Appendix D
Guidance for Coastal Flooding Analyses and Mapping
D.1	General Guidance
A variety of analytical methodologies may be used to establish Base Flood Elevations (BFEs) 
and floodplains throughout coastal areas of the United States. These methodologies are too 
voluminous to be included in these Guidelines. This Appendix itemizes references for the 
methodologies currently in use by FEMA for specific coastal flood hazards, provides general 
guidance for documentation of a coastal flood hazard analysis, specifies flood hazard analysis 
procedures for the Great Lakes coasts, and outlines intermediate data submissions for coastal 
flood hazard analyses with new storm surge modeling and revised stillwater flood level (SWFL).
[February 2002]
D.1.1	Coastal Flood Hazard Analysis Methodologies
The publications cited below were prepared for, and are available from, FEMA, or they are used 
to prepare a coastal flood hazard assessment and establish BFEs. The publications prepared for 
FEMA will be provided to the Mapping Partners responsible for performing coastal flood hazard 
analyses. The Mapping Partners responsible for final production of Flood Insurance Studies 
(FISs) for the Atlantic Ocean, Gulf of Mexico and Great Lakes shall obtain copies of the 
published data used to prepare the coastal flood hazard analyses and establish BFEs, and shall be 
familiar with the use and application of the information presented in the publications cited below.  
Mapping Partners responsible for final production of FISs for the Pacific Ocean coastal areas 
shall consult with the appropriate FEMA Regional Project Officer (RPO) to determine the 
appropriate methodologies that shall be followed.
Northeaster Flooding
Stone & Webster Engineering Corporation, "Development and Verification of a Synthetic 
Northeaster Model for Coastal Flood Analysis," 1978.
U.S. Department of the Army, Corps of Engineers, New England Division, Hydraulics and Water 
Quality Section, "Tidal Flood Profiles, New England Coastline," September 1988.
Hurricane Flooding
U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National 
Weather Service, Hurricane Climatology for the Atlantic and Gulf Coasts of the United States 
(NWS 38), April 1987.
Federal Emergency Management Agency, FEMA Coastal Flooding Storm Surge Model, 
Volumes 1, 2, and 3, August 1988.
Pacific Northwest Storm Flooding
CH2M HILL, Inc., "Determination of Flood Levels on the Pacific Northwest Coast for Federal 
Insurance Studies," Journal of Hydraulics Division, ASCE, D. E. Dorratcague, J. H. Humphrey, 
and R. D. Black, 1977, Vol. 103, 73-81.
U.S. Department of the Army, Corps of Engineers, Pacific Ocean Division, Manual for 
Determining Tsunami Runup on Coastal Area of Hawaii, August 1978.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report H-80-16, Tsunami-Wave Elevation Predictions for American Samoa, September 1980.
Tsunami Flooding
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report H-77-16, Tsunami-Wave Elevations, Frequency of Occurrence for the Hawaiian Islands, 
August 1977.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report CERC-87-7, Tsunami Predictions for the Coast of Alaska, Kodiak Island to Ketchikan, 
April 1987.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report H-80-16, Tsunami-Wave Elevation Predictions for American Samoa, September 1980.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report HL-80-18, Type 19 Flood Insurance Study: Tsunami Predictions for Southern California, 
1980.
U.S. Department of the Army, Corps of Engineers, Pacific Ocean Division, Manual for 
Determining Tsunami Runup on Coastal Area of Hawaii, August 1978.
Great Lakes Mapping of Coastal Flooding Areas
U.S. Department of the Army, Corps of Engineers, Revised Report on Great Lakes Open-Coast 
Flood Levels, Phases I and II, April 1988.
U.S. Department of the Army, Corps of Engineers, Great Lakes Wave Runup Methodology Study, 
June 1989.
Federal Emergency Management Agency, Guidelines for Great Lakes Wave Runup Computation 
and Mapping, June 1991.
Dewberry & Davis, Basic Analyses of Wave Action and Erosion with Extreme Floods on Great 
Lakes Shores, Draft Report, October 1995.
Federal Emergency Management Agency, Guidelines and Specifications for Wave Elevation 
Determination and V Zone Mapping - Great Lakes, Draft Report, August 1996.
Mississippi River Delta Flooding
Joseph N. Suhayda, Attenuation of Storm Waves over Muddy Bottom Sediments, August 1984.
Wave Height and Runup Analyses
National Academy of Sciences, Methodology for Calculating Wave Action Effects Associated 
with Storm Surges, 1977.
Federal Emergency Management Agency, Assessment of Current Procedures Used for the 
Identification of Coastal High Hazard Areas (V Zones), September 1986.
Federal Emergency Management Agency, Basis of Assessment Procedures for Dune Erosion in 
Coastal Flood Insurance Studies, January 1989.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Coastal 
Engineering Research Center, WIS Report 19, Hurricane Hindcast Methodology and Wave 
Statistics for Atlantic and Gulf Hurricanes from 1956-1975, April 1989.
Federal Emergency Management Agency, Wave Height Analysis for Flood Insurance Studies 
(Technical Documentation for WHAFIS Program Version 3.0), September 1988, amended with 
software, July 1989.
Federal Emergency Management Agency, Wave Runup Model Version 2.0 (RUNUP 2.0), 1991.
U.S. Department of the Army, Corps of Engineers, Shore Protection Manual, Volumes I and II, 
1984.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Automated 
Coastal Engineering System, Version 1.07, September 1992.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Coastal 
Engineering Research Center, WIS Report 20, Southern California Hindcast Wave Information, 
December 1992.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Coastal 
Engineering Research Center, WIS Report 30, Hindcast Wave Information for the U.S. Atlantic 
Coast, March 1993.

Evaluation of Coastal Structures
U.S. Department of the Army, Corps of Engineers, Shore Protection Manual, Volumes I and II, 
1984.
