REDUCING LOSSES INHIGH RISK FLOOD HAZARD AREAS:
A GUIDEBOOK FOR LOCAL OFFICIALSPrepared byThe Association of State Floodplain ManagersforThe Federal Emergency Management Agency1985

PREFACEAs indicated by its title, this publication is intended to provide guidance to localofficials in their efforts to reduce flood losses in high risk flood areas.
Since some of these high risk flood areas have not been specifically identified bythe Federal Insurance Administration, the implementation of appropriate floodplain man-
agement criteria for those areas is not required for participation in the National Flood In-
surance Program. However, for those communities which have experienced losses to lifeand property in those high risk flood areas and which have an interest in addressing thosehazards, the community options and management strategies which follow are available fortheir consideration and, where appropriate, their use. The community options, with ac-
companying examples of adopted local/state measures, or suggested model ordinance lan-
guage, should provide useful guidance to the local decision maker.
The Federal Insurance Administration believes that reducing flood damages inhigh risk flood hazard areas can and should be addressed at the local or state level.
Therefore, while not a condition of participation in the National Flood Insurance Pro-
gram, the use of these community options and management strategies is encouraged. Thisguidebookshould greatly facilitate that effort.
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HOW TO USE THIS GUIDEBOOKThis guidebook has been prepared to help local governments improve the effec-
tiveness of their floodplain management programs for high risk flood hazard areas. It isdesigned to:
1. Identify general areas where special risks are posed to life and property due to thedepth, velocity and duration of flooding, debris in the water or other factors.
2. Describe a process for amending existing regulations or adopting new regulationsfor high risk areas.
3. Provide examples of innovative community programs and approaches for high riskareas.
4. Direct guidebook users to sources of more detailed information on high risk areas.
Chapter 1 of this guidebook gives an overview of nine types of high risk areas.
Chapter 2 explains the importance of managing high risk areas and describes generic op-
tions and steps for improving their management. Chapters 3 through 11 provide descrip-
tions and guidance for managing development in high risk areas. All chapters follow acommon framework, where each of these items is included if appropriate:
The HazardExisting Mitigation EffortsOptions for ActionPolicy and Program ElementsMappingRegulatory ActionNonregulatory ActionSelected ReferencesAppendicesAppendices contain examples of ordinances, regulations, guidelines and descrip-
tions of community programs.
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TABLE OF CONTENTSpagedesignationChapter 1: The High Risk Areas....................................................AChapter 2: Community Options for Reducing Flood Risks....................................................BChapter 3: Alluvial Fans...................................................CChapter 4: Areas Behind Unsafe and Inadequate Levees....................................................DChapter 5: Areas Below Unsafe Dams...................................................EChapter 6: Coastal Flooding and Erosion.....................................FChapter 7: Flash Flood Areas...................................GChapter 8: Fluctuating Lake Levels....................................HChapter 9: Ground Failure Areas: Subsidence and Liquefaction ................................................IChapter 10: Ice Jam Flooding.......................................................................................................................JChapter 11: Mudslides.........................Kiv

at high risk because of the high velocity of the water, erosion and drainage channels me-
andering across the surface of the fan.
AREAS BEHIND UNSAFE OR INADEQUATE LEVEESTwenty-five thousand miles of levees line streams and rivers throughout theUnited States. Breaching or overtopping of levees causes unexpected floods that are deepand have high velocity. When levees are overtopped, floodwaters are held back from re-
turning to the river and inundation is prolonged .
AREAS BELOW UNSAFE OR INADEQUATE DAMSMore than 2000 communities are at risk from dams that have been identified asunsafe. Even dams classified as safe may be overtopped or breached by extraordinaryfloods, earthquakes, or improper maintenance. Flooding from breaching or overtopping isoften deep, of high velocity and likely to occur with little or no warning.
COASTAL FLOODING AND EROSION AREASErosion and flooding combine to increase flood damage along thousands of milesof coastline. The most serious problems are on barrier islands, along the Great Lakesshoreline and along the Gulf coast. Erosion removes natural protective barriers -beaches,
dunes and bluffs -causing direct damage as well as exposing buildings to larger wavesand storm surges.
FLASH FLOOD AREASAlthough they may occur in all fifty states, flash floods are most common in thearid and semi-arid west where there is steep topography, little vegetation and intense butshort-duration rainfall. They rank first as a cause of flood-related deaths in the UnitedStates. Heavy rains, sometimes in combination with spring snowmelt, often lead to rapidlyrising, fast moving water which can cause severe erosion as well as flood damage. Flashfloods occur in both urban and rural settings, principally along smaller rivers anddrainageways.
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WHY UPGRADE EXISTING PLANS AND REGULATIONS?
Existing community maps and regulations for flood hazard areas often provide in-
adequate protection for high risk areas. Most local regulations, adopted to implement stateand federal floodplain management guidelines, are designed to address normal flood haz-
ards. Here the depth of inundation is the primary factor causing damage and waters arerelatively free of sediment and debris. Flooding is temporary and the configuration of theflood channel is relatively stable. Areas subject to normal flood hazards include low ve-
locity flow areas along major rivers and streams and relatively flat coastal areas inun-
dated by the storm surge where waves and erosion are not major factors.
State and national criteria based upon such a concept of the "norm" have provensatisfactory for 70 to 80 percent of the country. However, the failure to consider otherflood damage factors has resulted in serious deficiencies in management approaches forthe high risk areas, including the following:
Maps usually understate hazards in areas with velocity, debris or other high riskproblems. For example, flood maps for alluvial fan areas designating them as shallowflooding areas incorrectly imply low risk. Usually the risks there are quite serious due tohigh velocities, debris and erosion.
Regulatory criteria designed for the "norm" also underestimate the hazard fromhigh velocity flow, erosion, debris loading and duration of inundation. This can result indamage or destruction of structures built in compliance with regulatory criteria.
THE HIGH RISK FACTORSDepth of inundation is the basic cause of damage in most floods and is also an im-
portant factor in high risk areas. Factors that cause additional damages in high risk areasinclude:
High velocity. The damage potential of flood waters increases dramatically, some-
times exponentially, with velocity. Velocity is determined by slope, waves and severalother factors. Unless the potential for high velocities is considered in building design,
floodproofed structures often collapse from the pressures and stresses applied by fastmoving water. Water moving at speeds of ten (or more) feet per second can undermine pil-
ings and slab foundations. Water velocity is a major cause of damage in four areas:
--Areas subject to coastal wave action (velocity zones), coastal inlets and overwashareas;
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CHAPTER 2: COMMUNITY OPTIONS FOR REDUCING FLOOD DAMAGESFloodplain regulations are the most effective way to reduce futureflood losses in high risk areas. They can keep people from locating inthe most dangerous areas and require safe building designs for otherflood prone areas. But regulations alone cannot deal with all high riskarea problems nor can they usually reduce flood damages to existingstructures. A variety of measures is often needed.
Regulations. Zoning, subdivision regulations, building codes and other special codescan be used to prohibit or to establish special conditions for development in high risk ar-
eas. Conditions include setbacks, additional freeboard or other elevation requirements forbuilding lots, roads, bridges, pipelines and buildings themselves.
Acquisition. Land can be purchased and structures relocated from high risk areas ei-
ther before a disaster or after buildings have been damaged in a flood. Acquired landscan then be used for public recreation and open space.
Flood warning systems and evacuation plans. Flood warning systems and evacuationplans are critical for areas protected by levees or dams and for areas where flood watersrise suddenly. A system can range from volunteer observers to highly automated equip-
ment. Warning systems and evacuation plans can save lives and may reduce losses to con-
tents of structures.
Engineering measures. Engineering measures have been applied to high risk areaswith varying degrees of success. Such measures include groins and bulkheads for coastalerosion areas, debris basins for alluvial fan and mudflow areas, pumping systems for in-
ternal drainage behind dikes and levees, the dewatering of mudflood and mudflow ar-
eas,and grouting and reinforcement for unsafe dams and levees.
Table 1 presents appropriate flood risk reduction techniques for each of the highrisk areas.
STEPS IN REDUCING HIGH RISK FLOOD LOSSESA comprehensive risk reduction program includes the seven steps described below.
If your community has no floodplain management program, or a minimal one, start at stepB-1

Table 1: Reducing Flood Losses in High Risk Areas..
SpecialRisk Area ofHazard Factors Occurrence Management OptionsAlluvial * Lack of Primarily moun-* Prohibit development on fans or, ifFans permanent tainous areas in it is to occur, require elevation ondrainage the west and pilings or other enclosures to protectchannels southwest against water velocities and debris.
* Velocity $ Map fans as high risk areas.
* Sediment * Develop and implement a drainageand debris master plan if development is to* Erosion occur on fans.
* Limit grading, paving, and channel-
ization unless consistent with masterplan.
* Construct floodwalls, drainage chan-
nels, debris basins.
Areas * Velocity Riverine areas * Map levees; assess their adequacy.
Behind * Duration throughout * Define inundation zones for areasUnsafe or * Suddenness the country behind unsafe or inadequate levees.
Inadequate * Require periodic inspection,
Levees maintenance of levees.
* Adopt building standards based onrisk of breaching or overtopping.
* Require pump systems; other methodsfor dealing with internal drainagebehind levees.
* Install or require installation ofwarning-systems and evacuationplans for areas protected by unsafeor inadequate levees.
Areas * Velocity Riverine areas * Coordinate floodplain managementBelow * Suddenness throughout and dam safety programs.
Unsafe or $ Debris in the country * Map dams; assess their adequacy.
Inadequate water * Identify inundation zonesforDamns inadequate or unsafe dams as ifdams were not in place; mapfloodway and flood fringe areas.
* Abate or require abatement of unsafeor inadequate dams.
* Restrict new development belowunsafe or inadequate dams.
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Table 1, cont.: Reducing Flood Losses in High Risk Areas.
SpecialRisk Area ofHazard Factors Occurrence Management OptionsAreas * Require dam owners to prepare damBelow. inspection schedules and maintenanceUnsafe or plans; meet yearly with dam ownersInadequate to review.
Dams, * Prepare or require dam owners tocont. prepare warning systems andevacuation plans for areas belowunsafe or inadequate dams.
* Manage reservoirs to optimize floodhazard reduction.
Coastal * Structural Barrier * Gather existing erosion studies andFlooding damage as islands, bluff historic data, prepare general orand buildings are areas (Great specific maps based upon these orErosion undermined Lakes, West other maps.
* Suddenness Coast), beaches * Adopt setback lines to prohibit* Complete (Louisiana) development in erosion prone landdestruction and on protective land features suchof land as dunes.
(in some * Adopt building performanceinstances) standards pertaining to depth andspecifications for pilings, groins,
seawalls, use of septic tanks, surfacedrainage.
* Acquire undeveloped coastline andrelocate structures.
* Construct groins, seawalls, rebuildbeaches and dunes.
Flash * Suddenness Principally * Collecthistorical data on flashFlooding * Velocity mountainous flooding; use it and engineering* Debris regions in studies to map flash flood(often) valleys with inundation areas.
steep slopes; * Prohibit development and otheralso urbanizing activities (e.g. campgrounds) inareas high risk areas.
Require that new development inother areas be constructedconsistent with water velocities andpotential debris.
* Install or require developers toprepare warning systems; prepareand implement evacuation plans.
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Table 1, cont.: Reducing Flood Losses in High Risk Areas.
SpecialRisk Area ofHazard Factors Occurrence Management OptionsFlash * Require that subdividers installFlooding, onsite flood detention; designcont. drainage systems to reduce flashflood potential.
* Mark areas.
* Construct reservoirs and otherengineering devices to reduceflash floods.
Long-Term * Long Primarily * Map historical bed of lake.
Fluctuations duration northern states * Adopt floodplain, shoreland andin Lake * Waves and (glacially wetland ordinances to directLevels ice formed lakes) development.
* Lake with water * Require elevation of structures andquality elevations public utilities on fill (not pilings).
degradation dependent * Prohibit septic and water systems inas flooded upon ground flood areas is development is tosewage water levels' occur.
systems fail lakes in * Adopt setback back lines or* Ground water western states additional freeboard if develop-
quality without ment is to occur to reduce damagedegradation outlets from waves and ice damage toas flooded structures.
wells act * Acquire flood-prone lands andas conduit relocate threatened structures.
to transfer Install pumps, other engineeringlake water works to reduce or stabilize laketo aquifers levels.
Ground * Collapse of San Francisco * Conduct special studies to deter-
Failure: structure Bay, Alaska, mine areas and levels of risk.
Liquefaction * Suddenness New Madrid $ Adopt special building designof flooding Fault Zone Area, standards for pilings, densities of.
other areas development, loading factors.
with saturated * Acquire highly unstable lands andsoils and relocate structures.
earthquakethreat* aB-4

Table 1, cont.: Reducing Flood Losses in High Risk Areas.
SpecialRisk Area ofHazard Factors Occurrence Management OptionsGround * Structural Houston/ * Prepare maps showing mines, organicFailure: damage and/ Galveston, soils, karst formations, areas subjectSubsidence or collapse New Orleans, to hydrocompaction, etc.
* Permanent Sacramento * Conduct frequent site inspectionsinundation Delta, and and restudies to determine currently* Increasing many other expected flood levels and revise 100-
flood areas year flood protection elevations.
elevations (localized) * Require pre-development site(over time) investigations.
* Damage to * Prohibit development in high riskbuildings, areas; require adequate foundationroads and support through zoning or buildingservice codes in other areas.
lines * Add freeboard to 100-year floodelevations.
* Limit ground water, oil & gaswithdrawal where it is causingsubsidence; computer models canpredict subsidence related to amountof withdrawal.
* Require reinjection of waterin oil & gas drilling operations.
* Purchase and relocate structures outof high risk areas.
Ice Jam * Unexpected Principally 35 * Collect historical data on ice jamFlooding flood levels northern states floods; use it or engineering studies* Suddenness including to map ice jam inundation areas.
* High velocity Alaska; jams * Adopt setback lines.
* Debris occur most * Require additional freeboard to(ice floes) often at protect against ice.
constriction * Adopt construction standards, esp-
points in ecially for floodproofing, thatriver valleys consider ice damage.
* Acquire hazardous lands and relocatestructures that cannot be protected.
* Develop a warning system andemergency action plan.
* Undertake remedial engineeringmeasures.
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Table 1, cont.: Reducing Flood Losses in High Risk Areas.
SpecialRisk Area ofHazard Factors Occurrence Management OptionsMudfloods * Debris. The arid and * Gather and use available data to mapand * Velocity semi-arid west; mud flow areas.
Mudflows (in some Appalachia * Require developers in slope areasinstances) with unconsolidated soils to prepare* Suddenness engineering studies.
* Prohibit development in high riskareas; require that developments inother areas be constructed on com-
pacted fill or with adequate founda-
tions on pilings to accommodate ex-
pected water and debris.
* Construct debris basins, retainingwalls, other remedial measures.
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evacuation plan. Upon learning the facts, the city governing body could, by resolution,
adopt this statement to guide further community action.
This new policy would form the basis for more specific plans or regulations, forenforcing protective laws to their fullest extent and for obtaining funds and other assis-
tance to plan and implement a risk reduction program. An initial declaration of policywill be refined as high risk areas are studied and more detailed plans are made for reduc-
ing potential future losses.
Step Two: Assess the General Location and Extent of HazardsThe second step is to identify and evaluate potential high risk areas. Where are thehigh risk areas in your community? Have there been past flood losses in such areas?
Often considerable public information already exists in the form of flood damagereports, flood records, flood maps, newspaper accounts or other historical data to suggestwhere high risk flooding has occurred. If damages have not occurred in the area before,
the potential risk may be unknown. For example, alluvial fans in the arid west are oftennot recognized as high risk areas due to lack of recent flood damage. People living half amile from a small meandering stream may not realize that the stream can change itscourse rapidly.
Hazard assessments can be conducted by emergency management personnel, plan-
ners, city engineers or consultants. Information on hazard assessment is available from thesources listed in the appendices of the individual chapters which follow.
Step Three: Map High Risk AreasOnce the general location of a high risk has been identified, mapping is usuallyneeded to determine the more precise extent of the area affected. Once areas are mapped,
regulations and other management measures can be adopted. Maps can be of two types:
1) General, indicating the area where conditions create the potential for dam-
age; or2) Specific, delineating locations of known frequency and level of flooding.
Generalized maps are useful for initial planning and zoning but often must besupplemented with more detailed onsite investigations when development is proposed.Sucha regulatory procedure is incorporated in the single district floodplain zoning ordinanceproposed in Volume 1 of Rexgulatiotnof Flood Hazard Areas to Reduce Flood Losses. (U.S.
Government Printing Office, 1971 and 1972.) The general map only establishes theB-8

On their own initiative or at the urging of the states, several hundred communitieshave adopted special hazard regulations for alluvial fan, mudflood, coastal erosion andother risk areas. Regulations are usually part of broader zoning, subdivision controls orbuilding codes. Strengthened regulatory approaches for high risk areas may include:
1) Absolute prohibition of development in areas of high risk, where developmentwill substantially increase flood heights or erosion on other lands or where engi-
neering solutions are impractical. Interim prohibitions or moratoria that stop recon-
struction are especially appropriate after a disaster.
2) Added elevation requirements through freeboard or increased base elevations toreflect the additional risk (e.g., wave heights, ice jams).
3) Strengthened performance standards to reflect not only water depth but alsovelocity, debris and other risk factors. Applicants for building permits orsubdivision plat approval can be required to undertake hydrologic and geologicinvestigations to specifically determine the hazards at sites and then to design theproposed structure consistent with the hazards.
Step Six: Implement and Enforce Plans and RegulationsAdoption is only the first step in implementing plans and regulations. Formulationof plans and regulations is primarily a technical effort; the implementation and enforce-
ment which must follow is in part an educational process. Administrators, elected offi-
cials, interest group leaders and the general public must be informed of the content ofplans and regulations and how they will work. Their support is essential to long-termsuccess.
Step Seven: Incorporating Nonregulatory ApproachesPlans and regulations alone cannot remedy threats to existing structures. A combi-
nation of education, public acquisition, financial incentives, warning and evacuation sys-
tems, technical assistance and engineering measures is often appropriate to reduce damagefrom high risk flooding. The appropriate combination will depend upon your community'sneeds, problems, levels of funding, amount of existing development and other factors.
Use of the recommended sources of information presented in Table 2 will aid inthe execution of your flood risk reduction program.
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Table 2: Sources of Mapping Assistance.
Type of Mapping Methods, DataHazardAlluvial * Topographic maps from U.S. Geological SurveyFan * County Soil Surveys from U.S. Soil Conservation ServiceFlooding (type of sediment)
* Aerial photographs -from U.S. Agricultural Stabilizationand Conservation Service (locate fan formations)
* Map methodology from Federal Emergency Management Agency(See bibliography for other methods.)
Areas Behind * FEMA flood mapsUnsafe or * U.S. Soil Conservation Service flood-mapsInadequateLeveesAreas Below * U.S. Army Corps of Engineers Dam Safety reportsUnsafe or * State Dam Safety Reports.
Inadequate * FEMA map feasibility study.
Darns * Colorado and California Dam Safety ProgramsCoastal * State maps and a variety of data from state coastal zoneFlooding management and floodplain management programs, state universityand sea grant and college programs.
Erosion * Historic and current maps from the U.S. Geological Survey,
U.S. Coast and Geodetic Survey, U.S. Agricultural Stabilization& Conservation Service, state university cartographers.
Flash * List of flash-flood prone communities, National Weather ServiceFlooding * FEMA flood maps* State floodplain management agenciesU.S. Geological Survey topographic maps* Records of events, damages and hydrologic studies from the U.S.
Army Corps of Engineers, Soil Conservation Service, state water resource and floodplain management agencies* Local newspaper archives, long-term residents.
rnkn * YT-ftnr~nl lalce Ievreldiata frnm UT. Genlnogicl Survev (tnnnornnhicburrLevelFluctuationmaps show lake area)
* State agency records (regular lake gauge reading program, specialstudies in conjunction with permits)
* Long-term residents (survey and photographs)
* State historical society (land survey records).
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Table 2, cont.: Sources of Mapping Assistance.
Type of Mapping Methods, DataHazardGround * General and detailed assessments of earthquake and liquefactionFailure: probability from U.S. Geological Survey.
LiquefactionGround * Geological studies, water atlas from U.S. Geological Survey karstFailure: strata, ground water information)
Subsidence * Soil surveys from U.S. Soil Conservation Service (organic soils).
* Mine and irrigation locations from state regulatory agencies.
* Historic events and damages from local newspaper archives* Information on karst terrain mapping methods and assistance instudies from Florida Sinkhole Research Institute.
Ice Jam * Historical records of ice jam floods from local newspaper archives.
Flooding * Historical data concerning locations where ice jam floods haveoccurred from long-term residents* Some flood insurance rate maps from the Federal Emergency Management Agency show ice jam flood-prone areas* Map method from U.S. Army Corps of Engineers Cold Regions Re-
search and Engineering Laboratory (see bibliography)
MAudfloods $ Historical records of events and damages from U.S. or stateand geological surveys, archives, university geology departmentsMudflows * Topographic maps from U.S. Geological Survey* Soil surveys from U.S. Soil Conservation ServiceB-12

meandering channel. Some progress has been made in mapping, regulating and managingfans consistent with their true hazard.
FederalIn 1982, the National Flood Insurance Program (NFIP) commissioned a study of mapping,
modeling and land management standards for alluvial fan areas. The study resulted in thedevelopment of suggested management standards for these zones on the fan: a channelizedzone, a braided zone and a sheet flow zone (see Figure 3-1, Appendix 3-A). In addition tothis study, the NFIP has promulgated mapping guidelines for flood insurance studycontractors (see Appendix 3-B). FEIMA'sRegion X has also drafted a model ordinance forcommunities with alluvial fan flood problems (see Appendix 3-C). This has been presentedto several communities.
The U.S. Geological Survey and the Corps of Engineers have also mapped somealluvial fan areas and are working on alluvial fan mapping methods.
StateState efforts to develop special maps and regulations for alluvial fans have beenlimited, although Colorado has recommended to local governments a model ordinance ad-
dressing fans and other geological hazard areas (see Appendix 3-D).
California's geologic hazard investigation and reporting system requires local gov-
ernments to identify and regulate geologic hazard areas. This requirement applies to sometypes of hazards on the fans. Developers seeking a building permit or subdivision ap-
proval for projects on fans must have a certified geologist prepare a geologic report assur-
ing the risk.
Nevada has developed an alluvial fan management handbook for local governmentsbut has not adopted regulatory requirements.
LocalMost of the innovative efforts to map, regulate and otherwise manage alluvial fanshave occurred at the local level.
Riverside County, California, has developed an alluvial fan methodology andmapped alluvial fans in the Cabazon area. It has also adopted special regul-
ations reflecting flood velocities, erosive force and debris.
Los Angeles County, California has mapped alluvial fans and adopted a gradingcode for these and other areas.
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FANAPEXCHANNELIZEDZONEBRAIDED SHEETFLOWZONE ZONEFigure 3-1. Hydraulic zones on a typical fan. Source: FEMA.
Watershed Slopeand VegetationFigure 3-2. Factors affecting flood hazards on alluvial fans.

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Figure 3-3. Topographic characteristics of typical alluvial fans and 
alluvial aprons (Wenatchee, Washington). Source: FEMA. 

Figure 3-4. Trailer park built on alluvial fan. Source: R. Platt. 


forested areas, fans may be more difficult to map. Topographic and soils maps may beused to identify areas with steep slopes and alluvium.
An outline of alluvial fan areas can, even without more detailed identification ofrisk zones within the fans, be an important "red flag" for land use decisions. Once out-
lined, fans can be zoned as high risk areas. Developers can be required to conduct de-
tailed studies of the flood risk and design accordingly.
Engineering methods, although quite expensive, are available for mapping fans inmore detail and determining the relative risks within the fans. With these maps, zoningregulation can be quite specific. However, site-specific studies and master planning willstill be needed as new development is proposed.
RegulationsRegulations for alluvial systems should have two principal goals: to prevent accel-
eration or diversion of runoff and increased erosion, and to insure that individual struc-
tures and infrastructures are adequately protected from high velocity flows, debris anderosion.
If the fan is undeveloped, future flood damages can be avoided by prohibiting de-
velopment. Development should only be permitted if a master plan has been prepared. Analluvial fan master plan should show the drainage system, roads, grading and fillingneeded for drainageways, debris walls and other flood protective measures, such as bankstabilization, erosion control measures and floodways to be maintained as open space.
Where the fan is in multiple ownership, the community should prepare the master plan.
Developers can be required to implement their portion as a condition of plat approval orbuilding permits. Las Vegas takes this approach. Where the fan is in single ownership,
regulations may require the developer to prepare a master plan for the fan as a whole.
Zoning, subdivision controls or grading codes can be adopted to limit developmentdensities, impervious surfaces and modifications to natural topography.
To help protect individual structures, include the following provisions in yourbuilding codes, zoning regulations, grading codes and subdivision regulations:
1. Prohibit building in areas where velocities exceed a selected threshold level(e.g., 7 feet per second).
2. Require that structures in other areas be elevated on stabilized fill or rein-
forced pilings to a height above the 100-year flood elevation, taking into ac-
count debris as well as water elevations.
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3. Require pilings below scour depth (see Figure 3-5).
4. Require slope protection for fill.
5. Require that fill be provided not only for individual structures but also forroads and public utilities since much of the damage due to alluvial fanflooding is to infrastructure.
Non-Regulatory ApproachesRegulations should be combined with non-regulatory options depending upon thelevels of existing development (see Figure 3-6). Two of the principal non-regulatoryapproaches for reducing losses on fans are to acquire fans or portions of fans and toconstruct debris basins and other engineering works to stabilize the drainage pattern onthe fan and reduce erosion as well as flooding.
AcquisitionFans may be kept in an undeveloped condition through public purchase rather thanregulation. Fans can be used as parks, recreation areas or open space where public accessis desirable. Such an approach is expensive but avoids constitutional problems and allowsactive public use of the fan.
Debris BasinsDams may be constructed on the upper portion of fans or along drainage channelsto collect sediment, rocks and floodwaters. Such dams and the resulting debris basin areeffective in temporarily stopping debris flows but are expensive and must be periodicallyemptied. Disposal of a large amount of debris is a major problem. The cities of Los An-
geles and San Diego have constructed debris basins.
Floodwalls, Channels. Other Engineering WorksA variety of engineering works such as flood walls and concrete channels can helpprevent channel migration and accommodate runoff. If any engineering works are to beconstructed on a fan, a master plan for development and drainage should be prepared.
The location and design of roads must be part of such a plan since roads often block orconvey flood waters.
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ELEVATEPAD&PROVIDEELEVATE PAD & PROVIDESLOPE PROTECTIONSFORHEIGHT\ | ~~~APPROVEDr1< PROTECTIONa/ | ~SCOURDEPTHNATURAL GROUNDSLOPE PROTECTION OPTIONI'PAD ELEVATIONMUST BE EQUAL TOOR GREATER THAN100 YEAR WATER SURFACEIF IN FRINGE AREANATURAL GROUND-a-EXTENDPILE SUFFICIENTLYBELOW SCOUR DEPTH TOSUPPORT STRUCTUREPILING OPTIONELEVATIONNO SCALEFigure 3-5: Suggested floodproofing criteria for structure in alluvialfan area. Source: Riverside County Flood Control andWater Conservation District's Cabazon Flood Study.

IMITED DEVELOPMENT 

Figure 3-6: Regulations should be combined with nonregulatory 
options depending upon the levels of existing development. 


Appendix 3-A: Suggested Development Guidelines for Various Hydraulic Zones on the Fan.
The following applications of management tools were recommended by FloodplainManagement Tools for Alluvial Fans, a report prepared for the Federal EmergencyManagement Agency (1981). The recommendations apply to each hydraulic zone on thefan and for the placement of single structures:
Channelized ZoneDevelopment prohibited unless whole-fan measures are implemented.
Braided ZoneBasements and mobile homes prohibited.
Streets aligned and designed to convey entire flood flow.
Use of local dikes to direct flows into streets.
Use of drop structures between homes built on high slopes to prevent excessiveerosion.
All management tools must be coordinated with tools in existing developments.
Whole-fan management tools can be used instead of the above provisions.
Shallow Flooding ZoneElevation of structures on piles or armored fill.
Street orientation to maximize flood conveyance.
If up-fan subdivisions use depressed streets or channels to convey floods, thesetools must be continued down to the fan toe.
Use of drop structures between homes built on high slopes.
Whole-fan management tools can be used instead of the above provisions.
Placement of Single StructuresIn undeveloped areas, place structures on armored fill or use local dikes providedthat no added flood damage to other structures results.
In developed areas, local dikes, channels and armored fill must tie in with existingflood control tools.
Elevation on piles should be used if above criteria cannot be met.
No single placement should be allowed in the channelized zone.
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In the lower region of the fan, flood flows split and form multiple channels. Forpurposes of this procedure, the concept of a single eguivalent channel is used to computeflood depths and velocities. Normal flow conditions are considered to exist in the multiplechannel region due to the relatively flatter slopes.
The probability of a point being flooded in a given flood event decreases from theapex to the toe of the fan because the downslope widening of the fan surface provides agreater area over which a channel of given width may occur.
b. Depth of FloodingFor flood mapping purposes, the depth of flooding computed on alluvial fans is thedepth of flow (depth of channel) in the channel that carries a given discharge to the toeof the fan surface.
c. Velocity of FloodingFor alluvial fan flood mapping, the velocity of flooding computed for alluvial fanflood mapping is the velocity of flow in the channel that carries the given discharge tothe toe of the fan surface.
d. AvulsionsDuring major floods on active alluvial fans, peak flows may abruptly abandon onechannel that had been formed during the flood, and form a new channel This phe-
nomenon, termed an avulsion, can cause a significant increase in the probability of flood-
ing at a given point on a fan because of the increased channel widths that may cross agiven contour during a given flood event. The treatment of avtilsions is an important fac-
tor in the application of the methodology presented in this Appendix.
3. FLOOD HAZARD ZONESSpecial flood Hazard Areas on alluvial fans are identified as Zone AO with thefollowing definition:
*Zone AO: Zone AO is the flood insurance rate zone that corresponds to the areasof 100-year shallow flooding (usually sheet flow on sloping terrain) whereaverage depths are between 1 and 3 feet. Average whole-foot depths derivedfrom the detailed hydraulic analyses are shown within this zone.
* Exception to the 3-foot depth limit for zone AO is permitted for alluvial fans whergapproved by the P0.
The Special Flood Hazard Area on each alluvial fan is subdivided into separateAO zones with similar depths and velocities. Zones are delineated that have depths orvelocities differing by an average of 1.0 foot in depth or 1.0 foot per second (fps) invelocity..
In areas of coalescent alluvial fans, separate depth-frequency relationships shouldbe developed for each source of flooding and combined based on the probability of theunion of independent events.
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Appendix 3-C: Excerpts from Sample Flood Damage Prevention Ordinance, Prepared byFEMA, Region X, Bothell, Washington.
5.2 STANDARDS FOR ALLUVIAL FANSAreas subject to alluvial fan flooding have irregular flow paths that result in ero-
sion of existing channels and the undermining of fill material. Those areas are identifiedon the Flood Insurance Rate Map as AO Zones with velocities.
1. All structures must be securely anchored to minimize the impact of theflood and sediment damage.
2. All new construction and substantial improvements must be elevated on pil-
ings, columns, or armoured fill so that the bottom lowest floor beam is ele-
vated at or above the depth number.
3. Use of all fill materials must be armoured to protect the material from thevelocity of the flood flow.
4. All proposals for subdivision development must provide a mitigation planthat identifies the engineering methods used to:
a. Protect structures from erosion and scour caused by the velocity ofthe flood flow.
b. Capture or transport flood and sediment flow through the subdivi-
sion to a safe point of deposition.
5. All mobile homes shall be prohibited within the identified hazard area ex-
cept within existing mobile home parks or subdivisions.
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Appendix 3-D: Excerpts from Colorado's Model Geologic Hazard Area Control Regulations.
The following model regulations for identification, designation, and control ofland use in areas of geologic hazard were prepared by the Colorado Geological Survey inaccordance with statutory charges contained in Colorado HB-1041. Whereas, at least to ourknowledge, comparable laws or regulations dealing with geologic hazard areas have neverbeen written, this has been a pioneer effort. However, since laws, regulations, and admin-
istrative procedures for floodplain hazard areas have been developed and tested duringthe past, they have drawn heavily upon the language of tested floodplain regulations indrafting these model regulations.
WHEREAS, authority for the governing body of a municipality or a county toadopt, amend, repeal, enforce and otherwise administer under the police power reasonableGeologic Hazard Area Land Use Control Regulations and orders pertaining to land usewithin the areas of its jurisdiction..., andWHEREAS, the uncontrolled use of land within geologic hazard areas...adverselyaffects the public health, safety and welfare of the citizens..., andWHEREAS, the governing body...is empowered...to designate and administer areasof state interest in a manner that will minimize significant hazards to public health andsafety or to property due to a geologic hazard, andWHEREAS, geologic hazards are declared to be matters of state interest and aredefined...to include but not be limited to avalanches, landslides, rockfalls, mud flows, un-
stable or potentially unstable slopes, seismic effects, radioactivity and ground subsidence;
...NOW,THEREFORE, the Board of County Commissioners (City Council) does en-
act the following Geologic Hazard Area Control Regulation:
SECTION 1.0 PURPOSESTo promote the public health, safety and general welfare, to minimize the effect ofsignificant hazards to public health and safety or to property due to a geologic hazard bythe proper administration of all land use changes within such geologic hazard areas, andto promote wise use of geologic hazard areas. This Geologic Area Control Regulation hasbeen established with the following purposes intended:
1.1 To reduce the impact of geologic hazards to life and property by:
1.11 Prohibiting certain land uses...
1.12 Restricting the uses which would be hazardous...
1.13 Restricting the uses which are particularly vulnerable to geologic hazards soas to alleviate hardship and reduce the demands for public expenditures forrelief and protection.
1.14 Restricting permitted land uses in geologic hazard areas, including publicfacilities...to be protected...by providing for geologic hazard investigationand avoidance or mitigation or hazard impacts at the time of construction.
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1.15 Adopting Chapter 70 of the Uniform Building Code...for the regulation ofexcavation and grading of lands...
1.2 To protect geologic hazard area occupants or users from the impacts of geologichazards which may be caused by their own, or other, land use and which is or maybe undertaken without full realization of the danger by:
1.21 Regulating the area in which, or the manner in which, structures designedfor human occupancy may be constructed...
1.22 Designating, delineating and describing areas that could be adversely af-
fected by geologic hazards so as to protect individuals from purchasing orimproperly utilizing lands for purposes which are not suited.
1.3 To protect the public from the burden of excessive financial expenditures from theimpacts of geologic hazard and relief by:
1.31 Regulating land uses within geologic hazard areas so as to produce a patternof development or a soundly engineered manner of construction which willminimize the intensity and/or probability of damage to property and loss oflife...
1.32 Regulating the cutting, filling, or drainage changes...which could initiate orintensify adverse conditions within geologic hazard areas.
SECTION 2.0 GENERAL PROVISIONS2.1 Jurisdiction: This regulation is applicable to all lands within Designated GeologicHazard Areas...
2.2 Boundaries: The boundaries of the Designated Geologic Hazard Areas shall be asthey appear on the official recorded Designated Geologic Hazard Area Maps asadopted... and kept on file...
2.3 Interpretation: In their interpretation and application, the provision ... shall be heldto be minimum requirements and shall be liberally construed in favor of the gov-
erning body... Interpretations... shall be consistent with GUIDELINES AND CRI-
TERIA FOR GEOLOGIC HAZARD AREAS prepared by the Colorado GeologicalSurvey...
2.4 Warning and Disclaimer of Liability: The degree of protection from geologic haz-
ards intended to be provided by this Regulation is considered reasonable for regu-
latory purposes, and is based on accepted geologic and scientific methods ofstudy...unforeseen or unknown geologic conditions or natural or man-made changesin conditions such as climate, ground water, drainage, or structural strengths of therocks and other geologic materials may contribute to future damages to structuresand land uses even though properly permitted...
2.5 Adoption of Official Maps: The location and boundaries of the Designated Geo-
logic Hazard Areas established by this Regulation are shoxvnupon the official Des-
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ignated Geologic Hazard Area Maps...which are hereby incorporated into thisRegulation...
SECTION 3.0 NONCONFORMING USES.
SECTION 4.0 DESIGNATED GEOLOGIC HAZARD AREAS.
4.1 Application4.2 Description of Designated Geologic Hazard Areas4.3 Description of Permitted Uses: The following open uses shall be permitted withinDesignated Geologic Hazard Areas...
4.31 Agricultural uses such as general farming, grazing, truck farming, forestry,
sod farming and wild crop harvesting;
4.32 Industrial-commercial uses such as loading areas, parking areas...and storageyards for equipment...easily moved or not subject to geologic hazard damage.
4.33 Public and private recreational uses not requiring permanent structures de-
signed for human habitation...if such uses do not cause concentrations ofpeople in areas during periods of high hazard probability.
SECTION 5.0 ADMINISTRATION5.1 Designated Geologic Hazard. Area Administrator...
5.2 Application for Development Permit...
5.3 Permit Review...
5.4 Permit Approval or Denial...
5.5 Mapping Disputes...
SECTION 6.0 ENFORCEMENT AND PENALTIESSECTION 7.0 AMENDMENTSSECTION 8.0 SEVERABILITYSECTION 9.0 DEFINITIONSC-21

SELECTED REFERENCES ON ALLUVIAL FAN FLOODINGCalifornia Department of Water Resources, 1980, California Flood Management: An Evalua-
tion of Flood Damage PreventionPrograms. Bulletin 199. Sacramento: Dept. of WaterResources.
Committee On Natural Disasters, Natural Research Council, and Environmental QualityLaboratory, California Institute of Technology. Storms, Floods and Debris Flows inSouthern California and Arizona--1978 dnd 1980. Proceedings of a Symposium,
September 17-18, 1980. Washington, D.C.: National Academy of Sciences.
Dawdy, D.R., 1979, Flood Frequency Estimates on Alluvial Fans. Journal of Hydraulics Divi-
sion, A.S.C.E. 105 (HYll)
Douglas, J.R., D.T. Larson, D.H. Hoggan, and T.F. Glover, 1980, Floodplain ManagementNeeds Peculiar to Arid Climates. Water Resources Bulletin 16: 1020-1029.
Edwards, K.L. and J. Thielman, 1982, Flood PlaintManagement Cabazon, California. Ameri-
can Society of Civil Engineers Meeting, April 26-30, 1982.
Federal Emergency Management Agency, 1982, Methodology for Analyvsisof Flood Hazardsoil Alluvial Fans. Washington, D.C.: IFEMA.
-----, 1985, Guidelines and Specifications for Flood InsuiranceStudy Contractors.Washington,
D.C.: FEMA.
Hays, W. (editor), 1981, Facing Geologicand Hydrologic Hazards: Earth-Science Considera-
tions. Geological Survey Professional Paper 1240-B. Washington, D.C.: U.S. Govern-
ment Printing Office.
Magura, L.M. and D.E. Wood, 1980, Flood Hazard Identification and Flood Plain Manage-
nient on Alluvial Fans. Water Resources Bulletin 16: 56-62.
Planning Research Company, 1980, Cabazon Flood Study. A Report on Flooding from SanGorginoRiver, Jenson Creek and Millard Canyon Creek. Riverside, California: River-
side County Flood Control District.
Roberts, B.R., E.W. Shanahan, Y.H. Chen, A.A. Fiuzat and H.J. Owen, 1981, Flood PlainManagement Tools for Alluvial Fans. Final Report to the Federal Emergency Man-
agement Agency. Palo Alto, California: Anderson-Nichols & Company.
Rodgers, W.P., L.R. Ludwig, A.L. Hornbarker, S.D. Schwochow, S.S. Hart, D.C. Shelton, D.L.
Scroggs and J.M. Saute, no date, Guidelines and Criteria for Identification and LandUse Controls of Geologic Hazard and Mineral Resources Areas. Denver, Colorado:
Colorado Geological Survey.
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Scullin, C.M., 1983, Excavation and Grading Code Administration, Inspection and Enforce-
ment. Englewood Cliffs, New Jersey: Prentice Hall.
Tettemer, J.M., no date, Angel Park: Keystone of a Master Plan on an Alluvial Cone. Unpub-
lished paper. Los Angeles, California: John M. Tettemer & Associates.
U.S. Geological Survey, 1981, Goals,Strategies, Priorities and Tasks of a National LandslideHazard-Reduction Program. Open File Report 81-987. Washington, D.C.: USGS.
U.S. Geological Survey, 1982, Goals and Tasks of the Landslide Part of a Ground Failure.Hazard Reduction Program. Circular No. 880. Menlo Park, California: USGS.
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Figure 4-1. Levees run the gamut from carefully designed and built 
structures to haphazard devices of unknown protective 
capability. Source: unknown. 


