation clearly
demonstrates that successful programs can beput into place with reasonable costs. Numerousexamples of responsible landslide hazardplanning and mitigation by private developersexist but are usually overshadowed by impro-per development that ignores the hazard.
Transfer of proven governmental and pri-vate sector landslide hazard mitigation tech-niques to other jurisdictions throughout thenation is one of the most effective ways of help-ing to reduce future landslide losses. Thisguide, prepared by the State of Colorado for theFederal Emergency Management Agency,builds upon the impressive efforts taken byColorado state and local governments in plan-ning for and mitigating landslide losses. TheFederal Emergency Management Agency hopesthat this guide and the accompanying plan forlandslide hazard mitigation will stimulate andassist other state and local governments, priv-ate interests, and citizens throughout the na-tion to reduce the landslide threat.
Arthur J. ZeizelProject OfficerFederal Emergency
Management Agency
vi
Acknowledgments
This project was funded in part by the FederalEmergency Management Agency TFEMA), theColorado Division of Disaster Emergency Serv-ices (DODES), the Colorado Geological Survey(CGS), and the U.S. Geological Survey (GrantNo. 14-08-0001-A0420).
The document was written and preparedby Robert L. Wold, Jr. (DODES) and Can-dace L. Jochim (CGS). Staffl contributorsincluded: William P. Rogers, Irwin M. Glass-man, and John 0. frulby. Additional contri-
butors included: David B. Prior of the CoastalStudies Institute of Louisiana State Universityand William J. Kockelman of the U.S. Geo-logical Survey. Project management was pro-vided by Arthur Zeizel (FEMA) and IrwinGlassman (DODES).
Other essential project personnel included:Cheryl Brchan (drafting and layout), NoraRimando (word processing), and DavidButler (editing).
Advisory Committee
John Beaulieu, Deputy State Geologist, Oregon
John P. Byrne, Director, Disaster Emergency Services,Colorado
William J. Kockelman, Planner, U.&. GeologicalSurvey, California
Peter Lessing, Environmental Geologist, WestVirginia Geological Survey
George Mader, President, William Spangle andAssociates, California
Dr. Robert L. Schuster, U.S. Geological Survey,Colorado
Dr. James E. Slosson, Chief Engineering Geologist,Slosson. and Associates, California
Darrell WalIer, State Coordinator, Bureau of DisasterServices, Idaho
vii
viii
Introduction
According to available information, landslidingin the United States causes an average of 25 to50 deaths (Committee on Ground Failure Haz-ards, 1985) and $1 to $2 billion in economiclosses annually (Schuster and Fleming, 1986).Although all 50 states are subject to landslideactivity, the Rocky Mountain, Appalachian, andPacific Coast regions generally suffer the great-est landslide losses (Figures la, b). The costs oflandsliding can be direct or indirect and rangefrom the expense of cleanup and repair orreplacement of structures to lost tax revenuesand reduced productivity and property values.
Landslide losses are growing in the UnitedStates despite the availability of successfultechniques for landslide management and
control. The failure to lessen the problem isprimarily due to the ever-increasing pressureof development in areas of geologically hazard-ous terrain and the failure of responsible gov-ernment entities and private developers torecognize landslide hazards and to apply ap-propriate measures for their mitigation, eventhough there is overwhelming evidence thatlandslide hazard mitigation programs serveboth public and privatPinterests by savingmany times the cost of implementation. Thehigh cost of landslide damage (Table 1) willcontinue to increase if community developmentand capital investments continue without tak-ing advantage of the opportunities that cur-rently exist to mitigate the effects of landslides.
Figure la. Map showing relative potential of different parts of the conterminous United Statesto landsliding (U.S. Geological Survey, 198 la).
1
Table 1. Estimates of minimum amounts oflandslide damage in the United States,1973-1983, in millions of dollars. All figuresare estimates. Figures queried are veryrough estimates (adapted from Brabb, 1984).
Damage 1973-1983State Priv. Ann.
Roads Prop. Total Avg.State ($M) ($M) ($M) ($M)
AlabamaAlaskaArizonaArkansasCaliforniaColoradoConnecticutDelawareDist. of ColumbiaFloridaGeorgiaHawaiiIdahoIllinoisIndianaIowaKansasKentuckyLouisianaMaineMarylandMassachusettsMichiganMinnesotaMississippiMissouriMontanaNebraskaNevadaNew HampshireNew JerseyNew MexicoNew YorkNorth CarolinaNorth DakotaOhioOklahomaOregonPennsylvaniaRhode IslandSouth CarolinaSouth DakotaTennesseeTexasUtahVermontVirginiaWashingtonWest VirginiaWisconsinWyoming
10.010.02.02.0
800.0?20.0
0.02.00.10.01.0?4.0
10.0?1.0
10.01.01.0
180.02.00.3
20.00.30.17.03.02.0?
10.0?0.42.0?
10.03.03.0
20.045.0
4.060.0?
2.0?30.050.0
0.00.0
16.0100.0
8.0200.0?
3.011.070.0?
270.00.24.0
0.50.00.00.0
200.0?50.0
0.00.00.10.00.00.51.0?1.0?1.00.30.3?
10.0?0.30.30.00.00.00.00.51.0?1.0?0.4?0.50.03.01.0
50.0?0.50.0
40.00.0
10.010.0?0.00.02.0
10.0?0.0
10.0?0.51.0
30.0?5.00.50.0
10.510.0
2.02.0
1000.0?70.0
0.02.00.010.01.0?4.5
11.0?2.0?
11.01.31.3?
190.0?2.30.6
20.00.30.17.03.53.0?
11.0?0.8?2.5?
10.06.04.0
70.0?45.54.0
100.0?2.0?
40.060.0?
0.00.0
18.0110.0?
8.0210.0?
3.512.0
100.0?275.0
0.74.0
1.051.00.20.2
100.0 ?7.00.00.20.80.00.1 ?0.451.1 ?0.2 ?1.10.130.13
19.0?0.230.062.00.030.010.70.350.3 ?1.1 ?0.08?0.25?1.00.60.47.0 ?4.550.4
10.00.2?4.06.00.00.01.8
11.0 ?0.8
21.0 ?0.351.2
10.0?27.50.070.4
EXPLANATION* High
' RMedium
m Low ?
D Low
w wJ Figure lb.Potential landslidehazard in Maine(Wiggins et al., 1978).
The widespread occurrence of landsliding,together with the potential for catastrophicstatewide and regional impacts, emphasizesthe need for cooperation among federal, state,and local governments and the private sector.Although annual landslide losses in the U.S.are extremely high, significant reductions infuture losses can be achieved through a comb-ination of landslide hazard mitigation andemergency management.
Landslide hazard mitigation consists ofthose activities that reduce the likelihood ofoccurrence of damaging landslides and mini-mize the effects of the landslides that do occur.The goal of emergency management is to mini-mize loss of life and property damage throughthe timely and efficient commitment of avail-able resources.
Despite their common goals, emergencymanagement and hazard mitigation activitieshave historically been carried out independ-ently. The integration of these two efforts ismost often demonstrated in the recovery phasefollowing a disaster, when decisions about re-construction and future land uses in the com-munity are made.
Emergency management, if well executed,can do much to minimize the loss and sufferingassociated with a particular disaster. However,unless it is guided by the goals of preventing orreducing long-term hazard losses, it is unlikelyto reduce the adverse impact of future disasters
2
Total (U.S.) 2010.3 442.2 2452.5 245.25
significantly. This is where mitigation becomesimportant (Advisory Board on the Built Envir-onment, 1983, p. 9).
Purpose of this GuidebookAs mentioned above, the development and im-plementation of landslide loss-reduction strate-gies requires the cooperation of many publicand private institutions, all levels of govern-ment, and private citizens. Coordinated andcomprehensive systems for landslide hazardmitigation do not currently exist in most statesand communities faced with the problem. Inmost states, local governments often take thelead by identiyring goals and objectives, con-trolling land use, providing hazard informationand technical assistance to property ownersand developers, and implementing mitigationprojects as resources allow. State and federalagencies play supporting roles-primarilyfinancial,, technical, and administrative. Insome cases, however, legislation originating atthe state or federal level is the sole impetus forstimulating effective local mitigation activity.
In many states there remains a need to de-velop long-term organizational systems at stateand local levels to deal with landslide hazardmitigation in a coordinated and systematicmanner. The development of a landslide hazardmitigation plan can be the initial step in theestablishment of state and local programs thatpromote long-term landslide loss reduction.
The purpose of this guidebook is to providea practical, politically feasible guide for stateand local officials involved in landslide hazardmitigation. The guidebook presents conceptsand a framework for the preparation of stateand local landslide hazard mitigation plans. Itoutlines a basic methodology, provides informa-tion on available resources, and offers suggest-ions on the formation of an interdisciplinarymitigation planning team and a permanentstate natural hazards mitigation organization.Individual states and local jurisdictions canadapt the suggestions in this book to meettheir own unique needs.
Because of its involvement in identifyingand mitigating landslide hazards, the state ofColorado was selected by the Federal Emer-gency Management Agency (FEMA) to producea prototype state landslide hazard mitigationplan. The technical information contained inthe plan was designed to be transferable toother states and local jurisdictions and suit-able for incorporation into other plans. Theplanning process can also serve as an exampleto other states and localities dealing with land-slide problems. The materials contained in theColorado Landslide Hazard Mitigation Plan(Colorado Geological Survey et al., 1988) wereintended to complement the information pre-sented in this guidebook. In an effort to pro-mote landslide hazard mitigation nationally,.FEMA has provided for the distribution ofthese two documents to all states. L
3
Landslide Losses andthe Benefits of Mitigation
The Landslide Hazar,Landsliding is a natural process whicand recurs in certain geologic settingEcertain conditions. The rising costs ofdamages are a direct consequence of tcreasing vulnerability of people and s-to the hazard. In most regions, the ovof occurrence and severity of naturallylandslides has not increased. What hied is the extent of human occupation,lands and the impact of human activithe environment. Many landslide danhave occurred might have been prevelavoided if accurate landslide hazard ition had been available and used.
Economic and Social Imlof Landsliding
Costs of LandslidingThe most commonly cited figures on Ilosses are $1 to $2 billion in economicand 25 to 50 deaths annually. HowevEfigures are probably conservative bec,were generated in the late 1970s. Sinitime, the use of marginally suitable lEincreased, as has inflation. Furthermiare no exhaustive compilations of lanidata for the United States, so these figbasically extrapolations of the availal
The high losses from landsliding;trated in Table 1. Surveys indicate thuto private property accounts for 30 tocent of the total costs (U.S. Geological1982). Examples of costs associated wdual landslide events from representsareas across the country include:
ALASKA-It has been estimated1978) that 60 percent of the $300 millage from the 1964 Alaska earthquakedirect result of landslides.
d; CALIFORNIA-In 1982 in the San Fran-
h occurs cisco Bay Region, 616 mm (24.3 in.) of rain fellh under in 34 hours causing thousands of landslideslandslide \ which killed 25 people and caused more than
the in- $66 million in damage (Keefer et al., 1987).tructures : TEXAS-In Dallas in the 1960s, a toppl-erall rate ing failure occurred in a vertical exposure of ay caused ; geological formation known as the Austinas increas- Chalk. This closed two lanes of a major down-of these town thoroughfare for eight months. Costs ofties on construction of remedial measures and con-nages that struction delays amounted to about $2.8 mil-
nited or lion (Allen and Flanigan, 1986).informa- V UTAH-In 1983, a massive landslide dam-
med Spanish Fork Canyon, creating a lake.The landslide buried sections of the Denver andRio Grande Western Railroad and U.S. High-
aacts ways 6, 50, and 89 and inundated the town ofThistle. The estimated total losses and recon-struction costs due to this one landslide rangefrom $200 million (University of Utah, Bureau
andslide of Economic and Business Research, 1984) tolosses $600 million (Kaliser and Slosson, 1988).
or, these WEST VIRGINIA-In 1975, landslideiuse they movements in colluvial soil damaged 56 housesce that in McMechen, West Virginia, located on a hill-ind has side above the Ohio River. This landslide wasore, there attributed to above normal precipitation. Mit-islide loss igation was accomplished by grading andgures are surface and subsurface drainage (Gray and)le data. Gardner, 1977).are illus-atdamage Impacts and Consequences50 per- of Landslidingl Survey, Economic losses due to landsliding include bothith indivi- direct and indirect costs. Schuster and FlemingLtive (1986) define direct costs as the costs of re-
placement, repair, or maintenance due to dam-I (Youd, age to property or facilities within the actualion dam- boundaries of a landslide (Figure 2). Suchwas the facilities include highways, railroads, irrigation
canals, underwater communication cables,
4
offshore oil platforms, pipelines, and dams. The cost of cleanup must also be included (Figure 3). All other landslide costs are considered to be indirect. Examples of indirect costs given by Schuster and Fleming (1986) include:
(1) reduced real estate values, (2) loss of productivity of agricultural or
forest lands, (3) loss of tax revenues from properties
devalued as a result of landslides, (4) costs of measures to prevent or mitigate
future landslide damage, (5) adverse effects on water quality in
streams, (6) secondary physical effects, such as
landslide-caused flooding, for which the costs are both direct and indirect,
injury or death. (7) loss of human productivity due to
Other examples are: (8) fish kills, (9) costs of litigation. In addition to economic losses, there are
intangible costs of landsliding such as personal stress, reduced quality of life, and the destruc- tion of personal possessions having great sen- timental value. Because costs of indirect and intangible losses are difficult or impossible to calculate, they are often undervalued or ignor- ed. If they are taken into account, they often produce highly variable estimates of damage for a particular incident.