U.S. Department of the Army, Corps of Engineers, Design of Coastal Revetments, Seawalls and 
Bulkheads, April 1985.
U.S. Department of the Army, Corps of Engineers, Waterways Experiment Station, Technical 
Report CERC-89-15, Criteria for Evaluating Coastal Flood Protection Structures, December 
1989.
Atlantic and Gulf Mapping of Coastal Areas
Federal Emergency Management Agency, Guidelines and Specifications for Wave Elevation 
Determination and V Zone Mapping, Final Draft, March 1995.
[February 2002]
D.1.2	Study Documentation
Mapping Partners responsible for producing coastal FISs must document fully the coastal flood 
hazard determination for each study.  This documentation shall identify the methodology 
employed as well as the computational approach and the input data used in the calculation of the 
coastal flood elevations.  The technical specifications under which all coastal FISs will be 
documented are provided in the various internal and public FEMA reports outlining the approved 
coastal storm surge elevation methodology that are referenced in Subsections D.1.1 and D.1.4.  
These reports include algorithms, computer codes, guidelines for model use, and examples of 
model runs.  
Although some of these reports provide relatively specific information on both the general 
procedures to be employed in processing the meteorological and hydrologic data, and the 
specifics of the hydrodynamic and windfield models to be employed, the reports contain no 
information on the application of the methodology to a particular coastal site.  Therefore, the 
Mapping Partner responsible for performing a coastal study shall document the specific 
meteorological and hydrologic data, ocean bathymetry, shoreline characteristics, surface and 
bottom friction coefficients, and other parameters used in the particular model application.  For 
this purpose, the Mapping Partner shall produce an engineering report for each coastal study.  
The purpose of the engineering report is to provide the detailed site-specific data needed by 
FEMA and the affected coastal communities to reconstruct or defend, on technical grounds, the 
study results.  In general, the documentation shall include the input data; modeling approach; 
model parameter values; and all assumptions, decisions, and judgments that influence model 
outputs.  The material to be included in the engineering report is summarized in the subsections 
below.  Although the emphasis is on coastal studies incorporating storm surge models, Mapping 
Partners using other methods shall nonetheless adhere to the appropriate subsections.  The 
Mapping Partner performing a coastal study shall obtain RPO approval for any deviations from 
the requirements documented in these Guidelines.  
[February 2002]
D.1.2.1	Introductory Material
In the first section of the engineering report, the Mapping Partner shall describe the geographic 
setting of the study site, discuss the local surge-producing climatology of both tropical and 
extratropical storms, and provide a history of extreme storm surges.  The Mapping Partner shall 
also report on unique aspects of each component of the stillwater flood elevation (SWEL) that 
was investigated (e.g., inverted barometer setup, wind transport, astronomical tide level, pre-
surge anomaly, wave action, and abnormal hydrological conditions).  The Mapping Partner also 
shall include a short discussion of the coastal study results and how they will be used in 
producing the Flood Insurance Rate Map (FIRM).  
[February 2002]
D.1.2.2	Outline of Methodology
In the second section of the engineering report, the Mapping Partner shall provide an outline of 
the basic technical approach employed in the study.  Topics to be covered include identification 
of the storm (wind) model, the hydrodynamic model, and the statistical procedure used to 
determine flood frequencies.  The purpose of this section is to outline the relationship between 
the technical material to be covered in the main body of the engineering report and the basic 
methodological approach used in the study.  This outline should be logically organized and 
sufficiently complete so that the detailed documentation that follows can be easily read and 
understood.  
[February 2002]
D.1.2.3	Storm Climatology and Storm Windfield Methodology
In this section of the engineering report, the Mapping Partner shall: 
*	Describe the basic climatological storm data used and the windfield methodology employed.  
*	Map, tabulate, and discuss in terms of local surge impact the storm paths used in the analysis.  
*	Tabulate and describe in written form the storm parameters (including central pressure 
deficit, radius to maximum wind, forward speed, shoreline crossing point, and shoreline 
crossing angle) used in the analysis.  
*	Identify sources of the basic data used to develop the storm climatology and the method used 
to sort the data and compare them with the National Weather Service (NWS) Hurricane 
Climatology for the Atlantic and Gulf Coasts of the United States (NWS 38).  
*	Describe the technique employed to determine the spatial/temporal distribution of storm 
occurrences (i.e., storms/nautical mile/year), derivation and discretization of storm intensity 
parameters, and exceedence probability distributions. 
*	Provide graphical presentation of the results, including an overlay with orientation of coast to 
storm path/direction.  
*	Provide a discussion of storm parameter independence and any unique storm model 
treatments.  
*	Give the exact equations used to parameterize the model windfield along with any unique 
values of all the appropriate coefficients and constants used. The windfield used in the 
analysis is a key component in the determination of the storm surge elevation. 
*	Include a diagram of the windfield model that gives the surface velocity structure as it 
changes radially outward from the storm center.  
*	Provide a comparative graph depiction of measured windfield(s) and modeled windfield, if 
available.  
*	Describe the method by which winds are reduced as the storm approaches land and moves 
inland in detail. 
*	Report the constants used in windspeed reduction.  
[February 2002]
D.1.2.4	Hydrodynamic Storm Surge Model
This section of the engineering report is to address the hydrodynamic storm surge model 
employed in performing the coastal study.  The model used to calculate the surge elevation has 
been described in detail in various FEMA documents and need only be cited by reference.  In this 
section of the engineering report, the Mapping Partner shall:
*	Report the unique model characteristics used for the study, including a discussion of the 
specific grid system and sub-grid systems employed, the grid used for bottom topography and 
shoreline, small-scale features such as harbors and barrier islands, and the location and 
conditions applied for the open boundaries to the grid.  