Types of LeveesFlood Control LeveesDuring the last three decades, the U.S. Army Corps of Engineers, theU.S. Department of Agriculture Soil Conservation Service, the U.S.
Bureau of Reclamation and the Tennessee Valley Authority havedesigned and constructed flood control levees. Most major federallevees are structurally sound, but levels of protection and maintenancevary. Their integrity may also be threatened by changing hydrologicconditions.
Emergency LeveesIn 1969, Congress authorized the U.S. Army Corps of Engineers toconstruct emergency levees, in cooperation with states and localgovernments. When flooding is imminent, the Corps will constructemergency protective devices if the community agrees to1. provide rights of way,
2. provide common labor,
3. supply fill,
4. retain responsibility for damages.
Theoretically, the community must also remove the levee and dispose ofmaterials. This last requirement, removal of all emergency levees, hasnot been steadfastly enforced. As a result, many miles of unsafe leveesnow exist.
Agricultural LeveesEarthen agricultural levees are typically constructed to protect croplandfrom frequent floods. While their failure may not cause significantproperty damage as long as structures are not built behind them,
agricultural levees may contribute to risks. Often built at the edge ofthe channel by the landowner and without adequate technical analysis,
agricultural levees can increase flood velocities or elevations upstream,
downstream or on adjacent lands. In addition, if the farmland is laterdeveloped, local communities and landowners will tend to assume thatthe levees provide a larger degree of flood protection than they do.
Other Locally Constructed LeveesIndependently constructed levees are often built by communities orindividuals after a history of frequent flooding Various designstandards and construction materials have been used. It is rarelypossible to determine the structural adequacy of these levees without anextensive evaluation.
D-3

Over the next ten years the City intensively developed the "former"
floodplain. This development included a new shopping mall locatednext to the project. In 1975, a survey of the channel centerline indi-
cated that approximately400,000cubic yards of sediment had accu-
mulated between the levees, significantly reducing the project's capac-
ity. The City had not dredged the channel annually during this period.
Local officials had believed that .high winter flows would scour the ac-
cumulated sediment and carry it out to sea.
The California Department of Water Resources threatened to dredgethe channel for the City and charge it for the cost. The City then beganto remove small amounts of the sediment in the channel; as ofDecember.1981 fewer than 100,000 cubic yards had been removed. TheCity is now unable to finance removal of the remainder of the sedimentestimated to cost $3 million initially and $200,000annual maintenance.
A recent evaluation indicates that at present the levees could containonly a 25 to 30 year flood, or 35,000 cfs without freeboard (Griggs andParis, 1981). While the FIRM indicates that the 100 year floodplain iscontained by the levees, an updated map depicting current conditionswould show most of downtown Santa Cruz to lie in the floodplain.
This example illustrates the sorts of problems that can affect a flood controlproject. The original design discrepancies have contributed to the current situation. Eventhough the tools and methods available to hydrologists have improved substantially sincethe 1950's, many hydrologic studies must still be based on scarce streamflow records andother historical data.
OPTIONS FOR ACTIONPolicy and Program ElementsIf there are levees in your community, adopt a policy and program with the fol-
lowing elements:
1. A policy statement that levees involve risks due to overtopping, inadequatedesign, inadequate maintenance, internal drainage and other factors;
2. A map of levee location, also indicating safety and degree of providedprotection. Inundation zone maps should be prepared for unsafe orinadequate levees;
3. A program for periodic levee inspection. The continued safety of the leveesystem depends upon maintenance;
4. Protective regulations for areas behind levees. At a minimum, newconstruction and rebuilding behind levees unable to provide protection fromthe 100-year flood event should be elevated or floodproofed. ForD-5

construction behind levees considered satisfactory to provide protectionfrom a 100-year flood (with necessary freeboard elevations) newconstruction should be equipped with drainage, pumping and other facilitiesto prevent internal drainage problems.
5. A regular schedule for communication between engineering, planning andemergency management personnel to provide consideration of levee hazardsin land use decisions.
MappingTwo types of maps can help you reduce risks from levees:
1. Levee location and assessment maps. Maps should be prepared locating alllevees in the community and indicating their degree of protection.
2. Inundation map. Flood inundation maps should be prepared for areasbehind inadequate or unsafe levees (see sample map, Figure 4-2).
Levee location maps can be prepared from air photos, engineering or public worksdepartment records, floodplain maps and field inspections. The levee location and assess-
ment map should show who constructed the levee and who is responsible for its mainte-
nance. Once levees are located, the degree of protection can be assessed with varying de-
grees of specificity based upon the following types of information:
1. Levee type (see above). This is the minimum indicator of degree ofprotection.
2. Levee design standard. Expressed as the recurrent interval of the flood thatthe levee is designed to contain. It can usually be determined from designplans.
3. Comparison of levee height to the 100-year flood elevation. Calculate thenumber of feet above or feet below or search for previous determinations inengineering reports.
4. Inspection and evaluation of the levee to determine design adequacy andmaintenance. This requires field surveys.
If a flood insurance study has been done for your community, it will indicate lev-
ees that may provide protection from the 100-year flood (see Appendix 4-A for FEMA re-
quirements). A staff engineer or consultant can make the field inspections necessary todetermine intended degree of protection, current conditions and maintenance record forother levees.
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Figure 4-2. Sample map segment showing how levee failure inundation 
areas could be designated. 

Figure 4-3. House behind levee in Soldiers Grove, Wisconsin being 
elevated after severe flooding in 1978. Source: T. Hirsch. 


Once location and assessment maps are completed, inundation maps can be pre-
pared for areas behind unsafe or inadequate levees. These are prepared much like a nor-
mal flood map, making the assumption that the levee will be overtopped. The inundationmaps should show:
1. The 100-year floodway and flood fringe as if the levee did not exist.
2. Potential velocity areas at low or weak points in the levee system whereovertopping or breaching would most likely occur.
Inundation maps should show areas subject to flooding from internal drainage aswell as those at risk due to potential overtopping or breaching. These areas can beidentified using historic flood data, local inquiries, topographic maps and field studies.
Areas where water is expected to collect to a depth of one foot or more during a specifiedstorm event should be mapped. FEMA's guidelines for mapping of ponding areas, inAppendix 4-A, may be applied.
RegulationsTwo types of regulations can reduce flood losses behind levees:
1. Standards for construction, maintenance and rebuilding of levees.
2. Land use controls and building standards for land behind levees.
In formulating your own regulations, check first to see whether your state damsafety or floodplain management program has established minimum standards for con-
struction and maintenance of levees. If so, they may be incorporated by reference in yourregulations. Another source of assistance is the U.S. Army Corps of Engineers which hasdeveloped standards for the design and construction of levees as well as interior drainage(see references).
In preparing your regulations, a minimum levee crest elevation related to thedesign flood elevation should be established. At least three feet of elevation (freeboard)
should be required over the normal regulatory flood elevation for structures (usually the100-year flood elevation) to ensure protection from waves, erosion and ice.
Land use standards for buildings and other structures behind "adequate" and "safe"
levees raise difficult questions. In one sense, no levee can be considered safe. And yet, todeny the protection afforded by a well-designed and maintained levee may be -unreason-
able. One approach being considered by Wisconsin is to compare "annual damages" of de-
veloping behind a levee, given that the levee will overtop for a flood event which exceedsthe design level of the levee. A direct comparison can be made between structuresD-S

elevated to the 100-year elevation and those built on grade behind a levee. In cases wherethe natural ground is 5-6 feet lower than the 100-year elevation, annual damages forstructures built "on grade" can be greater than structures which are elevated on fill, inspite of "100-year" protection by the levee. To equalize or "optimize" annual damages be-
hind a levee; regulations that require new structures to be elevated on fill must beadopted. Further discussion on this approach is contained in Appendix 4-B..
Non Regulatory ActionsBuilding StandardsPennsylvania has developed special building standards for new construction in ar-
eas protected by dikes or levees against 100-year flooding. Buildings must be able to resistspecified flood forces. A handbook for builders suggests some of the construction prac-
tices that meet the requirements (see reference section).
Warning and Evacuation SystemsA warning system and evacuation plan should be established for areas behind un-
safe and inadequate levees. Installation of the system could be made a requirement ofpermits for subdivision or rezoning. All residents and all applicants for construction per-
mits in the floodplain (as mapped without levees) should also be notified that they are inan area protected by such levees and are subject to flooding if the levees are breached orovertopped. Hold an annual public information meeting on the levee warning and evacua-
tion plan.
Inspection and MaintenanceWhere a local government agency has constructed or assisted in construction of lev-
ees, it should initiate a careful levee inspection and maintenance effort to protect backly-
ing landowners and avoid possible legal liability. Where levees have been constructed byanother level of government or by a private entity, communities should conduct their ownregular inspection programs as a safety check. They can then require upgrading forinadequate levees. The community engineer or a consultant should make an annualinspection of the levee system. Other community employees should be encouraged to makecasual checks for problems whenever they are in the vicinity of levees.
RelocationRelocation of development should be considered for areas behind inadequate leveesor levees where serious and recurring flood damages may result. Soldiers Grove, Wisconsinrelocated its entire business district to a hillside location after overtopping of a levee inD-9

1978 caused severe flood damage. Funding came from federal, state and local sources.
Some remaining low-tying structures were floodproofed or elevated on fill.
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Appendix 4-A: Excerpts from FEMA's Guidelines for Evaluating Local Flood-ControlStructures.
The following paragraphs describe procedures for evaluating earthen riverine lev-
ees. In evaluating the ability of levee systems to provide protection against the 100-yearflood, the following criteria and procedures shall be used.
1. Ownership. Privately owned, operated, or maintained levee systems will not beconsidered unless a local ordinance or State statute mandates operation and maintenance.
Levees for which the community, State, or Federal government has responsibility for op-
eration and maintenance will be considered provided that the criteria discussed below aremet.
2. Freeboard. A minimum levee freeboard of 3 feet shall be necessary, with an ad-
ditional 1 foot of freeboard within 100 feet of either side of structures within the leveeor wherever the flow is constricted, such as at bridges. An additional 0.5 foot above thisminimu is also required at the upstream end, tapering to the minimum at the downstreamend of the levee.
3. Field Inspection and Maintenance. The study contractor must make a field in-
spection to verify that the levee appears structurally sound and adequately maintained.
Certification from a Federal agency, State agency, or a registered professional engineerthat the levee meets the minimum freeboard criteria above and that it appears, on visualinspection, to be structurally sound and adequately maintained may be used in lieu of asite specific inspection by the contractor. Levees that have obvious structural defects, orthat are obviously lacking in proper maintenance, will not. be considered.
4. Internal Drainage. Where credit will be given to levees providing 100-year pro-
tection, the adequacy of interior drainage systems will be evaluated. Areas subject toflooding from inadequate interior drainage behind levees will be mapped using standardprocedures. Often, shallow flooding zones, or even numbered A zones, may be applicablein these instances.
5. Human Intervention and Operation. In general, levee evaluation shall not con-
sider human intervention (e.g., capping of levees by sandbagging, earthfill, or flashboards)
for the. purpose of increasing a levee's. design. level of protection during an imminentflood. Human intervention will only be accepted for the operation of closure structures(e.g., gates or stoplogs) in a levee system designed to provide at least 100-year flood pro-
tection, including adequate freeboard as described earlier. Where levee closures are in-
volved, FEMA must review and approve the operation plan prior to the study contractor'sassumption that protection against the 100-year flood does exist.
6. Analysis. For the area protected by a levee (inside) providing less than 100-yearprotection, the base flood elevation shall be computed as if the levee did not exist. For thearea outside of such a levee, the elevations to be shown are those obtained from either theflood profile that would exist at the time levee overtopping begins or the profile com-
puted as if the levee did not exist, whichever is higher.
This procedure recognizes the increase in flood elevation in the unprotected areathat is caused by the levee itself. This procedure may result in flood elevations beingshown as several feet higher on one side of the levee than on the other. .Both profilesD-ll

should be shown in the study report and labeled as "before levee overtopping" and "afterlevee overtopping", respectively. Separate Floodway Data Tables should be prepared foreach side of the levee, and these tables should be adequately labeled. The FIRM work mapshould show a line, running along the levee centerline, separating the areas of differentbase flood elevations and zones. ... Floodways will be delineated at the landside toe ofmainline and tributary levees that are credited on a map. This will assure that no devel-
opment will occur on the outside of the levee, which may jeopardize the levee's integrityor ef f activeness.
7. Certification. During the course of the Flood Insurance Study, when. the studycontractor determines that an area of a community has no special flood hazards because itis protected by a flood-control structure, the contractor must obtain from the agency re-
sponsible for the structure a written statement that the structure is properly designed,
constructed, maintained, and operated to provide protection from the 100-year flood. Thiscertification must be accompanied by copies of the applicable operation and maintenanceplans and forwarded to FEMA for approval as soon as possible.
8. Exception Procedures. FEMA will accept certification from another Federalagency that an existing levee system is designed, constructed, maintained and operated toprovide protection against the 100-year flood in lieu of the specific requirements of items2, 3, and 5 above. Under certain circumstances, FIA may also grant exceptions to theabove requirements or approve alternate analysis techniques. The Study Contractor mustobtain written approval of'all such exceptions or alternate analyses from the PO beforeproceeding.
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Appendix 4-B: Excerpts from the Levee Policy Proposed by the Wisconsin Department ofNatural Resources, 1984.
(1) GENERAL. Adequately designed, constructed and maintained levees, floodwallsand channel impvovements provide for reduced damages and relief from flooding. Thefollowing standards shall apply .to municipal floodplain zoning regulations for areaslandward of. levees, floodwalls and channel improvements.
(2) ADEQUATE LEVEES OR FLOODWALLS.
(a) A levee or floodwall shall be considered adequate if all of the, following criteria andthe requirements of sub. (b) are met:
1. a. Except as provided in sub. par. b. the minimum top elevation of the leveeor floodwall shall be 3 feet above the calculated 500 year flood profile withthe flood confined riverward of the proposed levee or floodwall, under ei-
ther of the following conditions in this subparagraph.
b. The minimum top elevation of a levee may be adjusted by the' departmentto an elevation of not less than 3 feet above the calculated 100 year profile.
..with the flood confined riverward of the proposed levee or floodwall, undereither of the following conditions in this subparagraph.
i. If the calculated expected annual damages to structures land-
ward of the proposed levee or floodwall that do not complywith [floodplain regulations] are equal to or less than thecalculated expected annual damages to structures landward ofthe proposed ,levee or floodwall that do comply with[floodplain regulations] at a flood with a recurrence intervalof less than 500 years, the minimum top elevation of the leveeor floodwall shall be at least 3 feet above the calculated pro-
file for that flood.
ii. If the department is' satisfied that the additional 3 feet ofheight above the calculated profile is not necessary to preventflood damages due to overtopping of the levee during the de-
sign recurrence interval flood, it may waive the requirementfor a portion of this added height.
2. U.S. Army Corps of Engineers standards for design and construction of lev-
ees and floodwalls shall be the minimum standard for levees and floodwalls.
3. Interior drainage shall be provided using designated ponding areas, pumpsor other similar means, in accordance with U.S. Army Corps, of Engineersstandards.
4. An emergency action plan, concurred in by the division of emergency gov-
ernment and approved by the department, shall be in effect for the areabehind the levee or floodwall that would be in the floodplain without theproposed levee or floodwall in place.
D-13

5. The municipality shall provide notification to all persons receiving con-
struction permits in the area behind the proposed levee or floodwall thatwould be in the floodplain without the proposed levee or floodwall in placethat they are in an area protected by a levee or floodwall which is subjectto flooding if the levee or floodwall is overtopped.
6. The levee or floodwall shall be annually inspected and certified, by a pro-
fessional engineer registered in Wisconsin, that the levee or floodwall meetsthe standards in Subds. 1.to 5. Annual reports of the inspection and certifi-
cation shall be sent to the department for review.
7. The department reviews and approves the material submitted under subds. 1.
to 5.
(b) No obstruction to flood flows caused by construction of levees or floodwalls maybe allowed unless amendments are made to the floodway lines, regional flood pro-
files, floodplain zoning maps and floodplain zoning ordinances. Calculations of theeffect of the levee or floodwall on regional flood heights shall compare existingconditions with the condition of the regional flood confined riverward of the pro-
posed levee or floodwall.
(c) Floodplain areas protected by an adequate levee or floodwall shall be desig-
nated as flood fringe but may be regulated as areas outside of the floodplain unless thedepartment determines that the levee or floodwall is no longer adequate.
(3) INADEQUATE LEVEES OR FLOODWALLS.If the department determines thatan existing levee or floodwall does not meet the criteria of sub. (2)(a), all floodplain areaslandward of the inadequate levee or floodwall shall be regulated as if the levee or flood-
wall does not exist.
(5) NEW CONSTRUCTION OF LEVEES, FLOODWALLS OR CHANNEL IM-
PROVEMIENTS.No anticipated changes in the flood protection elevations or floodplainand floodway limits, based upon proposed levees, floodwalls or channel improvements,
may be effective until the improvements are constructed, operative and approved by thedepartment.
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SELECTED REFERENCES ON FLOODING IN AREAS BELOW INADEQUATE LEVEES.Emergency Preparedness News, 1984, (March 7). Silver Spring, Maryland: EmergencyPreparedness News.
Federal Emergency Management Agency, et al., 1982, Interagency Hazard Mitigation Re-
port--Allen County, Indiana. Washington, D.C.: FEMA.
Griggs, G. B. and L. Paris, 1982, Flood Control Failure: San Lorenz River, California. Envi-
ronmental Management 6(5):407-417.
National Research Council, 1982, A Levee Policy for the National Flood Insurance Program.
Washington, D.C.: National Academy Press.
Pennsyslvania Department of Community Affairs, 1981, Handbook of Flood Resistant Con-
struction Specifications, Suggested for Use in Areas Protected by Dikes and Levees.
Harrisburg, Pennsylvlania: Dept. of Community Affairs.
Platt, Rutherford H., 1982, The Jackson Flood of 1979--A Public Policy Disaster. AmericanPlanning Association Journal (Spring): 219-231.
Vogt, R. and R. Watson, 1983, How Dams and Levees Affect Flood Hazard Areas: Evaluatingthe Standards. Prepared by the Wisconsin Dept. of Natural Resources for the Fed-
eral Emergency Management Agency. Washington, D.C.: FEMA.
Watson, R.M., 1984, Expected Annual Damages: with and without levees. Wisconsin Dept. ofNatural Resources. Unpublished.
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Figure 5-1. The Teton Dam, a Bureau of Reclamation project, collapsed in 1976 killing 11 people 
and causing millions of dollars in damages. The dams collapse illustrated, once 
again, that structural solutions to flood problems are not without inherent risks. 


Safety surveys for both new and existing dams have been carried out by manystates. Some states, such as California and Iowa, map inundation zones below all newdams. Colorado requires the owners of unsafe dams to prepare inundation zone maps. Asuggested inundation zone mapping procedure from Colorado is included in Appendix 5-B.
Wisconsin has drafted guidelines requiring community regulation of areas below unsafedams (see Appendix 5-C).
OPTIONS FOR ACTIONPolicy and Program ElementsA community with dams or downstream of dams in other governmental jurisdic-
tions should adopt a policy and program with the following elements:
1. A policy statement recognizing the inherent dangers in all dams due tounexpected failure or overtopping by a flood exceeding the level for whichthe dam was designed, by sedimentation, by earthquake or by other causes.
It may be prudent to assume that any dam can fail.
2. An assessment of all dams within or affecting the community to determinethe degree of protection provided, maintenance or rehabilitation needs foreach dam, and of the need for land use controls or emergency preparednessbelow the dam.
3. A process for regular review and updating of this information.
4. Maps of the inundation zones for areas below all unsafe or inadequatedams.
5. A set of stringent floodplain regulations for inundation areas below unsafeor inadequate dams.
6. Dam safety regulations requiring owners of unsafe or inadequate dams torepair or upgrade such structures.
7. A flood warning system and evacuation plan for areas below unsafe dams.
8. A schedule of regular (at least yearly) meetings with dam owners to insureproper dam operation and maintenance and to inform owners of new orproposed downstream developments. Reiterate your mutual interests inprotecting lives and property and in avoiding liability for any damages.
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9. A schedule of regular communication between engineering, planning andemergency management personnel to consider dam safety in land usedecisions and to update preparedness systems to reflect new developments.
10. A policy to give floodwater storage high priority in setting levels andtiming drawdown of reservoirs. Water users and the public should beeducated about the need for flood storage.
MappingTwo types of maps or surveys are needed to reduce threats posed by unsafe or in-
adequate dams:
1. An inventory of all dams in the community with an evaluation of theirsafety and effectiveness, and,
2. Inundation zone mapping for dams considered unsafe or inadequate.
A preliminary survey of dams in your community may be based, in part, on stateand federal surveys. Be aware that state and federal surveys often do not include smallstructures which may be of local concern. Air photos and field surveys can also be used tolocate structures. Local conservation officers are also often familiar with the location andcondition of dams. Once dams have been located, a more detailed investigation of safetyparameters is needed. State and federal surveys may help here as well. A number ofsources of technical assistance are available to assist in evaluating dams. If data are notavailable, it will be necessary to have surveys done by an engineer or engineeringgeologist.
In evaluating dams, consider design, construction and maintenance. Check spillwaycapacity even if the dam appears safe in other respects. A 1971 study by Biswas and Chat-
terjee of 300 dam failures concluded that 35% of them were the direct result of floods inexcess of the spillway capacity. Foundation problems such as seepage, piping, excess porepressures, inadequate cutoffs, fault movement and settlement of rockslides were the causeof 25% of the failures. Improper design or construction, inferior materials, wave action,
acts of war or lack of proper operation and/or maintenance accounted for the remaining40% of the failures (see Figure 5-2).
Once the location and degree of protection afforded by existing dams have beendetermined, inundation zones should be mapped for unsafe or inadequate dams. The in-
undation zone is the area that would be flooded in the event of a failure. While a dammay fail on a sunny day, the most likely and most dangerous situation is failure during aE-5

flood when water levels are highest (see Figure 5-3). It is advisable, therefore, to identifythe area that would be inundated by failure during the 100-year flood. Both the broadinundation zone and the floodway within this zone should be outlined.
There are several published methods for mapping inundation zones (see Appendix5-B for one example.) The analysis should be done by a professional engineer. Technicalassistance may be available from your state dam safety program or the U.S. Army Corpsof Engineers.
The inundation zone map has four important uses:
1. To establish the regulatory jurisdiction for zoning;
2. To identify the area needing evacuation or other emergency procedures inthe event of failure of the dam;
3. To promote consideration of the risk in land use planning;
4. To build citizen awareness of the potential hazard.
RegulationsDam safety regulations should address three topics:
1. Dam design standards;
2. Dam safety inspection and maintenance requirements; and3. Zoning of downstream areas.
State dam safety programs may already address the first two.
Design standardsDesign standards are most commonly adopted at the state level, but counties andcities in some states have adopted their own standards. Design standards should apply tonew dams and to the reconstruction of existing dams. Since dam specifications vary withthe purpose of the dam, location and other factors, each design should be reviewed by astaff engineer or consultant. The reviewer must judge whether the proposed design pre-
sents a hazard to the health, safety or welfare of the public.
Some state dam safety laws establish specific spillway requirements based on exist-
ing development and existing land use controls in the vicinity of the dam site. Adequatespillway capacity can prevent overtopping and upstream flooding from floods up to andincluding the design capacity of the structure. To ensure that the construction is done ac-
cording to plan, a professional engineer can be required to supervise the operation. Theowner can be required to file a bond.
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Floods inexcessofspillwaycapacityFoundation problems:Y/seepage, piping,
excess poreseismic fault movement,
groundsettlingK Improperdesign, construction,
poor materials, wave action,
act of war,improper operationFigure 5-2. Causes of dam failure.
SALEMl r ~~~~NELKRIDGEQFigure 5-3. The worse-case inundation scenario from the failure of theThistle Dam. A simply drawn map can help inform residentswho are at risk and ensure that the risk of dam failure isconsidered in land use decisions. Source: NationalResearch Council.

Inspection and MaintenanceInspection and maintenance should be required by your dam safety ordinance. Ifyour state has a dam safety law, find out whether it applies to the dams in your commu-
nity. If so, obtain the results or schedule of inspections. Dams are also inspected by theFederal Energy Regulatory Commission and under the Federal Dam Safety InspectionProgram. These reports will be useful.
Whether or not the dams in your community fall under one of these programs, es-
tablish a schedule for regular (at least yearly) inspection by municipal staff or consul-
tants. Encourage casual checks by municipal employees whose work brings them into thevicinity. If problems arise, request inspection by state or federal officials. Appendix 5-Ccontains a quick inspection procedure.
In your contacts with dam owners, review their maintenance plans. Obtain writtencertification of their ability and intent to operate and maintain the dam.
An unsafe dam may legally be a nuisance. If a dam owner cannot or will not re-
store safe conditions, contact state dam safety officials or your community's legal counsel.
ZoningThe best way to avoid danger in the event of a dam failure is to prohibit or care-
fully control development in inundation zones. Floodplain zoning, subdivision and build-
ing code requirements can be used to prohibit new development in the high risk area be-
low dams or to establish performance standards for elevation of new structures. The mostcritical area is in the floodway of the inundation zone where water velocities will be veryhigh.
Areas below dams should be zoned based on the design and structural integrity ofindividual dams. The following approach has been proposed by the State of Wisconsin:
Below dams that meet safety requirements:
Developed areas should be zoned as if the dam is in place during the 100-yearflood. Undeveloped areas should be zoned as if the dam does not exist since it maybecome unsafe or be removed.
Below dams that do not meet safety requirements:
Developed and undeveloped areas should be zoned as if the dam would fail duringthe 100-year flood.
Such zoning changes can be carried out by amendment to existing zoning, flood-
plain management, subdivision, building, stormwater management or other regulation.
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Figure 5-4. Buffalo Creek, West Virginia: Aftermath of a dam failure. The 
tangled wreckage shows the force unleashed when a dam fails. 
One hundred, twenty-five people lost their lives in this dam 
failure. Source: unknown. 

Figure 5-5. Routine dam inspection is a necessary part of a dam safety 
program. This rather dramatic erosion problem was identified 
during a routine inspection. Source: Minnesota Dept. of 
Natural Resources. 