Figure 2. Major damage to homes in Farmington, Utah as a result of 1983 Rudd Creek mudslide (photograph by Robert Kistner, Kistner and Associates).
Figure 3. Local volunteers form "bucket brigade" to help clean mud and debris from homes in Farmington, Utah in 1983 (photograph by Robert Kistner, Kistner and Associates).
Long-Term Benefits of Mitigation Studies have been conducted to estimate the potential savings when measures to minimize the effects of landsliding are applied. One early study by Alfors et al. (1973) attempted to fore- cast the potential costs of landslide hazards in California for the period 1970-2000 and the effects of applying mitigative measures. Under the conditions of applying all feasible measures at state-of-the-art levels (for the 1970s), there was a 90 percent reduction in losses for a bene- fit/cost ratio of 8.7:1, or $8.7 saved for every $1 spent. Nilsen and Turner (1975) estimated that approximately 80 percent of the landslides in Contra Costa County, California are related to human activity. In Allegheny County, Penn- sylvania, 90 percent are related to such activity according to Briggs et al. (1975).
are directly related to construction activities, appropriate grading codes can significantly decrease landslide losses in urban areas. Slos- son (1969) compared landslide losses in Los Angeles for those sites constructed prior to 1952, when no grading codes existed and soils engineering and engineering geology were not required, with losses sustained at sites after such codes were enacted. He found that the monetary losses were reduced by approximat- ely 97 percent.
Because most landslides triggered by man
5
The Cincinnati, Ohio StudyIn 1985, the U.S. Geological Survey, in cooper-ation with the Federal Emergency ManagamentAgency, conducted a geologic/economic develop-ment study in the Cincinnati, Ohio area. Thisstudy developed a systematic approach toquantitative forecasting of probable landslideactivity. Landslide probabilities derived from areproducible procedure were combined withproperty value data to forecast the potentialeconomic losses in scenarios for proposeddevelopment and to quantitatively identify thepotential benefits of mitigation activities.
The study area was divided into 14,255grid cells of 100-square meters each. Informa-tion calculated for each cell included: probabil-ity of landslide occurrence, economic loss in theevent of a landslide, cost of mitigation, andeconomic benefit of mitigation. This informa-tion was used to develop a mitigation strategy.In areas where both slope and shear strengthinformation were available, the optimum strat-egy required mitigation in those cells withslopes steeper than 14 degrees or where mater-ials had effective residual stress friction anglesof less than 26 degrees. This strategy yielded$1.7 million in estimated annualized net bene-fits for the community. In areas where onlyslope information was used, the best strategyrequired mitigation in those cells where slopeswere greater than 8 degrees. This yielded anestimated annualized net benefit of $1.4 mil-lion. Therefore, using regional geologic inform-ation in addition to slope information resultedin an additional $300,000 net benefit. TheCincinnati study cost only $20,000 to prepare(Bernknopf et al., 1985).
The Benefits of Mitigation in JapanJapan has what is considered by many to bethe world's most comprehensive landslide lossreduction program. In 1958, the Japanese gov-ernment enacted strong legislation that provid-ed for land-use planning and the constructionof check dams, drainage systems, and otherphysical controls to prevent landslides. Thesuccess of the program is indicated by thedramatic reduction in losses over time (Figure4). In 1938, 130,000 homes were destroyed andmore than 500 lives were lost due to landslides
in the Kobe area. However, since the Japaneseprogram went into effect, losses have decreaseddramatically. In 1976-one of Japan's worstyears for landsliding-only 2000 homes weredestroyed with fewer than 125 lives lost(Schuster and Fleming, 1986).
NUMBER OF DEAD OR
0 0 0 0 C C 000o
JULY 1938
JULY 1945
SEPT. 1947
JULY 1951
JUNE 1953
E JULY 1953
o AUG.1953
0 SEPT. 1958
Z AUG. 1959
Ln JUNE 1961
C0 SEPT. 1966
1 JULY 1967
Ad JULY 1967
-) JULY1972
z AUG.1972
-I JULY 1974
= AUG.19750e AUG.1975
SEPT.1976
MAY1978
OCT.1978
AUG.1979
AUG.1981
MISSING [TOP BAR)
-CD > 0 - - -
_ U U U U - - - - - -II'130,000
r _ _ _ _--- I - _ _ ,15,141
* _ _ _ U em U .. _ r19.754W
r
I-
r
I
- 0 0 0 N 0 0 0 0; CM CO 0 e N rcc 0 R o
NUMBER OF HOUSES DESTROYED OR BADLYDAMAGED [BOTTOM BAR]
Figure 4. Losses due to major landslidedisasters (mainly debris flows) in Japan from1938-1981. All of these landslides werecaused by heavy rainfall, most commonlyrelated to typhoons, and many were assoc-iated with catastrophic flooding (data fromMinistry of Construction, Japan, 1983).
Planning as a Means of LossReduction
The extent and severity of the landslide hazardin a particular area will determine the need fora landslide hazard mitigation plan.
6
1111
Communities that have landslide prob-lems are encouraged to assess the costs ofdamage to public and private property andweighl those costs against the costs of a land-slide reduction program. The prevention of asingle major landslide in a community maymore than compensate for the effort and cost ofimplementing a control program (Fleming andTaylor, 1980, p. 20).
Avoiding the costs of litigation is an addi-tional incentive to undertaking a local programof landslide hazard mitigation.
When landslide disasters do occur, the ex-istence of a program for loss reduction shouldhelp ensure that redevelopment planning takesexisting geologic hazards into account.
In the U.S., only a few communities haveestablished successful landslide loss reductionprograms. The most notable is Los Angeles,where, as mentioned above, loss reductions of97 percent have been achieved for new con-struction since the implementation of moderngrading regulations (Slosson and Krohn, 1982).
In communities that have achieved lossreductions, decisions about building codes,zoning, and land use take into account identi-fied landslide hazards. The U.S. GeologicalSurvey (1982) has found that these conuni-ties have in conmnon four preconditions leadingto successful mitigation programs: (1) anadequate base of technical information aboutthe local landslide problem, (2) an "able andconcerned" local government, (3) a technicalcommunity able to apply and add to the tech-nical planning base, and (4) an informed pop-ulation that supports mitigation program ob-jectives. While the technical expertise to reducelandslide losses is currently available in moststates, in many cases it is not being utilized.Still, the success of loss reduction measuresclearly depends upon the will of leaders topromote and support mitigation initiatives.
Local Government RolesAt the local government level, hazard mitiga-tion is often a controversial issue. Staff andelected officials of local governments areusually subjected to diverse and sometimesconflicting pressures regarding land use anddevelopment. Local officials, as well as build-ers, realtors, and other parties in the develop-ment process, are increasingly being held liable
for actions, or failures to act, that are deter-mined to contribute to personal injuries andproperty damages caused by natural hazards.Consequently, a model community landslidehazard management planning process shouldencourage citizen participation and review inorder to identity and address the perspectivesand concerns of the various community groupsaffected by landslide hazards.
Because most landslide damages are relat-ed to human activity-mainly the constructionof roads, utilities, homes, and businesses-thebest opportunities for reducing landslidehazards are found in land-use planning andthe .administration and enforcement of codesand ordinances.
The vulnerability of people to natural haz-ards is determined by the relationship betweenthe occurrences of extreme events, the proximi-ty of people to these occurrences, and thedegree to which the people are prepared to copewith these extremes of nature. The concept of ahazard as the intersection of the human sys-tem and the physical system, is illustrated inFigure 5. Only when these two systems are inconflict, does a landslide represent a hazard topublic health and safety.
Figure 5 The relationship of people, land-slides, and hazards (modified from ColoradoWater Conservation Board et a., 1985).
The effectiveness of local landslide mitiga-tion programs is generally tied to the abilityand determination of local officials to apply themitigation techniques available to them tolimit and guide growth in hazardous areas. Alist of 27 techniques that planners and mana-
7
gers may use to reduce landslide hazards intheir communities is presented in Table 2. Thekey to achieving loss reduction is the identifica-tion and implementation of specific mitigationinitiatives, as agreed upon and set forth in alocal or state landslide hazard mitigation plan.
Table 2. Techniques for reducing landslidehazards (Kockelman, 1986).
Discouraging new developments in hazardousareas by:
Disclosing the hazard to real-estate buyersPosting warnings of potential hazardsAdopting utility and public-facility
service-area policiesInforming and educating the publicMaking a public record of hazards
Removing or converting existing developmentthrough:
Acquiring or exchanging hazardousproperties
Discontinuing nonconforming usesReconstructing damaged areas after
landslidesRemoving unsafe structuresClearing and redeveloping blighted areas
before landslides
Providing financial incentives or disincentivesby:
Conditioning federal and state financialassistance
Clarifying the legal liability of propertyowners
Adopting lending policies that reflect riskof loss
Requiring insurance related to level ofhazard
Providing tax credits or lower assessmentsto property owners
Regulating new development in hazardousareas by:
Enacting grading ordinancesAdopting hillside-development regulationsAmending land-use zoning districts and
regulationsEnacting sanitary ordinancesCreating special hazard-reduction zones
and regulationsEnacting subdivision ordinancesPlacing moratoriums on rebuilding
Protecting existing development by:Controlling landslides and slumpsControlling mudflows and debris-flowsControlling rockfallsCreating improvement districts that
assess costs to beneficiariesOperating monitoring, warning, and
evacuating systems
Although certain opportunities forreducing landslide losses exist at the stategovernment level (selection of sites for schools,hospitals, prisons, and other public facilities;public works projects that protect highwaysand state property), the greatest potential formitigation is in the routine operations of localgovernment: the adoption and enforcement ofgrading and construction codes and ordinances,the development of land-use and open-spaceplans, elimination of nonconforming uses,limitation of the extension of public utilities,etc. For this reason, state mitigation plansshould emphasize mitigation activities thatwill essentially encourage and support localefforts. Local mitigation plans should provideguidelines and schedules for accomplishinglocal mitigation projects, as well as identifyprojects beyond local capability that should beconsidered in the state plan. U
8
Causes and Types of Landslides
What is a Landslide?The term "landslide" is used to describe a widevariety of processes that result in the percept-ible downward and outward movement of soil,rock, and vegetation under gravitational influ-ence. The materials may move by: falling, top-pling, sliding, spreading, or flowing.
Although landslides are primarily associ-ated with steep slopes, they also can occur inareas of generally low relief. In these areaslandslides occur as cut-and-fill failures (high-way and building excavations), river bluff fail-ures, lateral spreading landslides, the collapseof mine-waste piles (especially coal), and a widevariety of slope failures associated with quar-ries and open-pit mines. Underwater landslideson the floors of lakes or reservoirs, or inoffshore marine settings, also usually involveareas of low relief and small slope gradients.
Why Do Landslides Occur?Landslides can be triggered by both naturaland man-induced changes in the environment.The geologic history of an area, as well asactivities associated with human occupation,directly determines, or contributes to the con-ditions that lead to slope failure. The basiccauses of slope instability are fairly well known.They can be inherent, such as weaknesses inthe composition or structure of the rock or soil;variable, such as heavy rain, snowmelt, andchanges in ground-water level; transient, suchas seismic or volcanic activity; or due to newenvironmental conditions, such as thoseimposed by construction activity (Varnes andthe International Association of EngineeringGeology, 1984).
Human ActivitiesHuman activities triggering landslides aremainly associated with construction and invol-ve changes in slope and in surface-water and
ground-water regimes. Changes in slope resultfrom terracing for agriculture, cut-and-fillconstruction for highways, the construction -ofbuildings and railroads, and mining operations.If these activities and facilities are ill-conceiv-ed, or improperly designed or constructed, theycan increase slope angle, decrease toe or lateralsupport, or load the head of an existing or pot-ential landslide. Changes in irrigation or sur-face runoff can cause changes in surface drain-age and can increase erosion or contribute toloading a slope or raising the ground-watertable (Figure 6). The ground-water table canalso be raised by lawn watering, waste-watereffluent from leach fields or cesspools, leakingwater pipes, swimming pools or ponds, andapplication or conveyance of irrigation water. Ahigh ground-water level results in increasedpore-water pressure and decreased shearstrength, thus facilitating slope failure. Con-versely, the lowering of the ground-water tableas a result of rapid drawdown by water supplywells, or the lowering -of a lake or reservoir, canalso cause slope failure as the buoyancy pro-vided by the water decreases and seepagegradients steepen.
Natural FactorsThere are a number of natural factors that cancause slope failure. Some of these, such aslong-term or cyclic climate changes, are not dis-cernible without instrumentation and/orlong-term record-keeping.
ClimateLong-term climate changes can have a signifi-cant impact on slope stability. An overall de-crease in precipitation results in a lowering ofthe water table, as well as a decrease in theweight of the soil mass, decreased solution ofmaterials, and less intense freeze-thaw activity.An increase in precipitation or ground satura-tion will raise the level of the ground-water
.9
table, reduce shear strength, increase the weight of the soil mass, and may increase erosion and freeze -thaw activity. Periodic high-intensity precipitation and rapid snow- melt can signifcantly increase slope instability temporarily (Figure 7).