*	Describe and document the adjustment to land features to account for erosion.  
*	Describe and document the method used to determine average ground elevations and water 
depths within the cells of the grid system.  This discussion should be augmented by diagrams 
that show the grid systems as computer listings of the grid data used in the actual model 
calculations.  
*	Describe the method used to relate windspeed and surface drag coefficient is to be described.  
*	Discuss the Manning's "n" values used in the calculation of bottom and overland friction and 
provide values in tabular form.  This information will include a discussion of any sensitivity 
tests used to estimate these values in nearshore water.  Nearshore bottom and overland 
friction is an important part of the overall analysis and, therefore, shall be described with care 
and sufficient detail.  
*	Provide a graphical depiction of the model cells and grid system as an overlay to the 
bathymetric charts and topographic maps covering the study area, annotated with the 
individual cell inputs for the grid system. 
*	Discuss the method by which barriers, inlets, and rivers have been treated.  
*	Explain the procedures used to determine inland flooding, including parameterization of local 
features and selection of the friction factors used for the terrain.  
[February 2002]
D.1.2.5	Calibration and Verification of Hydrodynamic Storm Surge Model 
In this section of the engineering report, the Mapping Partner shall document the calibration and 
verification of the hydrodynamic surge model.  Once the hydrodynamic storm surge model and 
grid have been set up, calibration and verification are performed.  Calibration is done to 
determine the adjustable "tuning parameters" (e.g., Manning's "n", barrier overflow coefficients) 
and to validate the chosen grid schematization.  Verification is used to validate the model and 
grid for situations other than the case used to calibrate the model.  Sensitivity runs are used to 
make sure that small changes in the chosen grid and "tuning parameters," will not give rise to 
unacceptable large changes in the computed flood and tide levels.  Calibration and verification 
computer runs compare computed results with observed water levels.  Sensitivity runs compare 
computed results with other computed results.  
When observed (or model simulation) data are employed to calibrate (or compare) hydrodynamic 
storm surge model results with other available studies, the Mapping Partner shall give a complete 
description of this calibration procedure (or model comparison), including a listing of measured 
and simulated tidal data.  Calibration (and model comparison) is an important aspect of the 
model analysis; therefore, the Mapping Partner shall described these activities with sufficient 
detail and care to allow an independent reviewer to understand the exact procedures employed 
and the local historical records employed.  
[February 2002]
D.1.2.6	Statistical (Joint Probability) Methodology
If the joint probability method was used, the Mapping Partner shall summarize, map, and report 
the values and combinations used for storm parameters, annual storm density, spacing between 
storms, and the storm tracks used in the analysis in this section of the engineering report. In this 
section, the Mapping Partner also shall compare the information above with the probabilities 
reported in Hurricane Climatology for the Atlantic and Gulf Coasts of the United States (NWS 
38).  Specifically, the Mapping Partner shall:
*	Note the total number of simulations.  
*	Summarize tidal elevation data, if used, in sufficient detail to remove any doubt as to the 
values used in the simulations.  
*	Describe the method by which the tidal elevation data are convoluted with surge data 
including tidal constants and tidal records.  
*	Describe storm occurrence rate or storm density, the definition of the storm region used to 
define storm density, and storm kinematics and intensity with respect to their use in the joint 
probability calculation.  
*	Report and discuss comparisons to long-term gage statistics. 
*	Describe and report adjustments to account for the combined probability of coastal and 
riverine flooding for each area where such an approach was taken.  
[February 2002]
D.1.2.7	Unique Computer Programs
Several different computer codes may be used in the wind, hydrodynamic, and joint probability 
analysis.  Several basic computer programs have been listed in numerous FEMA reports.  In this 
section of the engineering report, the Mapping Partner shall list and describe any modifications 
of these programs and special data inputs used in the study.  
[February 2002]
D.1.2.8	Wave Height, Runup, and/or Erosion Analysis		
In this section of the engineering report, the Mapping Partner responsible for performing the 
coastal analysis shall reference the wave height, runup, and/or erosion analysis methodology used 
for the study.  Specifically, the Mapping Partner shall:
*	Document fully any deviation or expansion of that approach.
*	Describe the selection of input data, including a reference to source data and material.  
*	Document fully all erosion considerations.  
*	Include one or more transect location maps as appropriate. 
*	Include computer printout listings for input and output data as an appendix to the report, 
keyed to the transect location map(s). 
[February 2002]
D.1.2.9	References
In the final section of the engineering report, the Mapping Partner shall provide a complete list of 
technical references, including computer program references, indicating how to obtain copies of 
the exact program and the input data sources used in the analysis.  
[February 2002]
D.1.3	Great Lakes Wave Runup Computations and Mapping
Mapping Partners performing coastal studies for communities along the Great Lakes shoreline 
should use the wave runup analysis guidance in Section D.3.  Section D.3 provides a wave runup 
study flow chart, the detailed study procedure steps, sample computations, and mapping policies.  
An overview of the coastal study procedures is presented below.
[February 2002]
D.1.3.1	Wave Runup Calculation Procedures 
The guidelines for Great Lakes wave runup calculations have emerged from methodologies 
recommended by the Detroit District of the U.S. Army Corps of Engineers (USACE) in the study 
report entitled Great Lakes Wave Runup Methodology Study. The figures and tables in Section 
D.3 have been drawn from various references cited in this USACE study report.  Further 
guidance on the wave runup approach is included in Section D.3.  Although this guidance is 
subject to change based on new information and methodology improvement, it provides the 
framework and information on the application of the methodologies.