Nonregulatory ActionsWarning and Evacuation SystemsAny dam with development in the inundation zone of the maximum probable floodshould have a warning and evacuation system. Dam owners can be required to install andoperate the system. Emergency plans should be discussed at a public information meetingafter notification of all residents in the inundation zone.
Reservoir Management.
Reservoir management for flood control means regulating water levels and flowsfrom the pool behind the dam to allow for storage of flood waters. Management proce-
dures for flood control should be built into dam operating procedures and into legally es-
tablished levels and flows. Large reservoirs that are used for irrigation or power genera-
tion require particularly careful computation of drawdown curves based on long-termprecipitation records and hydrologic models in order to maximize water storage or powerproduction while allowing for flood storage.
For smaller reservoirs where storage capacity can be more quickly created, operat-
ing plans for accommodating floodwaters are often more easily prepared. Pool levels caneither be dropped for a specified length of time to accommodate anticipated seasonalflooding or the discharge can be increased in response to current weather forecasts.
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Appendix 5-A: A Sample Dam Safety Inspection Guide.
insert credits hereCONDITION OF DAMI. EMBANKMENTSa. Seepage: indicate the location of seepage areas and estimate quantity of flow. Notewhether flow is clear or carries material.
b. Slope stability: note areas of slumps or slides. Look for soft ground, depressions, orwet areas on the embankment. Note evidence of recent movement or trees whichare not growing vertically.
c. Surface erosion:note bare patches of soil or other evidence of erosion.
d. Animal burrows: inspect all earthen embankments for evidence of burrowinganimals.
e. Embankment-structure junctions: examine these junctions for evidence of sliding,
deformation or movement. Look for potential slippage planes and weakness zones.
Carefully check for seepage and erosion along junction planes.
f. Slope protection: note presence and condition of riprap along toe of embankments.
g. Vegetation: the embankment should have a good covering of grass, free from broadleaf vegatation, shrubs and trees. Note areas that lack suitable cover and especially.
note the presence of large trees on the dikes.
II. SPILLWAY(S)
a. Surface condition: Check for spillway spalling and areas of broken or missingconcrete. Check for effects of cavitation and freeze/thaw.
b. Cracks: Note width of existing cracks. Noting crack widths will allow monitoringof structural integrity.
c. Joints: look for misalignments or evidence that joint size has changed.
III. GATESa. Steel, timber: note number and size of each gate section.
b. Gate seals: examine for leakage and seal deterioration.
c. Gate pins: look for cracking of concrete near pins which could indicate potentialfailure. Check for pin deterioration, including metal corrosion.
d. Gate hoist and chains: determine if gate is operable and the condition of the liftingequipment.
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IV. MISCELLANEOUSa. Debris: examine trash racks for accumulated debris. Examine interior of drop inletsand outlet pipes for lodged trash and debris which could reduce flood capacity.
Note elevation of debris line around flowage to indicate level fluctuations andoperation of the dam.
b. WfTalkwayand railing: examine for missing or broken railings, broken steps, or othersafety related hazards. Check for access to controls during high-water.
c. Paint: look for rust spots or other evidence of deteriorated paint (particularly onstructural members of the dam).
d. Downstreamn apron: check for spalling, slumping, uplift, cracking or otherdeterioration. Note any undercutting of apron and give dimensions.
e. Stilling basin: examine stilling basin for scour and undercutting at the toe of thedam. Check for displaced or deteriorated stone. Check depth of water in thestilling basin if possible.
f. Foundation seepage: check for evidence of seepage, aquatic vegetation or areas ofdiscoloration. Note any changes from past seepage patterns, particularly new areasof seepage. Estimate quantity of seepage flow if possible.
g. Downstream channel: check for erosion and scour which could undermine the dam.
Also look for buildups of material (shoals or islands) which might indicateturbulent flows.
h. Other observations: list all-other observations which bear on the safety andperformance of the dam. Include past evidence of overtopping or failures. Includeany cultural changes, such as subdivision development below the dam, which couldchange the hazard classification of the dam.
BOATING SAFETYa. Warning devices and signs: describe the location of all signs and devices. Indicateneed for new signs and adequacy of existing signs.
b. Portage signs and facilities: indicate what provisions are needed for portaging andif such provisions have been made and are adequate.
HYDROPOWER USERa. Last date used for power: indicate, if known.
b. Current installed capacity: list rated kilowatt on generating unit.
c. Average powveroutput during inspection: list power output while you were inspectingthe dam (also any flow not being used for power).
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Appendix 5-B. Excerpts from "A Method for the Rapid Approximation of Dam FailureFloodplains in Colorado."
by William P. Stanton, P.E., Supervising Water Resource Specialist, Flood Control andFloodplain Management Section, Colorado Water ConservationBoard, July, 1983.
Pref ace.
Since 1890, there have been at least 130 known dam failures in Colorado.
Following the failure of Lawn Lake dam and subsequent flooding through the town ofEstes Park, Colorado on July 15, 1982, considerable attention has been focused onreducing damages from potential dam failure floods.
In January 1983, state agencies prepared a Flood Hazard Mitigation Plan forColorado which included recommendations to improve state programs in dam safety,
floodplain management and emergency preparedness. One of the ideas was arecommendation that the Colorado Water Conservation Board (CWCB)develop a techniquefor mapping approximate dam failure floodplains. below all dams in Colorado. Because nostate agency had a program to map dam failure inundation zones, the idea was to developa manual which would outline a simple, cost effective procedure which would allow damowners and local officials to determine an approximate inundation zone themselves.
On June 1, 1983, Governor Lamm signed House Bill 1416 which, among otherthings, directed the Division of Water Resources (State Engineer) to prepare a report onapproximately 238 dams in the state formerly classified as "high hazard." The hazardrating is determined by the potential for loss of human life or property damage in thearea downstream for a dam and does not pertain to the safety of the structure.
Each report included a map indicating the possible extent of flooding in the eventof failure to a point where such floodwaters would no longer exceed the boundaries ofthe 100-year floodplain. The dam failure floodplain for approximately 337 "moderatehazard", 1,680 "low hazard" dams and thousands of highway embankments and stock pondswhich were not included in H.B. 1416 remain to be mapped.
Knowing where the water might go from a dam failure flood may help to reducedevelopment in areas which effect the hazard rating of the dam. It may also help localofficials plan for emergency response activities which could reduce flood damages andsave lives.
1.0 Purpose.
The purpose of this document is to provide dam owners, floodplain managers,
emergency planners and citizens with a quick and simple method to find out where thewater from a dam failure might be reasonably expected to go. The suggested level ofdetail is intended to be consistent with readily available base map information. Theapproximate flood boundaries developed with this method are for planning purposes onlyand should be conservative, that is, the flooded area should be slightly overestimated.
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8. At major obstructions, such as highway or railroad bridges, an adjustment in theflood depths may be appropriate to reflect water backed up just upstream of theobstruction and shallower depth just downstream of the obstruction. By advancingor bending flood contours slightly downstream, a greater depth will be apparent,
and vice versa.
The procedure to estimate flood boundaries may be conservative for the followingreasons:
1. The topographic map contours show top of the water and not the true thalweg(lowest point in the channel). The depth of flow that was in the river at the timeof mapping will be added to the assumed depth.
2. A conservative stair-step approximation of the assumed attenuation curve wasused to interpret flood depths.
3. The flood boundary is shown as a heavy line which, on a scale of 1 inch equals2,000 feet, may be as much as 200 feet wide.
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Appendix 5-C: Wisconsin's Proposed Guidelines for Community Regulation of Areas BelowDams.
(1) General. Adequately designed, constructed and maintained dams provide reduceddamages and relief from flooding for developed areas. Areas downstream of damsshall be zoned and regulated by municipalities with floodplain zoning ordinancesin compliance with the standards in this section, to reduce potential loss of lifeand property located downstream of the dams. Except as provided in sub. (2), areasdownstream of all dams shall be delineated on floodplain maps.
(2) Exemptions. All dams having a structural height of 6 feet or less, or a storagecapacity of 15 acre feet or less, and all dams having a structural height of morethan 6 feet but less than 25 feet with a storage capacity of 50 acre feet or less areexempt from the requirements of this section.
(3) Safe dams.
(a) A dam is considered safe if the requirements in this paragraph are met.
1. The dam is structurally adequate to meet the conditions in ss. NR333.05(2)(g) and 333.07(4)(b).
2. The dam is hydraulically adequate to meet the standards in s. NR 333.07(2).
3. The dam has been certified by a professional engineer, registered inWisconsin, to meet the requirements of subds. 1. and 2.;
4. Written assurance of the dam owner's ability to operate and maintain thedam in good condition is obtained from the dam owner:
5. An emergency action plan to minimize loss of human life has been adoptedby the municipality for the area downstream of the dam based on theassumption that the dam fails during the regional flood; and6. The department reviews and approves the material submitted under subds. 1.
to 5.
(b) Developed areas downstream of a safe dam shall be zoned and regulated assum-
ing that the dam is in place during the regional flood.
(c) Undeveloped areas downstream of a safe dam shall be zoned and regulated as-
suming that the dam does not exist.
(4) Unsafe dams.
(a) if an existing dam does not meet the standards in Sub. (3)(a), the dam is consid-
ered unsafe.
(b) Both developed and undeveloped areas downstream of an unsafe dam shall bezoned and regulated assuming that dam failure occurs during the regional flood.
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(c) The regional flood profile of the area downstream of the dam shall be calcu-
lated in accordance with s. NR 333.05(2)(b)
(5) Construction of new dams.
(a) Dams constructed after the effective date of this rule shall be considered safeif the requirements in sub. (3)(a) are met.
(b) Developed areas downstream of the construction of a new dam shall be zonedand regulated as if the dam does not exist until construction is 100%complete and all theconditions of sub. (3)(a) are met.
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SELECTED REFERENCES ON FLOODING BELOWINADEQUATE DAMSAd Hoc Interagency Committee on Dam Safety, 1979, Federal Guidelines for Dam Safety.
Washington, D.C.: Federal Coordinating Council for Science, Engineering andTechnology, Washington, D.C. (Reprinted by the Federal Emergency ManagementAgency.)
Dewberry and Davis, 1982, Dam Safety Mapping Pilot Study. Prepared for the FederalEmergency Management Agency. Washington, D.C.: FEMA.
Federal Emergency Management Agency, 1982, Dam Safety Research--Current, Planned andFuture. Washington, D.C.: FEMA.
Graham, W.J. and C.A. Brown, 1982, The Lawvn Lake Darn Failure. Washington, D.C.: Bureauof Reclamation, U.S. Dept. of the Interior.
Jansen, R.B., 1980, Dams and Public Safety. Water Resource Technical-Report. Washington,
D.C.:U.S. Dept. of the Interior.
National Academy of Sciences, 1982, Committee on Safety of Non-federal Dams. Safety ofNon-federal Dams--A review of the Federal Role. -Washington, D.C.: NationalAcademy Press. (Reprinted by the Federal Emergency Management Agency.)
National Academy of Sciences, 1983, Committee on the Safety of Existing Dams. Safety ofExisting Dams--Evaluation and Improvement. Washington D.C. National AcademyPress.
National Weather Service, 1981, DAMBRK -The NWS Dam Break Flood ForecastingModel Users Manual. Hydrologic Research Laboratory, National Weather Service,
National Oceanic and Atmospheric Administration. Washington, D.C.: NOAA.
Owen, H. J., 1980, Flood Emergency Plans--Guidelines for Corps Dams. Prepared for theHydrologic Engineering Center. Davis, California: U.S. Army Corps of Engineers.
Tschantz, B. A., 1983, Report on Review of State Non-federal DanmSafety Programs. Pre-
pared by the Civil Engineering Department, University of Tennessee. Washington,
D.C.: Federal Emergency Management Agency.
Vogt, R. and R. Watson, 1983, HowrtDams and Levees Affect Flood Hazard Areas: Evaluatingthe Standards. Prepared by the Wisconsin Dept. of Natural Resources. Washington,
D.C.: Federal Emergency Management Agency.
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CHAPTER 6: COASTAL FLOODING AND EROSIONTHE HAZARDFrom California to the Great Lakes to Cape Cod, houses built along theimmediate coastline are often destroyed by a combination of caving ofbluffs or erosion of beaches and dunes and flooding. Combined erosionand flooding affects all coasts but is particularly serious on barrierislands and on exposed Atlantic and Gulf Coasts and the Great Lakes.
In 1971, the U.S. Army Corps of Engineers estimated that a quarter ofthe national shore front (20,500 miles) was subject to significant ero-
sion. Whileerosion losses were not systematically tallied, average annuallosses due to erosion in 1975 were conservatively estimated to exceed$300 million.
Erosion increases flood damages in several ways. Once a beach or dune is eroded,
high velocity waves penetrate further inland, often destroying buildings and infrastruc-
ture. In addition, erosion can permanently lower the elevation of beaches, bluffs anddunes, resulting in deeper flooding. Erosion also undermines pilings and foundations,
causing structures to topple into the water. Erosion and flood damage may be indistin-
guishable during major storms.
Coastal erosion is caused by hurricanes, winter storms, rising sea levels, tides andcurrents, and human activities. Most erosion damage occurs in major storms since the ero-
sive force of water is related to its velocity.
Coastal erosion and flooding affect bluff, beach, dune and marsh areas somewhatdifferently:
Bluff erosion occurs along the California and Oregon coasts; Lakes Michigan, Su-
perior and Erie; the Chesapeake Bay and unconsolidated shoreland areas along the Gulfand Atlantic coasts such as Cape Cod, Massachusetts. Bluff erosion is most serious wherethe coast consists of unconsolidated sediments and is caused primarily by waves. (SeeFigure 6-1). Other causes include currents, sea level rise, surface runoff and the activitiesof man.
Bluff erosion is irreversible. Unless the bluff is stabilized or the building movedback, houses built along bluffs are sooner or later destroyed. Many houses built at whatwas once considered a safe distance from the edge are now threatened. Bluff stabilizationor relocation of homes are both extremely expensive.
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The enormous erosive force of storm waves is illustrated by thefollowing description from a report on Great Lakes erosion:
Very few people, who have not lived on the shore, can visualize the ex-
traordinary energies that can be thrown against the shore by breakingwaves. At Duluth, waves 23 feet high have been recorded with hydraulicpressures of 2370 pounds per square foot. In November 1950, stormwaves on Lake AMichiganmoved a concrete cap on a breakwater atGary, Indiana. The concrete cap, 200 feet long and weighing 2,600 tons,
was moved four feet by waves 13.5 feet high. The wave pressure re-
quired to move the cap was calculated to have been as much as 2,500pounds per square foot (Hanson, et al., 1976).
Beach erosion occurs along all of the coasts but is most serious along the easternseaboard. Rapid erosion of wetlands rather than beaches along the Louisiana coast threat-
ens much of the Mississippi Delta. Wetlands rather than beaches form the interface herebetween the land and open sea. Most beaches are eroded by currents, waves and high tideseach year and, to some extent are rebuilt by the same natural processes. Beaches oftenretreat and rebuild dozens or even hundreds of feet each year.
Were it not for sea level rise, discussed below, most beaches would naturally re-
build. Although beaches naturally rebuild, houses constructed on eroding beaches do not.
Combined flooding and erosion is a serious problem not only for buildings located onbeaches but those in backlying areas subject to wave runup. During major storms, wavescan run up beaches to elevations twice the storm wave height above normal sea level.
Dune erosion is a serious problem along the Gulf and Atlantic coasts but also occursalong Lake Michigan and some stretches of the California, Oregon and Washingtonshorelands. Dunes are located shoreward of beaches and may rise from three to more than100 feet in height. Geologically, they are part of the beach system and provide a reservoirof sand for the beach. Historically, dunes are eroded and rebuilt by wind and waves,
gradually moving inland with sea level rise.
Severe erosion of dunes is common during a major hurricane or during a winterstorm like the Ash Wednesday Northeaster of 1962. The '62 storm leveled the dune systemalong much of the New York, New Jersey, Maryland and Virginia coasts, destroyingthousands of houses built on, in front of and immediately behind the dunes. People con-
tinue to locate houses on dunes to take advantage of the view and because their heightabove the water gives a sense, albeit false, of safety from flooding.
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Figure 6-1. Bluff erosion problems and some solutions. 
Source: Great Lakes Basin Commission. 

Figure 6-2. Shore erosion control structure in Massachusetts. 
Source: Jon Kusler. 


Permanent recession of beaches and dunes along the Pacific, is primarily due to sealevel rise. Until recently, the sea was rising at the rate of about 1 foot per century. Now,
this rate may be much greater, resulting in thousands of feet of shoreline retreat. (See in-
sert).
Importance of Sea Level RiseThe U.S. Environmental Protection Agency (EPA) has projected seriousincreases in sea level as a result of melting of the polar ice caps due toconcentration of atmospheric C02and other greenhouse gases(Hoffman, et al., 1983). EPA concluded that a global rise of between4.8 feet and 7.0 feet by year 2100 is possible. A one foot per centuryrise in sea levels will, on the average, cause beaches to migrate inland100 to 300 foot per century. The report describes the effect of sea levelrise:
"Sea level rise will have three major types of physicaleffects: shoreline retreat, increased flooding, and landwardmovement of salt water. Shorelines will retreat because verylow land will be inundated and other land along the shore willerode. For example, a thirty centimeter (one foot) rise in sealevel would erode most sandy beaches along the Atlantic andGulf coasts at least thirty meters (one hundred feet)."
"Whether or not EPA's projections, assumptions, andmethods are fully accepted, there is ample documentation ofserious long-term increases in sea level and landwardmigration of beaches, dunes, bluffs and barrier islands alongocean and Great Lakes shores. For further reading on sea levelrise see the paper by Hoffman, et al. in the bibliography."
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Figure 6-3. Barrier islands and dunes are forever shifting. 
Source: Jon Kusler. 

Figure 6-4. Beach erosion threatens tens of thousands of structures on 
barrier islands along the Atlantic coast. Source: NOAA. 


Figure 6-5. This bluff along Lake Michigan near Racine, Wisconsin is 
pictured on a calm day to highlight its vulnerability to wave 
action. Storm waves on Lake Michigan have been calculated to 
wield forces of up to 2500 pounds per square foot. 
Source: Jon Kusler. 

Figure 6-6: Buildings in the path of coastal floods seldom just get wet. 
Erosion worsens flooding as well as causing physical 
damage. Source: Jon Kusler. 


EXISTING MITIGATION EFFORTSEfforts have been made at all levels of government to separately address coastalflooding and erosion. While damages have been reduced, the combined erosion andflooding problem requires a coordinated approach to further reduce losses.
FederalFour major federal programs address coastal erosion. These include:
Federal Erosion ControlIn 1930 Congress created the Beach Erosion Control Board, a branch of the U.S.
Army Corps of Engineers, and authorized it to study erosion. The Corps' role was at firstlimited to studies; but was expanded by the Flood Control Act of 1936, which authorizedthe Corps carry out erosion control projects where federal interests were involved.
After the 1954 and 1955 hurricanes, Congress directed the Corps to developbroader hurricane protective measures and authorized federal payment of 70% of the con-
struction costs.
The March 1962 "Ash Wednesday" storm, which caused severe erosion along muchof the north Atlantic seaboard and essentially destroyed the dune systems in many locali-
ties, resulted in a public outcry for more federal involvement in beach erosion control.
Congress increased federal financial participation in erosion control projects to protectpublicly owned beaches and shores and some privately owned beaches (primarily asdemonstration projects).
Federal Flood InsuranceCongress reacted to recurring and serious erosion problems along the Great Lakesby directing the Federal Insurance Administration (FIA) to extend insurance coverage forthe collapse or subsidence of land along the shore of a lake or other body of water as aresult of erosion or undermining.... Standards for addressing erosion were also included inFIA guidelines for community programs. See Appendix 6-A.
To qualify, a community must prohibit man-made alteration of both sand dunesand mangrove stands within velocity zones. However, such an approach is minimal sinceFIA usually does not map sand dunes or mangroves as velocity areas. Coastal erosion isalso not separately mapped in the FIA program nor is it normally considered in floodmapping.
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Coastal Zone Management ProgramThe federal Coastal Zone Management Program has, since its inception in 1972,
encouraged state erosion mapping, planning and regulation. In order to qualify for federalgrants, state Coastal Zone Management plans are required to include the followingcomponents (CFR 023.26[1979]):
1. A method for assessing the effects of shoreline erosion;
2. Policy statements pertaining to erosion, including policies regardingpreferences for nonstructural, structural or no controls;
3. A method for designating areas for erosion control, mitigation and/orrestoration as areas of particular concern or areas for preservation andrestoration, if appropriate;
4. Procedures for managing the effects of erosion, including nonstructuralprocedures; and5. A list of legal authorities, funding programs and other techniques that canbe used to meet management needs.
Coastal Barrier Resources ActAdopted in 1982, this Act prohibits flood insurance after October 1, 1983, for allnew or substantially improved structures on certain undeveloped and unprotected barriersmapped by the U.S. Department of the Interior. No new expenditures or new financialassistance were to be made available for any purpose within the mapped barrier resourcessystem after the cutoff date, including the construction or purchase of structures, roads,
airports, boat landings or bridge causeways.
Congress considered such a prohibition necessary because: "Coastal barriers serve asnatural storm protective buffers and are generally unsuitable for development becausethey are vulnerable to hurricane and other storm damage and because natural shorelinerecession and the movement of unstable sediments undermine man-made structures."
(Findings of Fact, Coastal Barrier Resources Act of 1972.)
StateA number of coastal states have adopted planning and regulatory programs ad-
dressing bluff, dune and beach erosion. Some of these include:
1. North Carolina, Michigan and Rhode Island and have adopted 30-yearerosion recession lines for bluffs and other erodable areas as part oftheir coastal zone regulatory programs.
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2. Rhode Island, Maine, and North Carolina prohibit development on dunesas part of their coastal programs.
3. North Carolina, Rhode Island, and Maine prohibit development onbeaches (See Appendix 6-B for an excerpt of the policy portion ofthe North Carolina Ocean Hazard Area regulation).
4. Massachusetts tightly regulates the removal of beach materials. An Exec-
utive Order limits public investment on beaches (see Appendix 6-C).
5. California's Coastal Commission has adopted guidelines for bluff top de-
velopment which require. stringent erosion control measures for newdevelopment on bluff tops to assure stability (see Appendix 6-D).
LocalA number of local communities have adopted bluff, dune or erosion controlordinances. For example:
1. Onslow, North Carolina, Avalon, New Jersey, and many othercommunities, have adopted dune protection ordinances prohibiting ortightly controling dune alteration.
2. Sanibel and Pensacola, Florida and a number of other communitiesprohibit development on beaches.
Setbacks have also been established by some west coast communities in California,
Oregon and Washington and by east coast communities in Maine, Massachusetts, RhodeIsland, New York, Maryland, North Carolina and Florida.
OPTIONS FOR COMMUNITY ACTIONPolicy and Program ElementsA community with a combined flooding and erosion problem needs a policy andprogram recognizing the interrelationships between erosion and flooding and establishingminimum standards for location and design of structures. This policy should consider bothimmediate problems and long-term issues posed by sea level rise and retreat of the shore.
A policy concerning rebuilding and repair after major storm is also desirable.
A community policy and program should include the following elements:
1. A limitation on the expansion of roads, sewers and water supply to areaspotentially impacted by erosion;
F-9

2. Setbacks for all new structures in erosion areas reflecting the useful life ofthe structures;
3. Building code or zoning provisions including anchoring and pilingrequirements for structures outside of the setback area which may beimpacted by storm waves and erosion;
4. Dune and wetland protection provisions to preserve protective barriers;
5. Construction of erosion protective or beach nourishment works (where ab-
solutely necessary) for existing construction;
6. Public acquisition of selected high risk areas and relocation of structures.
It is particularly important that communities should, through public utility plans,
avoid new public infrastructure in rapidly eroding bluff, dune or beach areas. This policymakes sound fiscal sense for the community itself and will discourage new private con-
struction. It is consistent with broader Congressional policies to limit infrastructure onerodable coastal barriers.
MappingBoth erosion maps and revised flood maps are needed to properly consider com-
bined erosion and flood problems. National Flood Insurance maps, including flood insur-
ance rate maps prepared by FIA, traditionally do not reflect erosion.
FIA examined the possibility of mapping erosion areas in a 1977 workshopconcluding that erosion mapping was impractical at that time. The workshop revealed thecomplexity of combined erosion and flooding problems and the difficulties encounteredwith mapping or insuring erosion areas.
States have made considerable progress since 1977 in determining erosion recessionrates and in actually mapping erosion areas. Because of this, FIA has partially modifiedits policy. Flood Insurance Study contractors are now required to consider state-generatederosion and recession data where it is considered reliable. Erosion is not, per se, beingmapped.
State erosion maps indicating areas of bluff, beach, or dune erosion are now avail-
able for much of the coast from a variety of state and local sources, at differing scales.
Many of these maps have been prepared by state or local Coastal Zone Management Pro-
grams. Examples of innovative or comprehensive approaches include:
North Carolina's Coastal Zone Management Program studies indicatethat almost 40% of the ocean frontage is subject to a long-term erosion rateF-10

of 3 feet per year or more. Based on historic shoreline records, time seriesair photos and field information.. North Carolina has identified a 30-yearerosion recession line plus the recession expected from a 100-year storm formuch of the state's 320 miles of ocean frontage.
Michigan is identifying a 30-year recession line along 300 miles ofhigh risk Lake Michigan shoreline. High risk areas have been defined toinclude areas with recession rates of one foot or more per year. Dataincludes time-sequence air photos combined with historical shoreline dataand field studies.
Florida is establishing coastal construction setback lines along theAtlantic and Gulf coasts under its 1970 Beach and Shore Preservation Act.
Setbacks reflect dune/bluff erosion rates calculated through a time-seriesmodel. They are based upon 100-year storm surge and include waveelevations and anticipated erosion. More than 3,400 beach profiles and about1,200 offshore profiles have been developed. Aerial photographs are used asbase maps. Raw data are stored in a computerized system. The program hasdeveloped coastal construction setback lines for all 24 coastal countieshaving sandy beaches fronting on the Gulf or Atlantic.
RegulationsA community can reduce combined erosion and flooding damage for bluff, duneand beach areas through a combination of setbacks and performance guidelines. Ifdevelopment is to be permitted in high risk areas, much of cost and responsibility for thedetailed data-gathering and engineering may be shifted to developers.
The damage from bluff erosion can be reduced through regulations:
1. Setbacks for structures through zoning or building codes such as California hasdone for bluff top development,
2. Drainage codes or subdivision controls to require that surface and subsurfacedrainage systems be installed in bluff areas to reduce erosion and slumping;
3. Use sanitary codes to prohibit the use of septic tanks where additional sub-
surface drainage may increase slumping;
4. Use grading codes, zoning or subdivision controls to prohibit the removal ofsand and gravel from beaches in front of bluffs and the construction ofgroins and other activities which may increase beach erosion on other lands.
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Figure 6-7. Coastal mangroves like these in the Florida Keys reduce the 
height and force of hurricane waves and reduce erosion. 
Source: Jon Kusler. 

Figure 6-8. Reestablishing vegetation on sand dunes is critical to help 
keep sand in place. Beach users need to be aware of the 
value of dune plants. Source: Jon Kusler. 


To reduce damage from dune erosion:
1. Use dune protection ordinances, zoning, grading codes or subdivision regulationsto prohibit development on dunes. If development is to be permitted, requireadequate engineering (pilings, etc.) to withstand waves and erosion' andrequire reestablishment of natural vegetation. See the North Carolina statuteexcerpts in Appendix 6-B.
2. Use grading codes or zoning to prohibit extraction of sand from dunes, thebeach or offshore bars which act as reservoirs for sands.
3. Use zoning, grading codes or special codes to prohibit vegetation removal ondunes or activities such as cattle-grazing, off-road vehicles or footpaths thatmay destroy natural vegetation;
4. Use zoning or special codes to prohibit the use of groins and seawalls which mayincrease erosion in some areas while reducing it in others.
To reduce damage from beach erosion:
1. Use zoning, building codes, or subdivision controls to prohibit development onbeaches. If development is to occur, require adequate engineering towithstand waves and erosion;
2. Use zoning, grading codes or special regulations to prohibit extraction of sand,
gravel or other materials from the beach, dunes and offshore bars.
Massachusetts has prohibited removal of rocks and gravel from beachessince 1760. Restriction on the use of state and local funds were contained ina 1980 Executive Order (see Appendix 6-D).
3. Use zoning or special codes to prohibit or carefully control the use of groins,
seawalls, revetments and other structures that increase erosion in one areawhile reducing it in another.
Some state and local examples of bluff, dune and beach regulations include:
Bluf fsCalifornia's Coastal Zone Management Act, adopted in 1972, requiresthat new coastal development be designed to (a) insure geologic stability andstructural integrity; (b) not significantly contribute to erosion; and (c) notrequire a protective structure (e.g., groin) during the design life of thestructure. In 1976, the California Coastal Commission adopted guidelines forimplementing the Coastal Act, including a section entitled "GeologicStability of Blufftop Development." These guidelines, included in AppendixF-13

6-D, require a setback for development if the blufftop is deemed unstable.
The developer must have geotechnical studies performed by a registeredprofessional engineer and/or geologist. In granting a permit, the Commissionmay require that an applicant sign a waiver of all claim against the publicfor future liability or damage resulting from permission to build.
Michigan prohibits new structures in the 30-year erosion recessionarea along Lake Michigan under its 1970 shoreline zoning statute. Floodprotection from the 100-year storm is also required. Local governments aregiven the option of adopting regulations meeting minimum state standards.
Racine County, Wisconsin has adopted a 100-foot setback for bluff erosion areasalong Lake Michigan. Bluff areas are also being acquired. In order to better study ratesand causes of erosion, a volunteer "coast watch" was created. These volunteers monitorwave heights, rain, rates of erosion and other factors.
Highland Park, Illinois regulates development on bluffs and in ravine areas nearLake Michigan and established a 50-year setback requirement.
DunesNorth Carolina requires that all barrier island communities adopt dune protectionordinances. North Carolina more broadly addressed flooding and erosion in its 1974Coastal Zone Management Act, which is the most comprehensive in the nation. Under thislaw, the Department of Natural Resources has established regulatory guidelines formapped "ocean hazard" areas. Local governments are directed to regulate developmentconsistent with these guidelines. If they fail to do so, the state will directly regulatedevelopment.
Rhode Island prohibits building in its 30-year critical erosion setback area, underits 1976 Coastal Commission Statute. The state requires a minimum construction setbackof 50 feet from the-shoreline, prohibits building and rebuilding on dunes, requires thatnew structures in high hazard areas be elevated an additional six feet in addition to stormsurge elevation to allow for waves on top of flood waters, prohibits additional shorelineprotection on barriers, prohibits most new building on undeveloped barriers, and requireswind protection for structures in high hazard areas.
Examples of local dune protection ordinances include:
East Hampton, New York was severely damaged by the 1938 hurricane. Combinedcoastal erosion and flooding plague this wealthy Long Island community. Some of themost expensive development in the community is located on and behind the dune system.
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The community adopted a dune overlay district that includes all land within 100 feet ofthe dune crest. It has acquired between 400 and 500 scenic easements to protect wetlands,
dunes and other areas. The Nature Conservancy and the town both have active dune andwetland acquisition programs underway.
Avalon, New Jersey, a small barrier island town of 2,500 residents, adopted a dunesetback line in 1970. Its aggressive dune protection and reestablishment program won anOutstanding Conservation Advancement Achievement Award from the New JerseyAssociation of Natural Resources District in 1980. This program has involved planting ofbeach grass, erection of snow fences, control of foot traffic over the dunes and an activepublic education effort including mailing of dune protection information with its annualproperty tax bills.
BeachesMost state programs addressing bluffs, and dunes also tightly control developmenton beaches and the removal of beach materials. Other state and local regulations whichapply to beach and other areas include:
Florida's Beach and Shore Preservation Act of 1970 requires that flooding, erosionand wind protection be provided for all structures seaward of its coastal constructionsetback line. Protection elevations must allow for wave heights (including wave runup).
Buildings must be designed to withstand the impact of 140 mile per hour winds.
Structures are to have limited impact on the dune/beach system. Erosion must beconsidered. These requirements are, in general, more stringent than FEMA's, since theytake into account erosion, wave runup and the use of different approaches to surgemodeling.
Massachusetts has prohibited the removal of rocks and gravel from beaches since1760 to reduce erosion and storm damage. In 1980 Governor King adopted a barrier beachexecutive order tightly controlling the use of federal and state funds on barrier beaches.
See Appendix 6-C.
Examples of local regulations for beachand velocity zones include:
Gulf Shores, Alabama. In 1979, Hurricane Frederic destroyed or damaged over 500structures in this small barrier island community. Much of that damage was a result ofcombined erosion and flooding. Storm waves essentially destroyed the dune system andseverely eroded pilings and slab foundations. After the storm, the community adopted re-
vised regulations requiring deeper pilings, bracing of pilings and additional elevation toprovide protection from waves. The community also purchased some damaged properties.
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Pensacola Beach, Florida. This small barrier island community, located on SantaRosa Island, has both flood and erosion problems. It was severely damaged by HurricaneFrederic. Prior to Hurricane Frederic, the community had adopted a 50-foot dune setbackline. After Hurricane Frederic, the community adopted new regulations requiringincreased pile dimensions for elevated structures, minimum pile embedment (five feetbelow mean sea level), direct tie-ins betveen corner pilings and roof members, windloadprotection requirements for at least 140 mile-per-hour winds and minimum elevationrequirements of 13 feet.
Nonregulatory ActionsThe principal nonregulatory actions for bluff, beach and dune areas are erosioncontrol measures and relocation.
Erosion Control MeasuresErosion control may include both structural and nonstructural measures. To reduceerosion for bluff erosion areas:
1. Drain excess moisture from the site and strata susceptible to slumping throughsurface and subsurface drains;
2. Seal the ground surface to reduce infiltration and slumping;
3. Grade or terrace the bluff face to decrease the slope and increase stability. Thisis rarely practical for high bluffs. Once grading is completed, the terracedslope should be planted.
4. Stabilize the toe of the bluff through armoring or shore protection devices toreduce wave erosion and caving.
5. Build up and maintain a protective beach through beach nourishment, othertechniques;
6. Construct retaining walls or grout unstable slope areas.
For dune areas:
1. Replant dune vegetation;
2. Encourage reestablishment of dunes through snow fence or other devices thattrap sand transported to the dune area by winds, currents, waves;
3. Reconstruct dunes by mechanical means (e.g. grading, pumping, hauling).
For beach areas:
1. Construct bulkheads, seawalls, revetments groins;
2. Nourish the beach through pumping or hauling of sand from shore sources;
F-16

The potential impacts of proposed remedial measures to control coastal erosionshould be carefully studied before constructing bulkheads, seawalls, groins or other en-
gineering works. These measures have been criticized for exacerbating erosion in adjacentareas and causing environmental damage. They are temporary and costly. They increasethe beach profile and raise wave heights during, storms. Nevertheless, they may be theonly practical approach to protect existing structures in some situations.
A number of states, including Maryland and New Jersey, have beach erosion con-
trol programs. Some federal funds are available on a cost-share basis for various types oferosion control works including groins, bulkheads and beach nourishment. Most federalprograms are available to protect public areas but some funding is also available for pri-
vate protection. Technical and planning assistance and financial help are also available infrom some state beach erosion control programs.
Acauisition and RelocationPublic acquisition of undeveloped beach front areas for parks and other publicpurposes is often desirable. Acquisition can protect dunes, mangroves and natural protec-
tive barriers while preventing hazardous development.
Acquisition can be especially appropriate after flood disasters. Cituate, Mas-
sachusetts and Gulf Shores, Alabama relocated damaged structures with assistance byFEMA's Section 1362 relocation program. The key to taking advantage of post-disaster op-
portunities is pre-disaster planning.
Avalon, New Jersey and Sanibel, Florida are preparing pre-storm plans to guide re-
building, acquisition and other mitigation measures after the next disaster. This is a sen-
sible approach and will yield long-term benefits.
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Appendix 6-A. FEMA Guidelines for Community Regulations. CFR, Title 44 EmergencyManagement and Assistance Chapter 60.5 (1980).
60.5 Floodplain management criteria for flood-related erosion-prone areas. Theadministrator will provide the data upon which floodplain management regulations forflood-related erosion-prone areas shall be based. If the Administrator has not providedsufficient data to furnish a basis for these regulations in a particular community, thecommunity shall obtain, review and reasonably utilize data from the Administrator. How-
ever, when special flood-related erosion hazard area designations have been furnished bythe Administrator they shall apply. The symbols defining such special flood-related ero-
sion hazard designations are set forth in part 64.3 of this subchapter. In al cases the min-
imum requirements governing the adequacy of the flood plain management regulations forflood-related erosion-prone areas adopted by a particular community depend on theamount of technical data provided to the community by the Administrator. Minimumstandards for communities are as follows:
(a) When the Administrator has not yet identified any area within the communityas having special flood-related erosion hazards, but the community has indicated the pres-
ence of such hazards by submitting an application to participate in the Program, thecommunity shall:
(1) Require the issuance of a permit for all proposed construction, or other devel-
opment in the area of flood-related erosion hazard, as it is known to the community;
(2) Require review of each permit application to -determine whether the proposedsite alterations and improvements will be reasonably safe from flood-relater erosion andwill not cause flood-related erosion hazards or otherwise aggravate the existing flood-re-
lated erosion hazard; and(3) If a proposed improvement is found to be in the path of flood-related erosionor to increase the erosion hazard, require the improvement to be relocated or adequateprotective measures to be taken which will not aggravate the existing erosion hazard.
(b) When the Administrator has delineated Zone E on the community's FIRM, thecommunity shall:
(1) Meet the requirements of paragraph (a) of this sections; and(2) Require a setback for all new development from the ocean, Lake,bay, riverfrontor other body of water, to create a safety buffer consisting of a natural vegetative or con-
tour strip. This buffer will be designated by the Administrator according to the flood-re-
lated erosion hazard and erosion rate, in conjunction with the anticipated"useful life" ofstructures, and depending upon the geologic, hydrologic, topographic and climatic charac-
teristics of the community's land. The buffer maybe used for suitable open space pur-
posed, such as for agricultural, forestry, outdoor recreation and wildlife habitat areas,
and for other activities using temporary and portable structures only.
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Appendix 6-B: Excerpts of the North Carolina Ocean Hazard Area Regulations.
North Carolina Ocean Hazard AreasThe ocean hazard system identified by the Department of Natural Resources in-
cludes three components: (1) an "ocean erodible zone," which runs from the mean waterlandward equal to 30 times the long-term annual erosion rate plus the recession expectedin a 100-year storm; (2) a "high hazard flood area" defined to include open coasts subjectto wave action and flooding in a 100-year storm; and (3) inlet hazard areas definedthrough statistical analysis of past inlet movement.
A stringent minimum ocean setback is imposed, which requires that developmentbe located behind the furthest landward of four points: (1) 30 times the long-term annualerosion rate, measured from the vegetation line; (2) the crest of the "primary" dune(defined as the first dune with an elevation equal to the 100-year storm level plus sixfeet); (3) the landward toe of the frontal dune (defined as the first dune with sufficientheight, continuity, configuration, and vegetation to offer protective value); or (4) 60 feet,
measured from the vegetation, line.
.0302 SIGNIFICANCE OF THE OCEAN HAZARD CATEGORY(a) The primary causes of the hazards peculiar to the Atlantic shoreline are theconstant forces exerted by waves, winds, and currents upon the unstablesands that form the shore. During storms, these forces are intensified andcan cause significant changes in the bordering landforms and to structureslocated on them. Hazard area property is in the ownership of a large num-
ber of private individuals as well as several public agencies and is used by avast number of visitors to the coast. Ocean hazard areas are critical, there-
fore, because of both the severity of the hazards and the intensity of inter-
est in the areas.
(b) The location, and form of the various hazard area landforms, in particularthe beaches, dunes and inlets, are in a permanent state of flux, respondingto meteorologically induced changes in the wave climate. For this reason,
the appropriate location of structures on and near these landforms must bereviewed carefully in order to avoid their loss or damage. As a whole, thesame flexible nature of these landforms which presents hazards to develop-
ment situations immediately on them offers protection to the land, water,
and structures located landward of them. The value of each landform lies inthe particular role it plays in affording protection to life and property.
Overall, however, the energy dissipation and sand storage capacities of thelandforms are most essential for the maintenance of the landforms' protec-
tive function....
.0303 MANAGEMENT OBJECTIVE OF OCEAN HAZARD AREAS(a) The CRC recognizes that absolute safety from the destructive forces indige-
nous to the Atlantic shoreline is an impossibility for development locatedadjacent to the coast. The loss of life and property to these forces, however,
can be greatly reduced by the proper location and design of shoreline struc-
F-19

tures and by care taken in prevention of damage to natural protective fea-
tures particularly primary and frontal dunes. Therefore, it is the CRC's ob-
jective to provide management policies and standards for ocean hazard ar-
eas that serve to eliminate unreasonable danger to life and property andachieve a balance between the financial, safety, and social factors that areinvolved in hazard area development.
(b) The purpose of these regulations shall be to further the goals...with particu-
lar attention to minimizing losses to life and property resulting from stormsand long-term erosion, preventing encroachment of permanent structures onpublic beach areas, and reducing the public costs of inappropriately siteddevelopment.
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Appendix 6-C: Commonwealth of Massachusetts, Executive Order 181, 1980, BarrierBeaches.
PreambleA barrier beach is a narrow low-lying strip of land generally consisting of coastalbeaches and coastal dunes extending roughly parallel to the trend of the coast. It is sepa-
rated from the mainland by a narrow body of fresh, brackish, or saline water or marshsystem. It is a fragile buffer that protects landward areas from coastal storm damage andflooding.
The strenth of the barrier beach system lies in its dynamic character; its ability torespond to storms by changing to a more stable form. Frequently man induced changes tobarrier beaches have decreased the ability of landform to provide storm damage preven-
tion and flood control.
Inappropriate development on barrier beaches has resulted in the loss of lives andgreat economic losses to residents and to local, state and federal governments. The tax-
payer, who often cannot gain access to barrier beach areas, must subsidize disaster reliefand flood insurance for these high hazard areas.
Since barrier beaches are presently migrating landward in response to rising sealevel, future storm damagte to development located on the barriers in inevitable.
WHEREAS, the Commonwealth seeks to mitigate future storm damage to its barrierbeach areas;
NOW, THEREFORE, I, Edward J. King, Governor of the Commonwealth of Mas-
sachusetts, by virtue of the authority vested in me by.the Constitution and the laws of theCommonwealth, do hereby order and direct all relevant state agencies to adopt the follow-
ing policies:
1. Barrier beaches shall be given priority status for self-help programs and thispriority status shall be incorporated into the Statewide Outdoor Com-
prehensive Recreation Plan. The highest priority for disaster assistancefunds shall go towards relocating willing sellers from storm damaged barrierbeach areas.
2. State funds and federal grants for construction projects shall not be used toencourage growth and development in hazard prone barrier beach areas.
3. For state-owned barrier beach property, management plans shall be preparedwhich are consistent with state wetland policy and shall be submitted to theSecretary of Environmental Affairs for public review under the provisionsof the Massachusetts Environmental Policy Act.
4. At a minimum, no development shall be 'permitted in the velocity zones orprimary dune areas of barrier beaches identified by the Department of En-
vironmental Quality Engineering.
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5. Coastal engineering structures shall only be used on barrier beaches tomaintain navigation channels at inlets and then only if mechanisms are em-
ployed to ensure that downdrift beaches are adequately supplied with sedi-
ment.
6. Dredge material of a compatible grain size shall be used for barrier beachnourishment, if economically feasible.
7. The Coastal Zone Management Office shall coordinate state agency man-
agement policy for barrier beach areas.
F-22