Erosion Erosion by intermittent running water (gully
Figure 7. The remains of a
house where three children died in a
mudflow in Kanawha City, West Virginia. The movement was triggered by heavy
rainfall from a cloud- burst on July 9, 1973 (Lessing et al., 1976).
Figure 6. Aerial view of the Savage Island land- slide on the east shore of the Columbia River, Washington, 1981. This landslide was caused by irrigation water (photograph by Robert L. Schuster, U.S. Geological Survey).
ing), streams, rivers, waves or currents, wind, and ice removes toe and lateral slope support of potential landslides.
Weathering Weathering is the natural process of rock deter- ioration which produces weak, landslide-prone materials. I t is caused by the chemical action of air, water, plants, and bacteria and the physical
10
action brought on by changes in temperature (expansion and shrinkage), the freeze-thaw cycle, and the burrowing activity of animals.
Earthquakes Earthquakes not only trigger landslides, but, over time, the tectonic activity causing them can create steep and potentially unstable slopes.
Rapid sedimentation Rivers supply very large amounts of sediment to deltas in lakes and coastal areas. The rapid- ly deposited sediments are frequently under- consolidated, and have excess pore-water pressures and low strengths. Such deltaic sediments are often prone to underwater delta-front landsliding, especially where the sediments are rich in clay and/or contain gas from organic decomposition.
Wind-generated waves Storm waves in coastal areas are known to trigger underwater landsliding in deltas by cyclically loading weak bottom sediments.
Tidal or river drawdown Rapid lowering of water level in coastal areas or along river banks due to tides or river dis- charge fluctuations can cause underwater land- sliding. The process in which weak river bank or deltaic sediments are left unsupported as the water level drops is known as "drawdown."
Types of Landslides The most common types of landslides are des- cribed below. These definitions are based mainly on the work of Varnes (1978).
Falls Falls are abrupt movements of masses of geologic materials that become detached from steep slopes or cliffs (Figures 8a, b). Movement occurs by free-fall, bouncing, and rolling. De- pending on the type of earth materials invol- ved, the result is a rockfall, soilfall, debris fall, earth fall, boulder fall, and so on. All types of falls are promoted by undercutting, differential weathering, excavation, or stream erosion.
Topple A topple is a block of rock that tilts or rotates forward on a pivot or hinge point and then
~
I FIRM BEDDED ROCK
Figure 8a. Rockfall (Colorado Geological Survey et al., 1988).
Figure 86. Rockfall on US. Highway 6, Colorado (photograph by Colorado Geological Survey).
separates from the main mass, falling to the slope below, and subsequently bouncing or rolling down the slope (Figures 9a, b).
Slides Although many types of mass movement are included in the general term "landslide," the more restrictive use of the term refers to move- ments of soil or rock along a distinct surface of rupture which separates the slide material from more stable underlying material. The two major types of landslides are rotational slides and translational slides.
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Figure 9a. Topple (Colorado Geological Survey et al., 1988).
Figure 9b. Topple, western Colorado (photo- graph by Colorado Geological Survey).
Rotational slide A rotational slide is one in which the surface of rupture is curved concavely upward (spoon shaped) and the slide movement is more or less rotational about an axis that is parallel to the contour of the slope (FigureslOa, b). A "slump" is an example of a small rotational slide.
Translational slide In a translational slide, the mass moves out, or down and outward along a relatively planar surface and has little rotational movement or backward tilting (Figure 11). The mass com- monly slides out on top of the original ground surface. Such a slide may progress over great
Figure 1 Oa. Rotational landslide (modified from Varnes, 1978).
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I$ " m A
Figure 1 Ob. Rotational landslide, Golden, Colorado (photograph by Colorado Geological Survey).
distances if conditions are right. Slide material may range from loose unconsolidated soils to extensive slabs of rock.
GROUND SURFACE
Figure 11. Translational slide (Colorado Geological Survey et a/., 1988).
Block Slide. A block slide is a translational slide in which the moving mass consists of a single unit, or a few closely related units that move downslope as a single unit (Figure 12).
Lateral Spreads Lateral spreads (Figures 13a, b) are a result of the nearly horizontal movement of geologic
materials and are distinctive because they usually occur on very gentle slopes. The fail- ure is caused by liquefaction, the process whereby saturated, loose, cohesionless sedi- ments (usually sands and silts) are trans- formed from a solid into a liquefied state; or plastic flow of subjacent material. Failure is usually triggered by rapid ground motion such as that experienced during an earthquake, or by slow chemcal changes in the pore water and mineral constituents.
SLIP SURFACE
Figure 12. Block slide (Colorado Geological Survey et al., 1988).
Flows
Creep Creep is the imperceptibly slow, steady downward movement of slope-forming soil or rock. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or terracettes (Figures 14a, b).
Debris flow A debris flow is a form of rapid mass movement in which loose soils, rocks, and organic matter combine with entrained air and water to form a slurry that then flows downslope. Debris-flow areas are usually associated with steep gullies. Individual debris-flow areas can usually be identified by the presence of debris fans a t the termini of the drainage basins (Figure 15).
Debris avalanche A debris avalanche is a variety of very rapid to extremely rapid debris flow.
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Earthf low Earthflows have a characteristic "hourglass" shape (Figures 16a, b). A bowl or depression forms a t the head where the unstable material collects and flows out. The central area is narrow and usually becomes wider as it reach- es the valley floor. Flows generally occur in fine-grained materials or clay-bearing rocks on moderate slopes and with saturated conditions. However, dry flows of granular material are also possible.
Mudflow A mudflow is an earthflow that consists of material that is wet enough to flow rapidly and that contains at least 50 percent sand-, silt-, and clay-sized particles.
Lahar A lahar is a mudflow or debris flow that origin- ates on the slope of a volcano. Lahars are usually triggered by such things as heavy rain- fall eroding volcanic deposits; sudden melting
Figure 13a. Lateral spread (Colorado Geological Survey et al., 1988).
Figure 136. Lateral spread, Cortez, Colorado. (Photograph by Colorado Geological Survey).
of snow and ice due to heat from volcanic vents; or by the breakout of water from glaciers, crat- er lakes, or lakes dammed by volcanic eruptions.
SPREADING
OUT OF ALIGNMENT
Figure 14a. Creep (Colorado Geological Survey et al., 1988).
Figure 146. Creep, vicinity of Mt. Vernon Canyon, Jefferson County, Colorado (photo- graph by Colorado Geological Survey).
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Figure 15. Debris fan formed by debris flows (Colorado Geological Survey et al., 1988).
7gure 16a. Earth flow (modified from Varnes, 19 78).
Figure 166. Roan Creek earthflow near DeBeque, Colorado, 1985 (photograph by Colorado Geological Survey).
Subaqueous landslide * Landslides which take place principally or tot- ally underwater in lakes, along river banks, or in coastal and offshore marine areas are called subaqueous landslides. The failure of subaque- ous slopes may result from a variety of factors acting singly or together, including rapid lacus- trine or marine sedimentation, biogenic meth- ane gas in sediments, surface water storm waves, current scour, water level drawdown, depositional oversteeping, or earthquake stresses. Many different types of subaqueous landslides have been identified in different locations, including rotational and translation- al slides, debris flows and mudflows, sand and silt liquefaction flows. There is also evidence that, in some circumstances, subaqueous land- slides evolve into or initiate turbidity currents, which may flow underwater a t high speeds for long distances. Subaqueous landslides pose pro- blems for offshore and river engineering, parti- cularly for the construction and maintenance of jetties, piers, levees, offshore platforms and facilities, and for sea-bed installations such as pipelines and telecommunications cables.
Inter relations h i p of La ndsl id i ng with Other Natural Hazards (The
Multiple Hazard Concept) Natural hazards often occur simultaneously or, in some cases, one hazard triggers another. For example, an earthquake may trigger a land- slide, which in turn may block a valley causing upstream flooding. Different hazards may also occur at the same time as the result of a com- mon cause. For example, heavy precipitation or rapid snowmelt can cause debris flows and flooding in the same area.
The simultaneous or sequential occurrence of interactive hazards may produce cumulative effects that differ significantly from those ex- pected from any one of the component hazards.
Landsliding and Dam Safety The safety of a dam can be severely compromis- ed by landsliding upstream from the dam or on slopes bordering the dam's reservoir or abut- ments. Possible impacts include (1) the forma- *Discussion by D.B. Prior
15
tion of wave surges that can overtop the dam, (2) increased sedimentation with resulting loss of storage, and (3) dam failure.
Flood surges can be generated either by the sudden detachment of large masses of earth into the reservoir, or by the formation and subsequent failure of a landslide dam across an upstream tributary stream channel. Waves formed by such failures can overtop the dam and cause serious downstream flooding without actually causing structural failure of the dam.
Landsliding into upstream areas or reser- voirs can greatly increase the amount of sedi- ment that is deposited in the reservoir, ulti- mately reducing storage capacity. This increas- es the likelihood that the dam will be over- topped during periods of excessive runoff, caus- ing downstream flooding. Excessive sedimenta- tion can also damage pumps and intake valves associated with water systems and hydroelec- tric plants.
Actual dam failure could be caused by landsliding at or near the abutments or in the embankments of earthen dams.
Slide Mountain in Nevada. The mass slid into Upper Price Lake, an irrigation reservoir, dis- placing most of the water which overtopped and breached the dam, flowing into Lower Price Lake. This lake's dam was also breached. The water flowed into Ophir Creek where it collect- ed large amounts of debris and became a debris
In 1983 a large mass of rock detached from
flow. After traveling about four kilometers and dropping 600 meters in elevation, the debris flow emerged from the canyon onto the alluvial fan of Ophir Creek (total time-15 minutes). One person was killed, four injured, and num- erous houses and vehicles were destroyed (Figure 17) (Watters, 1988).
Rapid changes in the water level of res- ervoirs can also trigger landslides. When the water level in the reservoir is lowered (rapid drawdown), the subsequent loss of support provided by the water and increased seepage pressure can initiate sliding (Figure 18). Al- ternatively, the increase in saturation caused by rising water can trigger landslides on slopes bordering the reservoir.
Eisbacher and Clague (1984) describe an excellent example of the potential impacts of landsliding on dam safety: the 1963 Vaiont dam disaster in Italy. The Vaiont Dam, a hydroelectric dam, was completed in 1960 to impound the Vaiont Torrent, a major tributary of the Piave River in the southern Alps of Italy. The dam is 261 m high and spans a steep narrow gorge. The southern wall of the valley behind the dam is a steep dip slope. Within two months after the reservoir was filled, a 0.7 x 106 m3 mass of rock slumped away along the submerged toe of the southern embankment. Over time, deep-seated movement of the slope occurred in response to changing levels of the reservoir. As a result of these movements,
Figure 17. House destroyed by 1983 Slide Mountain, Nevada landslide (photograph by Robert J. Watters, University of Nevada, Reno).
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Figure 18. Jackson Springs landslide on the Spokane arm of Franklin D. Roosevelt Lake, Washington, 1969. This landslide was triggered by extreme drawdown of the lake (photograph by the U S . Bureau of Reclamation).
monitoring instruments were set up on the slope.In August and September of 1963, preci- pitation in the Piave Valley was three times higher than normal and infiltration of the precipitation into the slope probably contribut- ed to its eventual failure. The day before the catastrophic slope failure creep rates of 40cdday were registered.
On October 9-10, 1963, in the night, a large slab of the unstable slope failed and slipped into the reservoir. The volume of mater- ial was estimated to be 250 x 106 m3 (a slab 250 m thick). A wall of water 250 m high surged up the opposite side of the valley, then turned and overtopped the dam. The concrete dam held, and the wall of water (30 x lo6 m3) dropped into the narrow gorge below, scouring loose debris as it went and destroying several communities below the dam. At least 1,900 people were killed.
remained after the disaster, as a monument. The site of the dam has been left as it
Landsliding and Flooding Landsliding and flooding are closely allied because both are related to precipitation, run- off, and ground saturation. In addition, debris flows usually occur in small, steep stream channels and often are mistaken for floods. In fact, these events frequently occur simultane- ously in the same area, and there is no distinct line differentiating the two phenomena.
Landslides and debris flows can cause flooding by forming landslide dams that block valleys and stream channels, allowing large amounts of water to back-up (Figure 19). This causes backwater flooding and, if the dam breaks, subsequent downstream flooding. Also, soil and debris from landslides can "bulk" or add volume to otherwise normal stream flow or cause channel blockages and diversions crest- ing flood conditions or localized erosion. Fin- ally, large landslides can negate the protective functions of a dam by reducing reservoir capa- city or creating surge waves that can overtop a
17
dam, resulting in downstream flooding (asdescribed above).
In turn, flooding can cause landsliding.Erosion, due to rapidly moving flood waters,often undercuts slopes or cliffs. Once support isremoved from the base of saturated slopes,landsliding often ensues.
Landsliding and Seismic ActivityMost of the mountainous areas that are vul-nerable to landslides have also experienced atleast moderate seismicity in historic times.The occurrence of earthquakes in steeplandslide-prone areas greatly increases thelikelihood that landslides will occur and in-creases the risk of serious damage far beyondthat posed individually by the two processes.