Three types of shorelines are considered: a natural beach profile and two types of armored 
shoreline profiles (vertical wall and rock revetment).  Therefore, three runup methodologies 
corresponding to the three shoreline types are employed.  The flow of tasks begins with site 
profile data-gathering, tracks through various intermediate steps, such as the 1-percent-annual-
chance flood level determination, and the calculation of the deep water and shallow water wave 
height, and ends with the wave runup determination for each type of shoreline.  
[February 2002]
D.1.3.2	Wave Runup Computation Steps and Sample Calculations 
When the site location is identified, the Mapping Partner shall follow the step-by-step study 
procedures below to determine the maximum wave runup elevations to be used in coastal 
floodplain boundary delineations.  
*	Step 1.	Profile Data Gathering
*	Step 2.	1-percent-annual-chance Flood Level Determination
*	Step 3.	Offshore (Deep Water) Wave Height Determination
*	Step 4.	Nearshore (Shallow Water) Hmo, Hs, and Tp Computation
*	Step 5.	Wave Runup Computation
*	Step 6.	Determination of Maximum Wave Runup Elevation
[February 2002]
D.1.3.3	Delineation and Mapping Policy
Six general policies and 12 specific-case mapping policies accompanied with illustration 
diagrams may be used in the coastal FIS map delineation for Great Lakes coastal communities. 
(See Section D.3 for detailed information.)  Mapping Partners shall apply the general policies to 
all cases and the specific-case policy to a certain situation.  Three types of shoreline profiles are 
typical in the Great Lakes region and are used to classify the cases:  
*	Beach profile with a natural dune system;
*	Beach profile with a bluff system; and
*	Beach profile with coastal structures.
For each type of shoreline profile, the Mapping Partner shall consider four separate cases, 
depending on the computed wave height profile, wave runup height, 1-percent-annual-chance 
stillwater level, and the predicted post-storm erosion profile.  For other special cases that cannot 
be covered by the above policies, the Mapping Partner shall consult with the RPO.  
[February 2002]
D.1.4	Intermediate Data Submission for Coastal Flood Studies
Coastal analyses involving storm surge modeling are highly specialized and complex and require 
a highly specialized review process.  Experience has shown that attempting to make changes or 
corrections to coastal storm surge and wave height analyses after they have been run and mapped 
is not practical due to the time, cost, and contractual problems involved.  Many questions and 
problems that arise during the review process could be answered or resolved much more readily 
if these issues were raised early in the study process.  Therefore, FEMA has established 
intermediate data submission requirements to permit review of the Mapping Partner's progress on 
model development at appropriate milestones.  The Mapping Partner performing the study shall 
submit the data to the reviewing Mapping Partner, as specified by the RPO, in accordance with 
the sequence discussed below.  
The Mapping Partner will receive review comments within 30 days of the receipt of each data 
submission.  The Mapping Partner performing the study shall establish a work plan so that the 
interim review does not cause any delay in the submission of the FIS Report draft and the maps 
reflecting the results of the coastal study.
[February 2002]
D.1.4.1	Before Storm-Surge Model Calibration Runs Are Made
The Mapping Partner performing the study shall submit the following to the reviewing Mapping 
Partner before calibration runs are made:
1.	A large-scale map of the coastal area which delineates both the coarse grid basin(s) and fine 
grid basin(s);  
2.	A schematic of each basin (coarse grid and fine grid) showing sub-grid channel locations, 
widths, bed elevations, and proposed Manning's "n" values for each channel; 
3.	Historical evidence establishing the importance of various coastal flooding mechanisms (e.g., 
tropical and extratropical storms, rainfall and riverine events);  
4.	Basic data relating to the study area (e.g., documented storm erosion, available design analyses 
for shore protection or other coastal projects, historical shoreline changes);  
5.	Aerial photographs, coastal setback maps, and other maps used to determine more accurate 
topographic-bathymetric values and land cover features in the study area;  
6.	Table listing astronomical tide events and historical storms selected for use in model calibration 
and verification, and a plot showing the observed storm surge elevation against the predicted 
tide elevations;  
7.	Plots of exceedence probability vs. parameter value for the meteorological storm parameters 
that vary in the joint probability analysis, as developed for the study area following  NWS 38, 
with documentation to include a tabular presentation of all meteorological storm parameter data 
used in development of the exceedence probability curves; and  
8.	Table showing storm parameter values and assigned probabilities.  
[February 2002]
D.1.4.2	Before Operational Storm Surge Runs Are Made
The Mapping Partner performing the study shall submit the following to the reviewing Mapping 
Partner before operational storm surge runs are made:
1.	A map of each basin (coarse grid and fine grid) showing water depths, ground elevations, and 
Manning's "n" values for each grid cell; 
2.	A map of each basin (coarse grid and fine grid) showing barrier locations, barrier heights, 
barrier widths, barrier Manning's "n" values, location of inlets cutting through barriers, inlet 
widths, inlet bed elevations, inlet Manning's "n" values and inlet entrance and loss coefficients;
3.	A computer printout listing of the water depth, ground elevations, Manning's "n" values, barrier 
and inlet input, and the sub-grid channel input, and any other input data used in the calibration 
and verification runs and that will be used in the production runs;
4.	Description of sensitivity runs used to optimize model parameters for the study area, for 
example, in final choices of Manning's "n" values;  
5.	Tide and storm calibration results (including extreme water elevations and time histories) 
showing computed results and a comparison of these with observations where such 
observations are available;
6.	Grid overlay and work maps used in storm surge analyses for all fine and open-coast grid 
basins; and 
7.	Written documentation, including justification, of any modifications made to the standard 
FEMA storm surge methodology and a listing of the computer source code annotated where the 
modifications were made.  