Appendix 6-1): California Coastal Commission Statewide Interpretive Guidelines. Adopted1977.
Geological Stability of Blufftop DevelopmentSection 30253 of the 1976 Coastal Act provides that "new development shall: (1)
Minimize risks to life and property in areas of high geologic, flood and fire hazard; (2)
Assure stability and structural integrity, and neither create nor contribute significantly toerosion, geologic instability, or destruction of the site or surrounding area or in any wayrequire the construction of protective devices that would substantially alter natural land-
forms along bluffs and cliffs." Section 30251 provides that: "Permitted development shallbe sited and designed...to minimize the alteration of natural landforms..."
A bluff or cliff is a scarp or steep face of rock, decomposed rock, sediment or soilresulting from erosion, faulting, folding or excavation of the land mass. The cliff or bluffmay be simple planar or curved surface or it may be steplike in section. for the purposesof this guideline, "cliff" or "bluff" is limited to those features having vertical relief of tenfeet or more, and "seacliff" is a cliff whose toe is or may be subject to marine erosion.
"Bluff edge" or "cliff edge" is the upper termination of a bluff, cliff or seacliff. When thetop edge of the cliff is rounded away from the face of the cliff as a result of erosionalprocesses related to the presence of the steep cliff face, the edge shall be defined as thatpoint nearest the cliff beyond which the downward gradient of the land surface increasesmore or less continuously until it reaches the general gradient of the cliff. In a casewhere there is a steplike feature at the top of the cliff face, the landward edge of thetopmost riser shall be taken to the cliff edge.
To meet the requirements of the act, bluff and cliff developments must be sitedand designed to assure stability and structural integrity for their expected economic life-
spans while minimizing alteration of natural landforms. Bluff and cliff developments(including related storm runoff, foot traffic, site preparation, construction activity, irri-
gation, waste water disposal and other activities and facilities accompanying such devel-
opment) must not be allowed to create or contribute significantly to problems of erosionor geologic instability on the site or on surrounding geologically hazardous areas.
Alteration of cliffs and bluff tops, faces, or bases by excavation or other meansshould be minimized. Cliff retaining walls should be allowed only to stabilize slopes, orsea walls at the toe of seacliffs or to check marine erosion where there is no less envi-
ronmentally-damaging alternative and when required:
1. to maintain public recreational areas or necessary public services (such asprotection of coastal highways or energy facility) or to protect port areas;
2. to protect principle structures in existing developments that are in dangerfrom erosion; or3. in Los Angeles, Orange, and San Diego Counties, to infill small sections ofwall in subdivisions where a predominant portion of a wall is already inplace, provided that such infilling would have no substantial adverse envi-
ronmental effects.
F-23

A geologic investigation and report will be required when a development is pro-
posed to be sited within the area of demonstration as defined below.
As a general rule, the area of demonstration of stability (Illustration A) includesthe base, face and top of all bluffs and cliffs. The extent of the bluff top consideredshould include the area between the face of the bluff and a line described on the blufftop by the intersection of a plane included at a 20 degree angle from horizontal passingthrough the toe of the bluff or cliff, or 50 feet inland from the edge of the cliff or bluff,
whichever is greater. However, the Commission may designate a lesser area of demonstra-
tion in specific areas of known geologic stability (as determined by adequate geologicevaluation and historic evidence) or where adequate protective works already exist. TheCommission may designate a greater area of demonstration or exclude development en-
tirely in areas of known high instability.
The report should indicate the location of the cliff or bluff edge, the toe of thecliff or bluff and other significant geologic features by distance from readily identifiedfixed monuments such as the centerline of the road nearest the bluff or cliff.
The applicant for a permit for blufftop development should be required to demon-
strate that the area of demonstration is stable for development and that the developmentwill not create a ecologic hazard or diminish the stability of the area. The applicantshould file a report evaluating the geologic conditions of the site and the effect of thedevelopment prepared by a registered geologist or professional civil engineer with exper-
tise in soils or foundation engineering, or by a certified engineering geologist. The reportshould be based on an on-site investigation in addition to a review of the general charac-
ter of the area. Where there is a dispute over the adequacy of the report, the Commissionmay request that the report be reviewed by a state geologist from the Division of Minesand geology, the costs of that review and any necessary site inspections to be borne by theapplicant. The report should consider, describe and analyze the following:
1. cliff geometry and site topography, extending the surveying work beyondthe site as needed to depict unusual geomorphic conditions that might affectthe site;
2. historic, current and forseeable cliff erosion, including investigation ofrecord land surveys and tax assessment records in addition to the use of his-
toric maps and photographs where available and possible changes in shoreconfiguration and sand transport;
3. geologic conditions, including soil, sediment and rock types and characteris-
tics in addition to structural features, such as bedding, joints, and faults;
4. evidence of past or potential landslide conditions, the implications of suchconditions for the proposed development; and the potential effects of thedevelopment on landslide activity;
5. impact of construction activity on the stability of the site and adjacentarea;
6.-ground and surface water conditions and variations, including hydrologicchanges caused by the development (i.e. introduction of sewage effluent andF-24

irrigation water to the ground water system; alterations in *surfacedrainage);
7. potential erodibility of site and mitigating measures to be used to ensureminimized erosion problems during and after construction (i.e. landscapingand drainage design);
8. effects of marine erosion on seacliffs;
9. potential effects of seismic forces resulting from a maximum credibleearthquake;
10. any other factors that might affect slope stability.
The report should evaluate the off-site impacts of development (e.g. developmentcontributing to geological instability on access roads) and the additional impacts thatmight occur due to the proposed development (e.g. increased erosion along a footpath).
The report should also detail mitigation measures for any potential impacts and shouldoutline alternative solutions. The report should express a professional opinion as towhether the project can be designed so that it will neither be subject to nor contribute tosignificant geologic instability throughout the lifespan of the project. The report woulduse a currently acceptable engineering stability analysis method and should also describethe degree of uncertainty of analytical results due to assumptions and unknowns. The de-
gree of analysis required should be appropriate to the degree of potential risk presentedby the site and the proposed project.
In areas of geologic hazard, the Commission may require that a development per-
mit not be issued until an applicant .has signed a waiver of all claims against the publicfor future liability or damage resulting from permission to build. All such waivers shouldbe recorded with the County Recorder's Office.
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SELECTED REFERENCES ON COASTAL FLOODING AND EROSIONAssessment-of Research of Natural Hazards Staff, 1973, Coastal Erosion Report. Universityof Colorado, Boulder, Colorado.
Association of State Floodplain Managers, 1983, Preventing Coastal Flood Disasters: TheRole of the States and Federal Response, Proceedings of a National Symposium,
Ocean City, Maryland, May 23-25, 1983. Natural Hazards Research and Applica-
tions Information Center Special Publications #7. Boulder, Colorado: University ofColorado.
Balsillie, J.H., D.E. Athos, H.N. Bean, R.R. Clark, and L.L. Ryder, 1983,Florida's Programof Beach and Coast Preservation.In: Association of State Floodplain Managers, Pre-
venting Coastal Flood Disasters. University of Colorado, Boulder, Colorado.
Brown, A.J., 1983, California Coastal Storms, Jantuary-Maicah1983. In: Association of StateFloodplain Managers, Preventing Coastal Flood Disasters. University of Colorado,
Boulder, Colorado.
Clark, J., 1980, Coastal Environmental Management--Guidelinesfor Conservationof Resourcesand Protection Against StornmHazards. The Conservation Foundation, Washington,
D.C.
Clayton, G.R., 1983, Massachusetts' Coastal Floodplain Management Policy. In: Association ofState Floodplain Managers, Preventing Coastal Flood Disasters. University ofColorado, Boulder, Colorado.
Division of Land Resource Management Programs, 1979, The Shorelands Protection andAl'anagement Act. Michigan Department of Natural Resources, East Lansing,
Michigan.
Dolan, R., B. Hayden and H. Lins, 1980, Barrier Islands. American Scientist, 68(1): 16-25.
Federal Insurance Administration, 1977, National Flood Insurance Program. Proceedings ofthe National Flood Insurance Program Conference on Coastal Erosion.. Federal In-
surance Administration, Washington, D.C..
Gilman, C., 1983, Monitoringand Enforcement of the National Flood Insurance Program Reg-
ulations in ATewJersey Coastal and Barrier Island Municipalities. In: Association ofState Floodplain Managers, Preventing Coastal Flood Disasters. University ofColorado, Boulder, Colorado.
F-26

Great Lakes Basin Commission, Standing Committee on Coastal Zone Management, 1975,
Proceedings of the Recession Rate Workshop. Ann Arbor, Michigan: Great LakesBasin Commission.
--, Undated, The Role of Vegetation in Shoreline Management. Ann Arbor, Michigan:
Great Lakes Basin Commission.
Hanson, S.N., J.S. Perry and W. Wallace, 1976, Great Lakes Shore Erosion Protection. Madi-
son, Wisconsin: Wisconsin Coastal Zone Management Program.
Hildreth, R., 1980, Legal Aspects of Coastal Hazards Management. In: Coastal Zone '80, Pro-
ceedings of a Conference. New York: American Society of Civil Engineers.
Hoffman, J., D. Keyes and J. Titus, 1983, Projecting Sea Level Rise: Methodology, Estimatesto the Year 2100, and Research Needs. U.S. Environmental Protection AgencyWashington, D.C..
Jannereth, M.R., 1983, Michigan's High Risk Erosion Areas Program. In: Association of StateFloodplain Managers, Preventing Coastal Flood Disasters. University of Colorado,
Boulder, Colorado.
Joint FRC-GLBC Task Force for Great Lakes Shorelands Damage Reduction, 1974, AStrategy for Great Lakes Shoreland Damage Reduction. Federal Regional Council,
Chicago, Illinois.
Kuna, T., 1980, Soft Engineering Alternatives for Shore Protection. In: Coastal Zone '83.
Proceedings of a Conference. American Society of Civil Engineers, New York.
Kusler, J.A., et al., 1971, Regulation of Flood Hazard Areas to Reduce Flood Losses, Vol. 1,
U.S. Government Printing Office, Washington, D.C.
--------, 1972, Regulation of Flood Hazard Areas to Reduce Flood Losses, Vol. 2. U.S.
Government Printing Office, Washington, D.C.
--------,1984, Regulation of Flood Hazard Areas to Reduce Flood Losses, Vol. 3. U.S.
Government Printing Office, Washington, D.C.
Magoon, 0. and H. Converse (editors), 1983, Coastal Zone '83. Proceedings of the ThirdSymposium on Coastal and Ocean Management. American Society of CivilEngineers, New York.
McCarthy, R. and L. Tobin, 1983, Blufftop Regulatory Setbacks--A Regulatory Impossibility?
In: Magoon, 0. and H. Converse (eds.), Coastal Zone '83. American Society of CivilEngineers, New York.
F-27

Michigan Water Resources Commission, 1970, Great Lakes Shoreland Management and Ero-
sion Damage Control for, Michigan. Michigan Dept. of Natural Resources, EastLansing, Michigan.
Miller, H. Crane, 1977, Coastal Flood Hazards and the National Flood Insurance Program.
U.S. Department of Housing and Urban Development. Federal InsuranceAdministration, Washington, D.C..
Moore, J.W., and D.P. Moore, 1980, The Corps of Engineers and Coastal Engineering, A 50Year Retrospective. In: Coastal Zone '80. Proceedings of a Conference. AmericanSociety of Civil Engineers, New York.
Moul, R.D., 1983, Management Options: Can We Protect Our Coastal Barriers? In: Associationof State Floodplain Managers, Preventing Coastal Flood Disasters. University ofColorado, Boulder, Colorad.
Neal, W.J., O.H. Pilkey, Sr. and O.H. Pilkey, Jr., 1978, From Currituck to Calabash: Livingwith North Carolina's Barrier Islands, North Carolina Science and TechnologyResearch Center, Research Triangle Park, North Carolina.
Nordstrom, K.F. and N.P. Psuty, 1978, Coastal Dunes Dynamics: Implications for Protectionof Shorefront Structures. New Jersey Center for Coastal and Environmental Studies.
Rutgers University, Camden, New Jersey.
-----1983, The Value of Coastal Dunes as a Form of Shore Protection in California, U.S.A.
In: Coastal Zone '83. Proceedings of a Conference. American Society of CivilEngineers, New York.
O'Donnell, A.J., 1976, Drawing the Line at the Oceanfront, The Role of Coastal Constrzuc-
tion Set-Back Lines in Regulating Development of Florida's Coastal Zone. Universityof Florida, Gainesville, Florida.
Owens, D., 1983, Managing Development in Coastal Hazard Areas: State-Federal Relations.
In: Association of State Floodplain Managers, Preventing Coastal Flood Disasters.
University of Colorado, Boulder, Colorado.
Penland, S., D. Nommedal and W. Schram, 1980, Hurricane Inzpact on Dauphin Island. In:
Coastal Zone '80. Proceedings of a Conference. American Society of CivilEngineers, New York.
Pilkey, O.H., Sr., O.H. Pilkey, Jr., and R. Turner, 1975, How To Live W1ithAn Island. NorthCarolina Dept. of Natural Resources and Community Development, Raleigh, NorthCarolina.
F-28

CHAPTER 7: FLASH FLOOD AREASTHE HAZARDFlash floods, as their name implies, occur quickly. Flash flooding encompasses abroad range of flood problems on alluvial fans, in narrow and steep valleys, alongdrainage courses in urban settings, below unsafe dams and behind unsafe or inadequatelevees, and upom release of ice jam flooding. In these situations, flood waters not onlyrise rapidly but are high velocity and contain large amounts of debris. They tear outtrees, undermine buildings and bridges and scour out new channels.
The damage caused by flash floods has doubled in the last ten years. They nowrank first as a cause of weather-related deaths in the United States. Over three-quartersof all Presidentially declared disasters involve flash flooding. Examples of recent flashfloods with serious loss of life include:
* February, 1972, Buffalo Creek, West Virginia. -118 killed and hundreds ofhomes washed away as a dam made of coal mine waste material gave wayafter heavy rains.
* June, 1972, Rapid City, South Dakota and adjacent areas -236 dead and$100 million in property damage after a large, slow-moving thunderstormunleashed torrents of rain on the slopes of the Black Hills.
* July, 1976, Big Thompson Canyon, Colorado -139 drowned and millions inproperty damage after a thunderstorm deluged the western third of thecanyon with 12 inches of rain in less than 6 hours.
$ July, 1977, Johnstown, Pennsylvania. -77 dead and more than $200 millionin property damage when violent thunderstorms caused up to 11 inches ofrain to fall in a 7-county area over 9 hours. This contributed to the failureof several dams which compounded the stream flooding and accounted for44 of the deaths.
* September, 1977, Kansas City, Missouri. and adjacent areas -25 killed and$90-million in property damage when thunderstorms turned several streamsinto raging torrents, such as the "gentle" Brush Creek, which flows throughthe heart of Kansas City.
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* November, 1977, Taccoa, Georgia. -40 dead, half of them children, whenheavy rains ruptured an earthen dam and demolished residential structuresin the valley below.
Flash flooding occurs in all fifty states. Steeply sloping valleys in mountainousareas are the most common setting, but flash flooding can also occur along smallwaterways in urban areas. Urban flooding is an increasingly serious problem due toremoval of vegetation, placement of debris in channels, construction of culverts andbridges which constrict flood flows, paving and other replacement of ground cover byimpermeable surfaces which increase runoff, and construction of drainage systems whichincrease the speed of runoff.
The intensity and duration of rainfall and the steepness of watershed and streamgradients are the key factors in flash flooding. Other features include the amount of wa-
tershed vegetation and natural or artificial flood storage areas and the configuration ofthe streambed and floodplain. In general, the more intense the rainfall --the rate of rain-
fall or how much rain falls in a given period of time --the greater the probability offlash flooding. As one might also expect, the longer it rains in a given area, the greaterthe probability of flooding. Stationary or slow moving thunderstorms produce the most se-
rious flash floods because of their intensity and duration. A series of fast moving stormsover a short time can also produce huge volumes of runoff.
Flash floods cause greater damage than ordinary riverine floods because of thesuddenness of flooding (which may prevent evacuation), the velocity of the water and thedebris load. In addition, one, two or more flood crests may occur during a flash floodwhen a series of fast moving storms occur. Sudden destruction of structures and washoutof access routes may result in loss of life. Deaths are common when motorists underesti-
mate the depth and velocity of flood waters and attempt to cross swollen streams.
Collectively, many small subdivisions in a stream's watershed --not just the flood-
plain --can drastically increase flash flooding. Watershed changes are often not reflectedin current maps and regulations governing floodplain development, underestimating thedamage potential in urban settings.
EXISTING MITIGATION EFFORTSFlash flooding has not been separately treated in mapping, regulatory and insuranceefforts of the National Flood Insurance Program (NFIP) or most state programs. Neverthe-
less, more than 800 local governments have adopted flash flood warning, evacuation plan-
G-2

Figure 7-1. Too close for comfort: tourist cabins in Big ThompsonCanyon, Colorado housed many people who were unawareof flash flood dangers. One hundred, forty-four lives werelost in the 1978 flash flood here. Source: Rutherford Platt.
Figure 7-2. Flash flooding repeatedly damaged campgrounds atWhitewater State Park, MN. Area is now used only for day-
time activities. See further discussion in Appendix 7-B.
Source: Minnesota Dept. of Natural Resources.
4L

ning or other mitigation efforts for particular streams or reaches of streams. Often thesehave been adopted with state or federal assistance. Examples include San Diego and Ven-
tura Counties; California; Brattleboro, Vermont; Lycoming County, Pennsylvania; Keene,
New Hampshire; Estes Park, Colorado; and Tulsa, Oklahoma. Estes Park; Colorado; RapidCity, South Dakota; and Tulsa, Oklahoma have adopted restrictive floodplain regulationsfor flash flood areas. Many communities, including Denver, Colorado; Chicago, Illinois;
Tulsa, Oklahoma; Austin and Dallas, Texas;and King County, Washington have adoptedstormwater management regulations to require onsite detention and reduce increased run-
off due to urbanization. Rapid City, South Dakota; Larimer County, Colorado and Tulsa,
Oklahoma have purchased areas subject to severe flash flood problems and relocatedstructures.
At the federal level, the National Weather Service has prepared a list of 2000communities with potential flash flood problems. The Service issues flash flood watchesand warnings as part of its weather reporting service (See Insert). It has developed bothself-help and automated warning systems for implementation at the local level includingthe ALERT system which uses small microcomputers. Information about this system isavailable from the National Weather Service. The Soil Conservation Service, The Ten-
nessee Valley Authority, U.S. Army Corps of Engineers and U.S. Geological Survey havealso provided technical assistance to states and communities in developing and implement-
ing flash flood warning systems.
Several states have adopted their own flash flood warning systems or provide assis-
tance to local governments:
Colorado has designated canyons with flash flood potential. The StateDepartment of Transportation has erected "Climb to Safety" signsalong roads in canyons with flash flood potential.
Connecticut is implementing a two-tiered flood warning system incooperation with local governments and the weather service. Thissystem will include statewide warnings and individual townwarnings. Two towns, Norwich and Sothington have already joinedthe system and allocated $20,000 each. The system will involve 20 ofits own rain gaging stations; 5 weather stations, and a complete radionetwork. Data from the National Weather Service will be combinedwith data from the state and local gaging efforts.
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Maryland is cost-sharing in design, equipment and installation of local floodwarning systems as part of the watershed management program.
Warning systems must be coordinated with local response plans.
New York has developed a Prototype Local Flood Warning Plan, availablefrom the New York Department of Environmental Conservation.
All told, considerable progress has been made in identifying flash flood pronecommunities and in installing warning systems. Less progress has been made in adoptingevacuation plans, and other implementation measures.
OPTIONS FOR ACTIONFLASH FLOOD WATCHthere may be flooding;
stay alert;
watch for thunderstorms;
keep an eye on rivers and streams;
be ready to take necessary actions if a FLASH FLOOD WARNING is issuedor if flooding is observed.
FLASH FLOOD WARNINGthere is flooding;
act at once;
move out;
go to a safe area on high ground.
Policy and Program ElementsA community with a flash flood problem should adopt a policy and program withthe following elements:
1. A resolution or ordinance stating that certain flood areas are subject to specialrisks to life and property due to rapidly rising water and in some instances, highvelocity, erosion and debris.
2. The mapping or designation of streams or drainageways with potential for rapidinundation, high velocities and erosion or debris potential.
3. Regulations for new development in flash flood areas to either prohibit suchdevelopment or require that it be designed and located to withstand flash floodingand so that rapid evacuation is possible. Warning systems and evacuation plansshould be required for hotels and other establishments open to the public. WhereG-5

flooding will be worsened by development in the watershed, zoning andsubdivision regulations should adopt a zero excess discharge goal for stormwaterrunoff.
4. Implementation of flood warning systems and evacuation plans for areas withexisting development. (See Appendix 7-A for an inventory of organizations to beinvolved.)
5. Marking of flash flood areas with "climb to safety" or other indicators of risk.
6. Implementation of flood control measures (where appropriate) includingconstruction of levees, dikes, reservoirs.
7. Relocation of structures from truly high risk areas.
MappingA community should prepare maps for areas subject to flash flooding. If areas arealready mapped by the NFIP, the preparation of new overlay maps may be advisable.
NFIP maps indicate floodway and flood fringe boundaries but do not indicate areas withrapidly rising water, high velocity (except in floodways), debris or erosion potential. Newmaps may also be needed for smaller streams and drainageways which typically have notbeen mapped by the NFIP. In mapping flash flood areas, an inventory should also bemade of specific sites where threats to private and public safety may occur in the eventof a flash flood such as low road crossing at hotels, motels, houses or other structuresthreatened by the flood waters and having inadequate access.
A community effort to identify areas with flash flood potential can begin with thecollection of historical flood data. Local residents and newspaper accounts often indicatestreams or reaches of streams subject to flash flooding. Historical data can be supple-
mented with preliminary watershed surveys based upon topographic maps, soils maps, andair photos. High gradient streams in areas of steep topography with limited vegetation ornatural detention areas are often potential flash flood areas.
If sufficient funds are available, more detailed engineering studies can be used toidentify streams and reaches of streams with flash flood potential, areas along thesestreams subject to potential debris and erosion problems or areas where threats to publicor private safety may occur.
Stormwater runoff models are available to identify flash flood areas in urban set-
tings. See the selected reference for a description of some models. In general, these modelsrequire slope, soil and land use information. Regional streamflow and precipitation aswell as other data can often be obtained from published sources.
G-6

Figure 7-3. Elements of Automated Flash Flood Warning System. 


Marking of AreasVarious types of marking may be applied to flash flood areas. After one flood,
Crookston, MN posted markers on telephone poles and other public works indicating floodheights. Although this was not a flash flood, a similar approach could provide invaluableinformation for flash flood areas. After the Big Thompson Canyon disaster in 1976, theColorado Department of Transportation posted "climb to safety" signs along roads incanyons along the Front Range.
Acquisition and RelocationFor areas of very high flash risk or in the aftermath of a disaster, acquisition andrelocation of structures can provide a permanent solution to flash flood dangers. Reloca-
tion may be easier to promote in the aftermath of a flash flood disaster since structuresare often severely damaged. Rapid City spent $45 million and purchased the entire flood-
plain of Rapid Creek for open space use after the disaster in 1972.
Engineering WorksFlash floods dangers may be reduced by constructing dams and levees, floodwallsand other engineering works. However,such works may not be effective for small water-
sheds with buildings at risk at many sites along the streams and drainageways.
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Figure 7-4. The message on this billboard is prophetic. 


Figure 7-5. The marking of flood hazard areas is a very effective public 
education tool. Source: Jon Kusler. 


Appendix 7-A: Inventory of Public Service and Safety Organizations with Potential for orRole Related to Flood Warning and Evacuation Activities.
I | Leader's I I TelephoneI Organization I name I Address f numberI Civil DefenseI Firemen IPolice (Municipal)
Sherif F II State PoliceMunicipal Highway Depts.
County Highway Depts. I IState Highway Depts.
I Hospitals, Medical Clinics I II Ambulance Service PublicAmbulance Service PrivateCivil Air PatrolI HAM Radio OperatorsI Red CrossNational GuardOtherOther I I.
Other iI OtherI Other IG-14

flooding is available, a three-tier approach to flood warning is now,utilized in the White-
water River valley.
First, the NWS will continue to provide advance warning of approaching storms.
The NWS will issue severe weather watches and warnings directly to the park headquar-
ters, using radio communications if necessary.
Second, an automated flood warning system was installed in the Middle ForkWhitewater River watershed. This system consists of three precipitation gages and tworiver level sensing gages which utilize radio telemetry to send instantaneous, "real-time"
data to the park office. A microcomputer in the park office is used to receive, displayand store the rainfall and river level data.
Finally, volunteers in the Whitewater River basin provide backup rainfall data inthe event of hardware failure in the automated system.
Flood advisory tables, developed by the NWS, provide a means to predict whetherflooding is imminent, based on antecedent soul moisture conditions and rainfall amounts.
Once a decision is made that flooding is likely, a written response plan is set into action.
This "Flash Flood Emergency Preparedness Plan" details actions to be taken for variousanticipated levels of flooding.
While the primary beneficiary of this flood warning system is Whitewater StatePark and the public it serves, much of southeastern -Minnesota also benefits from thissystem. The NWSwill have direct access to the data from this system to be used to corre-
late actual rainfall intensities with radar images. More accurate and timely flash floodwatches and warnings should result.
G-16

Appendix 7-C: February 1985 Fort Wayne Flood Summary, excerpts from a paper byCarrol, T.R. and R.D. Marshall, 1985.
NWS Airborne Snow SurveyJanuary, 1985 was the fifth snowiest January on record in the Fort Wayne area.
From February 10 to 14, 1985, snowfall contributed to a total accumulation of 2.5 to 3.5inches of snow water equivalent over large portions of Indiana, Michigan, and Ohio. It isinteresting to note that a total snow water equivalent accumulation of 3 inches at FortWayne during the March 1 to 15 period has a reoccurrence interval of approximately 3300years (U.S.DOC/WB, 1964). Soil moisture neat the surface over the region was at (orabove) field holding capacity. On February, 15, 16, and 17 (Friday, Saturday, and Sunday),
the National Weather Service made airborne snow water equivalent measurements over 92flight lines covering 20,000 square miles in northern Indiana, southern Michigan, andnorthwestern Ohio.
The airborne data were sent digitally to the office in Minneapolis, checked for ac-
curacy, entered into SHEF format, and sent over AFOS approximately one hour after theaircraft landed each noon and evening during the three day survey. In this way, the ap-
propriate NWS offices had access to the airborne data within one hour after the aircraftlanded from each survey mission.
NWS WSFO and WSO Warnings and StatementsMonday, February 18, was a government holiday. Based on the airborne data, col-
lected on February 15-17, on February 18 WSOFort Wayne notified Allen, Adams, andDeKalb County government units that snowmelt flooding was possible for the region. OnTuesday, February 19, the Indianapolis WSFO issued a severe flood potential statementfor northern Indiana. Additionally, the Indiana Governor and various state agencies werewarned of the threat of severe snowmelt flooding for the northern portion of the stateduring the coming weekend. Weather forecasts for Thursday, February 21, called forabove freezing temperatures and precipitation. WSO Fort Wayne called a meeting onFebruary 21 with the Red Cross, Civil Defense, Lutheran Social Services, Salvation Army,
Church of the Brethern and the city of Fort Wayne to warn of the flooding threat overthe coming weekend. On February 25 at 1:15 PM, the Weather Service issued a crestforecast of 9.50 feet above flood stage for the Maumee River at Anthony Boulevard inFort Wayne. Thirty-four hours and forty-eight minutes later on February 27 at 12:03 AM,
the Maumee River at Anthony Boulevard in Fort Wayne crested at 9.55 feet above floodstage.
Flood Summary for 1978, 1982 and 1985Fort Wayne has experienced substantial snowmelt flooding during the century. Ma-
jor floods occurred in 1913, 1943, 1950, 1959, 1978, 1982 and 1985. The Table below sum-
marizes the four greatest floods on the Maumee River at Anthony Boulevard in FortWayne where flood stage is 15 feet. It is interesting to note that although the 1978 floodcrested 0.7 feet below the 1985 flood crest, the damage caused by the 1978 flood was over$50 million greater that the damage estimated for the 1985 flood by Fort Wayne officials.
G-17

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1. Install river gages, prepare emergency action plans, implement an early warningsystem (ALERT) in cooperation with the National Weather Service, and develop a floodproofing program,
-2. Build new dikes and repair and increase the height of old dikes,
3. Install backwater gates to prevent floodwater backup through the city water andsewage system,
4. Improve existing channels,
5. Acquire floodplain property,
6. Install emergency pumping stations, and7. Prepare damage survey reports.
In addition, the National Weather Service expanded the Airborne Snow SurveyProgram operational flight line network to cover much of the area in Indiana, Michigan,
and Ohio which experienced significant snowmelt flooding in 1982.1985 Flood CostsThe U.S. Army Corps of Engineers Reconnaissance Report (1984) provides a proce-
dure to estimate flood costs based on flood stage both with and without the implementa-
tion of the Fort Wayne 18 Month Work Program. Consequently, it is possible to take the1985 flood stage and estimate what the flood damage would gave been without the im-
plementation of the Work Program, the flood ALERT system, or the Airborne Snow Sur-
vey Program. The Table below summarizes the estimate of the 1985 flood costs withoutthe previously mentioned improvements.
ESTIMATED 1985 FLOOD COSTS WITHOUT IMPLEMENTATION OFTHE FORT WAYNE 18 MONTH WORK PROGRAM,
THE FLOOD ALERT SYSTEM, FORTHE AIRBORNE GAMMA RADIATION SNOWSURVEY PROGRAMFLOOD COSTS 1985(Feb. 1985 $) ESTIMATEStructure and Content Damage $8,954,000Public (city and county) Costs 7,239,000Agency Costs 1,681,000Evacuation-Residential 903,000Evacuation-Commercial 1,064,000Lost Wages ,739,000Lost Business Revenue 5,445,000Vehicle Operational Costs 541,000Opportunity Costs for Vehicle Occupants $433,000Total $27,999,000G-19

DISCUSSION AND SUMMARYMost of the recommendations suggested in the 18 Month Work Plan were imple-
mented before the 1985 flood. The flood ALERT system was installed and the operationalairborne flight line network was established in the region before the 1985 flood. Thesethree major improvements limited actual damage in the 1985 Fort Wayne flood to $4 mil-
lion. Consequently, it is reasonable to suggest that the improvements prevented approxi-
mately $24 million in 1985 flood damage.
The Work Plan improvements which were implemented were, no doubt, responsiblefor preventing a major portion of the $24 million damage .which would have likely oc-
curred, without the three improvements. Additionally, the flood ALERT system con-
tributed to damage prevention by providing essential hydrometrological data required foraccurate and timely flood forecasts. The airborne snow survey conducted one day after amajor regional sniowstorm and ten days before the flood crest provided information nec-
essary to issue an early severe-flood warning for the region. The early warning facilitatedtimely flood fight planning and consequently contributed to the prevention of subsequentflood damage.
It is, of course, impossible to accurately partition the relative merits of each of thethree major improvements implemented before the 1985 flood. It is possible, however, toarbitrarily assign various relative importances to each of the three major improvements toestimate, in a crude fashion, the contribution each improvement made to the total savingsof $24 million in damage prevention. The table below gives three arbitrary estimates ofthe percent of the total $24 million savings associated with each of the three major im-
provements. In the first case, if the Work Plan contributed 80 percent to the total flooddamage prevention, then the savings directly attributable to the Work Plan improvementwould be approximately $19 million. In a similar fashion, -the flood damage prevented as adirect result of the early warnings and river forecasts facilitated by the airborne snowsurvey data can be variously estimated from $700,00 to $2,400,000 depending on the rela-
tive importance placed on the airborne data.
FLOOD DAMAGE SAVINGS BASED ONIMPROVEMENT TYPEImprovement type Case I Case 2 Case 318 Month Work Plan 80% $19.2 85% $20.4 90% $21.6Flood ALERT system 10% $2.4 10% $2.4 7% $1.7Airborne Snow Survey 10% $2.4 5% $1.2 3% $0.7Note: $ in millionsThe $7,700 cost of the February 1985 Fort Wayne airborne snow survey was sub-
stantially less than the. projected flood damage prevented as a result of the early warningsand flood forecasts based on the airborne snow water equivalent data.
G-20

SELECTED REFERENCES FOR FLASH FLOODSBarr Engineering, Co., 1981, Flash Flood Warning System in Minnesota. Report prepared forthe Minnesota Dept. of Natural Resources.
Barrett, C.B., 1981, National Prototype Flash Flood Warning System. Paper presented to the4th Conference on Hydrometeorology, Reno, Nevada. Boston, Massachusetts:
American Meteorological Society.
Barrett, C.B., 1983, The NWS Flash Flood Program. Paper presented to the 5th Conferenceon Hydrometeorology, Tulsa, OK. Boston, Massachusetts: American MeteorologicalSociety.
Bartfeld, I. and D. Taylor, 1982, A Case Study of a Real-Time Flood Warning System onSespe Creek, Ventura County, California. Proceedings from a Symposium on Storms,
Floods and Debris Flows in Southern California and Arizona, 1978 and 1980.
Washington, D.C.:National Academy Press.
Benson, K.K. and J. Solstad, editors, 1983, Minnesota Flood Plain Management Newsletter,
Vol. 1, No. 2, May-July. St. Paul, Minnesota: Dept. of Natural Resources.
Carrol, T.R. and R.D. Marshall, 1985, Cost Benefit Analysis of Airborne Gamma RadiationSnow Water Equivalent Ft. Wayne Flood. Paper presented at 6th Conference onHydrometeorology, Indianapolis, Indiana. Boston, Massachusetts: AmericanMeteorological Society.
Carter, M., 1980, Natural Hazards Warning Systems, NHS Report Series No. 79-02.
Minneapolis, Minnesota: University of Minnesota.
Hydrology Subcommittee of the Federal Interagency Advisory Committee on Water Data,
1985, Guidelines on Community Local Flood Warning and Response Systems. Reston,
Virginia: U.S. Geological Survey.
Flood Loss Reduction Associates, 1981, Cooperative Flood Loss Reduction: A TechnicalManual for Communities and Industry. Lewisburg, Pennsylvania: SEDA Council ofGovernments and the U.S. Water Resources Council.
National Advisory Committee on Ocean and Atmosphere, 1983, The Nation's River andFlood Forecasting and WarningService. Spcieal Report to the President and Congress.
National Weather Service, 1977, Guide for Flood and Flash Flood Preparedness Planning,
U.S. Dept. of Commerce, National Oceanic and Atmospheric Administration,
National Weather Service. Silver Spring, Maryland: National Weather Service.
National Weather Service, no date, Guide for Flood and Flash Flood Preparedness Planning.
Prepared for Disaster Preparedness Service by H.J. Owen.
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WHAT CAUSES LAKE LEVEL FLUCTUATIONS?
Water level fluctuations on lakes can be caused by both natural andman-made events. Natural factors include precipitation, evaporation,
runoff, ground water, ice, aquatic growth, meteorological disturbancesand, in larger lakes, tides and crustal movement. Artificial factors in-
fluencing lake levels include dredging, diversions, consumptive use ofthe water and regulation by structural works. The role of long-tern?
climate trends is imperfectly understood but does play a part indefining the range of possible fluctuations.
Lonz-term fluctuations are the result of persistent low or high watersupply conditions affecting the basin. The extremely low levels of lakesafter the 1930's drought and the extremely high level of Great SaltLake at this time are examples of long-term fluctuations. The intervalsbetween periods of high and low levels and the length of such periodsvary widely and erratically. The extreme lake levels are likely to per-
sist eve l after the factors which caused them have changed.
Seasonal fluctuations reflect the annual hydrologic cycle. In the earlyspring, as a result of snowmelt, heavier rains and reduced evaporationover the basin, the water level begins to rise from winter low. This trendcontinues until the lake peaks in the summer. During the summer, morepersistent winds and drier air intensify evaporation; also the runoffand ground water flow reach their lowest values. As the water suppliedto the lake becomes less than the outflow, the water level begins thedownward trend to winter minimum.
Short-term?fluctuations are the most dramatic changes in water levelsand are caused by strong winds and by sharp differences in barometricpressure. These fluctuations usually last less than one day and do notrepresent any changes in volume of water of the lake.
Modified from "Great Lakes Water Level Facts", U.S. Army Corps ofEngineers, Detroit District.
Long duration flooding has serious implications. First, to map the 100-year flood-
plain is, in most cases, technically difficult or impossible if traditional methods are em-
ployed. Historical lake data, gage analyses and biological determinations based on landand aquatic vegetations are needed. Second, traditional regulatory requirements such aselevation of buildings on pilings or floodproofing of structures and utilities are inade-
quate since such protection approaches will not withstand years of water.
EXISTING MITIGATION EFFORTSFloodplain management programs have rarely addressed lake flooding. Many of theglaciated states do have shoreland management programs but most of these have primarilyaddressed lake management from the perspective of aesthetics, water quality and recre-
H-2

ation. Only when lake levels rise and flood structures does the need to incorporate flooddamage reduction parameters become apparent.
Some communities have adopted special management programs for lakes with long-
term fluctuations, for example:
Lake Pulaski. MinnesotaAfter 100 structures were flooded by rising lake levels, Wright County, MN, theCity of Buffalo, Buffalo Township and the Minnesota Department of Natural Resourcesentered into a cooperative agreement to regulate and manage Lake Pulaski, a 770-acrelake west of the Twin Cities Metropolitan area (see draft of management plan, Appendix8-A). While the complete story of this mitigation effort is quite complex and is not yetsuccessfully concluded, many of the mapping and regulatory procedures formulated heremay be applied elsewhere. See the insert on one approach to the mapping of thefloodplain of a lake and Appendix 8-B)
Lake Elsinore. CaliforniaFlooding due to rains and the limited outlet of the lake is a periodic phenomenonon Lake Elsinore and has occurred at least seven times over the last 200 years. Floodingon Lake Elsinore in 1980 damaged or destroyed over 400 structures and required theremoval of 450 mobile homes. The City of Lake Elsinore adopted revised floodplainregulations (see Appendix 8-C) prohibiting new development below the 100-year floodelevation unless structures are located on land. Their previous ordinance, which was ineffect at the time of the flood, had allowed new structures on pilings; this hadcontributed to flood damage. The city has also developed a plan for acquisition of flood-
prone properties to be funded by FEMA through its section 1362 program, state parkacquisition and local funding sources.
The Great LakesEight states of the highly industrialized North Central region border on the GreatLakes. The total area within the basin in the United States is 174,000 square miles, ofwhich 61,000 square miles is water. Except where bedrock outcrops or where protectiveworks have been constructed, the glacial debris comprising the shore of the Great Lakes ishighly erodible.
Shore erosion and flooding have been major problems, especially in periods of highlake levels such as the late 1920's, mid 1940's, early 1950's, early 1970's and the presenttime. Shore property damages increase with each high water period because of further de-
velopment of unprotected shorelands and continually increasing shore property values.
H-3

.