Landslide materials can be dilated by seismicactivity and thus be subject to rapid infiltrationduring rainfall and snowmelt. Some areas ofhigh seismic potential such as the New MadridSeismic Zone of the lower Mississippi Rivervalley may be subject to liquefaction and relat-ed ground failure.The Great Alaska Earth-quake of March 27, 1964 caused an estimated$300 million in damages. As mentioned eariler,60 percent of this was due to ground failure.Five landslides caused about $50 million dam-age in the city of Anchorage. Lateral spreadfailures damaged highways, railroads, andbridges, costing another $50 million. Flow fail-ures in three Alaskan ports carried awaydocks, warehouses, and adjacent transporta-tion facilities accounting for another $15
Figure 19. Aerial view of the Thistle landslide, Utah, 1983. This landslide dammed the SpanishFork River creating a lake which inundated the town of Thistle and severed three majortransportation arteries (photograph by Robert L. Schuster, U.S. Geological Survey).
18
million. Much of the landsliding was a directresult of the effect of the severe ground shak-ing on the Bootlegger Cove Formation. Theshaking caused loss of strength in clays andliquefaction in sand and silt lenses (U.S.Geological Survey, 1981a).
Landsliding and Volcanic ActivityThe May 18, 1980 eruption of Mount St. Helensin Washington state triggered a massive land-slide on the north flank of the mountain. Thevolume of material moved was estimated to be2.73 km 3. The landslide effectively depressur-ized the interior of the volcano; superheated
waters turned into steam and magmatic gasesalso expanded, resulting in a giant explosion(U.S. Geological Survey, 1981b).
Because human activity had been restrict-ed in the Mount St. Helens area due to pre-dictions of an eruption, loss of life was mini-mized. However, the eruption devastated landas far as 29 km from the volcano. The resultinglateral blast, landslides, debris avalanches,debris flows, and flooding took 57 lives andcaused an estimated $860 million in damage(Advisory Committee on the InternationalDecade for Natural Hazard Reduction, 1987). 0
19
(ChLRJIS 4Hazard Identification, Assessment,and Mapping
Hazard AnalysisRecognition of the presence of active or poten-tial slope movement, and of the types andcauses of the movement, is essential to land-slide mitigation. Recognition depends on anaccurate evaluation of the geology, hydrogeol-ogy, landforms, and interrelated factors such asenvironmental conditions and human activi-ties. Only trained professionals should conductsuch evaluations. However, because local gov-ernments may need to contract for such ser-vices, they should be aware of the techniquesavailable and their advantages and limitations.
Techniques for recognizing the presence orpotential development of landslides include:
* map analysis* analysis of aerial photography and
imagery* analysis of acoustic imagery and profiles* field reconnaissance* aerial reconnaissance* drilling* acoustic imaging and profiling* geophysical studies* computerized landslide terrain analysis* instrumentation
Map AnalysisMap analysis is usually one of the first steps ina landslide investigation. Maps that can beused include geologic, topographic, soils, andgeomorphic. Using knowledge of geologic mat-erials and processes, a trained person can ob-tain a general idea of landslide susceptibilityfrom such maps.
Analysis of Aerial Photographyand Imagery
The analysis of aerial photography is a quickand valuable technique for identifying land-slides, because it provides a three-dimensionaloverview of the terrain and indicates human
activities as well as much geologic information.In addition, the availability of many types ofaerial imagery (satellite, infrared, radar, etc.)make this a very versatile technique.
Analysis of Acoustic Imageryand Profiles*
Profiles of lake beds, river bottoms, and the seafloor can be obtained using acoustic techniquessuch as side-scan sonar and subbottom seismicprofiling. Surveying of controlled grids, withaccurate navigation, can yield three-dimension-al perspectives of subaqueous geologic phenom-ena. Modern, high resolution techniques areused routinely in offshore shelf areas to mapgeologic hazards for offshore engineering.Surveying and mapping standards for outercontinental shelf regions are regulated by theU.S. Minerals Management Service.
Field ReconnaissanceMany of the more subtle signs of slope move-ment cannot be identified on maps or photo-graphs. Indeed, if an area is heavily forested orhas been urbanized, even major features maynot be evident. Furthermore, landslide featureschange over time on an active slide. Thus, fieldreconnaissance is necessary to verify or detectmany landslide features.
Aerial ReconnaissanceLow-level flights in helicopters or small air-craft can be used to obtain a rapid and directoverview of a site.
DrillingAt most sites, drilling is necessary to determinethe type of earth materials involved in the slide,the depth to the slip surface and thus the thick-ness and geometry of the landslide mass, thewater-table level, and the degree of disruption
*By D.B. Prior
20
of the landslide materials. It can also providesamples for age-dating and testing the engin-eering properties of landslide materials. Fin-ally, drilling is needed for installation of somemonitoring instruments and hydrologic obser-vation wells.
Geophysical StudiesGeophysical techniques (the study of changesin the earth's gravitational and electricalfields, or measurement of induced seismic be-havior) can be used to determine some subsur-face characteristics such as the depth to bed-rock, zones of saturation, and sometimes theground-water table. It can also be used to de-termine the degree of consolidation of subsur-face materials and the geometry of the unitsinvolved. In most instances these methods canbest be used to supplement drilling informa-tion. Monitoring of natural acoustic emissionsfrom moving soil or rock has also been used inlandslide studies.
Computerized Landslide TerrainAnalysis
In recent years computer modeling of land-slides has been used to determine the volumeof landslide masses and changes in surfaceexpression and cross section over time. Thisinformation is useful in calculating the poten-tial for stream blockage, cost of landslideremoval (based on volume), and type and mech-anism of movement. Very promising methodsare being developed utilizing digital elevationmodels (DEMs) to evaluate areas quickly fortheir susceptibility to landslide/debris-flowevents (Filson, 1987; Ellen and Mark, 1988).Computers are also being used to performcomplex stability analyses. Software programsfor these studies are readily available for per-sonal computers.
InstrumentationSophisticated methods such as electronicdistance measuring (EDM); instruments suchas inclinometers, extensometers, strain meters,tiltmeters, and piezometers; and simple tech-niques such as establishing control pointsusing stakes can all be used to determine themechanics of landslide movement and to warnagainst impending slope failure.
Anticipating the LandslideHazard
One of the guiding principles of geology is thatthe past is the key to the future. In evaluatinglandslide hazards this means that future slopefailures will probably occur as a result of thesame geologic, geomorphic, and hydrologicsituations that led to past and present failures.Based on this assumption, it is possible toestimate the types, frequency of occurrence,extent, and consequences of slope failures thatmay occur in the future. However, the absenceof past events in a specific area does not pre-clude future failures. Man-induced conditionssuch as changes in the natural topography orhydrologic conditions can create or increase anarea's susceptibility to slope failure (Varnesand the International Association of Engin-eering Geology, 1984).
In order to predict landslide hazards in anarea, the conditions and processes that pro-mote instability must be identified and theirrelative contributions to slope failure estimat-ed, if possible. Useful conclusions concerningincreased probability of landsliding can bedrawn by combining geological analyses withknowledge of short- and long-term meteor-ological conditions. Current technology enablespersons monitoring earth movements to definethose areas most susceptible to liandsliding andto issue "alerts" covering time spans of hours todays when meteorological conditions known toincrease or initiate certain types of landslidesoccur. Alerts covering longer periods of timebecome proportionately less reliable.
Translation of TechnicalInformation to Users
According to Kockelman (personal comnmunica-tion, 1989), the successful translation of nat-ural hazard information for nontechnical usersconveys the following three elements in oneform or another:
(1) likelihood of the occurrence of an eventof a size and location that would causecasualties, damage, or disruption;
(2) location and extent of the efflects of theevent on the ground, structures, orsocioeconomic activity;
21
(3) estimated severity of the effects on theground, structures, or socioeconomicactivity.
These elements are needed because usu-ally engineers, planners, and decision makerswill not be concerned with a potential hazard ifits likelihood is rare, its location is unknown,or its severity is slight.
Unfortunately, these three pieces of infor-mation can come in different forms with manydifferent names, some quantitative and pre-cise, others qualitative and general. For a pro-duct to qualify as "translated" hazard inform-ation, the nontechnical user must be able toperceive likelihood, location, and severity of thehazard so that he or she becomes aware of thedanger, can convey the risk to others, and canuse the translated information directly in areduction technique.
Maps are a useful and convenient tool forpresenting information on landslide hazards.They can present many kinds and combina-tions of information at different levels of detail.Hazard maps used in conjunction withland-use maps are a valuable planning tool.Leighton (1976) suggests a three-stage appro-ach to landslide hazard mapping. The firststage is regional or reconnaissance mapping,which synthesizes available data and identifiesgeneral problem areas. This small-scale map-ping is usually performed by a state or federalgeological survey. The next stage is commun-ity-level mapping, a more detailed surface andsubsurface mapping program in complex pro-blem areas. Finally, detailed site-specificlarge-scale maps are prepared. If resources arelimited, it may be more prudent to bypass re-gional mapping and concentrate on a fewknown areas of concern.
Regional MappingRegional or reconnaissance mapping suppliesbasic data for regional planning, for conductingmore detailed studies at the community andsite-specific levels, and for setting priorities forfuture mapping.
These maps are usually simple inventorymaps and are directed primarily toward theidentification and delineation of regional land-slide problem areas and the conditions underwhich they occur. They concentrate on those
geologic units or environments in which addi-tional movements are most likely. Such map-ping relies heavily on photogeology (the geolog-ic interpretation of aerial photography),reconnaissance field mapping, and the collec-tion and synthesis of all available pertinentgeologic data (Leighton, 1976).
Regional maps are most often prepared ata scale of 1:24,000, because high-quality U.S.Geological Survey topographic base maps atthis scale are widely available, and aerialphotos are commonly of a comparable scale.Other scales commonly used include 1:50,000(county series), 1:100,000 (30 x 60 minuteseries), and 1:250,000 (1 x 2 degree series).
Community-Level MappingCommunity-level mapping identifies both thethree-dimensional limits of landslides andtheir causes. Guidance concerning land use,zoning, and building, as well as recommenda-tions for future site-specific investigations, arealso made at this stage. Investigations shouldinclude subsurface exploratory work in order toproduce a large-scale map with cross sections(Leighton, 1976). Map scales at this level varyfrom 1:1,000 to 1:10,000.
Site-Specific MappingSite-specific mapping is concerned with theidentification, analysis, and solution of actualsite-specific problems. It is usually undertakenby private consultants for landowners whopropose site development and typically involvesa detailed drilling program with downholelogging, sampling, and laboratory analysis inorder to procure the necessary information fordesign and construction (Leighton, 1976). Mapscales vary, but are usually not larger than oneinch equal to 50 feet.
Types of MapsThe three types of landslide maps most usefulto planners and the general public are (1)landslide inventories, (2) landslide suscepti-bility maps, and (3) landslide hazard maps.
Landslide inventoriesInventories identify areas that appear to havefailed by landslide processes, including debrisflows and cut-and-fill failures. The level of
22
detail of these maps ranges from simple recon-naissance inventories that only delineate broadareas where landsliding appears to haveoccurred (Figure 20) to complex inventoriesthat depict and classify each landslide andshow scarps, zones of depletion and accumu-lation, active versus inactive slides, geologicalage, rate of movement, and other pertinentdata on depth and kind of materials involved insliding (U.S. Geological Survey, 1982; Brabb,1984b) (Figure 21).
Simple inventories give an overview of thelandslide hazard in an area and delineateareas where more detailed studies should beconducted. Detailed inventories provide abetter understanding of the different landslideprocesses operating in an area and can be usedto regulate or prevent development in landslideareas and to aid the design of remedial meas-ures (U.S. Geological Survey, 1982). They alsoprovide a good basis for the preparation ofderivative maps such as those indicating slopestability, landslide hazard, and land use. Wiec-zorek (1984) described how to prepare a land-slide inventory map that can be used by plan-ners and decision makers to assess landslidehazards on a regional or community level. Theprocess consists of using aerial photography
U) T ~ A _WT ~ ' _ ~
with selective field checking to detect landslideareas, and then presenting the information inmap form using a coded format. The mapsshow any or all of the following: state of activi-ty, certainty of identification, dominant types ofslope movement, estimated thickness of slidematerial, and dates or periods of activity.
Landslide susceptibility mapsA landslide susceptibility map goes beyond aninventory map and depicts areas that have thepotential for landsliding (Figure 22). Theseareas are determined by correlating some ofthe principal factors that contribute to land-sliding, such as steep slopes, weak geologicunIits that lose strength when saturated, andpoorly drained rock or soil, with the past dis-tribution of landslides. These maps indicateonly the relative stability of slopes; they do notmake absolute predictions (Brabb, 1984b).
Landslide susceptibility maps can beconsidered derivatives of landslide inventorymaps because an inventory is essential for pre-paring a susceptibility map. Overlaying a geo-logic map with an inventory map that showsexisting landslides can identify specific land-slide-prone geologic units. This information canthen be extrapolated to predict other areas of
EXPLANATION
Areas inf erred to beunderlain by landslide
deposits
I r~~TOScale 1 :250,000
Figure 20. Detail from the landslide inventory map of the Durango 1 x 2 degree map, Colorado(Colton et ad, 1975).