The work maps listed in No. 6 above should generally be the 7.5-minute series U.S. Geological 
Survey quadrangle maps and the hydrographic charts that were used to gather topographic, 
bathymetric, roughness, and other input data for the storm surge calculations.  The Mapping Partner 
performing the study shall draw the grid pattern on the maps or use one or more transparent 
overlays registered to the work map(s) to indicate where the grid cells fall with respect to various 
map features.  The Mapping Partner also shall indicate the location and extent of each wave transect 
on the overlays or work maps.
[February 2002]
D.1.4.3	Before Operational Wave Elevation Determination Are Made
The Mapping Partner performing the study shall submit the following to the reviewing Mapping 
Partner before operational wave elevation determinations are made:
1.	Documentation of conclusions on the interaction between storm surge and astronomical tide;  
2.	Output of PROBS program for all open coast and fine grid basins;  
3.	Grid showing 10-, 2-, 1-, and 0.2-percent-annual-chance SWFLs for each open coast and fine 
grid basin; and  
4.	Location map of proposed transects to be used in the wave elevation determination analyses.
[February 2002]
D.1.4.4	Before Wave Elevation Determinations Are Mapped
The Mapping Partner performing the study shall submit a copy of all wave height and wave 
runup transect computations, and all modeling assumptions to the reviewing Mapping Partner 
before wave elevations and resulting BFEs are mapped.
[February 2002]


D.2	Wave Elevation Determination and V Zone Mapping: 
Gulf of Mexico and Atlantic Ocean
The mapping of V Zones under the NFIP began in the early 1970s.  The objective was to identify 
hazardous coastal areas in a manner consistent with the original regulatory definition of coastal 
high hazard areas as an "area subject to high velocity waters, including but not limited to 
hurricane wave wash."  The initial technical guidance for identifying V Zones was provided in a 
June 1973 report by the USACE, Galveston District entitled General Guidelines for Identifying 
Coastal High Hazard Zone, Flood Insurance Study - Texas Gulf Coast Case Study, prepared by 
the U.S. Army Corps of Engineers (USACE), Galveston District (1973).  The USACE report 
identified a breaking wave height of 3 feet as critical in terms of causing significant structural 
damage and illustrated procedures for mapping the limit of this 3-foot wave (V Zone) in two 
distinct situations along the Texas coast: undeveloped areas and highly developed areas.  
In June 1975, the USACE issued a follow-up report entitled Guidelines for Identifying Coastal 
High Hazard Zones which maintained the basic recommendations contained in the 1973 report 
for identifying V Zones in undeveloped and developed areas; however, the 1975 report also 
included guidance for determining effective fetch lengths, a technical discussion justifying the 3-
foot wave height criterion for V Zones, an abbreviated procedure for V Zone mapping in 
undeveloped areas, an expanded discussion of V Zone mapping in developed areas, and historical 
accounts of several severe storms that have impacted developed areas along the Atlantic and Gulf 
coasts.  
Between 1975 and 1980, the Federal Government (U.S. Department of Housing and Urban 
Development until 1978 and FEMA thereafter) published FIRMs with V Zones for 
approximately 270 communities along the Atlantic and Gulf coasts using the USACE guidance 
for V Zone mapping.  During this period, the procedures for determining and delineating V 
Zones in developed areas differed among studies. At that time, the regulatory BFEs, for both 
insurance and construction purposes, were the 1-percent-annual-chance stillwater elevations 
(SWELs), which consisted of the astronomical tide and storm surge caused by low atmospheric 
pressure and high winds.  Although V Zones were identified, the increase in water-surface 
elevation due to wave action was not included.  The Federal Government recognized that this 
practice did not accurately represent the flooding hazard along the open coast, but an adequate 
method for estimating the effects of wave action, applicable to most coastal communities, was 
not readily available at the time.  
In 1976, the National Academy of Sciences (NAS) was asked to provide recommendations about 
how calculations of wave height and runup should be incorporated in FISs for Atlantic and Gulf 
coast communities to provide an estimate of the extent and height of stormwater inundation 
having specified recurrence intervals.  The NAS concluded that the prediction of wave heights 
should be included in FISs for coastal communities and provided a methodology for the open 
coast and shores of embayments and estuaries on the Atlantic and Gulf coasts.  The 1977 report 
documenting the NAS findings, Methodology for Calculating Wave Action Effects Associated 
with Storm Surges included means for taking into account varying fetch lengths, barriers to wave 
transmission, and regeneration of waves likely to occur over flooded land areas.  NAS did not 
address the extent and elevation of wave runup, amount of barrier overtopping, and coastal 
erosion.  
In 1979, FEMA adopted the NAS methodology.  In 1980, FEMA issued Users Manual for Wave 
Height Analysis, which was subsequently revised in February 1981.  FEMA also introduced a 
computer program, Wave Height Analyses for Flood Insurance Studies (WHAFIS), in 1980.  
With WHAFIS, FEMA initiated a large effort to incorporate the effects of wave action on the 
FIRMs for communities along the Atlantic and Gulf coasts.  
Along the New England coast with its very steep shore, the NAS methodology proved to be 
insufficient. Structures that were shown as being outside of the SFHA on effective FIRMs 
experienced considerable wave damage from storms, most notably the northeaster of February 
1978, a near 1-percent-annual-chance flood event.  The need to account for the effects of wave 
runup was recognized. In 1981 FEMA approved a methodology that determined the height of 
wave runup landward of the stillwater line.  Stone & Webster Engineering Corporation 
developed the methodology in November 1981.  In 1987, FEMA modified its computer model 
for runup elevations slightly to increase the convenience of preparing input conditions. In 1990, 
FEMA modified the model again to improve computational procedures and application 
instructions to conform to the best available guidance on wave runup (Dewberry & Davis, 1990).  