Figure 8-1. When these photos were taken, these homes on Lake 
Pulaski, Minnesota had been under water for approximately 
three years. See discussion in Appendix 8-A. 
Source: Minnesota Dept. of Natural Resources. 


Most of the affected states have adopted management programs that require build-
ing standards and setbacks for new construction. There will, however, continue to bedamages to existing properties, many of which are part of the public infrastructure.
Great Salt Lake. UtahGreat Salt Lake is a "terminal" lake which means it receives inflow but has nooutlet. It is a remnant of Glacial Lake Bonneville which covered 20,000 square miles inUtah, Nevada and Idaho during the last Ice Age.
Since the Morman pioneers settled the valley in 1847, accounts of lake levels havebeen well documented. Typical fluctuations have been between 4191.55 and 4205 feet. In1963, the lake fell to a low of 4191.35 and there were concerns that the lake would go dry.
By 1975, its level had risen to 4202 and consideration was given to lowering the level bypumping water out into the desert. The level was maintained with minor fluctuationsuntil the fall of 1982 when it began to rise in response to a series of storms. BetweenSeptember 18, 1982 and June 30, 1983, the lake rose 5.2 feet; the greatest seasonal rise everrecorded. The level as of July 15, 1985 was 4209.4. Damage estimates for losses at the endof 1983 were approaching $500 million.
A solution to the problems associated with the Great Salt Lake is difficult. Theeconomic impact on the private sector has already been tremendous. The publicinfrastructure has also suffered. Structural solutions, such as upstream impoundments,
may not be economically or environmentally feasible. Regardless of the array of actionsthat are ultimately taken, a strong floodplain management program and strict land usecontrols need to be implemented.
OPTIONS FOR ACTIONPolicy and Program ElementsWhere there is potential for lake flooding problems, a policy and program with thefollowing elements may be appropriate:
1. A policy statement or resolution that long-term fluctuations in water levelsmay result in flood damages quite different than those for riverine flood-
ing;
2. A ban on roads, water and sewer extensions to areas subject to long-terminundation;
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3. A set of regulations that prohibit building in semi-permanently flooded ar-
eas. If building is to take place, it should occur only on fill with adequateaccess, water supply and waste disposal during times of high water;.
4. A strategy for relocating or protecting structures in areas subject to long-
term fluctuations;
5. If the lake extends across the boundaries of more than one unit of govern-
ment, a formal agreement that insures intergovernmental coordination andcooperation. The exact form of the agreement will vary with different statelaws. Examples of cooperative arrangements include joint powers agree-
ments, lake management districts and watershed districts. The managementplan for Lake Pulaski, Minnesota (see Appendix 8-A) contains a comprehen-
sive policy statement.
MappingWhere a lake is part of a river system (e.g., a reservoir), conventional flood mapsmay accurately portray lake flooding. When the lake is not part of a flowage, considera-
tion has to be given to the water budget of the lake and its watershed. Unfortunately, theclimatic, soil, lake level and ground water level needed exist to make a precise analysis israrely available. Biological and ecological characterization, historical high water remem-
brances, analysis of soils and analysis of landforms are alternative methods for outliningthe historical lake bed and potential flooding levels.
The following insert describes how biological and geomorphic data are used toestablish the Natural Ordinary High Water (NOHW) mark in Minnesota. The NOHW is theline that separates state regulations of the bed of the lake from local regulation of theshoreland. Several states have a similar mapping element although there is variation in thespecific parameters.
MIAPPINGTHE FLOODPLAIN OF A LAKE; ONE APPROACHResource management and riparian rights pertaining to an inland lake are de-
pendent upon identification and establishment of that lake's Natural OrdinaryHigh Wkater(AOH1,1) elevation. The NOSH is coordinated with the upper limit ofthe lake basin and defines the elevation (contour) on the lakeshore wvhichdelin-
eates the boundary of public wvaters.Identificationof the NOHW comes fronmanexamination of the bed and banks of a lake to ascertain the highest water levelwhere the presence and action of water has been maintained for a sufficientlength of time to leave recoverable evidence. The primary evidence used to iden-
tify the NOHWTof a lake consists of biological (vegetation) and physical fea-
tures found on the banks of the lake. Data depicting historic lake levels are of-
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ten useful only as supporting data in NOHW studies. This is because the avail-
able data generally are not of sufficient detail, continuity, frequency and/orlength of record to alone identify the NOHW.
Because trees are the most predominant and permanent expression of uplandvegetation,they are used as NOHW indicators wherever suitable species and sitescan be located. Particular attention must be given to the species of uplandgrowth selected for consideration. In general, willow and most ash are very wa-
ter tolerant; maples and elms tolerant; most birch intermediately tolerant andoak intolerant. The less tolerant trees make the best indicators, but factors inaddition to species also have to be considered such as age, the slope of ground,
the effect of water and ice action on the shoreline and the physical conditionand growing characteristics of the trees. Water dependent vegetation such ascattails will follow lake levels as they rise and fall and therefore provide littleevidence about the lake's NOHW,except in cases where more permanent vegeta-
tion does not exist. Trees, like people, will follow receding water levels and in-
fringe upon the lake basin. When water levels rise to reclaim the basin such treesare inundated and eventually die.
The tree analysis involves a relationship between the elevation of the ground atthe base of the tree and the diameter of the tree. Depending upon the species oftree selected and the slope of the ground, it can be generally stated that a treerequires a depth of unsaturated soil about equal to its trunk diameter to grow.
Most trees will not survive if water levels saturate their root systems for a suffi-
cient period of time and if they do survive, stress signs may be evident in thegrowing characteristics of the tree. The diameter, height, shape of the stem,
branch shape, branch spread and foliage density reflect the extent to which thetree roots have had an opportunity to penetrate into and spread through the soilto reach the elements that stimulate growth. A tree growing near the basin'sfringe will often indicate by its general appearance whether.its root system hashad breathing space and sufficient nourishment and support from the soil inwhich it grows. As an example, a seedling started in soil six inches above a zonesubject to saturation will grow normally until it reaches a diameter of approxi-
mately six inches,after which it will show by its general appearance the adversegrowing characteristics mentioned above.
Physical features searched for include soil characteristics, beachlines, beachridges, scarp or escarpment (more prominent scarp can often be found in theform of the undercutting of banks and slopes), ice ridges, natural levees, berms,
erosion,deposition, debris, washed exposed shoreline boulders, high water marks,
movement of deposits as a result of wave action, top and toe of bank elevationsas well as water levels. Caution is taken to be aware that many of the listed ge-
omorphologicalfeatures may take a long time to develop and also that severalsets of these features may be found. That is, a lake likely will have more thanone stage where the action of water has left recoverable evidence, however onlythe stage coordinated with the upper limit of a basin is used to assist in identi-
fying the NOHW level. As an extreme example, water level stages resulting fromthe drought years of the 1930's certainly were the result of natural conditionsextending over a number of years, but the resulting recoverableevidence is of nouse in NOHW determinations.
Credits: Excerpts from NATURAL ORDINARY HIGHWATER MARK DETER-
MINATION. Report for Pulaski Lake, MN. Minnesota Department of NaturalResources, Divisionof Waters,March 1985.
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RegulationsFloodplain zoning, shoreland zoning, subdivision control, building codes, and otherspecial codes can be used to establish:
Protection elevations. In determining protection elevations, allow substantial free-
board where there is the potential for wave action or ice damage. The amount of free-
board should be based on the fetch (open water area), anticipated wave heights, andthickness of the ice (if this is a factor).
Buffers and setbacks. Wisconsin, Minnesota, Washington and Maine require mini-
mum setbacks of 75 feet for new structures on all lakes.
No Fill. Requirements that structures be located on land, not on fill, at an eleva-
tion above the natural high water level.
Prohibit basements. Basements can be prohibited, use of the basement as livingarea can be prohibited.
Sanitary codes. Sanitary codes can be used to prohibit septic systems in expectedflood and high ground water areas where such systems will not function.
Well construction codes. Well construction can require proper abandonment of wellsto protect ground water and can contain requirements for siting new wells.
Flood loss reduction standards are often appropriately included not only in floodhazard reduction ordinances, but also in shoreland zoning, wetland protection and broaderland use controls.
Nonregulatory ActionsAcquisition and RelocationRelocating structures may be the only practical solution when long-term floodingrenders them useless. Relocation is taking place on Lake Elsinore and has been proposedfor some structures on Lake Pulaski.
Outlet ConstructionEfforts have been made on both Lake Elsinore and Pulaski to construct outlets, re-
ducing water levels. The problem with this approach is that it may be difficult to find aplace to put the excess water.
LeveesLevees have been constructed to reduce flooding on the Great Salt Lake. However,
levees are usually a temporary solution to flood problems.
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Appendix 8-A: A Management Plan for the Developed Lake Bed Area of Lake Pulaski,
Wright County, Minnesota.
INTRODUCTIONLake Pulaski is located near the center of Buffalo Township (Tl20N, R25W) inWright County Minnesota. The south half of the lake is located within the corporate limitsof the City of Buffalo.
A December 1981 report by the Division of Waters of the Department of NaturalResources (DNR) estimated the Natural Ordinary High Water level (NOHW) of Lake Pu-
laski to be at an elevation 968.8 or roughly seven feet above present levels.
On June 11, 1982, in accordance with state law and after public hearings, theCommissioner of Natural Resources signed an order officially establishing the 968.8 eleva-
tion as the NOHW of Lake Pulaski. All land located adjacent to Lake Pulaski that is be-
low this elevation is now considered lake bed. Upon signing this order, it is estimated thatroughly 100 structures are considered located on the bed of Lake Pulaski and at least 170structures will receive some water-related damage. At the 968.8 elevation, roughly 60 acresof land that is above the present lake level would be inundated by water.
This fact presents a very unusual but not unprecedented problem in Minnesota'shistory of shoreline management. Several lakes in eastern Minnesota have similar prob-
lems, such as Big Marine Lake in Washington County. However, this is the first time thatthe DNR has established the NOHW level to be above-this many residences before the lakereclaimed itself. Experience from these eastern lakes has shown that the combination oflakeshore owners trying to save their homes, together with conflicting and uncertain au-
thorities of state and local governments can lead to many problems. The Lake Pulaskiproblem is unprecedented in the respect that this is the first time state and local govern-
ments have had the chance to prepare for the problem in advance of its becoming severe.
The City of Buffalo and Buffalo Township contracted with Zack Johnson and As-
sociates to study the Lake Pulaski problem and to work with a local task force in makingrecommendations to state and local governments as to how to deal with it. The study enti-
tled "Lake Pulaski Area Development Study" was released in July of 1982 and it exploredmany possible solutions to the low development problems including artificial control ofthe lake level, filling and raising of all the structures, acquisition of the lake bed area,
relocation of homes, and adoption of development controls.
The task force which worked with Zack Johnson and Associates came up with sev-
eral recommendations on how to deal with the Lake Pulaski problem. Most of these rec-
ommendations involved non-structural means of addressing the problem. That is, theyconcluded that artificial manipulation of the lake level and massive relocation programswere not financially feasible. Instead, they recommended use of development controls(zoning), public information, and further study as the most cost-effective way of address-
ing the problem. The Department of Natural Resources supports the task force'srecommendations and hopes to see all of them carried out.
The purpose of this plan is to address the environmental, social, and regulatory is-
sues involved in future management of the lake bed area of Lake Pulaski and to lay outthe framework and policies which state and local governments will follow in administer-
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ing the area. The purpose is also to make this information available to local residents, de-
velopers, real estate agents and particularly lake bed owners, so that they fully under-
stand the legal limitations that govern the existing and future use of the lake bed area.
This plan is prepared under authority granted the Department of Natural Re-
sources in Minnesota Statutes, Section 104.03 (Flood Plain Management), 105.39 (Authorityof Commissioner -DNR-), 105.403 (Water and related land resources plans), 105.42 (Publicwater permits) and 105.48(Shoreland management).
GEOLOGY AND HYDROLOGYThe geology and other physical characteristics of Lake Pulaski are addressed inboth the "Lake Pulaski Area Development Study" and the Department's "Natural OrdinaryHigh Water Determination for Pulaski Lake". The size of Lake Pulaski has been measuredat 837 acres in 1858, 770 acres in 1953, and 786 acres in 1979. The watershed, that is allland that slopes towards Lake Pulaski, has been estimated to be roughly 3500 acres in size.
This results in a 3:1 watershed to lake area ratio, which is generally considered insuffi-
cient to maintain water levels in Pulaski. Therefore, it is assumed that the levels of Pu-
laski are in large part affected by ground water levels and ground water inflow(commonly referred to as being "spring fed").
Since ground water inflow is extremely difficult to measure and since the extentof and recharge capabilities of the aquifers affecting Lake Pulaski are largely unknown,
any calculations regarding projected levels and timing of those levels is impossible at thistime. The only thing that is known for certain is that levels in Lake Pulaski reached andstayed at elevation 968.8 feet for extended periods at least once and possibly twice withinthe past 125 years. It should be noted that there was also evidence that the lake had ex-
ceeded 968.8 feet by 2 or 3 feet sometime in the past.
Reading of the two previously mentioned reports is recommended for those inter-
ested in more detailed information on the physical characteristics and history of LakePulaski.
EXISTING REGULATORY AUTHORITIESPresently, five governmental units have some interest or authorities relating toLake Pulaski. They are the Federal Government, State Government, Wright County, theCity of Buffalo, and Buffalo Township. A summary of the general interests and authori-
ties of each unit follows:
Federal Government:
Direct authority over placement of fill in the lake or adjoining wetlands by theU.S. Army Corps of Engineers. No direct land use authority. Some Federal interest in Pu-
laski problems is through financial assistance type agencies such as HUD, VA, SBA, FHA,
etc. Some technical assistance available through SCS. Primarily federal interest is throughthe Federal Emergency Management Agency (FEMA) which administers the disaster assis-
tance programs and the Flood Insurance Program.
State Government:
DATR-Direct authority over all activities occurring below the ordinary high waterlevel. Indirect authority over all property located within 1000 feet of the lake, throughH-10

the Shoreland Management Program and indirect authority over all land located belowany estimated 100-year flood level; through the State Floodplain Management Program.
Permits are required of all individuals, companies, agencies, or government units doingany work that changes the cross-section of the bed of Lake Pulaski. Local governments arerequired to adopt and enforce ordinances relating to Shoreland and Floodplain areas thatmeet the minimum standards developed by the DNR.
Pollution Control Agency (PCA): Direct authority over water quality aspects of LakePulaski relating to community sewage discharge, feed .lot location and construction oflandfills. Indirect authority relating to individual sewage treatment systems and generalground and surface water quality.
Department of Health (DOH): Direct authority over well construction and location,
and commercial food or recreation related establishments. Well drillers have to be licensedand must follow DOH well code which specifies various elevation requirements and set-
backs.
Local GovernmentWright County: Has extensive direct land use authority which is administeredthrough the Wright County Planning and Zoning Ordinance. This ordinance contains pro-
visions which meet or exceed all DNR required shoreland and floodplain provisions. Thisauthority applies to the north one-half of the lake only. The County also. has taxing au-
thority over the area and property values of the area may affect county revenues.
City of Buffalo: Has extensive direct land use authority over the south one-half ofthe lake, which is administered through the City's zoning ordinance. This ordinance doesnot meet all of the DNR required shoreland and floodplain provisions, but the City re-
cently enacted a moratorium on any development below the ordinary high water level.
The City also has indirect control over land uses on Lake Pulaski through its municipalsewage collector system.
Buffalo Township: Has the authority to adopt extensive land use controls providedthey meet or exceed the county standards. These controls would apply to the north half ofthe lake only. However, the township presently addresses its land use concerns through theCounty planning process.
The primary tool by which governmental units control uses of land is through apermit or approval system. What follows is a listing of common development activitiesthat do or could occur in and around Lake Pulaski, and a summary of the various typesof permits and/or approvals that are required for each activity.
1. Erecting, moving or wrecking any building or structure. A building permit is re-
quired by either the City of Buffalo or Wright County any time this activity oc-
curs within their corporate boundaries. In the County, the permit may actually beissued by a Township Building Inspector, but a permit is not required for a build-
ing of less than 150 square feet of area. On the lake bed area, a permit would alsobe required by the DNR and possibly by the U. S. Army Corps of Engineers. Gen-
erally, DNR regulations would prohibit building or moving new structures onto thelake bed; the city or county would normally issue building permits provided thebuilding code and all other ordinance provisions are met. On the lake bed both theCity and County prohibit the construction or location of new structures.
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2. Remodeling, enlargement, repair or modification of existing structures. Abuilding permit is required for any of these activities either in the City or Countycontrolled areas. On the lake bed area, DNR permits would also be required, exceptfor minor repairs such as reshingling and painting. Under the county ordinance,
lake bed structures are classified as a nonconforming use which cannot be ex-
tended or expanded. However, the county ordinance does allow normal mainte-
nance of structures. The City does not differentiate between lake bed or non-lakebed areas.
3. Filling, excavation, landscaping, terracing, grading, and construction of retainingwalls. On the lake bed area, these activities all require a permit from the DNR.
Whether or not such permits are issued depends on the environmental effects and-
the purpose of the activity. Permits from the U. S. Army Corps of Engineers aregenerally needed when material is placed in the lake bed, but not for excavation.
In the county controlled lake bed area, placement of fill requires a conditional usepermit, which can be issued if the applicant can show that the fill has some bene-
ficial purpose and the amount is as small as possible. Outside of the lake bed area,
but within the county controlled shoreland area, a land alteration permit is re-
quired any time more than 50 cubic yards of earth is to be moved. Within city con-
trolled lake bed and shoreland areas, a specific permit is not required for any ofthese activities but they may be controlled by the City when done in conjunctionwith another controlled activity.
4. Subdivision of land. In the County controlled area any division of property ormoving of lot lines requires approval of the County. Simple lot line adjustmentsare handled through the Board of Adjustment. Division of tracts of land for devel-
opment requires that platting procedures be followed and requires County Board ofCommissioner's approval. Within the City, any time property is divided into parcelssmaller than 2 and one-half acres in size or 150 feet in width, platting provisionsmust be followed and City Council approval is required.
5. Installation, repair, replacement, removal or use of individual on-site sewagetreatment systems. Within the County controlled area, a permit is required prior toinstallation, alteration or repair of any individual on-site sewage disposal system.
On the lake-bed area, a DNR permit may also be required as such installation orrepair would involve a temporary or permanent change of the cross-section of thebed of the lake. Within the City, on-site systems are prohibited and hook up topublic sewer is required.
RECOMMENDED POLICIES AND REGULATORY CHANGESFrom reading the preceding section, one can see that the authority of the federal,
state, and local government units often overlap as regards control of the lake bed area. Inexamining the various policies relating to each of the involved permit requirements, it be-
comes obvious that none of the affected regulations or ordinances were really designed todeal with this unique situation. Therefore, it is felt that some general policies must firstbe agreed upon by the state and local governments, before the regulatory conflicts can besorted out. These recommended policies and the action needed to implement the policiesfollow:
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Appendix 8-B: Minnesota Department of Natural Resources, Conservation Regulations.
Standards for Local Government Regulation of Shoreland Areas4.22 High Water ElevationIn addition to the setback requirements of Section 4.21:
For lakes, ponds or flowages: No structure, except boat houses, piers and docks,
shall be placed at an elevation such that the lowest floor, including basementfloors, is less than three feet above the highest known water level. In those in-
stances where sufficient data on known high water levels are not available, the el-
evation of the line of permanent shoreland vegetation shall be used as the esti-
mated high water elevation. When fill is required to meet this elevation, the fillshall be allowed to stabilize, and construction shall not begin until the property hasbeen inspected by the Zoning Administrator.
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Appendix 8-C: Ordinance Prohibiting Construction, Additions and Alterations o-f Buildingsat or below Certain Levels.
ORDINANCE No. 604AN ORDINANCE OF THE CITY OF LAKE ELSINORE, CALIFORNIA, PROHIBITINGTHE CONSTRUCTION OF NEW BUILDINGS, ADDITIONS OR ALTERATIONS, INCERTAIN AREAS OF THE CITY AT OR BELOW CERTAIN ELEVATIONS.
The Mayor and the City Council of the City of Lake Elsinore, California, do or-
dain as follows:
Section 1: No person, firm or corporation shall construct any building upon anyproperty within the City of Lake Elsinore with the foundation or basement lower thanthe elevation of 12.70'mean sea level around the lake and along the channel to the spill-
way. Development on the Temescal Wash floodplain or within 5.vertical feet of the 100year floodplain shall be subject to review on a case by case basis. No building permit shallbe issued -by the City which is in violation of the provisions of this ordinance andOrdinance No. 603.
Section 2: That any and all septic tanks, cesspools, leach lines, seepage pits shall notbe constructed until written approval is obtained from the Department of Health of theCounty of Riverside.
Section 3: This ordinance shall remain in full force and effect until July 1, 1981,
at which time this ordinance shall be of no effect except that the Ordinance No. 603 shallremain in full force and effect.
Section 4: The City Clerk shall cause this ordinance to be published as required bylaw.
Section 5: This ordinance is determined to be an urgency measure for the preserva-
tion of the Public Health, Safety and Welfare of the City of Lake Elsinore and will be-
come effective immediately upon its adoption to reduce the possibility of injury anddamage to persons or property due to possible, flooding.
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SELECTED REFERENCES ON FLOODING DUE TO FLUCTUATING LAKE LEVELSArnow, T. 1984, Water Level and Water-Quality Changes in Great Salt Lake, Utah, 1847-1983.
Circular 913. Washington, D.C.: U.S. Geological Survey.
Carnelian-Marine Watershed District, 1982, Overall Plan in Northeastern Washington County.
St. Paul, Minnesota: Carnelian-Marine Watershed District.
Cohen, P. and J. Stinchfield, 1984, Shoreland Development Trends. Report #4, ShorelandUpdate Program. St. Paul, Minnesota: Minnesota Dept. of Natural Resources.
Federal Emergency Management Agency, 1985, Fluctuating Lakes: Case Studies and Miti-
gation Opportunities (draft), Denver, Colorado: FEMA Region VIII.
International Great Lakes Levels Board, 1973, Regulation of Great Lakes Water Levels, Re-
port to the International Joint Commission. Washington, D.C. and Ottawa, Ontario: In-
ternational Joint Commission.
Joint Federal Regional Council, 1974, A Strategy for Great Lakes Shoreland Damage Re-
duction. Chicago: Great Lakes Basin Commission Task Force for Great LakesShorelands Damage Reduction.
Kay, P.A. and H.F. Diaz, 1985, Problems of and Prospects for Predicting Great Salt LakeLevels. Logan, Utah: University of Utah.
Minnesota Dept. of Natural Resources, 1980, Carnelian-Marine Watershed District miscel-
laneous files.
-------1982-84 Lake Pulaski correspondence files.
Novitzki, R.P. and R.W. Devane, 1978, WisconsinLake Levels: Their Ups and Downs. Madi-
son, Wisconsin: U.S. Geological Survey and University of Wisconsin.
U.S. Army Corps of Engineers, 1983, Devil's Lake Basin, North Dakota: Pre-ReconnaissanceEvaluation Report. St. Paul, Minnesota: St. Paul District, Corps of Engineers.
------, 1983, Final Section 205 Detailed Project. Report, Flood Control Project at Devil's Lake,
North Dakota. St. Paul, Minnesota: St. Paul District, Corps of Engineers.
------,1984, Great Lakes Water Level Facts. Detroit, Michigan: Detroit District, Corps of En-
gineers.
U.S. Geological Survey, 1976, Hydrologic Relations Between Lakes and Aquifers in aRecharge Area Near Orlando, Florida. Water Resources Investigation 76-65. Wash-
ington, D.C.:U.S. Government Printing Office.
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CHAPTER 9: GROUND FAILURE AREAS: SUBSIDENCE AND LIQUEFACTIONTHE HAZARDSubsidence and liquefaction are two types of ground failure which canlower the ground surface, causing or increasing flood damage in areasof high ground water, tides, storm surges or overbank stream flow.
Mudflows and landslides are other types of ground failures which cancause flood damage. Subsidence is the most common type of failureand occurs in at least 38 states.
Both natural processes and human actions cause subsidence. Principal naturalcauses include solution (karst topography), consolidation of subsurface materials such aswetland soils and movements in the earth's crust. Principal human causes include mining,
inadequate compaction of fill material during construction and withdrawal of oil or wa-
ter from subsurface deposits. Human activities frequently accelerate natural processes.
Subsidence can increase flood damages in two ways. First, the land surface can belowered so that it is more frequently or more deeply flooded. Second, subsidence canblock or otherwise alter drainage patterns leading to deeper or unexpected flooding.
Causes of subsidence that have increased flooding problems include:
Withdrawal of Oil, Gas, Water. The withdrawal of oil, gas and water from belowthe earth's surface results in the collapse of the grain structure and compaction of subsur-
face materials causing the land surface to sink. The harbor at Long Beach, California hassubsided as much as 27 feet due to oil and gas withdrawals. In the Houston-Galvestonarea of Texas, 2500 square miles have subsided one foot or more. Areas of Seabrook andBaytown, Texas, are now subject to flooding from daily tides.
Compactionof Organic Soils. Subsidence occurs in organic wetlands as the soils arecompacted by fills and development and as ground water is withdrawn. The groundsurface then settles, but not at an even rate. Development on coastal wetlands in coastalareas is most likely to experience subsidence.
Underground mining. Underground mining, both past and present, is the cause ofsubsidence in an estimated 220 counties in 42 states. Locally, this subsidence has worsenedflooding and drainage problems in Pennsylvania and Illinois.
Karst Terrain. As ground water percolates through limestone, it dissolves the rock,
forming cavities or caverns. Fluctuating ground water levels can cause these caverns andI-1

Figure 9-1. These houses in Brownwood Subdivision are flooded by 
daily tides because withdrawal of fluids has resulted in 2.5 
meters of subsidence. Source: R. Platt. 


Figure 9-2. Organic soils like these are easily compressed, leading to 
subsidence. Source: unknown. 

Figure 9-3. Subsidence on organic soils has resulted in structural 
damage to this house in New Orleans. Source: 6. Cox. 

I 

i 


overlying surface materials to collapse suddenly, forming sinkholes. The land surface canalso sink slowly and irregularly, resulting in flooding.
Localized flooding occurs when natural drainage into and through caverns isblocked by silt, waste or rock dumped into caves and subsurface drainage channels. Voidsin the limestone cannot always be detected. Cavern formation and collapse may beartificially accelerated by man's activities, for example withdrawal of ground water,
which may have occurred far away from the site of the collapse.
Subsidence and flooding due to construction on organic soils is a widespreadproblem. There are an estimated 6.4 million acres of filled wetlands within metropolitanareas. The annual cost of subsidence damiage in these areas has been estimated at $58 mil-
lion and is expected to increase as the result of urban expansion onto lands normally con-
sidered unsuitable for development. In some cases, the cost of building streets to adequatestandards in subsidence prone areas exceeds conventional construction costs by 80 percent.
Organic soil compaction has also been a problem in agricultural areas. Drainage ofthe Delta Islands of the Sacramento-San Joaquin Delta has resulted in lowering thesurface of many of the islands to 10-15 feet below sea level. Subsidence can destroy theintegrity of flood control levees and may necessitate continuous upgrading and mainte-
nance of the levee system.
The risk of flood damage is higher in subsidence areas than in typical floodplainlands because the flood hazard is always increasing and the level of protection affordedby protection measures such as levees is always decreasing.
Liquefaction is another type of ground failure that contributes to flood problems. It istriggered by earthquakes. Liquefaction occurs when seismic shock waves pass throughunconsolidated and saturated soil. Vibrations allow the soil grains to move freely andpack more closely together. Suddenly, instead of a soil structure with water in the porespaces, there are groups of grains in a fluid matrix. The load of the overlying soil andbuildings is transferred from the soil grains to the pore water. If the pressure on the wa-
ter causes it to drain away, the overlying soil and structures will sink or tilt. If the watercannot drain away, the water pressure rises. When the water pressure equals the down-
ward pressure of the overlying strata and structures, the saturated soil layer will becomeliquid and flow. On steep slopes (greater than 3%) where the saturated layer is at or nearthe surface, soil, vegetation and debris can flow rapidly downslope with the liquefiedmaterial. These flow failures can result in the movement of material for miles. On gentleI-4

slopes (0.3 to 3%) where the saturated layer is below the surface, huge blocks of soil canmove 10 to 100 feet or more. Such failures are termed lateral spread.
Although strictly it is speaking not a flood problem, liquefaction can result inserious flooding of structures built on fill or saturated soils as in portions of SanFrancisco or Anchorage. In the 1964 Alaska earthquake in Prince William Sound, 60% ofthe $500 million in damages was due to ground failure.
EXISTING MITIGATION EFFORTSFlood-related subsidence and liquefaction areas have not been extensively mappedor regulated, nor are ground failure conditions reflected in flood mapping for insuranceand other management purposes. The failure to integrate mapping, regulation and othermanagement of these natural hazards is a reflection of the fragmentation of re-
sponsibilities for these activities at all levels of government. Better integration can be ex-
pected in the future as a result of the current focus on more comprehensive approaches toemergency management.
SubsidenceSome of the earliest efforts to prevent subsidence began in California. Ground wa-
ter overdraft in the Santa Clara Valley from 1920 to the late 1960's resulted in 13 feet ofsubsidence. By 1969, subsidence had essentially stopped due to recharge of ground waterand importation of surface water through the State Water Project.
Frequently, the remedy for the subsidence problem requires a regional rather thana site specific approach. The Harris-Galveston Subsidence District and the Active GroundWater Management Areas in Arizona are examples, of the kinds of institutional arrange-
ments that have been established to solve regional problems. In both cases, the purpose isto reduce subsidence by regulating ground water overdraft. The enabling legislation of theHarris Galveston Subsidence District is summarized and presented in Appendix 9-A; ex-
cerpts from the proposed district plan are presented in Appendix 9-B.
One of the problems in mitigating karst and/or sinkhole hazards has been the lackof ability to find them in the subsurface before they result in land surface collapse. Im-
proved detection techniques as well as better management of surface water drainage areintegral parts of sinkhole hazard mitigation. The stormwater management program inBowling Green, Warren County, Kentucky addresses both flooding and land use in sink-
hole areas.
I-5

Illinois and Pennsylvania have adopted regulatory programs to reduce subsidencedue to the extractions of minerals. Several techniques are employed to reduce the subsi-
dence threat including leaving rock pillars and filling cavities with compacted minewaste. Impacts of these and other alternatives on the hydrology for the area have to becarefully considered because of the potential for impacts on quantity and quality of flow.
LiquefactionConsiderable progress has been made in determining where liquefaction is likely tooccur. The characteristics of the liquefaction prone area are:
I. geologically young, unconsolidated sands and silts.
2. presence of the water table within 50 feet of the land surface.
Progress has also been made in determining the frequency of "shaking" which pro-
duces liquefaction areas. For example, in the San Fernando Valley in California, datasuggest that such levels of shaking occur approximately once every 45 years.
The relationship between liquefaction and flooding is that most liquefaction proneareas are in the floodplains of active seismic areas. In the Los Angeles area, the areasmost prone to liquefaction include the floodplains of the Los Angeles, Santa Anna andSan Gabriel Rivers and flood control basins. In the New Madrid seismic zone of the Cen-
tral Mississippi Valley, liquefaction can occur as far as 150 kilometers away from theepicenter of a major earthquake. Again, the most liquefaction prone areas are the flood-
plains and, in this case, hundreds of miles of levees could be affected.
OPTIONS FOR COMMUNITY ACTIONPolicy and Program ElementsA community policy and program to address subsidence and liquefaction problemsshould include the following elements:
1. A statement by the legislative body that subsidence and liquefaction areproblems which are to be reflected in ongoing floodplain management;
2. Mapping of subsidence and liquefaction areas with, if possible, determina-
tion of the rates of subsidence and frequency of liquefaction-producingevents.
3. Adoption of development controls for subsidence and liquefaction areas.
Man-made causes of subsidence such as ground water extraction should beI-6