23
Detail from mapshowing recently( ~~~~~~~~~~~~~~active and dormantlandslides near LaHonda, central SantaCruz Mountains,California. Informa-
- O0 tion shown on thismap includes: state
N K ~~~~' of activity, dominant... ~~~~~~~~~~~~~~~type of slope move-
000 ) ~~~~~~~ment, direction of~9504 movement, scarp
1 ~~~~~~~~~~location, depth anddate of movement.See map for detailedexplanation.
/ ~~(Wieczorek, 1982.)
606 k ~~~~~~~~~~EXPLANATION
~~ix ~ ~ Stable slopes
I Liii ~Normally stableslopes
JEUnstable slopes
Old landslide
0 ~~~~~~~~~~~~~~~~~deposits
Scale 1:24,000
Figure 22. Detail from map showing relative slope stability in part of west-central King County,Washington (Miller, 1973).
24
potential landsliding. More complex maps mayinclude additional information such as slope,angle, and drainage.
Landslide hazard mapsHazard maps show the areal extent of threat-ening processes: where landslide processeshave occurred in the past, where they occur
now, and the likelihood in various areas that alandslide will occur in the future (Figure 23).For a given area, they contain detailed inform-ation on the types of landslides, extent of slopesubject to failure, and probable maximum ex-tent of ground movement. These maps can beused to predict the relative degree of hazard ina landslide area.
EXPLANATIONSusceptibility of areaU- 1 r | likely to fail
-E High
M Mod(
~ Low
= Very
m LUquE
3rate
low
)factio n
N
Scale 1 :62,50
Figure 23. Detail from map showing slope stability during earthquakes in San Mateo County,California (Wieczorek at aL, 1985).
25
Transferring and Encouragingthe Use of Information
A major part of any effective landslide loss-re-duction program must be the communicationand use of technical information (informationtransfer). Often individuals or groups do nottake mitigative action because they do notunderstand what to do, or lack training on howto do it. The mitigation and/or avoidance oflandslide hazards and the reduction of land-slide losses require that appropriate informa-tion be communicated to, and effectively usedby, planners, decision makers, and emergencyresponse personnel.
According to Kockelman (personal com-munication, 1989), various terms are used todescribe the transfer of information to users,namely "disseminate," "communicate," "circu-late," "promulgate," and "distribute." Oftenthese terms are interpreted conservatively. Forexample, an agency or person might simplyissue a press release on hazards or distributeresearch information to potential users. Suchactivity rarely results in the adoption of effec-tive hazard reduction techniques.
Kockelman notes that no clear, concise de-finition or criteria for effective informationtransfer has been offered or can be found in theliterature, except by inference or by analysis ofwhat actually works for lay persons. Therefore,he uses "transfer" to mean the delivery of anunderstandable product in a usable format to aspecific person or group "interested" in, or re-sponsible for, hazard reduction, plus assistanceand encouragement in the selection and adop-tion of an appropriate reduction technique.Only when all these criteria have been methave researchers, translators, and transferagents fulfilled their objectives.
The effective use of landslide informationto reduce danger, damages, or other lossesdepends not only on the efforts of the producersof the information, but also on (1) the users'interest, capabilities, and experience in
hazard-related activities, (2) the existence ofenabling legislation authorizing federal, state,and local hazard-reduction activities, (3) theavailability of funds and adequate, sufficientlydetailed information in a readily usable andunderstandable form, (4) the use of effectiveinformation communication techniques, and (5)the existence of qualified staff at all levels ofgovernment with the authority to take mitiga-tive action.
Information TransferMethods for transferring and/or obtaininglandslide information are listed in Table 3.These methods should be used by any landslideinformation collection, interpretation, andtransferral program designed for planners anddecision makers. Some of these services areprovided by state agencies, map sales offices,geologic inquiries staffs, public inquiries offi-ces, universities, and, in the course of ordinaryday-to-day contacts with the public, by theproducers of landslide hazard information. Inaddition, many research workers have providedsuch services on a limited and informal basis.
Table 3. Examples of resources available forobtaining / transferring landslide information(adapted from U.S. Geological Survey, 1982).
Educational Services* Universities and their extension divisions
through courses, lectures, books, and dis-play materials
* Guest speakers and participants at lectur-es in regional and community educationalprograms related to the application ofhazard information
* Seminars, conferences, workshops, shortcourses, technology utilization sessions,training symposia, and other discussionsinvolving user groups
26
Table 3. Continued
* Oral briefings, newsletters, seminars,map-type "interpretive inventories,"open-file reports, reports of cooperatingagencies, and "official-use only" materials(released via news media)
* Radio and television programs that explainor report hazard-reduction programs andproducts
* Meetings with local, district, and stateagencies and their governing bodies
* Field trips to potentially hazardous sitesby state, local, or federal agencies, andprofessional societies
Information Sources* Annotated and indexed bibliographies of
hazard information and lists of pertinentreference materials
* Local, state, and federal policies, procedur-es, ordinances, statutes, and regulationsthat cite or make other use of hazardsinformation
* Hazards information incorporated intolocal, state, and federal studies and plans
* User guides relating to earth-hazardsprocesses, mapping, and hazard-reductiontechniques
Users of Landslide Hazard InformationAmong the potential users of landslide hazardinformation are people at national, state, region-al, and community levels in both the public andprivate sectors. Three general categories can beidentified: (1) scientists and engineers who usethe information directly, (2) planners and deci-sion makers who consider hazards among otherland-use and development criteria, (3) develop-ers and builders; financial and insuring organi-zations, and (4) interested citizens, educators,and others with little or no technical expertise.These people differ widely in the kinds of infor-mation they need and in their capabilitiesto use that information. Examples ofpotential users are listed in Table 4.
Table 4. Potential users of landslide hazardinformation (modified from U.S. GeologicalSurvey, 1982).
City, County, and Area-WideGovernment Users
City and county building, engineering, zoning,safety, planning, and environmentalhealth departments
City and county offices of emergency servicesCounty tax assessorsLocal government geologistsMayors, county commissioners, and city council
membersMulticounty (regional) planning, development,
and emergency preparedness agenciesMunicipal engineers, planners, and adminis-
tratorsPolice, fire, and sheriffs departmentsPublic works departmentsRoad departmentsSchool districtsSpecial districts (water, sanitation, urban
drainage)
State Government Users*Attorney General's OfficeDepartment of Administration
State Buildings DivisionDepartment of HealthDepartment of HighwaysDepartment of Local AffairsDepartment of Military Affairs
National GuardDepartment of Natural Resources
Geological SurveyWater Conservation BoardWater Resources
Department of Public SafetyEmergency Management Agencies
Department of RevenueState Planning and Budgeting Office
*NOTE: Names and functions of state agenciesvary from state to state and this list shouldbe adapted accordingly.
27
Table 4. Continued
Federal Government UsersDepartment of Agriculture
Farmers' Home AdministrationForest ServiceSoil Conservation Service
Department of the ArmyArmy Corps of Engineers
Department of CommerceNational Bureau of StandardsNational Oceanic and Atmospheric
AgencyDepartment of Housing and Urban
DevelopmentFederal Housing Administration
Department of the InteriorBureau of Land ManagementBureau of ReclamationGeological SurveyNational Park Service
Department of the NavyDepartment of Transportation
Federal Highway AdministrationEnvironmental Protection AgencyFederal Emergency Management AgencyGeneral Services AdministrationMembers of Congress and their staffsNuclear Regulatory CommissionSmall Business Administration
Private, Corporate, andQuasi-Public Users
Civic and voluntary groupsConcerned citizens, homeowners associationsConstruction companiesConsulting planners, geologists, architects, and
engineersEconomic development committeesExtractive, manufacturing, and processing
industriesFinancial and insuring institutionsLandowners, developers, and real estate agentsNews mediaUtility and transmission companiesUniversity departments (including geology,
civil engineering, architecture, urban andregional planning, and environmentalstudies departments)
Other National UsersApplied Technology CouncilAmerican Association of State Highway and
Transportation OfficialsAmerican Public Works AssociationAmerican Red CrossAssociation of Engineering GeologistsAssociation of State GeologistsCouncil of State GovernmentsEarthquake Engineering Research InstituteInternational Conference of Building OfficialsNational Academy of SciencesNational Association of CountiesNational Association of Insurance
CommissionersNational Governors' AssociationNational Institute of Building SciencesNatural Hazards Research and Applications
Information Center, University of ColoradoNational League of CitiesProfessional and scientific societies (including
geologic, engineering, architecture, andplanning societies)
United States Conference of Mayors
Most states have professional planners,engineers, or geologists available who canmake interpretations from available hazardinformation. Specialists from the federal gov-ernment who are skilled in the translation oftechnical data can also assist states. As sug-gested in Chapter 4, the most effective use oflandslide information is achieved when mapsare prepared that indicate the location, sever-ity, and recurrence potential of landslides.
Developing an Information Base:Sources of Landslide Hazard
InformationSome of the organizations that produce orprovide landslide hazard information are listedin Table 5.
28
Table 5. Examples of producers and provid-ers of landslide hazard information (adaptedfrom U.S. Geological Survey, 1982).
American Institute of Professional GeologistsAmerican Society of Civil EngineersAssociation of Engineering GeologistsCounty extension agentsEducators (university, college, high school)Museum of Natural HistoryState Department of HighwaysState Geological SurveyHazard researchers, interpreters, and mappersInternational Conference of Building Officials
Journalists, commentators, editors, and othernews professionals
Local seismic safety advisory groupsNational Governors' AssociationNatural Hazards Research and Applications
Information Center. University of 'ColoradoPublic information offices (federal and state)U.S. Army Corps of EngineersU.S. Bureau of Land ManagementU.S. Bureau of ReclamationU.S. Forest ServiceU.S. Geological SurveyU.S. Soil Conservation Service
29
Landslide Loss-Reduction Techniques
A significant reduction in landslide losses canbe achieved by preventing or minimizing theexposure of populations and facilities to land-sliding; by preventing, reducing, or managingthe actual occurrence of landslides; and byphysically controlling landslide-prone slopesand protecting existing structures.
Subsidized insurance is not considered aloss-reduction technique because it does notprevent or reduce losses but merely transfersthe loss to other segments of the population.Indeed, it may encourage lenders to develophazardous lands because they are indemnifiedby uninvolved taxpayers. The insurance indus-try could become a strong promoter of hazardsreduction if it would establish its rates to re-flect relative risks. Most homeowners' insur-ance policies exclude coverage for groundmovements, including landslides.
Preventing or MinimizingExposure to Landslides
Vulnerability to landslide hazards is a functionof a site's location, type of activity, and frequen-cy of landslide events. Thus, the vulnerabilityof human life, activity, and property to land-sliding can be lowered by total avoidance oflandslide hazard areas or by restricting, prohi-biting, or imposing conditions on hazard-zoneactivity. Local governments can accomplish thisby adopting land-use regulations and policiesand restricting redevelopment.
Land-Use RegulationsLand-use regulations and policies are often themost economical and effective means of regula-tion available to a community-particularly ifenacted prior to development. However, wherepotentially hazardous land is privately ownedwith the expectation of relatively intense dev-elopment and use, or where land optimallysuited for development in communities is in
short supply, there is strong motivation andpressure to use the land intensively. Land-useregulations must be balanced against econ-omic considerations, political realities, andhistorical rights.
Various types of land-use regulations anddevelopment policies can be used to reducelandslide hazards. Some of these methods arelisted in Table 2, Chapter 2. Responsibilityfor their implementation resides primarilywith local governments, with some involve-ment of state and federal governments and theprivate sector.
Reducing the Occurrence ofLandslides and Managing
Landslide EventsAs discussed in Chapter 3, many landslidesoccur as a direct result of human activities.The excavation and grading associated withthe construction of buildings, highways, trans-mission lines, and reservoirs can createconditions that will ultimately result in slopefailure. The development and enforcement ofcodes for excavation, grading, and constructioncan prevent such landslides. A review of thestate of the art and standards of performanceof hillside and flatland urban developmentfrom the 1950s to the early 1980s is availablein a training manual (Scullin, 1982). This man-ual describes the mitigation of several geologichazards: landsliding, subsidence, expansivesoils, drainage, and earthquakes. The conceptsand technical applications described in thisbook may be applied in short-or long-termplanning regarding geologic risks anywhere.
Building and Grading CodesDesign, building, and grading codes are
regulatory tools available to local governmentagencies for achieving desired design andbuilding practices. They can be applied to both
30
is i; ;~~~~~~~~~~~~~~~~~~~~~~~~~~_
new construction and pre-existing buildings. In-rare cases, such as those involving large off-shore structures, the effect of landslides can beconsidered explicitly as part of the design, andthe facility can be built to resist landslide dam-age. In some cases, existing structures in land-slide-prone areas can be modified to be moreaccommodating to landslide movement. The ex-tent to which this is successfiul depends on thetype of landsliding to which the structure isexposed. Facilities other than buildings (e.g.,gas pipelines and vater mains) can also bedesigned to tolerate ground movement. Codesand regulations governing grading and exca-vation can reduce the likelihood that construc-tion of buildings and highways will increasethe degree to which a location is prone tolandslides. Various codes that have been devel-oped for federal, state, and local implementa-tion can be used as models for landslide-dam-age mitigation. A fundamental concern withdesign and building codes is their enforcementm a uniform and equitable way. (Committee onGround Failure Hazards, 1985, p. 15).