Two additions were made to the NAS methodology in 1984 to account for coastal situations 
involving either marsh grass or muddy bottoms.  The NAS methodology did not account for 
flexible vegetation; in particular, marsh plants.  Experts surmised that the motion of submerged 
marsh plants absorbed wave energy, reducing wave heights.  In 1984, a FEMA task force 
examined this phenomenon in detail and developed a methodology that adjusted the wave height 
to reflect energy changes resulting from the flexure of various types of marsh plants and the 
wind, water, and plant interaction (FEMA, 1984).  FEMA incorporated the new methodology 
into WHAFIS.  
The muddy bottom situation occurs only at the Mississippi Delta in the United States.  The 
Mississippi River has deposited millions of tons of fine sediments into the Gulf of Mexico to 
form a soft mud bottom in contrast to the typical sand bottom of most coastal areas.  This plastic, 
viscous bottom deforms under the action of surface waves.  This wave-like reaction of the 
bottom absorbs energy from the surface waves, thus reducing the surface waves.  A methodology 
was developed for FEMA to calculate the wave energy losses due to muddy bottoms (Suhayda, 
1984).  Waves in the offshore areas are tracked over the mud bottom, resulting in lower incident 
wave heights at the shoreline.  This is a phenomenon unique to the Mississippi Delta, and FEMA 
has not incorporated the methodology into WHAFIS. 
In 1988, FEMA upgraded WHAFIS to incorporate revised wave forecasting methodologies 
described in the 1984 Edition of the USACE Shore Protection Manual (USACE, 1984) and to 
compute an appropriately gradual increase or decrease of SWELs between two given values 
(FEMA, September 1988).  
In the performance of wave height analyses and the preparation of FISs, erosion considerations 
were left to the judgment of FEMA contractors.  Coastal erosion was to be considered a hazard 
when there was historical evidence of erosion from previous storms, but prior to 1986, objective 
procedures for treating erosion were not available.  Consequently, some shorefront dunes were 
designated as stable barriers to flooding and some were not.  In 1986, FEMA initiated studies 
aimed at providing improved erosion assessments in FISs for coastal communities.  
In response to criticisms indicating a significant underestimation of the extent of Coastal High 
Hazard Areas, FEMA undertook an investigation to reevaluate V Zone identification and 
mapping procedures.  The resulting report, entitled Assessment of Current Procedures Used for 
the Identification of Coastal High Hazard Areas (V Zones) presented a number of 
recommendations to allow for more realistic delineation of V Zones and to better meet the 
objectives of the NFIP for actuarial soundness and prudent floodplain development (FEMA, 
1986).  One recommendation was for full consideration of storm-induced erosion and wave 
runup in determining BFEs and mapping V Zones.  As part of its investigation, FEMA performed 
a study of historical cases of notable dune erosion.  In this quantitative analysis, field data for 30 
events (later increased to 38 events) yielded a relationship of erosion volume to storm intensity as 
measured by flood recurrence interval.  For the 1-percent-annual-chance storm, FEMA 
determined that, to prevent dune breaching or removal, an average cross-sectional area of 540 
square feet is required above the SWEL and seaward of the dune crest.  That standard for dune 
cross section has a central role in erosion assessment procedures.
The USACE Coastal Engineering Research Center (CERC) performed a study of the available 
quantitative erosion models for FEMA (Birkemeier, Kraus, Scheffner, & Knowles, 1987).  
USACE determined that only empirically based models produce reasonable results with a 
minimum of effort and input data, that each available model for simple dune retreat has certain 
limitations, and that dune overwash processes are poorly documented and unquantified.  After 
further investigations, FEMA decided to employ a set of extremely simplified procedures for 
objective erosion assessment (FEMA, November 1988).  These procedures have a direct basis in 
documented effects due to extreme storms and are judged appropriate for treating dune erosion in 
FISs for coastal communities.  
As the official basis for treating flood hazards near coastal sand dunes, FEMA published new 
rules and definitions in the Federal Register that became effective on October 1, 1988.  FEMA 
included the following revised definition in Section 59.1 of the NFIP regulations:  
Coastal high hazard area means an area of special flood hazard extending from offshore to the 
inland limit of a primary frontal dune along an open coast and any other area subject to high 
velocity wave action from storms or seismic sources.  
FEMA also added a clarification of this matter, a definition of primary frontal sand dune, in 
Section 59.1:  
Primary frontal dune means a continuous or nearly continuous mound or ridge of sand with 
relatively steep seaward and landward slopes immediately landward and adjacent to the beach and 
subject to erosion and overtopping from high tides and waves during major coastal storms.  The 
inland limit of the primary frontal dune occurs at the point where there is a distinct change from a 
relatively steep slope to a relatively mild slope.  
FEMA also included a new section in Part 65 of the NFIP regulations, identifying a cross-
sectional area of 540 square feet as the basic criterion to be used in evaluating whether a primary 
frontal dune will act as an effective barrier during the 1-percent-annual-chance flood.  Another 
consideration is the documented historical performance of coastal sand dunes in extreme local 
storms.  
In 1989, USACE completed a review for the NFIP regarding coastal structures as protection 
against the 1-percent-annual-chance flood (Walton, Ahrens, Truitt, & Dean, 1989). Predictions of 
wave forces, wave overtopping, and wave transmission for commonly occurring structures were 
among technical topics addressed in the USACE report.  The guidelines in this Appendix 
incorporate procedural criteria recommended by the USACE for evaluating structural stability.
[February 2002]
D.2.1	Organization and Overview
Figure D-1 presents a flowchart of appropriate procedures for defining coastal hazards of the 1-
percent-annual-chance flood.  Fundamental aspects of the 1-percent-annual-chance flood are 
addressed in the following sequence: 
1.	SWEL, 
2.	Accompanying wave conditions, 
3.	Stability of coastal structures, 
4.	Storm-induced erosion, 
5.	Wave runup and overtopping, and 
6.	Overland wave heights.  
Determination of SWELs usually involves detailed statistical analyses, but added effects due to 
surface wave action are treated by simplified deterministic methodologies. This strategy avoids 
any potential complications due to conditional probabilities for simultaneous flooding effects.  