Table9-1:Data Needs and ManagementOptionsforSubsidence:Source:HRB-Singer,Inc.,froma reportpreparedfor U.S. HUD,1977.
GEOLOGICAND PEDOLOGICPARAMETERSCONSIDEREDREQUIREDTESTDATADETECTIONAND PRE-
DICTIONTECHNIQUESUSEDSITEENGINEERINGANDFOUNDATIONALTERNATIVESLOCAL AREALUndergroundmining (bit-
uminouscoal)
Seam thicknessThicknessof overburdenLithology of overburden,
mine roof, mine floorSpan(of void)
Minimumpillar diameterPercentage extractionTime since miningRemnantpillar patternWatertable levelFracturingAngle of draw (limit angle)
Angle of breakMining history ofarea (PA)
Subsurface investiga-
tion for multifamilyhousing (PA)
Mining historyfrommaps, recordsBoringsBorehole cameraGrade beamsCaissonsGroutcolumnsFly ash injectionFlushingDaylightingStructural slabsor raftsDrained org-
anic wetlandsSoil compositionSoil compactionSoil shrinkageSoil decompositionWatertable levelsBuried canalsDrainageSoil thicknessMPS'srequire boringsand evaluations ofengineeredfoundationfor subdivisions andsingle family dwellings;
borings, soils tests,
and foundations reportsfor multifamily con-
struction (LA)
BoringsMaps:
GeologicPedologicVegetationPiles (timber)
Raymondpiles(highrises)
KelleyslabConventionalslab,
Types 1, 2, and 3Mud jackingSurchargingMaintainingwaterlevelRemoving organicsoilLithologyWater tablefluctuationPumping ratesand volumesDischarge of water intolimestoneOverburdenFracture patternsSoilsand boringdatafor multifamily units(PA)
Minimum 100-footborings for high rises(FA)
BoringsSeismictestsGravitymeteringAerial photographyTopographicmapsResistivity(PA)
Air rotarydrilling(PA)
Slab on grade AvoidingsinkholePiles areasGrouting Maintaining waterSpread footings tablelevelsRaft foundationFillingshallowcavitiesStabbingoverdeep cavitiesBRAB Slab (PA)
SUBSIDENCECONDITIONSinkholeformation

regulated. Structures should be constructed at elevations reflecting antici-
pated subsidence rates.
Since subsidence and liquefaction are often regional problems, they must be ad-
dressed at several levels: by individual property owners, by subdividers or developmentsand by groups of municipalities. Coordination of these efforts is essential. Municipalitiesmust direct new development toward more stable areas and establish building standards.
Developers have the responsibility to use adequate design and construction techniques.
MappingDifferent procedures are needed for mapping subsidence or liquefaction areas.
SubsidenceData needs and management options for subsidence areas are given in Table 9-1.
Subsidence due to fluid withdrawal. Areas subject to subsidence due to fluid with-
drawal can often be identified only through time-series topographic information indicat-
ing actual lowering of the ground surface. Once identified, rates can be estimated. Analy-
sis of an aquifer's water budget by computer modeling can also be used to suggest likelyareas of subsidence and, in some cases, the rates of subsidence.
A general idea of the potential for subsidence due to ground water withdrawal canbe obtained by comparing withdrawal with recharge on a regional basis. The U.S. Geologi-
cal Survey publishes hydrologic atlases for many areas of the country that indicateaquifer recharge rates.
More sophisticated computerized models have been developed to evaluate groundwater recharge and withdrawal and express the results in terms of projected subsidence. Atwo model system developed by the U.S. Geological Survey has been applied to the Hous-
ton-Galveston area. The first model uses data on ground water pumpage to predictchanges in the ground water level. Long-term reduction of ground water changes in levelsis likely to result in subsidence. A second model relates changes in the water table level tochanges in the land surface elevation.
Subsidence on organic (wetland) soils. Organic wetland soils can be identified withsoil maps and onsite inspections. Generally, the entire area underlain by organic soilshould be designated a subsidence risk area. If water table records are available, areas ofnaturally dropping water table levels are particularly high risk.
Subsidence on Karst Terrain. Karst areas are underlain by limestone and other wa-
ter soluble minerals that can be identified on geologic maps prepared by the U.S. or StateI-8

Geological Surveys. However, the presence of these deposits does not necessarily mean thatkarst conditions exist. Even where geologic maps show karst areas, predicting specific sub-
sidence and flooding in karst is difficult without field studies including soil boring anddye tests.
Where development is located in gradual sinkholes (forming depressions withoutoutlets) and the flood threat is due to surface drainage into the sinkholes, standard runoffmodels can be used to predict flood levels with a few modifications. Bowling Green, Ken-
tucky has made the following assumptions with the use of such models:
1. The city assumes no outflow since sinkholes may be filled, blocked orflooded beyond drainage capacity.
2. The city uses a 24-hour rainfall event. While hourly intensities are used innon-karst areas, the interval is longer for sinkholes since they drain muchmore slowly than stream channels.
3. The city assumes runoff levels with maximum urbanization.
4. The city adds at least one foot of freeboard above the 100-year elevationcontour.
Bowling Green requires developers to map flood depths in sinkhole basins sincethere are many, small (1-1/2 acre) sinkhole drainage basins in the area.
The Florida Bureau of Geology in cooperation with the Florida Sinkhole ResearchInstitute is currently mapping areas of the state drained by sinkholes. They are developingmethods to characterize drainage into and through sinkholes based on vegetation and soilfactors that affect infiltration of Water.
LiouefactionThe U.S. Geological Survey and state geological surveys have been particularly active inmapping liquefaction-prone areas. The urban areas of San Diego, Los Angeles, San Fran-
cisco, Salt Lake City, Seattle, Albuquerque, Anchorage and Reno are currently being stud-
ied. Figure 9-4. depicts the regulated liquefaction areas near San Francisco Bay in Red-
wood City, California. These areas were mapped by the USGS and are regulated by thecity. FEMA is continuing evaluations of the impacts of a severe earthquake in the activeseismic areas of the west and the New Madrid Seismic Zone. Mapping of liquefactionzones is one of the products of these studies.
1-9

-----Boundary of Area underlain by mud 

Area underlain by bay mud 

Figure 9-4. Part of a map showing the area of Redwood City, CA underlain by bay 
mud. The map is attached to the building code which requires 
supplemental structural design and construction standards for all 
new development. Source: U.S.G.S. 

4

I------

Firm sediment or bedrock 

A B 

Figure 9-5. Damage due to differential compaction of soils. In A, soils have settled 
homogeneously. In B., the presence of the sand body results in 
differential settling with subsequent structural damage to the house. 
Source: U.S.G.S. 


RegulationThe type of regulation needed to reduce damage in subsidence and liquefactionareas depend on the cause and severity of the subsidence or liquefaction (see Table 2 forsummary of regulatory options). There are two basic approaches to subsidence-relatedflood damages:
1. Regulate the cause of the subsidence.
2. Regulate land use or construction practices in subsidence areas.
The first approach is not generally applicable to liquefaction (which is due to nat-
ural causes); the second approach is appropriate for both subsidence and liquefaction.
Regulations for subsidence and liquefaction areas may take several forms:
Building codes can be used to establish special foundation requirements for struc-
tures on organic soils or in liquefaction areas. See Appendix 9-C for building code provi-
sions adopted by Jefferson Parish, Louisiana to reduce damage to development on organicsoils.
There are two design approaches for liquefaction areas:
1. Determine the depths to which liquefaction may occur through soil testingand surveys, then require piles to be placed to the bottom.
2. Determine the area subject to liquefaction, then "load" it prior to develop-
ment so that the pore water is forced out and soil density is increased.
Where subsidence or liquefaction potential exists but detailed studies are lacking,
require developers to conduct geologic and engineering studies to determine actual risksand design accordingly. This type of ordinance would identify the geographic areas withpotential risk, establish study requirements, and specify qualifications for studycontractors.
Zoning and building codes can be used to require additional freeboard in flood-
plain regulations to reflect subsidence. Such regulations can also be used to reduce damagein karst terrain. For example, the Bowling Green, Warren County, Kentucky stormwatermanagement program addresses both the cause of flooding and land uses. Filling of sink-
holes which will block drainage and cause flooding is prohibited. The floodplain or-
dinance also requires mapping and restricts development below the 100-year flood eleva-
tion in sinkhole basins. The subdivision ordinance requires drainage plans for all newdevelopment and on-site detention to prevent increase in stormwater runoff.
Infrastructure plans, zoning, subdivision controls or other regulations can be usedto establish standards for public and public works in subsidence and liquefaction areas.
1-11

Unit construction can be required for roads, walks and other paved surfaces, expansionloops can be required for utility pipes and lines.
Special codes can be used to regulate ground water withdrawals, the removal of gasand oil or the mining of minerals. See Appendix 9-A for excerpts from the enablingstatute and regulations from the Houston-Galveston Coastal Subsidence District.
Table 9-2 summarizes the options for various types of subsidence.
Nonregulatory Actions.
Nonregulatory actions for reducing damage include:
Construction of Retention Basins and Drainage SystemsA community can construct retention basins and drainage systems for karst terrainto reduce runoff into depressions where existing development is located.
RelocationIn some places, for example the Brownwood subdivision in Baytown, Texas, wheresubsidence has lowered the ground surface to below sea level, relocation is the onlypractical alternative. More than 200 houses have been purchased in this subdivision andrelocated or demolished with funds from FEMA's Section 1362 program and local fundingsources.
Control of Surface Water Elevations in Organic Soil AreasSurface water elevations should be carefully controlled for large lowlying areas oforganic soil that must be saturated to remain stable.
In lowland areas of organic soils which are drained by canals, drainage and subsi-
dence go hand-in-hand. Canals are dug deeper in the attempt to drain the lowest lands.
Deep canals drain water from the surface water table and cause subsidence. The landowners, again subject to flooding, will want still deeper canals, and the cycle begins anew.
Areawide monitoring of drainage canal levels and ground water table levels cou-
pled with subsidence records and regional hydrologic data can be used to determine opti-
mum water levels in the canals and ground water. Expert hydrologic advice is needed.
1-12

Table 9-2: Regulatory Options for Subsidence-Related Flooding*Regulate Cause -Regulate Land-Useand Constructionn -_:ni Q-i1e Mot-D-n[,:11lrPrhii --zPomtinC _tN U0 L ax yapplicable.
AIU1IIULL UYV~iU1i1IL 111 1subsidence prone areas.
Adopt construction codes for build-
ings, walks and drives and utilities..
Include freeboard requirementbased on subsidence potential.
Adopt disclosure requirement forreal estate.
Karst Terrain Prohibit ground water Prohibit development in highwithdrawals which may risk areas.
result in. subsidenceof land above. Adopt disclosure requirement forreal estate transactions.
Prevent filling orother blockages to Adopt storm water managementdrainage in sinkholes regulations where flooding maywhere such blockages be due to drainage into sinkholes.
may cause flooding.
Fluid Withdrawal Control ground water Prohibit construction in severelyor oil and gas with-subsiding areas.
drawals.
Require freeboard in floodplain re-
Adopt reinjection gulations to reflect subsidence rates.
requirements for oiland gas fields. Adopt disclosure requirements forreal estate transactions.
Abandoned Mines; Require special brac-
ing or mining toavoid possible sub-
sidence reclamationof mined areas.
Prohibit development in high riskareas.
Require purchase of. surfaceeasement or development rightsfor new mining ventures.
Adopt disclosure requirementsfor real estate transactions.
I-13%airgan1uGOU11z

Public Awareness of SubsidenceSubsidence is often a continuing and not obvious process. Individuals who own propertyin a subsiding area face an ongoing repair job. Newcomers to an area may not considersubsidence when selecting property or constructing a building. If they do, they may valuepractical advice on available remedial measures and alternatives. Guidance throughbrochures or slide programs is valuable. Civic groups could be encouraged and assisted toact as a clearinghouse for information.
I-14

Appendix 9-A: Outline and Excerpts from an Act of the Texas Legislature.
HOUSE BILL NO. 552,
relating to the creation, establishment, administration, powers, duties, functions, and fi-
nancing of the Harris-Galveston Coastal Subsidence District.
Sec. 1. PURPOSE AND INTENT(a) The purpose of this Act is to provide for the regulation of the withdrawalof ground water within the boundaries of the district for the purpose ofending subsidence which contributes to or precipitates flooding, inundation.
or overflow of any area within the district including without limitation ris-
ing waters resulting from storms or hurricanes.
Sec. 2. DEFINITIONS. In this Act:.
(a) "Subsidence" means the lowering in elevation of the surface of land by thewithdrawal of ground water.
Sec. 3. CREATIONSec. 4. BOUNDARIES.
(a) The district shall include all of the area located within the boundaries ofHarris County and Galveston County.
Sec. 5. BOARD OF DIRECTORS.
(a) The district shall be governed by a board of directors composed of 15 mem-
bers.
Sec. 6. POWERS AND DUTIES IN GENERAL.
The board-shall administer the provisions of this Act...Withdrawals of ground watercovered by the Provisions of this Act are subject to reasonable rules, regula-
tions, and orders adopted by the board, taking into account all factors in-
cluding availability of surface water, economic impact upon persons and thecommunity, degree and effect of subsidence upon the surface of land, anddiffering topographical and geophysical characteristics of land areas withinthe district.
Sec. 7. GENERAL MANAGER.
Sec. 8. EMPLOYEES.
Sec. 9. DISTRICT OFFICESec. 10. MINUTES AND RECORDS OF THE DISTRICT.
I-15

Sec. 11. SUITSSec. I2. SEALSec. 13. RULES AND REGULATIONS.
(a) After notice and hearing under Section 14 of this Act, the board shall adoptand enforce rules and regulations that are designed to expeditiously and ef-
fectively effectuate the provisions of this Act and accomplish its purposes,
including rules governing Procedure before the board.
Sec. 14. HEARINGS.
Sec. 15. COMPELLING TESTIMONY, SWEARING WITNESSES, AND SUBPOENAS.
Sec. 16. DISTRICT PLAN(a) Under Section 14 of this Act, the board shall formulate a plan to controland prevent subsidence within the district. The plan shall accomplish thispurpose by the reduction of ground water withdrawals to amounts whichwill restore and maintain sufficient artesian pressure to-control and preventsubsidence....
Sec. 17. PLANNING PROCEDURES.
Sec. 18. TEMPORARY REGULATION.
Sec. 19. PERMIT REQUIREMENT.
Sec. 20. TERM OF PERMITSec. 21. RENEWAL OF PERMIT.
Sec. 22. APPLICATION FOR PERMIT.
Sec. 23. NOTICE AND HEARING ON PERMITSec. 24. DECISION AND ISSUANCE OF PERMIT.
(b) In deciding whether or not to issue a permit and in setting the terms of thePermit, the board shall consider, along with the purpose of this Act and all.
other relevant factors:
(1) the district plan;
(2) the quality, -quantity, and availability of surface water at pricescompetitive with those charged by suppliers of surface water withinthe district;
I-16

(3) the economic impact on the applicant from grant or denial of thepermit, or the terms prescribed by a permit, in relation to the effecton subsidence that would result.
(c) The board shall grant a permit to an applicant whenever it is found uponpresentation of adequate proof that there is no other adequate and availablesubstitute or supplemental source of surface waters at prices competitivewith those charged by suppliers of surface water within the district andthat compliance with any provision of this Act, or any rule or regulation ofthe district, will result in an arbitrary taking of Property or in the practicalclosing and elimination of any lawful business. occupation, or activity, ineither case without sufficient corresponding benefit or advantage to thepeople.
(d) If the board decides to issue the permit, the permit shall be issued to theapplicant stating the terms prescribed by the board.
(e) The permit shall include the following:
(1) the name and address of the person to whom the permit is issued;
(2) the location of the well;
(3) the date the permit is to expire;....
Sec. 25. PERMIT NOT TRANSFERABLE.
Sec. 26. ANNUAL REPORTS.
Sec. 27. BOARD INVESTIGATIONS.
Sec. 28. ANNUAL GROUND WATER WITHDRAWAL DETERMINATION.
Sec. 29. REGULATION OF SPACING AND PRODUCTION.
(a) In order to minimize as far as practicable the drawdown of the water tableand reduction of artesian pressure and to control and prevent subsidence,
the board may provide for the spacing of wells and regulate the productionof ground water from wells, taking into consideration, among other relevantfactors, the economic impact on well-owners and the resulting effect on sub-
sidence.
Sec. 30. REQUIRING WATER-METERING DEVICES.
Sec. 31. ACCESS TO PROPERTY.
Sec. 32. MONITORING AND SUPERVISIONS OF DISTRICT.
Sec. 33. RESEARCH AND STUDIES.
1-17

Sec. 34. COOPERATION WITH AND ASSISTANCE OF OTHER GOVERNMENTAL EN-
TITIES.
Sec. 35. CONTRACTS.
Sec. 36. APPEAL OF DISTRICT ACTIONS.
Sec. 37. PERMIT FEE.
Sec. 38. SPECIAL ASSISTANCE.
Sec. 39. GRANTS, PURCHASES, GIFTS, LEASES. ETC.
Sec. 40. OWNERSHIP OF UNDERGROUND WATER.
Sec. 41. SURFACE-WATER LAWS NOT APPLICABLE.
Sec. 42. SALE AND DISTRIBUTION OF WATER PROHIBITED.
Sec. 43. EXCLUSIONS.
Sec. 44. DISBURSEMENT OF FUNDS.
Sec. 45. ACCOUNTS AND INDEPENDENT AUDIT.
Sec. 46. DEPOSITORY BANKS.
Sec. 47. PENALTIES.
Sec. 48. CONSTITUTIONAL FINDINGS.
Sec. 49. EMERGENCY.
1-18

Appendix 9-B. Excerpts of the Harris-Galveston Coastal Subsidence District Proposed Dis-
trict Plan, July 16, 1985.
I. Purpose and Intent:
It is the purpose and intent of this Plan to establish policy in the areas of technicalresearch and studies, water conservation, public information, regulation, permits and en-
forcement and equity and discretion; and to set forth a Regulatory Action Plan which di-
vides the district into regulatory areas and establishes regulatory. objectives for each area.
LI. Definitions: section omittedIII. BackgroundThe Harris-Galveston Coastal Subsidence District was created...to regulate thewithdrawal of groundwater within Harris and Galveston Counties. The District was cre-
ated "...for the purpose of ending subsidence which contributes to or precipitates flooding,
inundation, or overflow of any area within the district, including without limitation ris-
ing waters resulting from storms or hurricanes."
In 1976, the District adopted a District Plan, written as an interim plan designed tohave an immediate impact on the subsidence problem in the area most vulnerable to thedamaging effects of subsidence. The 1976 Plan recognized its technical deficiencies andprovided that a new plan would be adopted when a broader technical basis for regulationwas established.
In adopting the 1976 Plan, the District focused on the southeastern part of HarrisCounty and all of Galveston County and was primarily concerned with the elimination ofsubsidence and the reduction of potential damage caused by flooding in that area. Muchprogress in controlling subsidence in that area, known as the ACE, has been made. Aroundthe Houston Ship Channel,, for example, less than one-tenth of one foot of subsidence hasbeen recorded in the last eight years. No subsidence was recorded in 1984. Water-level in-
creases in the aquifer system in amounts up to 150 feet have been measured. Two signifi-
cant factors have contributed immensely to successful results in the ACE: (1) theavailability of surface water and (2) the conservation of water by industry. Theavailability of surface water in this area alone has been of tremendous benefit in curbingsubsidence. Surface-water supplies, however, are not available in other areas currentlyexperiencing rapid rates of subsidence. Without surface-water supplies, a dramaticreduction in groundwater pumping, and consequently in subsidence rates, cannot beexpected. Construction of surface-water treatment facilities and transmission lines isabsolutely essential for controlling subsidence.
During the time that the District focused on the ACE, extensive growth was expe-
rienced in western Harris County. As a result, groundwater withdrawal has increaseddramatically and subsidence has become an issue for local governments and concerned cit-
izens. Although inland areas are not at risk from storm surge and coastal flooding,
groundwater withdrawal in those areas affects subsidence not only in the inland areas butalso in the coastal areas. While the emphasis of the first District Plan was to control sub-
sidence in the ACE, the intent of this Plan is to extend the focus to inland areas as well.
1-19

IV. PolicyThis portion of the Plan establishes policy...regarding technical research and stud-
ies, water conservation, public information, regulation, permits and enforcement andequity and discretion. These policies are designed to support the regulation ofgroundwater withdrawal to control subsidence on a regional basis. Because subsidence is aregion-wide problem requiring solutions achieved through concerted efforts, the Districtwill work with other entities in the region to -implement this Plan.
A. Technical Research and Studies.
...the District has completed several technical projects that provide a more sophisti-
cated basis for regulatory policy. They include...:
1. A well data base...to maintain accurate and up-to-date information on well lo-
cation, ownership, construction, pumpage and permit status...
2. The maintenance and operation of thirteen subsidence monitors at eleven loca-
tions...Each monitor provides a continuous record of elevation change and represents theonly subsidence information available between releveling surveys. ...The potentiometricsurface of each aquifer is measured annually and analyzed with respect to the previousyear's pumpage.
3. A comprehensive, regional releveling completed in 1978 and limited relevelingsurveys in 1976 and 1983. The relevelings, while periodic, provide elevation data on abroad geographical basis.
4. A two-phase, comprehensive water management study completed in 1982. Thisstudy developed and refined "state-of-the-art" computer models to give the District theability to evaluate the effects of varying pumpage patterns over time to predict the re-
sulting subsidence. The capability of the computer modeling system has been used to fore-
cast rates and amounts of subsidence in different locations and to project surface-wateruse necessary to meet the objectives and requirements of this Plan.
...Although the technical accomplishments...have contributed significantly to theability to evaluate and control subsidence, there are at least four areas that require im-
mediate attention...:
1. An engineering study, or studies, to determine and evaluate the effects of in-
land subsidence on flooding.
2. Additional subsidence monitors in areas that are not adequately covered by ex-
isting monitors.
3. A regional releveling in 1986 and every six to ten years thereafter.
4. The continued study of the effect of subsidence. on surface drainage in theHouston area by evaluating changes in the topography of well fields.
1-20

B. Water ConservationThe District will support water conservation efforts. to help control subsidence andto optimize the use of a valuable natural resource. Conservation measures may be requiredas a condition on certain well permits to reduce groundwater pumpage...
C. Public InformationThe District believes that dissemination of information is vital in controlling sub-
sidence and recognizes the value of the support of an informed public...
D. Regulation...The District will determine the effect of subsidence on flooding in inlandareas...Until this determination is made, the District will regulate groundwater withdrawalto control subsidence in those inland areas.
The number of regulatory areas and the boundaries of each may change as condi-
tions change. Relevant factors to be considered in establishing or changing area bound-
aries include changes in pumpage, changes in groundwater levels, relationship of subsi-
dence to flooding and the availability of surface water...
E. Permits and EnforcementThe District may deny permits or limit groundwater withdrawal...the District willweigh the public benefit against individual hardship....In carrying out its purpose, the Dis-
trict is empowered to require the reduction of groundwater withdrawal to amounts thatwill restore and maintain sufficient artesian pressure to control and prevent subsidence....
F. Equity and DiscretionThe District recognizes that the burden of controlling subsidence should be borneby all users of groundwater. Groundwater withdrawal by any person must be regulatedwhen it works in concert with other groundwater withdrawal to produce subsidence, eventhough that person's groundwater withdrawal of itself would be incapable of producingsubsidence...
V. Regulatory Action PlanThis portion of the Plan...translates the legislative mandate of the District and thepolicy of this Plan into specific objectives and requirements. It divides the District intoeight areas and establishes requirements for each area. For purposes of information, italso estimates future water requirements and projects subsidence.
A. Regulatory ObjectivesThe legislative mandate to end "subsidence which contributes to or precipitatesflooding, inundation or overflow of any area within the district..."
I-21

B. Division of the District into AreasFor the purpose of regulation, the District is divided into eight areas which arebased on a commonality of regulatory interests and goals as well as economic and techni-
cal considerations. These areas are interrelated...
C. Regulatory Requirements1. Area Onea. Through 1989, as a general rule, increases in groundwater withdrawal will notbe permitted.
b. Beginning in 1990, groundwater withdrawal must be reduced so that no morethan 10% of the total -water use is from ground water.
2. Area Twoa. Through 1989, as a general rule, increases in groundwater withdrawal may bepermitted so long as surface-water use is not reduced.
b. In 1990 groundwater withdrawal must be reduced so that no more than 20% ofthe total water use is from groundwater.
c. Thereafter through 1998, increases in groundwater withdrawal may be permit-
ted so long as surface-water use is not decreased. Then in 1999, groundwater withdrawalagain must be reduced so that no more than 20% of the total water use is fromgroundwater.
d. Thereafter through 2006, increases in groundwater withdrawal may be permit-
ted so long as surface-water use is not decreased. Then in 2007, groundwater withdrawalagain must be reduced so that no more than 20% of total water use is from groundwater.
e. Thereafter through 2-14 years, increases in groundwater withdrawal may bepermitted so long as surface-water use is not decreased. Then in 2015, groundwaterwithdrawal again must be reduced so that no more than 20% of the total water use isf rom groundwater.
f. Thereafter through 2020, increases in groundwater withdrawal may be permit-
ted so long as surface-water use is not decreased.
D. Estimated Water Requirements and Projected SubsidenceThe District has projected total water demand and established regulatory require-
ments that permit limited amounts of groundwater to be withdrawn...It is necessary thatsurface water supply the difference between groundwater and total demand. If the sur-
face-water supply is inadequate, then total water demand must decrease. The optionsavailable to reduce total water demand are limiting growth and implementing mandatorywater conservation programs.
I-22

In projecting total water demand, the District has modified prior growth projec-
tions using actual developments of the past few years. As new official growth projectionsbecome available, regulatory requirements may be changed.
In showing the amounts of groundwater that will be permitted, the District gener-
ally will allow, in areas other than the coastal area, growth on groundwater between theyears in which additional surface water realistically can be introduced given the time andcost necessary to construct surface-water treatment facilities and transmission systems.
Using its computer modeling system, the District predicts that implementation ofthis Plan may result in additional subsidence....This subsidence is the amount expected tooccur given the realistic capability of other entities to develop surface-water supplies andconstruct treatment and transmission systems....
1-23

Appendix 9-C Excerpts of Building Code and Related Regulations of the Parish of Jeffer-
son, Louisiana.
Part X Detailed RegulationsChapter 28 -Excavation, Footings and FoundationsArticle 2801. Subsoil InvestigationWhere the soil bearing capacity for spread foundations or the pile load capacity isnot known, undisturbed soil borings shall be made under the direction of the LouisianaRegistered Civil Engineer or Louisiana Registered Architect, experienced in soil mechan-
ics. Number and depth of borings shall be influenced by the importance,. type, size, andlocation of the structure...An engineering analysis establishing soil bearing capacity, pileload capacity, depth of foundation, expected settlement, depth of the ground water table,
and the like, as applicable, shall be made....This data required shall be obtained from aminimum of one soil boring for structures under three stories and not over 10,000 squarefeet ground floor area, two soil borings for other structures less than 15,000 square feet ofground floor area and one additional boring for each 15,000 square feet of ground floorarea.
ARTICLE 2802. Excavations.
(a) Design. All excavations for structures covered by this code shall be designed in ac-
cordance with established engineering principles. The design shall utilize soil char-
acteristics determined by borings and laboratory tests...
ARTICLE 2803. Foundations.
Foundations shall be built upon naturally solid ground. or upon properly compactedfill material, or shall be built with pilings. Foundations shall be constructed of masonry,
plain concrete, reinforced concrete, or of piling materials described in this chapter....
ARTICLE 2804. Spread Foundations.
(a) Design. Footings are to be so designed that the, allowable bearing capacity of thesoil shall not be exceeded.
(b) Soil Bearing Capacity.
1. The Director may accept the soil bearing capacity established by the engi-
neering analysis.. as meeting minimum requirements.
2. In addition to the engineering analysis, or in lieu thereof, the Director mayrequire load bearing tests of the soil...to determine the allowable bearing ca-
pacity of the soil. The method of testing shall be in accordance with ASTMDl 194 "Standard Methods of Testing the Bearing Capacity of Soil for StaticLoad on Spread Footings." On all tests, the location of the ground watertable shall be noted. The allowable soil bearing shall be one-half the load atthe yield point. However, settlement of the test plate at allowable load shallnot exceed one-quarter of the gross settlement.
1-24

-


1. Residential piles shall comply with all applicable requirements of this chap-
ter as provided in this article. Piles shall be properly held in line or ade-
quately tied together at their butt end by means of continuous reinforcedconcrete or equivalent construction. Pile butts shall be protected by a mini-
mum of 3 inches of concrete around their perimeter. All piles for a buildingor a structure should extend to the same depth unless adequate provisionsfor a differential settlement within the building or structure have beenmade. The Director shall be notified by the party installing the piles at least24 hours in advance of any pile driving....
2. When pile foundations are required, maximum design load capacities havebeen established for various types and embedments of piles. These valuesare tabulated for each area which requires pile foundations and are shownon the U.S. Soil Conservation Survey Maps of the East Bank of JeffersonParish... and the West Bank of Jefferson Parish...In soil type (13) SharkeyClay, a special foundation may be used in lieu of a pile supported founda-
tion, provided the foundation design is prepared by or under the direct su-
pervision of a Louisiana Registered Civil Engineer or Louisiana RegisteredArchitect experienced in soil mechanics; such drawings and specificationsshall be designated per lot and square and be imprinted with this seal, andthese plans shall be approved by the Department of Inspection & Code En-
forcement, prior to issuance of the building permit....
The Standards of the Code regarding the need for a pile foundation or the maxi-
mum design load capacity for the particular type of pile may be superseded by a subsoilinvestigation which is performed in accordance with Article 2801 or a pile load testwhich is performed in accordance with Article 2805 provided the subsoil investigation orpile load test is located within a 150 foot radius of the proposed foundation for a singleboring or pile test...
4.(c) Site Filling. The use of the pile capacities contained in this article shall, belimited only to situations in which downdrag is not a significant factor.
Design use of these capacities shall be limited to areas where fill is less than 2 feetin thickness unless the area is brought to grade for an adequate preload period prior todriving piles. Recommended preload periods are as follows:
Fill Thickness Preload2 to 3 feet 2 to 3 months3 to 4 feet 3 to 6 months4 to 5 feet 6 to 9 monthsSpecific considerations must be made for construction over filled canals, ditches,
or. unusual local conditions. The thickness of the fill shall be measured from the naturalground surface. This shall be determined with a minimum of 5 elevations taken on eachcorner of the structure and in the middle of the structure.
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SELECTED REFERENCES ON FLOODING DUE TO GROUND FAILUREAllen, A.S., 1969, GeologicalSettings in Subsidence. In Varnes, D.J. and S. Kiersch, eds. Re-
view in Engineering Geology 2: 305-342. Boulder, Colorado: Geological Society ofAmerica.
Beck, B.F., 1985, Sinkholes: Their Geology, Engineering and Environmental Impact. Pro-
ceedings of First Multidisciplinary Conference on Sinkholes.
Canderib, Fleissig and. Associates, 1973, Demonstration of a Technique for Limiting the Sub-
sidence of Land over Abandoned Mines, Final Report, Rock Springs, Wyoming. Wash-
ington, D.C.: U.S. Dept. of Housing and Urban Development.
Federal Emergency Management Agency, 1979, A Preliminary Study of Subsidence Miti-
gation Policies and Technologies.Incomplete draft. Washington, D.C.: FEMA.
, 1983, The National Earthquake Hazard Reduction Program: A Report to the Congress,
Detailed Program Information. Fiscal Year 1982.Washington, D.C.: FEMA.
Fowler, L.C., 1981, Economic Consequences of Land Surface Subsidence, Journal of the Irri-
* gation and Drainage Division, Proceedings, ASCE 107 (1R2): 151-159.
Gabrysch, R.K. and C.W. Bonnet, 1974, Land-surface Subsidence in the Areas of Burnett,
Scott and Crystal Bays near Baytown, Texas. Water Resources Investigation 21-24.
Washington, D.C.:U.S. Geological Survey.
------,1975, Land-surface Subsidence. in the Houston-Galveston Region, Texas. Report 188.
Austin, Texas: Texas Water Development Board and U.S. Geological Survey.
Gary, M., R. McAfee, J. Wolf and C.L. Wolf, eds, 1977, Glossary of Geology. Washington,
D.C.: American Geological Institute.
General Analytics, Inc. 1974, State of the Art of Subsidence Control and Abandoned Mines.
Report by the Comptroller General. Washington, D.C.: U.S. Government PrintingOffice.
Helm, D.C., 1982, Conceptual Aspects of Subsidence due to Fluid Withdrawal. In Narasimi-
ham, T.N., Ed. Recent Trends in Hydrology. Special Paper 189. Boulder, Colorado:
Geological Society of America.
Holzer, T.L., 1977, Ground Failure in Areas of Subsidence due to Ground Water Decline in theU.S. Proceedings, International Symposium on Land Subsidence. Publication 121.
Anaheim, California: International Association of Hydrological Services.
, 1984, Man-Induced Land Subsidence. Boulder, Colorado: Geological Society ofAmerica.
1-27

Hooper, M.G., S.T. Algermissen and E.E. Dobrovolny, 1983, Estimzationof Earthquake Ef-
fects Associated with a Great Earthquake in the New Madrid Seismic Zone. CUSEPPReport No. 82-3. U.S. Geological Survey Open File Report 83-179. Washington, D.C.:
USGS.
Johnson, C., 1976, The Undermining of Butte, Montana.The Washington Post, November 22.
Kopper, W. and D. Finlayson, 1981, Legal Aspects of St bsidence Due to W,1ellPumping. Jour-
nal of the Irrigation and Drainage Division, Proceedings, ASCE 107 (1R2): 137-149.
Lee, S. and D.R. Nichols, 1981, Subsidence. In: Hays, W.W., ed. Facing Geologic and fly-
drological Hazards, Earth-Science Considerations. Professional Paper 1240-B. Wash-
ington, D.C.: U.S. Geological Survey.
Lofgren, B.E., 1969, Land Subsidence due to Application of Waiters.In Varnes, D.J. and G.
Kierzch, eds. Reviews in Engineering Geology 2. Boulder, Colorado: Geological So-
ciety of America.
Morton, D.R., 1979, A Selected Bibliography of Recent Subsidence Studies, University ofColorado, Natural Hazards Research and Applications Information Center. Boulder,
Colorado: University of Colorado.
Nuttli, O.W.,1981,Evaluationof Past Studies and identification of Needed Studies of theEffects of Major Earthquakes Occurring in the New Madrid Fault Zone. CUSEPP Re-
port No. 81-1 (Preliminary). Kansas City,-Missouri: FEMA.
Pewe, T.L. and M.K. Larson, 1982, Origin of Land Subsidence and Earth Fissures in North-
east Phoenix, Arizona. City of Phoenix.
Poland, J.F., 1969, Land Subsidence in the Western United States. In Olson, R.H. and M.W.
Wallace, eds. Geological Hazards and Public Problems Conference Proceedings.
Washington, D.C.: U.S. Government Printing Office.
------, 1981, Subsidence in the United States due to Ground-water Withdrawal. Journal of theIrrigation and Drainage Division, Proceedings ASCE 107 (IR2):115-135.
Poland, J.R. and J.H. Green, 1962, Subsidence in the Santa Clara Valley, California--AProgress Report. Water Supply Paper 1619-C. Washington, D.C.: U.S. GeologicalSurvey.
Poland, J.F. and G.H. Davis, 1969, Land Subsidence due to WIfithdrawalof Fluids. In Varnes,
D.J. and G. Kiersch, eds. Reviews in Engineering Geology. Boulder, Colorado: Geo-
logical Society of America.
Ruesink L.E., 1977, Subsidence Costs Analyzed. Water Research in Action 2(1):2-8.1-28

Seed, H.B. and I.M. Indriss, 1967, Analysis of Soil Liquefaction: Niigata Earthquake. Journalof the Soil Mechanics and Foundations Division, Proceedings of the ASCE 93 (Sm-
3): 83-108.
Stephens, J.C. and W.H.Spier, 1969, Subsidence of Organic Soils in the USA. In Proceedingsof the International Symposium on Land Subsidence. Tokoyo, Japan.
Strange, W.E., 1983, Subsidence Monitoring for State of Arizona. Rockville, Maryland: U.S.
Dept. of Commerce.
U.S. Dept.. of Housing and Urban Development, 1977, The Nature and Distribution of Sub-
sidence Problems Affecting HUD and Urban Areas (Tasks A and E.). Prepared by theEnergy and. Natural Resources Program Development, (HRB)-Singer, Inc. Wash-
ington, D.C.: U.S. Dept of Housing and Urban Development, Office of Policy De-
velopment and Research.
U.S. General Accounting Office, 1979, Alternatives to Protect Property Owners from Dam-
ages Caused by Mine Subsidence. Report by the Comptroller General, Washington,
D.C.: U.S. General Accounting Office.
U.S. Geological. Survey, 1983, GeologicPrinciples for Prudent Land Use--A Decision Maker'sGuide for the San Francisco Bay Region, Professional Paper 946. Washington, D.C.:
U.S. Government Printing Office.
Youd, T.L. and D.K. Keefer, 1981, Earthquake-Induced Ground Failures. In W.W.Hays, ed.
Facing Geologic and Hydrological Hazards, Earth-Science Considerations. U .S. Ge-
ological Survey Professional Paper 1240-B.Washington,. D.C.:USGS.
1-29