Emergency ManagementEmergency management and emergency plan-ning contribute to landslide loss reduction bysaving lives and reducing injuries. Such plan-ning can also protect and preserve property inthose cases where property is mobile or whereprotective structures can be installed if suffi-cient warning time is available.
Emergency management and planningconsist of identifying potential hazards, deter-mining the required actions and parties respon-sible for implementing mitigation actions, andensuring the readiness of necessary emergencyresponse personnel, equipment, supplies, andfacilities. An important element of emergencymanagement is a program of public educationand awareness informing citizens of their po-tential exposure, installation of warning sys-tems, types of warnings to be issued, probableevacuation routes and times available, andappropriate protective actions to be taken.
A warning system may include the moni-toring of geologic and meteorologic conditions(e.g., rates of landslide movement, snowmeltrunoff, storm development) with potential forcausing a catastrophic event or the placementof signs instructing people within a potentiallyhazardous area of proper procedures (Figure24). Automatic sensors, located within land-
slide-prone areas, with effective linkages to acentral communication warning facility and,thence, to individuals with disaster manage-ment responsibilities, are also sometimes used.Warning systems can be long-term or tempor-ary-used only when high risk conditions existor while physical mitigation methods are beingdesigned and built (Figure 25).
CLIMBTO
i
SAFETY!
IN CASE OF AFLASH FLOOD
Figure 24. Sign placed in some of the hazard-ous mountain canyon areas of Colorado.
Controlling Landslide-ProneSlopes and Protecting
Existing StructuresPhysical reduction of the hazard posed byunstable slopes can be undertaken in areaswhere human occupation already poses a risk,but where measures such as zoning are pre-cluded by the cost of resettlement, value orscarcity of land, or historical rights. Physicalmeasures can attempt to either control andstabilize the hazard or to protect persons andproperty at risk.
It is not possible, feasible, or -even necessar-ily desirable to prevent all slope movements.Furthermore, it may not be economically fea-sible to undertake physical modifications insome landslide areas. Where land is scarce,however, investment in mitigation may in-crease land value and make more expensiveand elaborate mitigation designs feasible.
31
device
Figure 25. Schematic of a warning system (by Robert Kistner, Kistner and Associates).
Landslide control structures can be costlyand usually require considerable lead time forproject planning and design, land acquisition,permitting, and construction (Figure 26). Suchstructures may have significant environmentaland socioeconomic impacts that should be con-sidered in planning.
Precautions Concerning Relianceon Physical Methods
Although physical techniques may be the onlymeans for protecting existing land uses in haz-ard re. solt rlianep nn them mqv reate afalse sense of security. An event of greater sev- Figure 26. Rudd Creek debris basin ierity than that for which the project was de- Farmington, Utah constructed in 19nsigned may occur, or a structure may fail due to (photograph by Robert Kistner, Kistnaging, changing conditions, inadequate design, Associates).
1_84.er and
32
Channel
FINAL DESIGN IN Fi
< BY INSTALLERS
Parts ListStrokCabhUsedSpeaSolarBatteReguRelalCabligateand vPowe(DonatColoraand Lii
SubtEConti
Total $1351
or improper maintenance. The result could becatastrophic if the hazard zone has been devel-oped intensively.
Design Considerations and PhysicalMitigation Methods
When designing control measures, it is essen-tial to look well beyond the landslide mass it-self. A translational slide may propagate overgreat distances if the failure surface is suffici-ently inclined and the shear resistance alongthe surface remains lower than the drivingforce. Debris flows can frequently be bettercontrolled if mitigation efforts emphasize sta-bilizing the source area along with debris con-tainment in the runout area. An understandingof the geological processes and the surface- andground-water conditions, under both naturaland human-imposed conditions, is essential toany mitigation planning.
Some factors that determine the choice ofphysical mitigation are:
* type of movement (e.g., fall, slide, aval-anche, flow);
* kinds of materials involved (rock, soil,debris);
* size, location, depth of failure;* process that initiated movement;* people, place(s), or thing(s) affected by
failure;* potential for enlargement (certain types
of failures [e.g., rotational slides, earth-flows, translational slides] will enlargeduring excavation);
* availability of resources (funding, laborforce, materials);
* accessibility and space available forphysical mitigation;
* danger to people;* property ownership and liability.
The physical mitigation of landslides usu-ally consists of a combination of methods.Drainage control is used most often; slopemodification by cut and fill and/or buttresses isthe second most frequently used method. Theseare also, in general, the least expensive tech-niques (Figure 27).
Various types of physical mitigation met-hods are listed in Table 6.
Figure 27. Retaining wall, Interstate 70, nearVail, Colorado (photograph by ColoradoGeological Survey).
Table 6. Physical mitigation methods (Colo-rado Geological Survey et aL, 1988).
A. Physical Mitigation Methods for Slides andSlumps
1. Drainagea. Surface drainage
1) ditches2) regrading3) surface sealing
b. Subsurface drainage1) horizontal drains2) vertical drains/wells3) trench drains/interceptors,
cut-off drains/counterforts4) drainage galleries or tunnels5) blanket drains6) electro-osmosis7) blasting8) subsurface barriers
2. Excavation or regrading of the slopea. Total removal of landslide massb. Regrading of the slopec. Excavation to unload the upper part
of the landslided. Excavation and replacement of the
toe of the landslide with othermaterials
3. Restraining structuresa. Retaining wallsb. Pilesc. Buttresses and counterweight fillsd. Tie rods and anchors
33
Table 6. Continued
e. Rock bolts/anchors/dowels4. Vegetation5. Soil hardening
a. Chemical treatmentb. Freezingc. Thermal treatmentd. Grouting
B. Physical Mitigation Methods for DebrisFlows and Debris Avalanches
1. Source-area stabilizationa. Check damsb. Revegetation
2. Energy dissipation and flow controla. Check damsb. Deflection wallsc. Debris basinsd. Debris fencese. Deflection damsf. Channelization
3. Direct protectiona. Impact spreading wallsb. Stem wallsc. Vegetation barriers
C. Physical Mitigation Methods for Rockfalls1. Stabilization
a. Excavationb. Benchingc. Scaling and trimmingd. Rock bolts/anchors/dowelse. Chains and cablesf. Anchored mesh netsg. Shotcreteh. Buttressesj. Dentition
2. Protectiona. Rock-trap ditchesb. Catch nets and fencesc. Catch wallsd. Rock sheds or tunnels
34
P laI P ep atio? nPlan Preparation
Determining the Needfor a State Plan
In order to determine the need for a state land-slide hazard mitigation plan, individual statesmust first assess the vulnerability of their pre-sent and future population to the hazard.Vulnerability is the susceptibility or exposureto injury or loss from a hazard. People, struc-tures, community infrastructure systems'(transportation, water supply, communications,and electricity), and social systems are allpotentially vulnerable.
An assessment of statewide vulnerabilityto geologic hazards is a product of the technicalassessment of the problem, based on scientificstudies and investigations, and an assessmentof capabilities, in the public and private sec-tors, to respond to and mitigate the hazardsand potential impacts identified. Before re-sources are invested in hazard mitigationmeasures, the social and economic costs andimpacts associated with landsliding need to bedetermined and put into perspective.
The next step in recognizing the overallvulnerability of the state to the landslide ha-zard is the identification of specific commun-ities, areas, and facilities at risk. The existenceand effectiveness of local programs and sys-tems for mitigating landslide problems in com-munities experiencing actual or potential im-pacts must then be determined.
Although landslides can potentially affectentire regions or states, the hazards them-selves are local problems first, and local gov-ernments remain on the `front lines" of thebattle to reduce losses.
Landslide loss reduction in the UnitedStates is primarily a local responsibility. Whilethe federal government plays a key role in re-search, in the development of mapping tech-niques, and in landslide management on feder-al lands, the reduction of landslide losses
through land use management and the appli-cation of building and grading codes is essen-tially a function of local government (Sangreyand Bernstein, 1985, p. 9).
The purpose of a state landslide hazardmitigation plan is to encourage and support lo-cal mitigation efforts and address serious land-slide problems, beyond local capability, thatthreaten lives and property and have potentialregional or statewide implications. Strategiesand projects developed in, the planning processare therefore based on an assessment of whatcan be accomplished locally and the level of sup-plemental assistance that will be required tolessen the problem. State and federal assis-tance picks up where local efforts stop; gen-erally local resources must first be exhausted.
A key element in, the planning process anda major recommendation of this guidebook isthe establishment of a permanent state 'organi-zation, representing the various levels and re-sponsibilities of government, to focus the atten-tion of state government on natural hazardmitigation issues.
Federal Disaster Relief and EmergencyAssistance Act (Section 409)
In presidentially-declared disasters, the pre-paration of a state plan that identifies andevaluates hazard mitigation opportunities ismandated by Section 409 of the Robert T. Staf-ford Disaster Relief and Emergency AssistanceAct (Public Law 93-288, as amended) as acondition of receiving federal disaster assis-tance. This requirement was originally enactedin 1974 under Section 406 of the DisasterRelief Act to encourage identification, evalua-tion, and mitigation of hazards at the state andlocal government levels. The requirements ofSection 409 are triggered by a major disaster oremergency declared by the President and applyto all types of declared emergencies and disas-
35
ters. A hazard mitigation clause is incorporatedinto the FEMA/State agreement for disasterassistance, thereby establishing the identifica-tion of hazards and the evaluation of hazardmitigation opportunities as a condition for re-ceiving federal assistance.
The Federal Emergency ManagementAgency (FEMA) is responsible for adminis-tering the Section 409 requirements and hasprepared implementing regulations (44 CFR206, Subpart M) that specify federal, state, andlocal responsibilities under Section 409. Underthe regulations, a state hazard mitigation co-ordinator is designated by a governor's author-ized representative to prepare a hazard mitiga-tion plan and to ensure its implementation.States may establish a group of individualsfrom state and local agencies to assist in pre-paring the "409 plan," which must be complet-ed and submitted to FEMA within 180 daysafter the presidential declaration.
With the passage of the Stafford Act in1988, a hazard mitigation funding programwas authorized for the first time under Section404 of the Act. This mitigation-measures fund-ing program provides up to 50 percent federalfunding for activities identified under Section404, thus making preparation of a good hazardmitigation plan more important than ever be-fore. The identification of mitigation opportun-ities under this program follows the evaluationof natural hazards under Section 409. Totalfederal funds available under Section 404 arelimited to 10 percent of the permanent restora-tive work funded under FEMA's Public Assis-tance Program. Implementation regulations forSection 404 can also be found in 44 CFR 206,Subpart M.
In state-declared disasters, some statesrequire the development of local hazard mitiga-tion plans as an eligibility requirement of stateemergency relief.
The Planning TeamStates undertaking plan development shouldfirst consider assembling a state planning teamto manage the research and writing of theplan. The planning team could be in the form ofa working group, directed by state representa-tives and supported by representatives of local
government, the private sector, and academia.Typically, the group would gather, interpret,and assemble the technical information thatforms the basic structure of the landslide haz-ard mitigation plan.
The interagency efforts of post-disasterhazard mitigation teams in presidentially-de-clared disasters have demonstrated that suchworking groups representing a broad range ofstate and federal agencies can successfullydevelop a host of innovative and cost-effectivemitigation ideas.
The planning team should include indivi-duals knowledgeable about geology, engineer-ing, emergency management, and communitydevelopment and planning. Depending on thenature of landslide problems, the team mightalso include individuals involved in naturalresources management, highway constructionand maintenance, state and regional planning,and others as conditions warrant.
The responsibilities of individual teammembers would include researching and writ-ing those sections of the plan that relate totheir area of expertise. Team members wouldalso participate in meetings with planners,emergency managers, policy makers, andelected officials in local and state governmentand, to the extent possible, seek the input andparticipation of private industry, professionaland volunteer organizations, and interestedcitizens. An initial analysis of existing mitiga-tion plans and emergency management capa-bilities in landslide-impacted jurisdictions willenable the planning team to identify the mostserious problems and to develop projects thatbuild on efforts already in progress. This as-sessment of local landslide conditions and localcapabilities to deal with them should identify awide variety of practicable mitigation solu-tions. This will facilitate the coordination ofstate support and the identification of unmetlocal needs that can be presented for possiblestate action.
Local jurisdictions impacted by landslidesshould be encouraged to form their own localplanning teams-composed of decision makers,planners, emergency managers, engineers,geologists, and officials from law enforcement,fire safety, and emergency medical services-toformulate local plans and mitigation strategies.
36
The Planning ProcessThe planning process recommended for the de-velopment of a landslide hazard mitigationplan follows a series of steps that are basic tomitigation planning:
(1) analysis of the types of landslide haz-ards in the state and a general assess-ment of the vulnerability of people andproperty to the state's landslidehazards;
(2) identification of specific areas of thestate where landslides have the mostserious or immediate potential impactsand a detailed analysis of their vulner-abilities;
(3) translation and transfer of technicalinformation on hazards and vulnera-bilities to users such as decision mak-ers,. community planners, and emer-gency management officials;
(4) assessment of resources and mitiga-tion programs available in the publicand private sectors to deal with theidentified potential impacts;
(5) determination of local capability shortt-falls and unmet needs in order to ap-ply technical and financial assistancewhere it can best contribute to thereduction of future losses;
(6) formulation of goals and objectives forstate and local landslide hazard miti-gation plans, and the development ofcost-effective mitigation projects thataddress identified vulnerabilities;
(7) establishment of a permanent statehazard mitigation system to prioritizeand promote mitigation goals and ob-jectives and to secure and direct fund-ing for implementation;
(8) periodic evaluation and modification ofthe plan and planning process.