The sequence for treating these effects is entirely consistent in principle; for example, added 
wave effects are not resolved within the equations commonly used to simulate coastal storm 
surges and establish SWEL for the 1-percentannual-chance flood.  
The order indicated in Figure D-1 for activities, assessments, and analyses also outlines the 
organization of topics treated in these guidelines.  Subsection D.2.2 provides general data 
requirements for conducting a coastal study, including that data needed as input to computer 
models.  Subsection D.2.3 discusses requisite evaluation of coastal structures potentially 
providing wave and/or flood protection.  Subsection D.2.4 considers the erosion assessment 
needed to project the configuration of the shore profile during the 1-percent-annual-chance flood.  
Subsection D.2.5 treats wave runup, wave setup, and overtopping occurring at shore barriers in 
flood conditions.  Subsection D.2.6 addresses the analysis of nearshore wave heights and wave 
crest elevations relevant to a study.  Each of these sections provides guidance on the models and 
procedures for treating individual transects at a study site.  
FEMA has established specific models and procedures for the evaluation of shore structures, 
erosion, wave runup, and wave heights in the determination of coastal flood hazards.  For many 
coastal areas, all four topics must be considered for an adequate treatment; for other coastal 
areas, application of only one or two of the FEMA methodologies may be required to produce 
reasonable results.  Table D-1 lists some typical shoreline types and the models that should be 
used for them.  
Table D-1.  Model Selection for Typical Shorelines	
	TYPE OF SHORELINE	
MODELS TO BE APPLIED

EROSION
RUNUP
WHAFIS
Rocky bluffs

x
x
Sandy bluffs, little beach
x
x
x
Sandy beach, small dunes
x

x
Sandy beach, large dunes
x
x
x
Open wetlands


x
Protected by rigid structure

x
x
























Figure D-1.  Procedural Flowchart for Defining Coastal Flood Hazards


The remaining material in these guidelines adopts a more comprehensive view toward 
completion of an FIS.  Subsection D.2.7 addresses the integration of basic results into a coherent 
map for flood elevations and hazard zones.  Subsection D.2.8 defines required documentation of 
the process, decisions, and data used in determining coastal flood hazards for a community.  For 
consistency with the NFIP and compatibility with FISs, these guidelines use standard English 
units for all variables.
[February 2002]
D.2.2	Data Requirements for Coastal Flood Hazard Analyses
To conduct a study for a coastal community, the Mapping Partner performing the study shall first 
collect the wide variety of quantitative data and other site information required in ensuing 
analyses.  This subsection describes how coastal flood elevations and boundaries are determined, 
including an outline for the storm expected to cause the 1-percent-annual-chance flood, and 
characteristics of nearshore seabed through upland regions.  Some data are directly input to 
computer models of flood effects, and other data are used to interpret and integrate the calculated 
results.  
Each computer model of a separate flood effect is executed along transects, which are cross 
sections taken perpendicular to the mean shoreline to represent a segment of coast with similar 
characteristics.  Thus, collected data are compiled primarily for transects, in turn situated on 
work maps at the final scale of the FIRM.  Work maps are used both to locate and develop the 
transects, and to interpolate and delineate the flood zones and elevations.  
Aside from needed quantitative information, the Mapping Partner shall collect descriptions of 
previous flooding and the community in general to aid in the evaluation of flood hazards and for 
inclusion in the FIS Report.  The Mapping Partner shall start data collection at the community 
level and proceed with county, state, and Federal agencies.  The Mapping Partner also shall 
contact private firms specializing in topographic mapping and/or aerial photography, following 
up suggestions provided by government agencies.  
[February 2002]
D.2.2.1	Stillwater Elevations
The Mapping Partner shall determine the SWELs in a rational, defensible manner and shall not 
include contributions from wave action either as a result of the mathematics of the predictive 
model or of the data used to calibrate the model.  Only the 1-percent-annual-chance SWEL is 
required for the coastal analyses, although 10-, 2-, and 0.2-percent-annual-chance elevations are 
provided in the FIS Report, and the 0.2-percent-annual-chance floodplain boundary is mapped on 
the FIRM.  
SWELs may be defined by statistical analysis of available tide gage records or by calculation 
using a storm surge computer model.  A minimum of 20 years of recorded tide data is needed if 
the SWEL is to be based on tide gage records alone.  Measured tide levels are preferred over 
synthetic models provided they have a significant period of continuous record over 20 years and 
can accurately represent the geographic area of the study.  FEMA has available a self-contained 
hurricane storm surge model that can provide flood elevations (FEMA, August 1988) and a 
synthetic northeaster model that simulates the wind and pressure fields of an extratropical storm 
for input to a storm surge computer model (Stone & Webster Engineering Corporation, 1978).  
The Mapping Partner shall use these computer models for complex shorelines where gage 
records are limited, nonexistent, or non-representative, and usually indicate appreciable 
variations in flood elevations within a community.  FEMA also has specified procedure and 
documentation for coastal flood studies using a storm surge model, as presented previously in 
Subsections D.2.2, D.2.3 and D.2.4.  Of particular importance here, the surge model study can 
provide winds and water levels over time likely with the 1-percent-annual-chance flood.  
[February 2002]
D.2.2.2	Selected Transects
The Mapping Partner shall locate transects with careful consideration given to the physical and 
cultural characteristics of the land so that they will closely represent conditions in their locality.  