CHAPTER 10: ICE JAM FLOODINGTHE HAZARDAn ice jam is an accumulation of floating ice fragments that causesbridging or damming of a river. The flooding caused by ice jams issimilar to flash flooding. The formation of a jam results in a rapidrise of water at the point of the jam and upstream. Failure of the jamresults in sudden flooding downstream. Flooding as a result of ice jamformation is a problem in 35 out of the 50 states. States particularlyprone to such flooding are Alaska, Vermont, Maine, New Hampshire,
Washington,Idaho, Minnesota,Wisconsin,Iowa, Illinois and Oregon.
The formation of an ice cover on a river or stream depends upon such factors asflow velocity, turbulence, surface disturbances (wind) and temperature. Successive days ofbelow zero temperatures are often required to form an ice cover on a rapidly flowingstream.
Knowing how ice jams form is the key to knowing when and where to expect them.
Ice jam formation depends on both the weather and the physical conditions in the riverchannel.
Flooding due to ice jams or other ice conditions can occur at different times andin different ways:
1. Ice can cause flooding during fall freeze-up due to the formation of frazilice. Frazil ice forms when temperatures drop but a swift current preventsthe formation of an ice cover. Frazil forms in the stream, floats downstreamuntil it reaches an area that is slower moving and frozen over, then attachesitself to the underside of the ice cover. It may accumulate to the point offorming a hanging dam. Frazil can also attach itself to the stream bed,
forming anchor ice.
2. Ice can cause flooding during mid-winter periods of very low temperaturewhen the stream channel freezes completely solid. Additional water comingdown the stream freezes on top of the solid ice until the channel is blockedand the stream flows overland, flooding and freezing on adjacent lands.
Solid ice formed in this way frequently blocks culverts.
3. Ice can cause flooding at spring breakup due to a combination of ice condi-
tions creating the classic ice "jam". Most often, rising water levels in theJ-1

river or stream from snowmelt and rainfall break the existing ice cover intolarge chunks. These floating ice masses lodge at bridges or other constric-
tions, creating dams. Rapid flooding may occur, first upstream, then down-
stream as the mass of ice and water finally breaks free. Huge ice massesmoving downstream can shear off trees and destroy buildings above thelevel of the flood waters. Damage due to ice is not confined to rivers. Onlakes, floating ice masses have been known to shove houses hundreds of feetfrom their foundations. Pressure ridges, folds formed as ice expands withinthe confines of the lake banks, can rise several feet above the ice surface.
Damages from ice jam flooding usually exceed those of clear water flooding be-
cause of:
1. Higher than predicted flood elevations;
2. Rapid increase in water levels upstream and downstream.
3. Physical damage caused by ice chunks.
EXISTING MITIGATION EFFORTSIce jam flooding has not been extensively addressed in flood hazard planning, reg-
ulations or management at any level of government. Until recently NFIP flood maps andthose prepared by other agencies and states rarely reflected the potential for ice jams. In1982, the NFIP adopted guidelines for identifying and mapping potential ice jam floodingareas as part of flood insurance studies (see Appendix 10-A). While predicting exactlywhen and where ice jams will occur is difficult, likely locations can be identified usingsuch an approach.
Research on ice jam flooding has been carried out by the Cold Regions ResearchLab of the U.S. Army Corps of Engineers in Dartmouth, New Hampshire. The Corps hasalso experimented with "ice booms," mechanical removal of ice, and other techniques toreduce ice jam problems.
OPTIONS FOR ACTIONPolicy and Program ElementsA community policy and program for ice-related flooding should include the fol-
lowing elements:
J-2

1. Adoption of a resolution or policy statement that ice can cause floodingmore frequently and at higher levels than the predicted 100-year flood;
2. Mapping of potential ice jam areas such as bridges, natural constrictions inthe valley wall as well as potential upstream and downstream inundationareas;
3. Adoption of supplementary regulations including additional setbacks orbroadened floodway designations for high velocity flood areas and strength-
ened performance standards for pilings or floodproofing in flood fringe ar-
eas subject to ice-related damages;
4. Installation of warning systems and evacuation plans for areas where seri-
ous ice-jam flooding may occur;
5. An analysis of whether remedial engineering measures such as enlargementof culverts or bridge crossings are effective and whether such actions willmake ice jam problems greater in other parts of the river;
6. Preparation for short-term remedial actions to clear ice when a jam occurs;
7. Coordination of the activities of floodplain management, transportation andnavigation officials.
MappingSeveral options are available to a community in mapping ice jam areas:
1. Map locations potentially susceptible to ice jam flooding and the boundariesof inundation areas using historical evidence of ice jam flooding. Such evi-
dence may include air photos taken during or immediately after the floodwhile fragments of ice are still present, high water marks, scars on trees,
and other physical damage caused by ice. Historic evidence can also begathered from newspaper archives and interviews with long-term residents.
Existing flood maps, topographic maps, air photos, soil maps or other mapsmay be used as base maps.
2. In the absence of or to supplement historical evidence, carry out engineeringstudies to identify locations and boundaries of areas subject to inundation.
Include subzones within these areas subject to high velocity flows. Federalor state flood-mapping contractors can conduct engineering studies. Poten-
tial ice jam and ice damage areas can be identified based upon depth offlow, river profile, valley cross-sections and other factors discussed below.
J-3

Modifications to flood maps or the preparation of new maps to reflect ice jamflooding may involve several options:
1. The floodway should be broadened to encompass areas needed to conveyflood flows during the jam and adjacent areas threatened by with floatingice.
2. The flood fringe boundaries should be broadened both upstream and down-
stream of anticipated jam areas to reflect higher flood elevations.
In the last decade technical standards for identifying ice jam inundation areashave improved substantially. Although there are uncertainties in predicting exactly whenand where an ice jam will occur, the nature and extent of a possible ice jam at a givenlocation can be anticipated with fair accuracy based on:
1. The anticipated ice thickness;
2. The strength of the ice (estimated by measuring the number of "degreedays"');
3. The difference between water level just after the formation of a stable icecover and the water level expected in spring thaw.
The other factor controlling ice jam formation is river morphology (see Figure 11-
1). Ice jams typically form:
1. Wherever river slope decreases due either to natural or human causes suchas the headwaters of a reservoir.
2. Any constriction in the channel, such as a bend or bridge abutments.
3. Shallow reaches where the ice can freeze to the bottom.
In mapping ice jams as part of broader floodplain mapping efforts designed toidentify the 100-year floodplain, the major difficulty is the development of frequencyrelationships. FEMA's guidelines (Appendix 10-A) describe three possible approaches.
RegulationSeveral options are available for strengthening a community's regulations to reduceice jam damage:
1. Amend floodway maps, as described above, to extend floodway restrictionsto the high risk area.
2. As an alternative to a broadened floodway, the high risk areas can beseparately zoned as open space through setbacks or open space zoning. SuchJ-4

LIKELY ICE JAM AREAS)-0"2. Culverts thatcan freeze solidwDAM5. Channel constriction,
such as a bridge4. Naturalchannelconstriction, Isuch as bendsFigure 10-1. Likely ice jam areas.

restrictions can be applied to high velocity flow areas only or to the entirearea subject to ice damage.
3. Add freeboard to protection elevations for structures in flood fringe areasto reflect added heights when jams occur or to protect against-damage fromfloating ice. The amount of freeboard can be based on historic evidence ofice jam inundation or ice damage. For example, a federal hazard mitigationteam suggested an added two feet of freeboard in flood fringe areas in re-
sponse to severe ice jam flooding in Monroe, Michigan.
4. Amend building codes to include strengthened performance specificationsfor structures elevated on pilings in high velocity flow or ice damage areas.
Alternatively, prohibit pilings altogether in ice jam inundation areas; allowonly elevation on fill.
Nonregulatory OptionsPrincipal nonregulatory options include relocation, removal or modification of ob-
struction, channel modification, ice retention and diversion structures and warning sys-
tems. Several case studies are discussed in Appendix 10-B.
RelocationFor areas subject to frequent and severe ice jam flooding and ice damage, acquisi-
tion and relocation of structures may be the only permanent way to reduce damages.
Public purchase of land and buildings and relocation of residents are particularlyappropriate after an ice jam disaster because ice often totally destroys structures. Reloca-
tion is expensive and requires careful planning to be successful. Residents must be in-
volved in the planning as early as possible.
A short-term moratorium on rebuilding after a disaster can facilitate relocation.
Warning Svstems and Evacuation PlansBecause of the suddenness of ice jam flooding and the high velocity, ice-ladenflows when a jam breaks, a warning system and an evacuation plan similar to those forunsafe dams, levees or other flash flood areas are appropriate.
Removal or Modification of ObstructionsBridges, culverts, low head dams -even brush and debris in the channel -can causeice jam flooding. Removing brush and debris and old or obsolete structures may be cost-
effective. Rebuilding structures to increase channel capacity and decrease resistance towater and ice flow is another option. For example, replacing a single bridge reduced flooddamages by about 80% for two similar flood events in Adams County, North Dakota.
J-6

Figure 10-2. This railroad bridge is an example of a man-made structure 
that can restrict the flow of ice and debris and result in an 
ice jam. Source: St. Paul District, U.S. Army Corps 
of Engineers. 

Figure 10-3. Large chunks of ice have jammed at a small dam. 
Source: St. Paul District, U.S. Army Corps of Engineers. 


Figure 10-4. The tremendous force of the ice is toppling the tree which 
is just to the right of the center of the picture. 
Source: Illinois Dept. of Transportation. 

Figure 10-5. This house has been protected from flood and ice damage 
by being elevated on fill. Source: Mary Fran Myers. 


Channel ModificationsDeepening a channel or straightening a stream can help reduce ice jam problems.
The U.S. Army Corps of Engineers is currently studying channel modification as a tech-
nique for reducing damage. However this approach is expensive, and dredging is oftenneeded to maintain the new channel configuration. Dredging may even worsen ice jam-
ming downstream because deepened areas allow increased formation of frazil ice in theflowing water which attaches to the bottom of the ice cover downstream.
Ice Retention and Diversion StructuresDiversion channels can divert floodwaters away from the site of jams. The U.S.
Army Corps of Engineers Cold Regions Research Laboratory has constructed a physicalmodel for.a high level diversion channel.
Piers which retard ice movement or break up ice are a second possibility. TheCorps of Engineers has completed this type of project on the Narraguagus River inCherryfield, Maine.
A third option is an ice retention dam. The Corps has also tried this at the Cherry-
field site.
An ice boom is a fourth possibility. An ice boom on the Allegheny River in OilCity, PA controls ice at freeze-up so that ice jamming is minimized at break-up. The boomis submerged at high flows. This approach was used to help protect the Allegheny's wildand scenic river character.
Other Preventative or Remedial ActionsWhen ice-jamming is likely to occur or has already occurred, several other types ofremedial actions are possible to reduce flooding and ice damage. These include dusting,
mechanical removal, blasting, controlling the flow of water by surging, and the use of icebreaking ships. See insert.
DustingDusting is the spreading of dark, environmentally safe substances on the ice sur-
face. The dark material absorbs and retains the sun's heat and speeds melting of the ice.
Dusting materials must be dry and uniformly sorted. Application is usually from the airwhich is not always easy on narrow or sinuous rivers. The weather can seriously limit thesuccess of this approach since cloudy skies greatly slow melting and even a slight coveringwith snow will almost entirely negate the dusting. Despite the difficulties, dusting hasbeen used quite successfully. It was, in fact, the recommended solution for probable icejam formation in 1984 on the main stem of the Upper Mississippi River.
J-9

Mechanical RemovalConstruction equipment may be used to mechanically remove jammed ice. If thejam has formed at a bridge, a dragline or backhoe may be used to physically removeblocks of ice from the river. Mechanical removal, while relatively safe, is slow and expen-
sive and only suitable where access is available.
Blasting.
Blasting to break the ice jam can be effective as an emergency technique, but it isalso dangerous and can result in downstream flooding. Blasting begins at the head of thejam, where holes are bored through the ice and charges, usually a mixture of ammoniumnitrate fertilizer and fuel oil (ANFO), are placed beneath the ice and detonated.
Surging"Surging" is accomplished by opening and closing the gates of a dam to abruptlychange the discharge of the river. The sudden increase in flow velocity and stage maybreak up a jam. However, if the increased flow is not successful in dislodging the jam,
flooding problems can worsen. This method can only be used where control structuresexist.
Ice Breaking.
Ships have been used to break up sheet ice. This is a slow, expensive process andmost inland rivers are not suited for ice breakers.
Ice Storage.
On smaller streams, it may be possible to use the natural floodplain to "store" iceand prevent jams. Land areas on the outside of bends would be mechanically graded tofacilitate the movement of ice onto them during the breakup. Hardwood, Vermont is tak-
ing advantage of shallow floodplain areas to store ice to prevent downstream jams. Ice isbeing held in place by tires tied together by steel cable. The tires and cable are removedduring the summer.
J-10

Appendix 10-A: Analysis of Ice Jam Flooding excerpts from FEMA's Guidelines andSpecifications for Flood Insurance Study Contractors,1985.1. INTRODUCTIONAn ice jam may be defined as an accumulation of ice in a stream which reducesthe cross-sectional area available to carry the flow and increases the watersurface eleva-
tion. The accumulation of ice is usually initiated at a natural or manmade obstruction ora relatively sudden change in channel slope, alignment, or cross-section shape or depth. Innorthern regions of the United States, where rivers can develop relatively thick ice coversduring the winter, ice jamming can contribute significantly to flood hazards. When histor-
ical records are examined, ice jams are typically found to occur in the same locations.
This is because the necessary conditions for genesis of an adequate ice supply and ob-
struction of its downstream transport determine the, specific areas where ice jams will oc-
cur. In areas likely to be selected for a detailed FIS, historical documentation is usuallyavailable that will indicate if ice jam caused-flooding is a significant factor warrantingconsideration in the study. In cold regions of the country where ice jams are typical, theStudy Contractor should investigate historical floods for evidence of ice jam contributionas part of the study reconnaissance effort. Where ice jams historically contributed toflooding in a community, they should be evaluated using the procedures described in thisAppendix (when appropriate).
2. TYPES OF ICE JAMSIce jams have been classified in numerous ways by various investigators. Calkins(Reference 1) has classified ice jams as freezeup-or breakup-types, moving or stationarytypes, and floating or grounded types. Freezeup-type jams 'are associated with the forma-
tion and accumulation of frazil ice, which eventually forms a continuous ice cover.
Freezeup-type jams usually do not need to be addressed in a FIS because they are not as-
sociated with large discharge events, which are necessary to cause flooding problems.
However, the Study Contractor should be aware of possible exceptions. Breakup-type jamsare frequently associated with rapid rises in river stage, resulting from rainfall and/orsnowmelt, and usually occur in the late winter or early spring. Because of the large vol-
umes of ice that may be involved and the greater discharges associated with them,
breakup-type jams are predominant in ice jam-caused flooding and are typically the typerequiring investigation in a FIS.
Moving, ice does increase water levels; however, these effects are minor 'comparedto those of stationary jams and usually do not need to be considered in a FIS. Floating-
type ice jams are considered to be those where the ice is not grounded to the channel bot-
tom and significant flow takes place beneath the ice cover. Grounded-type jams are char-
acterized by an ice cover that is partially grounded to the bed of the channel, with mostof the flow being diverted into the overbank and floodplain areas. Grounded-type jamsare typical of shallow, confined stream sections, while floating-type jams are typical ofdeeper rivers. Both of these stationary-type ice jams can cause significant effects andshould be addressed in a FIS.
3. RECONNAISSANCEWhile conducting the reconnaissance effort for a FIS, the Study Contractor shalldetemine whether ice jamming has historically resulted in flooding within the communityJ-11

under study. Where such flooding has occurred, the reconnaissance effort should be inten-
sified to acquire as much data as possible concerning ice jam events in the community, onthe streams being studied, and in the region. Such data should include, but not be limitedto: locations of ice jams, dimensions, ice volumes, causes, associated river stages dis-
charges, frequency of occurrence, lateral and upstream extent of flooding, season of oc-
currence, and other contributing or correlative factors. The nature of ice jamming com-
mon to the site should also be investigated (i.e.,whether freezeup-or breakup-type jamsare typical and whether grounded-or floating-type jams are typical). Because very littledocumented data are usually available, all possible sources of information must be inves-
tigated, including photographs, local residents, newspapers, community officials, Stateagencies, and Federal agencies.
During the field reconnaissance, the Study Contractor should investigate Physicalevidence of ice jams, such as high-water marks, damage to structures or scars on trees,
which may provide useful data for the analysis or support for the study results.
4. ANALYSESDifferent methods may be used for establishing flood elevations in areas subject toice jam flooding, depending on the availability of data and the nature of the ice jammingphenomena that occur at the site of interest. The methods outlined herein are applicableprimarily to stationary-type (floating or grounded) ice jams that occur during periods ofice breakup. These types of jams have historically resulted in major flooding in certainregions of the United States. The Study Contractor should be aware of conditions thatmay warrant alternate analytical methods, and should seek approval of alternate methodsfrom the PO before proceeding.
The approaches below are based on the development of stage-frequency relation-
ships for two different populations (ice jam flood stages and free flow flood stages),
which are then combined into a single composite curve for flood stages at a site understudy. Depending on the availability of ice jam stage information, ice-jam stage-frequencyrelationships may be determined directly or indirectly as discussed below. The directmethod is preferred where applicable.
Direct ApproachIf sufficient data exist at the site of interest, an ice-jam stage-frequency distribu-
tion can be established directly by fitting a frequency curve to historical ice stage data.
This approach is recommended where ice jam stages are available for more than two sig-
nificant events (i.e., overbank flooding) that span more than a 25-year period of recordand where hydraulic conditions have not changed appreciably since those events. Histori-
cal stages will permit the computation of plotting positions and fitting a frequency curveon probability paper. Weibull plotting positions are recommended for this purpose.
This approach is preferred over the indirect approaches discussed in the following sec-
tions of this Appendix because the joint probabilities of various hydrologic and hydraulicfactors, such as discharges, ice volumes, and ice thickness, are inherently included in thefrequency analysis.
J-12

= 

= 

= 


1. Ice-jam stage frequency is a function of ice jam season discharge frequency.
2. Ice jams are of the breakup type.
3. Ice jams are of the stationary type.
4. For all jams, the ice thickness will be given by the equilibrium relationship de-
veloped by Pariset et al. (Reference 2) and the -stage-discharge relationship wvillbe de-
termined by adjusting the standard step-backwater technique for flow under an ice coverof -equilibrium thickness.
5. For grounded-type jams, the stage-discharge relationship at the point of ice jamformation will be that resulting from complete or neatly complete blockage of the normalchannel, with flow being carried in the overbank floodplain areas.
(2) General Procedures. To apply the indirect approach, certain procedures areused. First, a free-flow stage-frequency distribution is established for each cross sectionby using standard backwater modeling to establish stage-discharge relationships. Usually,
the four standard discharges (10-, 50-, 100-, and 500-year return intervals) will providesufficient points to establish the stage-frequency curve for each cross section on normalprobability paper.
The water year is then separated into an "ice jam season" and a "free flow season'based on the historical occurrence of ice jams in the region and, in particular, in thestream under study. .The season should encompass the period when breakup-type ice jamsnormally occur and will likely vary with the latitude and elevation of the stream beingstudied.
Ice jams tend to be associated with one of the seasonal peak flows because ice jamstypically form during rises in river stage that break up the ice sheet. All ice jam seasonannual peak flows should be fitted to a frequency curve. Weibull plotting positions arerecommended for this purpose. For ungaged streams, ice jam season discharge-frequencyrelationships must be established by regional analysis of seasonal flows for gaged streams.
Usually, the establishment of regional ice jam season discharge-drainage area curves willbe sufficient for this purpose.
The ice jam season discharge-frequency curve is then converted to a conditional(given that an ice jam occurs) stage-frequency curve. This is done at each cross sectionsubject to ice jam flooding using the HEC-2 program, with the ice cover option. This op-
tion takes into account the hydraulic aspects of flow under ice, such as a reduction inflow area, increased wetted perimeter, and ice roughness. Inputs required to utilize thisoption include the normal HEC-2 input, the thickness of ice in the channel and overbanks,
Manning's "n1value for the underside of the ice cover, and the specific gravity of the ice.
The Study Contractor is referred to documentaion prepared by the U.S. Army Corps ofEngineers; Hydrologic Engineering Center (Reference 3) on the use of this option. Therecommended ranges for "n" values are from 0.015 to 0.045 for unbroken ice and from 0.04to 0.07 for ice jams. The specific gravity of normal ice is approximately 0.92, which is therecommended value for this analysis. Where major floods are caused by ice jams, the as-
sumption of equilibrium ice thickness is probably reasonable because sufficient upstreamconditions exist to generate the ice volumes needed. Unless there is strong evidence to thecontrary, the ice thickness used in the analysis should be the approximate equilibriumJ-14

= 


thickness, as computed according to the Pariset formulation (Reference 2), should be as-
sumed unless alternate thicknesses can be justified.
5. PRESENTATION OF RESULTSFIS ReportA discussion of historic ice jam flooding should appear in Section 2.3 (PrincipalFlood Problems) of the FIS report.
Section 3.1 (Hydrologic Analyses) of the report should include a discussion of anydischarge-frequency analysis for the ice jam season, if used. Similarly, the statisticaltreatment of stage-frequency analyses for ice jam and non-ice jam events should be dis-
cussed. The historical data used in the analyses should be referenced in the discussionalong with its source and how it was used. The Summary of Discharges Table should bebased on analysis of the full year and footnoted to that effect.
Section 3.2 (Hydraulic Analyses) of the FIS report should include a discussion ofhow free flow and ice jam stages were computed, whether stages were computed directlyfrom stage-frequency analyses or indirectly analyzed. The approximate channel blockageand ice thickness assumed should be discussed, if used. The relationship of the computedice jam stages to historic floods should be discussed. An example of stage-frequencycurves for combined floods should be provided for the point of obstruction, or arepresentative cross section within the community should-be provided if the former isoutside the corporate limits. The discussion should also indicate that floodways were com-
puted only for free flow conditions.
The "Regulatory" column of the Floodway Data Table should be prepared using the100-year flood elevations established from the composite ice-jam and free-flow seasonstage-frequency curves and footnoted to that effect. All other columns in the FloodwayData Table shall be based on the 100-year free flow conditions.
ProfilesThe flood profiles shown in the FIS shall be based on the elevations establishedfrom the composite ice-jam and free-flow stage-frequency analysis.
MapsFIRM shall be developed based on the elevations established from the compositeice-jam and free-flow stage-frequency analyses performed at each cross section. Floodwaysshall be established and plotted based on the 100-year flood discharges and hydraulics as-
suming free flow conditions. The lateral extent of a major historic ice jam may be indi-
cated on the work map if it is well documented, does not hamper interpretation, and isappropriately annotated as such.
6. REFERENCES1. U.S. Army Cold Regions Research and Engineering Laboratory, Technical Note,
Methodology for Ice Jam Analysis, D. J. Calkins, October 1980.
J-16

2. E. Pariset, R. Hausser, and A. Gagnon, Formation of Ice Covers and Ice Jams in Rivers.
Journal of the Hydraulics Division, ASC,. November 1966.3. U.S. Army Corps of Engineers. Hydrologic Engineering Center, Analysis of Flow in IceCovered Streams Using Computer Program HEC-2, February 1979.
J-17

-

-

-


-

-


-


Solution: Modify release schedule during freeze-up.
Implemented:. Some modification of the releases.
Performance: Insufficient data have been collected.
6. Chaudiere RiverReport: a) Projects to alleviate ice jams on the Chaudiere River, by Deslauriers,
Proceedings of Eastern Snow Conference 1965, pp. 115-127.
b) Ice control structures for river break-up, by Michel, Proceedings, 11thCongress of IAHR,1965, Vol. 5, pp. 37-48.
Location: Quebec.
Problem: Ice jam flooding at break-up.
Causes: a) Thick ice accumulations at freeze-up.
b) No river channel storage at break-up for the ice due to freeze-up of thickice.
Solution: Construct a 60-ft-high dam upstream of the flooded area.
Implemented: 1967.
Performance: Ice jam flooding occurs now in the pool behind the structure and not in thecommunity. It .is considered very successful.
J-21

SELECTED REFERENCES ON FLOODING DUE TO ICE JAMSAshton, G.D., 1978, River Ice. Ann. Rev. Flood Mech. 10:369-92.
--,1979,River Ice. American Scientist 67(l):38-45.
Bates, Roy and Mary Lynn Brown, 1982, Meterological Conditions CausinigMajor Ice JamFormation and Flooding on the Ottawgucchee River, Vermont. Special Report 82-6.
Washington, D.C.: U.S. Army Corps of Engineers Cold Regions Research andEngineering Laboratory.
Billifalk, L., 1982, Breakup of Solid Ice Covers Due to Rapid Water Level Variations. SpecialReport 82-03. Washington, D.C.: 'U.S. Army Corps of Engineers Cold RegionsResearch and Engineering Laboratory.
Calkins, D., 1980, Methodology for Ice Jam Analysis. Technical Note. Washington, D.C.: U.S.
Army Corps of Engineers Cold Regions Research and Engineering Laboratory.
-1984,Personal-Communication.
Deck, D. and C. Gooch, 1981, Ice Jam Problems at Oil City, Pennsylvania. Special Report 81-
9. Washington, D.C.: U.S. Army Corps of Engineers Cold Regions Research andEngineering Laboratory.
Donahue and Associates, Inc., 1982, Flood Control Feasibility Study for City of Fond duLac, Wisconsin,Report to the City.
Federal Emergency Management Agency, 1982, Guidelines and Specifications for FloodInsurance Studies, Appendix C: Analysis of Ice Jam Flooding. Washington, D.C.:
FEMA.
Gerard, R., 1980, Notes for a Short Course on Ice Engineering for Rivers and Lakes.
University of Wisconsin Extension.
Killaby, H.H., 1887, The Fork on the River Missouri at St. Joseph. Transactions of theCanadian Society of Civil Engineers 1:48-67.
Pariset, E., R. Hausser and A. Gagnon, 1966, Formation of Ice Covers and Ice JanmsinRivers. Journal of the Hydraulics Division, Proceedings of the ASCE 92: 11-19.
U.S. Army Corps of Engineers, 1975, CRREL Technical Publications, Washington, D.C.: ColdRegions Research and Engineering Laboratory.
-,1979, Analysis of Flowv in Ice Covered Streams Using Computer Program HEC-2.
Washington, D.C.: Hydrologic Engineering Center.
J-22

------,1980, Section 206 Floodplain Management Assistance Historical Ice Jam Flooding inMaine, New Hampshire and Vermont. Washington, D.C.: New England Division, Corpsof Engineeers.
----1980, Special Flood Hazard Information: Snake River Ice Jams. Walla Walla, Wash-
ington, Walla Walla District. Corps of Engineers.
------,1981, CRREL Technical Publications, Supplement I January 1976 to 1 July 1981.
Washington, D.C.: Cold Regions Research and Engineering Laboratory.
-----1982, Ice Engineering. Engineering Manual No. 1110-2-1612. Washington, D.C.: Corps ofEngineers.
------1983, CRREL Technical Publications, Supplement 1 July 1981 to 1 February 1983.
Washington, D.C.: Cold Regions Research and Engineering Laboratory.
J-23

CHAPTER 11: MUDSLIDESTHE HAZARDMudfloods and mudflows are a major problem in sparsely vegetatedmountains or hilly areas of the West and Southwest with low rainfalland unconsolidated soils. When rains do occur, runoff is rapid due tothe lack of vegetative cover. Moving water quickly picks up soil androck particles. The resulting mixtures of water and sediment rangefrom muddy water to partly solid "mudslides'. Although primarily awestern problem, mudfloods and mudflows occur in Appalachia andelsewhere.
Mudf lows and mudfloods are often caused, in part, by rain falling on terrain thathas been denuded by forest fires and brush fires. Once denuded, hills do not retainrunoff. Even small rainfalls can cause flash-flooding.
MUDFLOOD AND MUDFLOWThe National Academy of Science (1983) suggested the followingdefinitionsfor theseterms:
Mudflood: Refers to a flood in which the water carries heavy loads ofsediment (as much as 50% by volume) including coarse debris.
Mudfloods typically occur in drainage channels and on alluvial fansadjacent to mountainous regions, although they may occur on flood-
plains as well.
Mudflow: Refers to a specific subset of landslides where the dominanttransporting mechanism is that of a flow having sufficient viscosity tosupport large boulders within a matrix of smaller sized particles.
Mudflows may be, confined to drainage channels or may occurunconfined on hillslopes.
There are no reliable estimates of the annual cost of damage due to mudfloods ormudflows. Los Angeles County has estimated over 2 million individuals may be at riskfrom mud and other debris flows in this county alone. Estimates of total damage causedby landslides, of which mudslides are a substantial component, range up to one billionK-1

dollars a year. Recent floods in the west and southwest have had large mudflood andmudflow damage components.
Mudflows and mudfloods start with moving water or a stationary mass of saturatedsoil. Mudfloods usually originate as sheet flow or as water flowing in drainage channels,
rivers or streams. Waters pick up sediment or debris as they flow. In contrast, mudflowsoften originate as a mixture of stationary soil and water. When the mixture gets wetenough it begins to move as a mass, either on its own (by force of gravity) or triggered byanother event (such as an earthquake or a sudden flow of debris laden water). See Figures11-1 and 11-2.
Sediment-laden waters and mudflows cause more severe damage than clear waterflooding for several reasons. The force of debris-laden water can be hundreds of timesgreater than clear water, destroying pilings and other protective works. Structures are of-
ten totally destroyed. The mud and debris may fill drainage channels and sediment basins,
causing floodwaters to suddenly inundate areas outside of the floodplain. The combina-
tion of sediment and debris is more damaging to buildings and their contents than clearwater. Even where structures remain intact, sediment often severely damages or destroysrugs and contents and must be physically removed with shovels or hoses. Repeated wash-
ings are needed and stains are often permanent.
EXISTING MITIGATION EFFORTSMudflows and mudfloods have not been extensively mapped, regulated or otherwisemanaged at federal, state or local levels. The most innovative and hazard-specificregulation has been undertaken by the State of Colorado and a number of communities inCalifornia, including Los Angeles County. Some regulations have also been adopted inUtah.
FederalThe U.S. Geological Survey has studied mudflows and other debris flows quite ex-
tensively and has prepared reports to their identification and management. It has mappedpotential mudflow and mudslide areas in the San Francisco Bay Region, along theWasatch front near Salt Lake City (see Figure 11-3), and in the Appalachian region. TheU.S.G.S. has recently proposed a national landslide reduction program which would in-
clude mudflood and mudflow phenomenon.
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In 1969 Congress amended the National Flood Insurance Act by expanding the definitionof flood to include "mudslide" and to authorize FIA mapping and flood insurance for"mudslide" areas. Pursuant to this mandate, FIA undertook some experimental mapping inLos Angeles County, California, adopted regulatory guidelines for local regulation ofmudslide areas (see Appendix li-A) and requested the National Research Council to helpdevelop a more detailed mapping methodology. In 1974, the Council recommended a gen-
eral susceptibility approach for delineating areas based on topographic, soil and geologicfactors. However, FIA considered this approach inadequate to meet legal requirements. In1980, FEMA asked the Research Council to evaluate the general applicability of themethodology that had been applied in Los Angeles County. This study concluded that themethodology was not transferable to other locations.
StateIn 1974, the Colorado legislature adopted a land planning act designed to assist lo-
cal governments manage areas of state interest. Areas of state interest were defined in-
clude geologic hazard areas subject to a "geologic phenomenon which is so adverse to past,
current or foreseeable construction or land use as to constitute a significant hazard topublic health or safety or to property." The statute listed these specific hazards:
1. Avalanche,
2. Landslides,
3. Rock falls,
4. Mudflows and debris fans,
5. Unstable or potentially unstable slopes,
6. Seismic effects,
7. Radioactivity,
8. Ground subsidence,
9. Expansive soil and rock.
The Colorado Geological Survey was directed to help local governments identifygeologic hazard areas and adopt management guidelines. In carrying out this task, theSurvey has prepared guidelines and a number of excellent reports which may be of inter-
est to other states including Guidelines and Criteria for Identification and Land-Use Con-
trols for Geologic Hazard and Mineral Resource Areas (Colorado, Geological Survey, 1979;
see Appendix 3-D).
K-3

Figure 11-1. Debris may begin to flow as a mass when it becomes wet. 
Gravity, earthquakes or a sudden flow of debris-laden water 
could be the triggering mechanism. Source: U.S.G.S. 

Figure 11-2. Recent land failure is evident. Source: Jon Kusler. 


" 


The State Geological Surveys in California and Utah also helped communities reg-
ulate mudslide areas by preparing, maps indicating geologic, seismic and slope stabilityproblems.
LocalSeveral dozen communities now regulate development in mudflows, mudflood areasor broader debris flow areas. Some of the most interesting include:
Los Angeles County, California has developed a method for identifying mudfloodand other debris areas. Using records of debris flow compiled over a 40-year period, theCounty Flood Control District has determined potential flooding and debris volume foreach major canyon in the area. Applying a 50-year frequency rainfall standard in a"burned watershed" computation, the District has prepared mudflood maps. The Districtreviews all tract and building plans in mapped areas (see Appendix 11-B). All develop-
ments must be designed to accommodate expected water and debris.
San Bernardino, California. As a result of a 1979 forest fire in Harrison Canyonnorth of San Bernardino, four mudflows occurred in the city in 1980, damaging 30 struc-
tures. After the third, the city passed an emergency ordinance prohibiting repair of dam-
aged structures and began to acquire these structures. Assisted by FEMA with fundingfrom the Section 1362 Program, the City has acquired 26 structures. It has also imple-
mented erosion control measures in the upper canyon and constructed retaining walls inthe lower areas.
OPTIONS FOR COMMUNITY ACTIONPolicy and Program ElementsA community with mudflood and mudflow problems should adopt a mitigation pol-
icy and program with the following elements:
1. A policy statement or resolution that mudfloods or mudflows createsevere risks to life and property;
2. Mapping of mudflood and mudflow areas as part of a flood mapping pro-
gram or as part of a broader geologic hazards or resource management ef-
fort;
K-6

3. Adoption of regulations requiring slope stability analysis and either pro-
hibiting development in unstable areas or establishing performance guide-
lines for new development;
4. Notification of landowners in potential mudslide areas; and5. Preparation and implementation of plans for remedial action such asdebris basins and dewatering of unstable slopes.
MappingThe National Flood Insurance maps often include (but do not specifically indicate)
mudflood areas along major streams. Mudflow and-mudslide areas on valley slopes andalong smaller rivers and streams have rarely been mapped. As indicated earlier, the U.S.
Geological Survey has mapped areas subject to potential mudflows and other debris flowsin the San Francisco Bay area, along the Wasatch front near Salt Lake City and in theAppalachian region.
Two approaches are available for communities without maps or where maps do notspecifically indicate mudflow or mudflood problems. The first is to prepare of specialmaps indicating hazards. For example, Los Angeles County has prepared its own mapsbased upon soils, topography and slope. The second is to shift the burden to developers toassess hazards in areas within a defined distance of water course or on slopes greater thana defined amount (e.g., 15%).The latter approach is used more often. Relative slope stabil-
ity categories are given in Appendix li-F; these categories help identify potential mud-
flow areas, but are less useful in the delineation of mudflood areas.
RegulationsTwo principal regulatory approaches have been applied to date:
1. Prohibition of all new development on slopes through setbacks or openspace zoning for high risk areas.
2. Adoption of performance standards for fill, grading, or design ofstructures.
Los Angeles County, California takes the latter approach. Building and grading codespermit building on slope areas only under these conditions:
1. It does not increase water depths on neighboring lands;
2. It does not deflect water onto neighboring properties;
3. Structures are designed to withstand the force of anticipated flows.
K-7

Developers must conduct geologic studies and design structures consistent with theregulatory guidelines. According to a study conducted by Slossen and Krohn, the ordi-
nance has reduced slope failures since adoption (see Table 11-1). See Appendices for por-
tions of the Los Angeles grading code (see Appendix 11-B) and excerpts from ordinancesof Whittier and Ventura, California (Appendices 11-C and ll-D). See also Appendix il-Efor excerpts from the Uniform Building Code which pertain to cuts and fills.
Table 11-1 Slope Failures in the City of Los Angeles (1978 storms)
DollarNumber of Number of Percent ValueDescription Sites Failures Failure (millions)
Pre-1963 (before modern code) 37,000 2,790 7.5 40-49Post-1963 (modern code) 30,000 210 0.7 1-2Note: The categories of failure are (1) soil slippage and erosion (28 percent); (2) mudflowand debris flow (30 percent); (3) slump/arcuate landslides, pre-1963 and natural slopes (22percent); (4) reactivation of old failures, pre-1963 (8 percent); (5) new bedrock landslides,
pre-1963 (5 percent); (6) shallow fill slope and some natural slope failure, post-1963 (7percent, with the modern code promulgated in April 1963).
Source: Slosson and Krohn (1979).
Nonregulatory ActionsPrincipal nonregulatory actions to reduce hazards in mudflow and mudflood areasinclude debris basins, acquisition and planting and other soil conservation measures.
Debris BasinsDebris basins resemble dry reservoirs and operate in much the same way. They areused extensively in Los Angeles County and some other western communities to trap de-
bris flows. The Japanese depend on an estimated 200,000 of these structures.
Debris basins are costly but they are effective in reducing mud damage. Debristrapped in the basins must be periodically removed by mechanical means to maintain thebasin's effectiveness.
K-8

HOME CONSTRUCTED IN CANYON BOTTOM7/-
HOME CONSTRUCTED IN BOTTOM OF CANYON OVERRUN BY DEBRIS)ATHWAY PROVIDES FOR SAFE ROCK & MUD FLOWSFigure: 11-4. Design and construction standards can be applied to reducerisk to structures.