Step 1-Hazard AnalysisA complete hazard analysis is the result of theidentification of the state's landslide hazardareas, the identification of the most vulnerablelocations, and the assessment of potentialimpacts on people and property in vulnerableareas. Where possible, the hazard analysisshould provide planners with information about
hazard location, description, frequency, history,existing impacts, potential impacts, and, to theextent possible, probability of occurrence.
The use of land-use maps in conjunctionwith detailed maps exhibiting the extent andseverity of landslide hazards in an area helpsofficials to determine vulnerability to land-slides, mitigation priorities, and the most ap-propriate mitigation measures.
Appropriate land use management, effec-tive building and grading codes, the use ofwell-designed engineering techniques forlandslide control and stabilization, the timelyissuance of emergency warnings, and the avail-ability of landslide insurance can significantlyreduce the catastrophic effects of landslides. Allof these approaches require, as a starting point,the identification of areas where landslides areeither statistically likely or immediately immin-ent, and the representation of these hazardouslocations on maps (Committee on Ground Fail-ure Hazards, 1985, p. 2).
The planning team should assemble exist-ing mapped landslide susceptibility data thatportray the distribution of various types oflandslides and the likelihood of their occur-rence. The team will need maps sufficientlydetailed to determine the character, location,and magnitude of landslide problems.
Step 2-Identification ofImpacted Sites
Once the nature and distribution of the hazardand the vulnerability to landsliding of variouscommunities, areas, and facilities has been de-termined, site-specific evaluations of the poten-tial impacts of landsliding should be perform-ed. Based on the hazard analysis, those sitesdetermined to present the greatest threat tolives and property should be subject to furthersite analysis and mitigation planning.
Impact is the effect of a hazard event onpeople, buildings, and the infrastructure. Theimpacts of landsliding range from the incon-venience of debris cleanup to the life-threat-ening failure of a landslide-formed dam. Thesimultaneous or sequential occurrence of otherhazards such as flooding or earthquakes withlandsliding can produce effects that are greateror qualitatively different from those producedby landsliding alone.
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Step 3-Technical Information TransferAs discussed in Chapter 5, individuals orgroups often do not take mitigative actionsbecause they do not understand the signifi-cance of the threat, what to do to reduce it, orlack information and training on how to do it.Therefore, once landslide hazard informationhas been gathered, it must be communicated toplanners, policy makers, emergency responsepersonnel, and the public. Maps are one of thebest methods of transferring such information.Landslide information can be used in the de-velopment, review, and approval of land-useplans, community development plans, emer-gency management plans, and hazard mitiga-tion plans. In order for landslide information tobe more widely incorporated into communityplanning and planning for landslide mitigation,the technical staff that produces the informa-tion must tailor it so that it is understandableand usable by the various parties involved inthe development process. Producers of informa-tion should also ensure that potential users areaware of available data, as well as researchplanned or in progress. Conversely, nontechni-cal users of landslide information should takesteps to improve their skills in interpreting andapplying the information.
The difficulty of translating technical in-formation for nontechnical users highlights theimportance of retaining the services of qualifi-ed technical experts throughout the planningprocess. According to Fleming and Taylor(1980, p. 4), "solutions to the technical prob-lems are only a part of the process of achievinglandslide hazard reduction. The political prob-lem of transferring the information into agovernmental system to reduce hazards anddamages is perhaps more formidable than thetechnical one."
Step 4-Capability AssessmentCapability assessment is a determination ofpublic, private, and volunteer resources in acommunity that are available to support emer-gency management and hazard mitigation act-ivities designed to reduce losses from a particu-lar hazard. Resources include not only equip-ment, supplies, and materials, but, more im-portantly, people, expertise, plans, programs,
and cooperative agreements with other juris-dictions and private industry. Private compan-ies have a vested interest in the mitigation pro-cess because private losses often exceed publiclosses in natural disasters, and also becauseprivate firms may receive insurance benefits(lower premiums, reduced liability) for a demon-strated commitment to reducing future losses.
The assessment of local capabilities shouldidentify the most vulnerable elements of thecommunity, the current level of mitigation act-ivity, the status of emergency managementplanning, and opportunities for state and fed-eral mitigation assistance.
The checklist provided in Table 7 can assistlocal jurisdictions in preparing plans for land-slide hazard mitigation and emergency man-agement as well as assisting state planningteams in assessing local mitigation efforts.
Table 7. Types of information that should beconsidered in an assessment of a commun-ity's landslide hazards and capabilities (mod-ified from Weber et al., 1983).
A. Maps1. Base map2. Landslide inventories3. Landslide susceptibility maps4. Landslide hazard maps
B. Physical (Geologic) Information1. Scope (boundaries of areas subject to
landslides)2. Frequency (historical occurrences by
date, location, description, andimpacts)
a. Reportsb. Newspaper articlesc. Eyewitness accounts
3. Hazard characteristicsa. Predictabilityb. Potential speed of occurrencec. Potential impact forcesd. Magnitudee. Worst-case scenario
C. Social (Human) Information1. Land Use
a. Existing (map)b. Future (map)c. Zoning (map)
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Table 7. Continued
2. Population at riska. Number of people/total dwelling
unitsb. Variability (difference in day/night
populations)3. Property at risk (infrastructure)
a. Use/functionb. Assessed value
4. Economic activity at risk (commercial,,industrial, tourism)
a. Employmentb. Gross revenues
5. Critical services and facilities at riska. Accessb. Policec. Fired. Communicationse. Schoolsf. Health care (hospitals, nursing
homes)g. Utilitiesh. Emergency management facilitiesi. Thansportaion
6. Aggravating influences (roads,structures, landscaping, removal ofvegetation, or other land uses thatcontribute to landslide hazard)
D. Landslide Hazard ManagementCapabilities
1. Landslide hazard mitigation activitiesa. Land-use regulationsb. Land-use plansc. Building and grading codesd. Design and location standards*e. Development and redevelopment
plansf. Landslide control structuresg. Monitoring/instrumentationh. Acquisition and relocation projectsi. Public utility extension guidelinesj. Planning team formationk. Land exchanges1. Real estate disclosure requirementsm. Lending and financing policiesn. Additional public workso. Private sector involvementp. Special assessment districtsqq. Tax adjustments
2. Emergency management activitiesa. Warning systemsb. Emergency plans (life-saving,
evacuation, facility-specific)c. Public -education/hazard awareness
campaignsd. Training exercises
3. Local financial capabilities and needsa. Funds availableb. Major resource shortfallsc. State and federal programs and
grantsd. State and federal technical
assistance
By comparing local risks and possible im-pacts with the capability of a jurisdiction torespond to those risks, a state planning teamcan identify major resource deficiencies, orunmet needs, that become the basis for projectsin the state plan. Unmet needs are technicaland financial resource needs that exceed thecap abilities of the communities at risk. Inmany cases, these resource shortfalls representsubstantial obstacles to reducing the impacts offuture landslides on people, property, and ess-ential services.
Step 5-Determination of UnmetLocal Needs
Based on the analysis of local capabilities, un-met needs that should be considered by stateand federal governments are identified and astate mitigation assistance strategy is formu-lated. In order to determine unmet needs,specific human activities should be examinedto evaluate potential impacts on public healthand safety, public and private property, com-merce, and the community at large. Groupmeetings and individual interviews can yieldsufficient information to determine the mostcritical needs of local governments and to de-velop priority mitigation projects for state act-ion. Less urgent needs can be addressed infuture projects. The state planning teamshould also identify existing local mitigationprojects so that state projects can be coordinat-ed to support their efforts.
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Step 6-Formulation of Goalsand Objectives
Fundamental to a mitigation program is theestablishment of a system for landslide mitiga-tion planning and management at the stateand local government levels. The establishmentof a permanent state system to effect mitiga-tion projects should be considered. This man-agement system would help ensure that:
* existing hazardous conditions are dealtwith expeditiously,
* new landslide hazards are assessed andprioritized,
* new options are developed and evalu-ated,
* intergovernmental and interagencytechnical advice and mitigative actioncan be coordinated,
* priorities are established for high- andmoderate-risk situations that arebeyond local government capability,
* decisions are made and fundingobtained and spread over a period oftime that is commensurate with statefiscal capabilities,
* feedback is evaluated and needed pro-gram adjustments made, and
* a systematic approach to mitigation isestablished.
Local Landslide Hazard MitigationLocal jurisdictions should institute mitigationprograms that coordinate landslide hazard in-formation and mitigation needs with state gov-ernment and the private sector. Local mitiga-tion systems should effectively employ stateassistance and be ready to take on new prob-lems as solutions to old problems are found.Local mitigation plans need to be in place sothat work on mitigation projects can begin assoon as funds become available.
Effective local systems are important tostate planning because they provide directionfor state action. A comprehensive local hazardmitigation program should be based on com-munity consensus, developed through localplanning committees with citizen support andinvolvement, and should conform to local goalsand objectives and budget constraints. Localgovernments involved in landslide hazard miti-
gation face a number of important planningchallenges, including: (a) the preparation ofemergency management plans that ensure thetimely warning and evacuation of people inhigh-risk areas; (b) the formation of localplanning committees to identify unmet localneeds and schedule the implementation of mit-igation projects; (c) the coordination of public,private, and volunteer resources; and (d) theintegration of landslide hazard informationinto community development plans in order toprotect existing development and guide, dis-courage, or restrict future development inlandslide-prone areas.
Local hazard mitigation and emergencyplanning are generally carried out separatelyfrom the basic planning of local government.Integrating hazard information into the com-prehensive or master plan of a community,however, better enables a jurisdiction to guidethe activities of builders, investors, and devel-opers in areas known to be hazardous. Com-munities that have an adequate base of tech-nical information about local landslide prob-lems, and that have succeeded in applying thisinformation to development and planning de-cisions, have met an important precondition tomost types of mitigation. Land-use plans thatconsider available hazard information demon-strate to developers and to the public thatpublic health and safety concerns are import-ant factors in community development. Accord-ing to Olshansky and Rogers (1987, p. 957),"By incorporating landslide hazard informationinto long-term local plans, local governmentsgive developers advance notice of land usepolicies and the reasons for those policies."
Development of Mitigation ProjectsThe identification of areas in the state that arevulnerable to catastrophic landslide losses willenable the planning team to formulate thegoals and objectives of the state plan, whichmay be expressed in the plan in the form ofprioritized mitigation projects. With the sup-port of the planning, technical, and policy-mak-ing staff of state and local agencies that haveresources, capabilities, or statutory responsi-bilities relating to landslide hazard manage-ment, the planning team should be able todevelop an initial group of projects.
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A wide range of project ideas and opinions,representing the perspectives of planning, geol-ogy, engineering, emergency management, pri-vate industry, elected leadership, and others,should be solicited to enable the planning teamto determine the cost effectiveness, feasibility,and political and social implications of eachpossible approach. The highest initial priorityshould be assigned to those projects that estab-lish a permanent system in state governmentfor continuous support of state hazard mitiga-tion opportunities. A second priority should bestate support to long-term mitigation programsin local government and the private sector.Another ongoing priority should be the identi-fication of and participation in state and fed-eral programs that can provide funding supportfor mitigation initiatives.
Although implementation of many recom-mendations may be difficult if financial re-sources are linited, government agenciesshould be encouraged to use the plan and itsidentified projects as a resource in formulatingannual work programs, budgets, and policystatements concerning landslides. Projects thatmodify existing programs or improve coordina-tion are usually relatively low-cost and standthe best chance of being implemented first.Funds to implement the more costly projectsshould be aggressively sought from state legis-latures, the federal government, and the priv-ate sector.
Projects recommended in the state planshould include a brief statement of the prob-lem, a general statement of the recommendedsolution, a description of short- and long-terminitiatives, a designated lead agency; and a pre-liminary estimate of cost effectiveness, wherepossible. Projects should contribute toward aneffective and coordinated state/local landslidemanagement system, and should be flexibleboth in content and priority to allow for modi-fication during the implementation process.Local jurisdictions should report their accom-plishments and important unmet needs to thestate mitigation organization so that newstate/local strategies can be developed. Newprojects should be introduced into the systemas new landslide threats are identified and asnew approaches to old problems are found.
Step 7-Establishment of a PermanentState Hazard Mitigation Organization
A permanent state hazard mitigation organi-zation should be created to coordinate the re-sources of state, local, and federal agencieswith landslide hazard mitigation responsibil-ities and authorities. For states with seriouslandslide problems, establishment of a perm-anent organization institutionalizes in stategovernment the consideration of opportunitiesto reduce landslide losses. In Colorado, this hasbeen accomplished by an Executive Order(Figure 28) that formalizes landslide hazardmitigation planning within a natural hazardsmitigation council.
States with no existing system for hazardmitigation should consider establishing anorganization that also addresses and promotesthe mitigation of other hazards impacting thestate. Most of the public agencies involved inlandslide hazard mitigation-those concernedwith geology, natural resources, highways,climatology, water resources, emergency man-agement, and others-are also involved withproblems of flooding, drought, and, dependingupon location, hurricanes, and earthquakes.Although the focus and extent of short-termmitigation activities at any given time maydepend upon the prevailing threats, the organ-ization should maintain a broader, long-termperspective on all of a state's natural hazards.An all-hazards approach should result in anefficient, multi-purpose process that can gainthe support and approval of state leadershipand the public.
The role of the state mitigation organiza-tion should essentially be a continuation of theactivities performed by the state planningteam and those coordinating agencies with arole in landslide mitigation that participated inthe development of the plan. One type of org-anization might consist of a state mitigationcouncil supported by working groups. Thecouncil would be made up of decision makersselected from key state, local, and federal agen-cies and could include representatives from thegovernor's office and the state legislature. Re-presentatives from local and regional govern-ments and academia may also be included inworking groups.
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STATE OF COLORADOEXECUTIVE CHAMBIERS
136 Slae COpitolD.on-, Colorado --2v11,92Phone (303) 00003-1 B 044 89
Roy Rome,G.--rn
EXECUTIVE ORDER
ESTABLISHING A COUNCIL FOR THE IMPLEMENTATION OFSTRATEGIES TO MANAGE MITIGATION OF NATURAL HAZARDS IN COLORADO
WHEREAS, various natural hazards have caused physical and financialimpacts in Colorado and will continue to do so; and
WHEREAS, these impacts have resulted in unexpected costs to stateand local governments as well as degradation of the state's health,safety, environment, infrastructure and economy; and
WHEREAS, the opportunities to significantly manage floods,landslides, wildfires and other natural hazards are identifiable andshould be executed as funding is available; and
WHEREAS, mitigation recommendations can be effectively prioritizedand managed by a state council, supported by interagency working groups;and
WHEREAS, a need exists to provide formal recognition, authority andresponsibilities to this organizational structure;
NOW, THEREFORE, 1, Roy Romer, Governor of the State of Colorado, byvirtue of the authority vested in me under the constitution and laws ofthe State of Colorado, including the Colorado Disaster Emergency Act of1973, 24-33.5-701, et seq., hereby Order:
1. The Colorado Natural Hazards Mitigation Council is hereby created.The council will be. chaired by the Colorado Department of NaturalResources and consist of as many as 25 representatives. The followingorganizations or groups shall be appointed by the Governor:
- The Governor's Office- State departments of Natural Resources, Highways, Local Affairs,
Public Safety, Health and Agriculture- The Colorado Municipal League and Colorado Counties, Inc.- The Natural Hazards Center, University of Colorado- Business community- The Federal Emergency Management Agency (Region VIII) and the
National Weather Service (National Oceanic and AtmosphericAdministration)
- U.S. Army Corps of Engineers- Elected local officials from areas of the state with high-risk
natural hazards- The general public
Executive Order B 044 89Page Two
The Speaker of the House of Representatives, the President of theSenate, the Minority Leader of the Senate and the Minority Leader of theHouse of Representatives may each appoint one legislativerepresentative. All members will serve for a term of two years withreappointments permitted at the pleasure of the Governor. The Governorwill appoint the chairperson.
2. The chairperson will appoint a steering committee and an executivesecretary to carry on the administrative activities of the council.
3. The responsibilities assigned to the council are to:
a. Identify vulnerability to various natural hazards and evaluatethe options available to mitigate such risks.
b. Review current mitigation plans for such hazards as wildfires,droughts and avalanches.
c. Develop a unified management strategy with recommendationsconcerning state, federal or local mitigation responsibilities.
d. Prioritize hazards statewide.
e. Assist local government in seeking funding to implement hazardmitigation recommendations.
f. Meet at the call of the chairperson, but no less frequentlythan once a year.
g. Prepare an annual work program and status report coveringprogress achieved and provide periodic updates to the Governor andthe state legislature.
h. Inform local government and the general public of theactivities and recommendations of the council.
The council is directed to place high priority on use of the ColoradoFlood Hazard Mitigation Plan and Landslide Hazard Mitigation Plan, andshould coordinate and prioritize the projects contained in these plansand any other plans dealing with natural hazards.
Given under my hand and theExecutive Seal of the Stateof Colorado, this _2,!a day
Roy Romer7 rGovernor VJ
I .I .Figure 28. Executive Order establishing Colorado Natural Hazards Mitigation Council.
The council should be responsible for prior-itizing strategies and projects, securing anddirecting funding, and monitoring overall prog-ram effectiveness to ensure that policies anddirected measures are implemented in a timelyand efficient fashion. Since funds for the imple-mentation of many of the recommended pro-jects will not likely be immediately available,an ongoing and aggressive search for fundingsources will be a major role of the council.State and federal support should be obtainedimmediately for those projects that addresslandslides where potentially catastrophic orserious economic impacts have been identified.
The responsibilities of the working groupswill be to: (1) review risks and options and pro-vide additional information to the council onceprojects have been selected from the plan for
implementation, (2) monitor identified land-slide areas and collect and interpret informa-tion about emergency situations as they occur,(3) prepare new projects as needed to meetchanging conditions, (4) implement projects asfunding becomes available, (5) recommend pro-jects for funding by government and the priv-ate sector as specific needs arise, and (6) pro-vide technical support to the council, includingrecommendations on project priority.
Step 8-Review and RevisionA continuous process for evaluating mitigationprogress and for maldng adjustments to theprogram should be a part of any hazard mitiga-tion system. Procedures for review and revisionof plans and the planning process are discussedin the following chapter. Ii
43
n~(Q)
Review and Revision of the Plan andthe Planning Process
In order to ensure the timely implementationof mitigation projects recommended in thestate landslide mitigation plan, the proposedstate hazard mitigation organization will needto establish an ongoing system for evaluationand modification of the planning process. Inaddition to tracking progress of the programand providing a record of local and state mit-igation achievements, a review process per-mits the adjustment of program priorities. Itallows the state mitigation organization tomonitor and become familiar with the types ofproblems that are likely to be encountered infuture projects, so that planning strategies canbe developed.
The criteria, decisions, and methods usedin applying the landslide research findings toplanning and decision making can be of valueto other jurisdictions in which similar hazardsexist, and for which adequate landslide in-formation is available. The adaption to, andadoption by, other jurisdictions depends uponthe presence of similar public awareness, en-abling legislation, hazard issues, priorities,community interest, innovative decisionmakers, and staff capabilities (U.S. GeologicalSurvey, 1982, p. 44).
While the exact nature of the evaluationsystem should be determined by the mitiga-tion organization in each state based on speci-fic needs, it is recommended that any systemfor evaluating the success of state landslidehazard mitigation programs include thefollowing components:
* an inventory of landslide costs,* an evaluation of mitigation projects and
techniques,* cost-benefit analyses of local mitigation
programs.
Inventory of Landslide CostsAn effort should be made to document all land-slide-related losses in the state as they occur,particularly direct damage to roads and high-
ways, homes and businesses, and facilities andservices, so that decisions can be made regard-ing the level of mitigation assistance requiredto reduce losses in an area and so that thecost-effectiveness of individual projects can bedetermined. The inventory should provide asummary of landslide incidents and associatedfinancial impacts on individuals, companies,municipalities, and local, state, and federalgovernments. The inventory should include alist of occurrences, the location, type of event,cause of event, facilities damaged, total costs ofdamages and/or repair and replacement, andmaps and photographs of affected areas. To theextent possible, an estimate of indirectdamages should also be made.
Understanding the cost and significanceof natural disasters allows officials at all levelsof government to make decisions about howmuch money should be allocated to disasterprevention rather than to the repair of dam-aged facilities and disaster relief after an event(Fleming and Taylor, 1980 p. 1).
Evaluation of Mitigation Projectsand Techniques
The state hazard mitigation organizationshould establish procedures for the periodicreview and evaluation of the status of individ-ual mitigation projects, those proposed, com-pleted, and in progress. The effectiveness oflandslide hazard mitigation efforts varies ac-cording to the physical, economic, and politicalconditions existing in the local areas. Accord-ing to Kockelman (1986, p. 47), "Very fewsystematic evaluations have been made ofhazard-reduction techniques, even fewer forlandslides specifically." A careful assessment ofthe cost effectiveness of each project will helpguide decisions of the state hazard mitigationorganization about the implementation offuture projects.
44
(0111JAST
The occurrence of actual landslide disas-ters and the identification of new landslidethreats will also necessitate an adjustment ofplanning priorities. Maintaining flexibility inthe system will enable the state organization toapply limited funds and resources to effortsthat are most likely to contribute to the reduc-tion of future losses.
Examples of Innovative MitigationApproaches
The evaluation process will produce a record ofboth mitigation achievements and failures,each of which will help educate officials in-volved in solving landslide problems. Examplesof innovative mitigation techniques that havebeen successfully implemented are not only ofvalue as guidance in other jurisdictions, butwill also provide justification for gaining fundsand support for new projects. Additionally,promoting mitigation success stories increasespublic education and awareness of landslidehazards, as well as public confidence in govern-ment hazard mitigation programs.
Analyses of Local MitigationPrograms
A critical feature of the proposed planning pro-cess is the development and maintenance oflines of communication between local and statemitigation systems and between state andfederal systems. In order for state mitigationassistance to adequately support local efforts,local programs must periodically report to thestate their unmet needs, i.e., desired projectsthat are determined locally to be needed, butare beyond local resource capabilities.
Local reports of mitigation needs andactivities in progress will help state officialsdetermine program effectiveness and fundingpriorities. Landslides that present potenti-ally catastrophic impacts and local mitigationprograms that have demonstrated the ability toproduce mitigation results should be amongthe top priorities considered for state or fed-eral assistance. U
45
Approaches for OvercomingAnticipated Problems
The process of developing and implementinglong-term state and local landslide hazard mit-igation programs is beset with certain obsta-cles to success. The most significant problem isgenerating the resolve and motivation to or-ganize, implement, and fund such a broad-scaleeffort. The expenditure of the time and moneynecessary to derive long-term benefits is notalways attractive to state or local leaders. Un-fortunately, sometimes only an actual disasterwill provoke action. Developing creative ap-proaches to financing and obtaining leadershipsupport for mitigation projects is an ongoingchallenge to mitigation proponents. Neverthe-less, it is clear that the ultimate costs to tax-payers are likely to be significantly increasedwhen mitigation activities are postponed.
Organizational ProblemsThe need for the plan preparation team andsubsequent permanent hazard mitigation or-ganization to be broadly representative, multi-disciplinary, and intergovernmental presentssome immediate organizational and coordina-tion problems. An important first step in or-ganizing such a group is to ensure that allelements of the team concur with their rolesand assignments before work begins. Thisagreement should be formalized in a contract,memorandum of understanding, or some otherdocument. A further recommendation is that aproject manager be appointed early on toschedule meetings, tend to administrative andfinancial details, ensure deadlines are met, anddirect and coordinate the effort.
The project manager should be selectedfrom the state organization designated as thelead agency and one of his or her first tasks isto integrate the broad range of technical, plan-ning, community, and organizational expertiseavailable into an effective working team. Elim-
inating jargon and arriving at acceptable term-inology for planning may require some com-promise among team members. On-site visitsto selected landslide areas within the state andthe collection of pertinent reports and litera-ture are important steps that the planningteam should undertake. It may also be usefulto organize a technical advisory committee thatwould meet occasionally to review draft planmaterial and to provide overall guidance andrecommendations.
Management ProblemsThe research and writing efforts involved increating a state plan will involve geologists,engineers, planners, emergency managers,elected officials, and interested citizens. Theintegration of these many points of view is adifficult management task but necessary if theplan is to be practical and usable for the man-agement and mitigation of landslide hazards.The project manager, with guidance and helpfrom other members of the team, must managethis work and establish tasks, assignments,and completion dates. In order to obtain a clearand consistent document, an editor with somebackground in natural hazards, earth sciences,planning and/or mitigation technology shouldbe employed.
Financial ProblemsRegardless of the source or sources of fundingfor development of the plan, careful manage-ment of a budget will be required to ensure allproject expenses are accommodated (staff costs,travel expenses, fees for editing, printing,graphics, etc.). Since the planning process willinvolve several agencies working on independ-ent tasks, periodic reviews of the budget shouldbe conducted to prevent overruns.
46
Coordination ProblemsBecause of the difficulty involved in man agingsuch a comprehensive effort, it is important toset realistic deadlines and to allow sufficienttime for necessary coordination of involvedagencies and integration of the various work-elements. The involvement of all levels of gov-ernment will necessarily affect progress in planpreparation, and time must be allowed forobtaining concurrence and approval from gov-ernmental agencies contributing to the miti-gation process. In addition, executive and/orlegislative leadership that will formally
approve the plan should be kept informed ofthe work and made aware of the plan well inadvance of publication.
Finally, in order to produce a single, cleardraft of the plan, it is also necessary tocoordinate the word processing systems of theparticipating agencies. If compatibility betweencomputer systems is not possible, the variouselements of the plan may have to be re-enteredinto one system. The time and expense of planpublication (typesetting, printing, distribution)should also be determined as soon as possibleto permit identification of realistic deadlines. 0
47
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