Other Engineering AvvroachesOther engineering solutions to mudflow problems include retaining walls and"dewatering" of soils through horizontal wells, subsurface drains and other techniques.
Aco uisitionAs noted above, San Bernardino, California used acquisition to remove structuresfrom a high risk mudflow area. Acquisition has also been used "preventatively" in someLos Angeles County canyons to acquire undeveloped land for park and recreation pur-
poses and to reduce future damage potential.
Planting and Other Soil Conservation MeasuresSan Bernardino stabilized hillsides in newly burned areas through replanting, theplacement of straw and other slope stabilization techniques. Application of such tech-
niques, both pre-and post-disaster, has broad potential for reducing future damages fromnewly burned areas.
Land Owner EducationBuyers, builders and homeowners should be provided with information concerningpotential hazard areas. See Appendix 11-F.
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Appendix 11-A Criteria of the Federal Emergency Management Agency for CommunityParticipation in the National Flood Insurance Program.
...Floodplain management criteria for mudslide (i.e., mudflow)-prone areas.
The Administrator will provide the data upon which floodplain management reg-
ulations shall be based. If the Administrator has not provided sufficient data to furnish abasis for these regulations in a particular community, the community shall obtain, review,
and reasonably utilize data available from other Federal, State or other sources pendingreceipt of data from the Administrator. However, when special mudslide (i.e., mudflow)
hazard designations have been furnished by the Administrator, they shall apply. Thesymbols defining such special mudslide (i.e., mudflow) hazard designations are set forth in64.3 of this subchapter. In all cases, the minimum requirements for mudslide (i.e.,
mudflow)-prone areas adopted by a particular community depend on the amount oftechnical data provided to the community by the Administrator. Minimum standards forcommunities are as follow:
(a) When the Administrator has not yet identified any area within the community asan area having special mudslide (i.e. mudflow) hazards, but the community has in-
dicated the presence of such hazards by submitting an application to participate inthe Program, the community shall:
(1) Require permits for all proposed construction or other development in thecommunity so that it may determine whether development is proposedwithin mudslide (i.e., mudflow)-prone areas;
(2) Require review of each permit application to determine wheter the proposedsite and improvements will be reasonably safe from mudslides (i.e., mud-
flows). Factors to be considered in making such a determination should in-
clude but not be limited to (i) the type and quality of soils, (ii)any evidenceof ground water or surface water problems, (iii) the depth and quality ofany fill, (iv) the overall slope of the site, and (v) the weight that any pro-
posed structure will impose on the slope;
(3) Require, if a proposed site and improvements are in a location that mayhave mudslide (i.e., mudflow) hazards, that (i) a site investigation and fur-
ther review be made by persons qualified in geology and soils engineering,
(ii) the proposed grading, excavations, new construction, and substantial im-
provements are adequately designed and protected against mudslide (i.e.
mudflow) damages, (iii) the proposed grading, excavations, new constructionand substantial improvements do not aggravate the existing hazard by creat-
ing either on-site or off-site disturbances, and (iv) drainage, planting, water-
ing, and maintenance be such as not to endanger slope stability.
(b) When Administrator has delineated Zone M on the community's FIRM, the commu-
nity shall:
(1) Meet the requirements of paragraph (a) of this section; and(2) Adopt and enforce a grading ordinance or regulation in accordance withdata supplied by the Administrator which (i) regulates the location of foun-
dation systems and utility systems of new construction and substantial im-
provements, (ii) regulates the location, drainage and maintenance of all ex-
K-11

cavations, cuts and fills and planted slopes, (iii) provides special require-
ments for protective measures including but not necessarily limited to re-
taining walls, buttress fills, subdrains, diverter terraces, benchings, etc., and(iv) requires engineering drawings and specifications to be submitted for allcorrective measures,, accompanied by supporting soils engineering and geol-
ogy reports. Guidance may be obtained from the provisions of the 1973 edi-
tion and any subsequent edition of the Uniform Building Code, sections7001 through 7006, and 7008 through 7015. The-Uniform Building Code ispublished by the International Conference of Building Officials, 50 SouthLos Robles, Pasadena, California 91109.
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Appendix 11-B: Excerpts from the City of Los Angeles Official Grading Regulations.
DEPARTMENT OF BUILDING AND SAFETY, CITY OF LOS ANGELES BUILDINGBUREAU, RULE OF GENERAL APPLICATION--RGA 4-67From James E. Slosson and James P. Krohn, "Southern California Landslides of 1978 and1980" in Storms, Floods, and Debris Flows in Southern California and Arizona in 1978 and1980, Proceedings of a Symposium, September 17-18, 1980, National Academy Press,
Washington, D.C.
Subject: Rules and Regulations for Supervision on Hillside Tract Grading--RR 23352The permittee shall employ a registered civil engineer or land surveyor to prepare his de-
sign of grading plans for all hillside grading. The design civil engineer or land surveyorshall prepare his design in accordance with good planning practice, applicable Codes andto the restrictions imposed thereon as determined by detailed studies of the site and mate-
rials to be graded. These studies shall be performed by a soils engineer and an engineeringgeologist approved by the City of Los Angeles and shall be submitted prior to issuance ofpermits. The design civil engineer or land surveyor shall furnish sufficient supervisionduring construction to obtain compliance with the plans, as approved.
The permittee shall employ a soils engineer and an engineering geologist prior to planningthe tract, whose duties shall be: to work closely with the design civil engineer or land sur-
veyor, to examine surface and subsurface conditions in accordance with the Rule of Gen-
eral Application dealing with "Subsurface Exploratory Work" and to submit reportsthereon. These reports, in conjunction with the Ordinance, shall form the basis for the de-
sign of the grading project. These reports shall be based upon a detailed topographic basemap of the area to be graded and shall include specific conclusions and recommendationsfor avoidance or correction of all known existing or anticipated geologic hazards on oraffecting the site or contiguous property.
The soils engineer, in addition to his pre-grading exploratory work, shall provide inspec-
tion during the placement of all compacted fill in accordance with the requirement of theOrdinance, the approved plans and good engineering practice. In addition, he shall followthe progress of the job sufficiently close to determine that the recommendations of hispre-grading report are followed. If conditions which require modification of plans are en-
countered during grading, he shall submit a report of his findings and recommendationsfor change of plans to the permittee and the design civil engineer, the engineering geolo-
gist and the department.
The engineering geologist, in addition to his pre-grading exploratory work, shall provideinspection during the actual grading process at least as often as determined to be appro-
priate by the Department or Board, with periodic in-grading inspection reports submittedat intervals determined by the Department. Such grading inspection by the engineeringgeologist is to determine that the conditions of his pre-grading report are as anticipated.
If conditions which require modification of the plans are encountered during grading, heshall submit a report of his findings and recommendations to the committee, design civilengineer or land surveyor, soils engineer and the Department.
The soils engineer, at the completion of grading, shall submit a certified report of com-
paction tests for all fill located within the limits of the tract and/or offsite grading areas.
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The soils engineer's final report shall also include: a statement that all sub-drains were in-
stalled, his professional opinion of the suitability of the fill placement area and the abil-
ity of the natural materials to support the compacted fill without excessive settlement ofthe -fill or potential damage to structures erected thereon, a statement to the effect that hehas inspected all cuts and fills and that in his opinion they meet the design requirements.
The report shall be referenced to a dated as-graded plan prepared by the design civil en-
gineer or-land surveyor.
The engineering geologist at the completion of grading shall submit a final geologic reportstating that: he had maintained the required in-grading inspection, the recommendationsof his pre-grading report(s) have been followed, that in his professional opinion all knownadverse geologic conditions have been corrected or provided for, future adverse geologicconditions are not anticipated, and all lots or sites are geologically suitable and safe forconstruction. The report shall include the geologist's certification that he has inspected allcut slopes and sidehill fill placement areas prior to placement of fill. He shall also certifythat all sub-drain placement areas were inspected prior to installation of the sub-drains.
The report shall be referenced to a dated as-graded plan prepared by the design civilengineer or land surveyor.
Upon completion of grading, the civil engineer or land surveyor responsible for the designshall submit an as-graded plan to the Department for approval of all work covered by thegrading permit(s) and shall include the following:
1. The plan shall be at a 1 inch = 40 feet scale and shall show the locations ofstreets, pads, slopes, structures, pertinent elevations, original contours and finished eleva-
tions, other pertinent information required to show the as-graded condition, and shall bedated.
2. The plan shall bear-the signature of the design civil engineer or land surveyorwhich shall certify that he has inspected the site, reviewed the plans and that the workshown and completed is in accordance with his design.
If, for any reason any of the three professional persons is terminated during the progressof the grading work, he and the committee shall immediately notify the Department inwriting. Such termination may result in temporary delays in the grading operations untilsatisfactory arrangements are made to assure the Department that competent professionalsupervision is provided.-When one or all three of the professionals of record are termi-
nated, the new professionals shall submit to the Department a letter of certification thatthe previous professional's designs, reports and recommendations have been reviewed, allprovisions of the Board or Department required as conditions of the grading permit willbe complied with during the course of the work, and he or they shall review the detailed40-scale grading plans and thus assume his or their responsibility as herein specified forall future grading on the project. The letters shall be referenced to the approved gradingplans prepared by the design civil engineer or land surveyor.
The certification submitted by the civil engineer or land surveyor shall pertain to thetract as built. The certification shall apply to the angle of stability of cut and fill slopes,
compaction requirements, drainage provisions, and in general, all safety features incorpo-
rated in a well-graded hillside job. Engineers and geologists employed for the developmentshall not be deemed to be responsible for the work if alteration work not under their con-
trol is undertaken after the grading certificate has been issued.
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RULE OF GENERAL APPLICATION--RGA 5-67Subject: Regulations for Hillside Exploratory Work--RR 23353The following rules and regulations shall apply on required hillside surface and subsur-
face exploratory work:
Surface and subsurface exploratory work shall be performed by a soils engineer and anengineering geologist approved by the City of Los Angeles on all hillside grading work,
except wherein waived by the Department Staff or Board, Such exploratory work shall beperformed for the purpose of obtaining detailed information on which the soils engineerand the engineering geologist shall base recommendations for a grading project. The workshall be based upon a detailed, accurate topographic base map prepared by the registeredcivil engineer or land surveyor. The map shall be of suitable scale, and shall cover thearea to be graded,. as well as adjacent areas which may be affected by the grading. Themap shall include the existing and proposed contours, locations of streets, pads, slopes,
structures, and pertinent elevations.
The engineering geologist's and soils engineer's exploratory work shall be conducted at lo-
cations considered most likely to reveal any subsurface weaknesses which may lead tolandslide, slump or settlement failures. Particularly, an investigation shall be conductedwhere the stability will be lessened by the grading or where any of the following condi-
tions are discovered or proposed:
1. At fault zones where past land movement is evidenced by the presence of faultgouge.
2. At contact zones between two or more geologic formations. 3. At zones oftrapped water or high water table quite often associated with conditions 1and 2 above.
4. At bodies of intrusive materials.
5. At historic landslides or where. the topography is indicative of prehistoric land-
slides.
6. At-adversely sloped bedding planes, short range folding, overturned folds, etc.
7. At locations where a fill slope is to be placed above a cut slope.
8. At proposed cuts exceeding 25 feet in height unless in competent rock or oflesser heights in rock of questionable stability.
9. At the locations of all proposed fills.
10. Where any side hill fills are proposed.
11. Wherever water from rainfall, irrigation, private sewage disposal systems, orother probable sources from both the grading project and adjoining properties is likely toreduce the subsurface stability.
12. Where the proposed grading may adversely affect the existing or future stabil-
ity of adjoining properties. The investigation shall be sufficient to outline the problemsand solutions to these problems.
The soils engineer and engineering geologist shall submit written reports of their findingsto the permittee and the design engineer or land surveyor. Their reports shall include butnot necessarily be limited to the following minimum data based upon detailed surface andsubsurface investigation:
a. The engineering geologist's report shall include a detailed geologic map showingbedrock, soil, alluvium, faults, shears, prominent joint systems, lithologic contacts, seeps orK-15

springs, soils or bedrock slumps, landslides or failures and other pertinent geologic fea-
tures existing on the proposed grading site. Geologic cross-sections, prepared to reasonablydepict anticipated geologic substructure, shall also be included in sufficient number anddetail. The report also shall include detailed logs,of all borings, test pits or other subsur-
face data obtained during the course of his investigation. The subsurface exploration shallextend to sufficient depth into the bedrock to expose the deepest rock affecting the pro-
posed grading. The report shall include specific details and observations for the soils en-
gineer's use in analysis of the stability of cut slopes in zones of shallow or perched sub-
surface waters that may affect slope stability.
b. The soils engineer's report shall include a map of the proposed, grading siteshowing the locations of all subsurface .exploratory test pits or borings. Detailed logs ofthe test pits' or boring, including the approximate locations of all soil or rock samplestaken for laboratory testing, shall also be included. In addition, laboratory test results, soilclassification, shear strength characteristics of the soils and other pertinent soil engineer-
ing data shall be presented.
Sufficient cross-sections and cut and fill slope stability analyses shall be included to sub-
stantiate recommendations concerning the vertical height and angle of all slopes on theproject.
Other aids in exploratory work may be used but subsurface exploratory work sufficient tosupport the findings shall be performed.
Both the engineering geologist's and soil engineer's reports -shall describe the grading pro-
ject as to its location, topographic relief, drainage, geologic and soils types present, thegrading proposed, the effects of such grading on the site and adjoining properties, andshall contain specific conclusions concerning the feasibility and anticipated future stabil-
ity of the overall project and an analysis of the property on a lot-by-lot basis. Specificrecommendations for the correction of all known and/or anticipated geologic hazards onthe grading project must be included.
Subject: Board Ruling--Stilt Supported Buildings Erected on Slopes Exceeding Two Hori-
zontal to One Vertical--RR 22851Recomnmendation'Approval for the Department to issue permits for stilt supported dwellings on caissons orpiers where located over a fill slope exceeding two horizontal to one vertical. The Su-
perintendent of Building shall determine that good engineering practice would permit theconditional use of such a dwelling subject to compliance with the following 'conditionsand such other precautions found to be reasonable and necessary.
1.All footings shall be designed by a licensed engineer and extend through the filla minimum of 3'-ff into the underlying bedrock but not less than the depth required toresist the lateral load by friction or passive resistance as determined by the foundationengineer.
2. All caissons shall be reinforced for their full length with a minimum of four No.
4 bars tied with 1/4" hoops at 12" o.c.
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3. All caissons or pier. footings shall be tied laterally in two directions at theground surface with grade beams or tie beams a minimum of 12" x 12" cross-section rein-
forced with a minimum of four No. 4 bars tied with 1/4" hoops at 12"o.c.
4. All roof drainage is collected and conducted to the street in a non-erosive de-
vice.
5. No additional fill from the footing excavation is placed on the slope.
6. All loose brush and debris shall be removed from the site prior to starting con-
struction.
7. The fill placed upon this property is susceptible to downhill creep which must bepresumed and allowed for in the design. The designing engineer shall provide supportagainst downhill creep which shall not be less than 1000 lbs. per linear foot acting uponeach caisson or pier for the full length of its penetration through the fill. If the designingengineer or the Department finds that a greater force is probable, the design shall bemodified accordingly.
The above requirements do not preclude consideration of other design methods if per-
formed by an engineer versed in soil mechanics; and if the design is based upon ex-
ploratory evidence substantiated by engineers who are approved by the Board to makesuch investigations.
Exception: Where there is no fill or fill is less than 12"in depth, caissons or piers shall bedesigned to resist a minimum horizontal force of 1000lbs. acting downhill on each caissonor other type of footing. Caissons or piers shall be tied together in two directions by gradebeams as required in Item No. 3.8. The site shall be planted as required by the Department to prevent surface ero-
sion.
9. Items 1, 2, 3 and 7 listed above may be omitted if continuous footings are usedthroughout. Continuous footings shall be reinforced with a minimum two No. 4 bars at topand bottom of the footing.
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Appendix 11-C: Excerpts of Resolution-No. 5056, a Resolution of the City Council of theCity of Whittier Establishing Regulations for Citizen Participation in the Federal FloodInsurance Program.
now therefore, be it resolved by the City Council of the City of Whittier:
1. That a permit shall be obtained before construction or development begins withinany area of ...Mudflow Hazard...designated as Zone M on the FIRM.
2. The application for a permit shall include, but not limited by the following:
c. A soils engineering and geology report examining data on the distribution,
nature and strengths of existing soils. Conditions and recommendations fordevelopment must be certified by a registered civil engineer experienced insoils engineering....
5. The following standards shall be required for development in Mudflow Hazard Ar-
eas:
A. Subdivision ProposalsL. Siting, orientation and design of any improvement shall be to mini-
mize mudflow damage.
2. Lot designs and the location of proposed improvements shall permitaccomodation of debris from mudflow without damage to improve-
ments and with access to a street to provide for clean up and re-
moval.
3. An overflow route for mud and debris associated with the mudflowshall be provided in order to direct overflow away from slopes andimprovements and toward safe points of discharge.
4. Accomodation of Mudflowa. Design of streets shall provide for conveyance of mudflowunless other channel or debris basin is provided.
b. If a channel is proposed as part of development its design willprovide for the conveyance of the 100 year mudflow, its de-
sign will be open and it will collect and distribute flow in amanner that does not endanger properties above or below theproject site.
c. If a debris basin is proposed as part of development, its designwill accommodate the 100 year mudflow plus freeboard. Ac-
cess will be provided for removal of material.
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Appendix 11-D: Ventura County Land Development Manual (reproduced in part).
CHAPTER 7: GRADING7000. General. All grading for land development is subject to the Ventura County Ordi-
nance Code (UBC Chapter 70). Although grading plans are required as. part of the im-
provement plan package, the plan check fees, agreements, bonding, inspection and certifi-
cations are handled under the provisions of the Grading Ordinance. Appurtenances tograding (i.e.+drainage devices, fences, walls, etc.) must conform to the Standard Land De-
velopment Specifications.
7107. Preliminary Grading Plan. The Developer may desire to accomplish some grading ofthe site prior to approval of the grading plans. In this case the grading plan may be ap-
proved, and a grading permit issued on a preliminary basis. Soils and geologic reports willbe required and all other conditions of approval of a grading plan must be met. Gradingplans processed in this manner must bear the following statement: CAUTION: PRELIMI-
NARY GRADING PLAN. This plan is approved as a preliminary grading plan only. Thisapproval does not include approval for placement of base materials, or construction ofcurb and gutter or any other' street improvement. Grades are subject to change before ap-
proval of the road. improvement plans. This note must be removed by change order at thetime the road improvement plans are submitted for approval.
7108. Modification to Requirements of the Grading Ordinance. Modification of en-
gineering requirements of the Grading Ordinance, such as steeper slopes or use of rock inshallow fills, will be made only on the. basis of soils engineering reports, geological re-
ports, etc., including recommendations for grading procedures and design criteria. Suchreports must include calculations, where appropriate, allowing a quick check by Countypersonnel. Anticipated modifications should be indicated at the tentative map stage priorto engineering design. Approval of modifications shall be obtained prior to the issuance ofa-grading permit for either a grading plan or a preliminary grading plan.
7109. Caution in Regard to Cut/Fill Line. Where a cut/fill line crosses a building pad, seeUBC Section 29-03(e) as modified by the Ventura County Ordinance Code.
7110. Engineering Geology and Soils Engineering Reports. Engineering geology and soilsengineering reports must be submitted if required by the Building Official (UBC Sections7006(e) and (f)). Reports required by the Building Official must be submitted through thedeveloper's engineer. Three copies of each report required plus one grading plan must besubmitted to Subdivision Engineering for review. County review of such reports shall betransmitted to the Engineer as well as the Soils Engineer and Engineering Geologist, asapplicable.
The following criteria are for determining whether soils and geologic reports are required:
1. A soils engineering report may be required if:
a. The depth of cut or fill is 3 feet or greater, orb. The fill is to support structural footings, or.
c. An engineered cut or fill is required.
2. An engineering geology report as well as a soils engineering report may be required forprojects in hillside areas and in other areas within the County wherein the County StaffEngineering Geologist believes geologic hazards may exist. A hillside area is defined asK-19

one where any of the following conditions exist or are proposed within the project area orthe area of any off-site work in connection with the proposed project:
a. Finish cut or fill slope faces with vertical heights in excess of 10feet.
b. Existing slope faces steeper than 10 horizontal to 1 vertical, having a verticalheight in excess of 10feet.
7111. Employment of Engineering Professionals. The owner of land on which engineeredgrading is to be performed shall execute an agreement with the County to provide profes-
sional services. Such agreement shall be acknowledged by each of the professionals in-
volved.
7112. Responsibilities of Engineering Professionals. The Engineering Professionals em-
ployed by the property owner on grading work will include the Civil Engineer, the SoilsEngineer and the Engineering Geologist. The Civil Engineer's duties will include:
1.Preparation of the grading plan.
2. Design of surface drainage, irrigation and other surface features.
3. Survey and staking of the work.
4. Coordination of the other engineering professionals.
5. Provide "Rough Grading and Final Grading Certification."
6. Preparation of the "As-Built" grading plan.
7. Representing the owner for contacts by the County.
8. Certification of "As-Built" grading plan.
9. Perform such other work as is necessary to comply with the ordinance and to insureproper completion of the work in accordance with good engineering practice.
The Soils Engineer's duties will include:
L. Investigation and report on existing soil conditions.
2. Advising the Civil Engineer on soils problems affecting grading.
3. Inspection and testing of soils moved, exposed, disturbed or processed during construc-
tion. The Soils Engineer or his representative shall be on the site at all times when grad-
ing is in progress.
4. Testing completed soil masses to determine building foundation requirements.
5. Certifying that the plans and specifications are in conformance with his recom-
mendations and to the final acceptability of the grading.
6. Design of subdrainage, erosion control, buttresses, and other soil connected features.
7. Perform such other work as is necessary to comply with the ordinance and to insureproper completion of the work in accordance with good engineering practice.
The Engineering Geologist's duties include:
1.Investigation, mapping, and report of existing geological conditions.
2. Advising The Civil Engineer and Soils Engineer on geological conditions which may af-
fect grading.
3. Reviewing geological conditions during construction to see if modification of the grad-
ing plan is required.
4. Certifying that the plans and specifications are in conformance with his recom-
mendations and the final grading is stable in regard .to geological conditions.
5. Perform such other work as is necessary to comply with the ordinance and to insureproper completion of the work in accordance with good engineering geological practice.
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As each of the engineering professionals employed in grading has a responsibility for cer-
tification of the work on completion of the project, none of the engineering professionalsshould be changed during the course of the project. If a change occurs, the new engineer-
ing professional must satisfy himself as to the work performed by his predecessor throughcertifications from his predecessor, field review, soil explorations and testing. or combina-
tions of these or by other methods so that he will be able to certify to the entire projecton completion. When changes are being made, grading will be stopped until the new pro-
fessional has agreed to take responsibility for the work.
The Civil Engineer shall sign and place his registration stamp or number on the gradingplan. The Soils Engineer and Engineering Geologist shall indicate, by a suitable statement,
signature, registration or certification stamp of number and date on a print of the grad-
ing plan submitted to the County, that the plan incorporates all recommendations made bythem.
7400. Standard Variances from the Code. Sections 7009 through 7012 of UBC allow theBuilding Official to approve variances from the UBC where such variance is recom-
mended by the Soils Engineer or Engineering Geologist.
CHAPTER 8: CONSTRUCTION8000. General. When the improvement and grading plans have been signed and the permitsissued by the County Surveyor, the County responsibility for control of the land develop-
ment is transferred from Subdivision Engineering to Construction Inspection. A construc-
tion engineer and an inspector will be assigned by the County to watch the constructionto insure that the grading and the construction of road improvements meet the minimumrequirements of County ordinances and standards. This assignment in no way relieves thedeveloper from the responsibility for inspection and supervision of construction, or of anyresponsibility for meeting the requirements of the plans, permits, Grading Ordinances,
and the Standard Land Development Specifications or for assuming construction in accor-
dance with recommendations of the Soils Engineers and Engineering Geologist.
8300. Grading Inspection. Inspection of grading is accomplished under the Grading Ordi-
nance. It is emphasized that the Grading Ordinance is directed particularly to grading ofprivate property, and that the responsibilities of the Developer, Developer's Engineer, De-
veloper's Soils Engineer. and Developer's Engineering Geologist are assigned under theGrading Ordinance. Omissions from the plans of any work required by the Grading Ordi-
nance will not excuse the developer from any responsibility for compliance.
8006. Grading Reports. The Building Official requires that the compaction test data, in-
cluding results, location and elevation, be available for inspection on the site at all timesduring business hours: or, reports are to be mailed daily to the Building Official's desig-
nated representative. The method of reporting shall be determined at the preconstructionconference at the option of the Soils Engineer.
The Building Official requires sufficient inspection by the Engineering, Geologist to as-
sure that all geologic conditions have been adequately considered. Where geologic condi-
tions warrant, the Building Official may require interim geologic reports. These reportsmay be required to include, but need not be limited to reporting, inspection of cut slopes,
canyons during clearing operations for ground water and earth material conditions,
benches prior to placement of fill, and possible spring locations.
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Appendix ll-E: Excerpt from the Uniform Building Code.
Paragraph 7009. CUTS(a) General. Unless otherwise recommended in the approved soils engineering and/orengineering gwology report, cuts shall conform to the provisions of this section.
(jb) Slope. The slope of cut surfaces shall be no steeper than is safe for the intendeduse. Cut slopes shall be no steeper than two horizontal to one vertical.
(c) Drainage and Terracing. Drainage and terracing shall be provided as required byParagraph 7012.
Paragraph 7010. FILLS(a) General. Unless otherwise recommended in the approved soils engineering report,
fills shall conform to the provisions of this section. In the absence of an approvedsoils engineering report, these provisions may be waived for minor fills not in-
tended to support structures.
(b) Fill Location. Fill slopes shall not be constructed on natural slopes steeper than twoto one.
(c) Preparation of Ground.The ground surface shall-be prepared to receive fill by re-
moving vegetation, noncomplying fill, topsoil, and other unsuitable materials, scar-
ifying to provide a bond with the new fill, and, where slopes are steeper than fiveto one and the height is greater than five feet, by benching into sound bedrock orother competent material as determined by the soils engineer. The bench under thetoe of a fill on a slope steeper than five to one shall be at least 10-feet wide. Thearea beyond the toe of the fill shall be sloped for sheet overflow, or a paved drainshall be provided. Where fill is to be placed over a cut, the bench under the toe offill shall be at least 10-feet wide, but the cut must be made before placing fill andapproved by the soils engineer and engineering geologist as a suitable foundationfor fill. Unsuitable soil is soil which, in the opinion of the building official or thecivil engineer or the soils engineer or the geologist, is not competent to supportother soil or fill, to support structures, or,to satisfactorily perform the other func-
tions for which the soil is intended.
(d). Fill Material. Detrimental amounts of organic material shall not be permitted infills. Except as permitted by the building official, no rock or similar irreduciblematerial with a maximum dimension greater than 12 inches shall be buried orplaced, in fills.
EXCEPTION: The building official may permit placement of largerrock when the soils engineer properly devises a method of placemnt,
continuously inspects its placemnt, and approves the fill stability. Thefollowing conditions also apply:
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A. Prior to issuance of the grading permit, potential rock disposal ar-
eas shall be delineated on the grading plan.
B. Rock sizes greater than 12 inches in maximum dimensions shall be10 feet or more below grade, measured vertically.
C. Rocks shall be placed so as to assure filling of all voids with fines.
(e) Compaction.All fills shall be compacted to a minimum of 90 percent of maximumdensity, as determined by UBC Standard No 70-1. Field density shall be determinedin accordance with UBS Standard No. 70-2 or equivalent, as approved by the build-
ing official.
(f) Slope. The slope of fill surfaces shall be no steeper than is safe for the intendeduse. Fill slopes shall be no steeper than two horizontal to one vertical.
(g) Drainage and Terracing. Drainage and terracing shall be provided and the areaabove fill slopes and the surfaces of terraces shall be graded and paved as requiredby Paragraph 7012.
Paragraph 7011. SETBACKS(a) General. The setbacks and other restrictions specified by this section are minimumand may. be increased by the building official or by the recommendation of a civilengineer, soils engineer, or engineering geologist, if necessary for safety and stabil-
ity or to prevent damage of adjacent properties from deposition or erosion or toprovide access for slope maintenance and drainage. Retaining walls may be used toreduce the required setbacks when approved by the building official.
(b) Setbacks from Property Lines. The tops of cuts and toes of fill slopes shall be setback from the outer boundaries of the permit area, including slope-right areas andeasements.
(c) Design Standards for Setbacks. Setbacks between graded slopes (cut or fill) andstructures shall be provided.
Paragraph 7012 DRAINAGE AND TERRACING.
(a) General. Unless otherwise indicated on the approved grading plan, drainage facili-
ties and terracing shall conform to the provision of this section.
(b) Terrace. Terraces at least six feet in width shall be established at not more than30-foot vertical intervals on all cut or fill slopes to control surface drainage anddebris, except that where only one terrace is required, it shall be at mid-height. Forcut or fill slopes greater than 60 feet and up to 120 feet in vertical height, one ter-
race at approximately mid-height shall be 12 feet in width. Terrace widths andspacing for cut and fill slopes greater than 120 feet in height shall be designed bythe civil engineer and approved by the building official. Suitable access shall beprovided to permit proper cleaning and maintenance.
Swales or ditches on terraces shall have a minimum gradient of five percent andmust be paved with reinforced concrete not less than three inches in thickness oran approved equal paving. They shall have a minimum depth at the deepest pointK-24

of one foot and a minimum paved width of five feet. A single run of swale orditch shall not collect runoff from a tributary area exceeding 13,500 square feet(projected) without discharging into a down drain.
(c) Subsurface Drainage. Cut and fill slopes shall be provided with subsurfacedrainage as necessary for stability.
(d) Disposal. All drainage facilities shall be designed to carry waters to the nearestpracticable drainage way approved by the building official and/or other appropri-
ate jurisdiction as a safe place to deposit such waters. Erosion of ground in thearea of discharge shall be .prevented by installation of nonerosive down drains orother devices.
Building pads shall have a drainage gradient of two percent toward approveddrainage facilities, unless waived by the building official.
EXCEPTION: The gradient from the building pad may be one percentiIf all of the following conditions exist throughout the permit area:
A. No proposed fills are greater than 10 feet in maximum depth.
B. No proposed finish cut or fill slope faces have a vertical height inexcess of 10 feet.
C. No existing slope faces which have a slope face steeper than 10horizontally to one vertically have a vertical height in excess of 10 feet.
(e) -Interceptor Drains. Paved interceptor drains shall be installed along the top of allcut slopes where the tributary drainage area above, slopes towards the cut and hasa drainage path greater than 40 feet measured horizontally. Interceptor drains shallbe paved with a minimum of three inches of concrete or gunite and reinforced.
They shall have a minimum depth of twelve inches and a minimum paved width of30 inches measured horizontally across the drain. The slope of drain shall be ap-
proved by the building official.
Paragraph 7013. EROSION CONTROL(a) Slopes. The faces of cut and fill slopes shall be prepared and maintained to controlagainst erosion. This control may consist of effective planting. The protection forthe slopes shall be installed as soom as practicable and prior to calling for finalapproval. Where cut slopes are not subject to erosion due to the erosion-resistantcharacter of the materials, such protection may be omitted.
(b) Other Devices. Where necessary, check dams, cribbing, riprap, or other devices ormethods shall be employed to control erosion and provide safety.
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Appendix 11-F: What the Buyer, Builder, or Homeowner Should Look For. Excerpt from areport on landsliding for Allegheny County, PA, Briggs et al. 1975..
The buyer, builder, or homeowner must always bear in mind that areas susceptibleto landslides commonly are larger than most indiviual properties. Thus, it pays to look notonly at the property in question but also at adjacent areas, particularly those upslope anddownslope. If the property slopes more steeply than about 15 percent (15. feet of drop orrise vertically in 100 feet of horizontal distance), or if adjacent uphill or downhill slopes(or both) are significantly steeper than the slope of the property, site examination shouldbe made. In addition, if the property is on relatively flat ground on a ridge top or in avalley, but close to a fairly steep slope, an examination of the slope is recommended.
(1) Cracks in buildings. Most older buildings have minor cracks, but these probablyresult largely from normal settlement. In general, the fact that a building is old and showsno significant damage is an indication that the building probably will remain undamagedby landsliding. Many or large cracks in newer structures are reasons for concern, althoughthe cause of cracking may well be something other than landsliding. Major cracks com-
monly are repaired by owners, but evidence of repair usually is visible on close examina-
tion. Wet basements may be evidence of cracks in the foundation.
(2) Cracks in brick walls around yards and other outside brick and concrete features.
Unlike buildings, which generally are set in bedrock, most yard walls and other ancillaryfeatures rest on soil. They thus are sensitive to creep which can cause cracking or can pullsuch features away from structures.
(3) Doors and windows that jam. A door that sticks or otherwise does not seem tofit well or a sash window that jams may be evidence that the frame of a house has beenwarped.
(4) Retaining walls, fences, curbs, gas meters, posts supporting parches, and other fea-
ttuzresout of plumb or not aligned in a normal way.
(7) Tilted trees, grapevines, reeds. Trees are probably somewhat less reliable indica-
tors of slope movement than are manmade objects, for trees on slopes tend to bend out-
ward somewhat as they seek sunlight. However, trees leaning at appreciable angles ornumbers of trees leaning in different directions strongly suggest areas of landsliding orstrong creep. Many grapevines and reeds have been observed on many prehistoric land-
slide deposits, perhaps as a result of water conditions within the deposits. They thus aregeneral indicators-of possbile instability.
(8) Tilted utility poles and taut or sagging wires. Most utility poles are more or lessvertical and aligned when new, and wires between poles usually sag uniformly, so appre-
ciable tilting of poles and variations in amount of sag of wires between adjacent poles areabnormal and noteworthy.
(9) Cracks in the ground. Cracks more or less parallel to a slope usually are indica-
tions that the slope is moving.
(10) Steplike ground features. Slumping of ground usually results in steplike scarpsthat may range from very low to many feet high. When relatively new, the "risers" of thescarps usually expose fresh earth. Older scarps may have subdued angles because of ero-
K-26

sion and may be vegetated, making them more difficult to identify. Whether old or new,
these features are evidence of unstable conditions.
(11) Hummocky ground. Hummocks, low mounds, are common irregularly spacedfeatures of the toes and lower ground surfaces of both prehistoric and recent landslides.
They do not occur naturally on any other surfaces. in Allegheny County.
(12) Water seeps. Seeps and springs are very common at the toes of landslide de-
posits. Water from seeps on upper slopes may saturate the ground and so contribute to themobility of downslope materials.
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