The transects are to be placed closer together in areas of complex topography, dense 
development, unique flooding, and where computed wave heights and runup may be expected to 
vary significantly.  Wider spacing may be appropriate in areas having more uniform 
characteristics.  For example, a long stretch of undeveloped shoreline with a continuous dune or 
bluff having a fairly constant height and shape, and similar landward features may require a 
transect only every 1 to 2 miles, whereas a developed area with various building densities, 
protective structures, and vegetation cover may require a transect every 1,000 feet.  
Good judgment exercised in placing required transects will avoid excessive interpolation of 
elevations between transects, while also avoiding unnecessary study effort.  In areas where runup 
may be significant, the proper location of transects will be governed by variations in shore slope 
or gradient.  On coasts with sand dunes, the Mapping Partner shall site transects according to 
major variations in the dune geometry and the upland characteristics.  In other areas where 
dissipation of wave heights may be most significant to the computation of flood hazards, the 
Mapping Partner shall base transect location on variations in land cover: buildings, vegetation, 
and other factors.  Generally speaking, the Mapping Partner shall site a separate transect at each 
flood protection structure.  However, if areas with similar characteristics are scattered throughout 
a community and have the same SWEL, the Mapping Partner may apply the results from one 
transect at various locations within this common area.  This should be done only after careful 
consideration is given to topographic and cultural features to assure the accurate representation of 
the coastal hazards.  
The Mapping Partner shall locate the transects on the work map with the input data compiled on 
a separate sheet for each transect.  The data for the transect are not taken directly along the line 
on the work map; they are taken from the area, or length of shoreline, to be represented by the 
transect so that the input data depict average characteristics of the area.  Because of this, the 
Mapping Partner may find it is useful to divide the work map into transect areas for data 
compilation.  
[February 2002]
D.2.2.3	Topography
The topographic data must have a contour interval no greater than 5 feet or 1.5 meters.  FEMA 
does not require more detailed information such as spot elevations or a smaller contour interval, 
although they can be useful in the definition of the dune or bluff profile and in the delineation of 
floodplain boundaries.  The topographic data, usually in the form of maps, must be recent and 
reflect current conditions or, at a minimum, conditions at a clearly defined time.  Transects need 
not be specially surveyed unless available topographic data are unsuitable or incomplete.  The 
Mapping Partner shall examine the topographic data to confirm that the information to be used in 
the analysis and mapping represents the actual planimetric features that might affect 
identification of the coastal hazards.
If possible, the Mapping Partner shall field-check shore topography to note any changes due to 
construction, erosion, coastal engineering, and other factors.  The Mapping Partner shall 
document any significant changes with location descriptions, drawings, and/or photographs.  The 
community, county, and state are usually the best sources for topographic data.  The Mapping 
Partner shall examine USGS 7.5-minute series topographic maps.  The USGS maps may have a 
5-foot contour interval; if not, they are still often useful as reference or base maps.  
[February 2002]
D.2.2.4	Land Cover 
The land-cover data include information on buildings and vegetation.  Stereoscopic aerial 
photographs can provide the required data on structures and some of the data on vegetation.   The 
Mapping Partner shall ensure that aerial photographs are not more than 5 years old unless they 
can be updated by surveys.  Local, county, or state agencies may have the coastline photographed 
on a periodic basis, and may provide photographs or permission to obtain them from their source.
Aerial photographs can provide the required data on tree- and bush-type vegetation.  However, 
although they are useful in identifying areas of grass-like vegetation, they cannot identify specific 
types.  National Wetland Inventory maps from the U.S. Fish and Wildlife Service and color 
infrared aerial photographs can provide some more specific data required for marsh plants.  
Ground-level photographs are also useful in providing information on plants.  State offices of 
coastal zone management, park and wildlife management, and/or natural resources should be 
able to provide information. The Mapping Partner also may contact local universities with 
coastal studies and/or Sea Grant programs.  The Mapping Partner may conduct field surveys in 
lieu of the above sources, but are more cost effective when used only to supplement or verify 
data obtained from these sources.  
[February 2002]
D.2.2.5	Bathymetry
The Mapping Partner may acquire bathymetric data from National Ocean Service nautical charts, 
although any reliable source may be used.  The bathymetry must extend far enough offshore to 
include the breaker location for the 1-percent-annual-chance flood; although that depth may not 
be exactly known during the data collection phase, the Mapping Partner may assume that a mean 
water depth of 40 feet will encompass all typical breaker depths.  Bathymetry further offshore 
also may be useful in interpreting likely differences between nearshore and offshore wave 
conditions and necessary where offshore waves are more readily specified.  
[February 2002]
D.2.2.6	Storm Meteorology
The 1-percent-annual-chance flood elevations represent a statistical summary and likely do not 
correspond exactly to any particular storm event.  However, the meteorology of storms expected 
to provide approximate realizations of the 1-percent-annual-chance flood can be useful 
information in deciding recurrence intervals for historical events and in assessing wave 
characteristics likely associated with the 1-percent-annual-chance flood.  An important 
distinction of the flood source from Delaware to Maine is whether the 1-percent-annual-chance 
flood is more likely to be caused by a hurricane or by a Northeaster.  The Mapping Partner shall 
establish this distinction in the course of defining the SWELs, because time history of water 
levels can be radically different in the two possible cases (see Figure D-2).  
For a Northeaster, commonly a winter storm occurring between October and March, sustained 
winds seldom reach much above 60 mph, storm surge has relatively modest magnitude, and surge 
coincidence with spring high tides is usually required to attain the 1-percent-annual-chance 
SWEL.  Extreme storms that occurred with lower tides can indicate wind and wave conditions 
also likely to accompany the 1-percent-annual-chance flood.  Thus, the Mapping Partner can 
assemble a fair amount of pertinent historical evidence regarding expected meteorological 
conditions for the 1-percent-annual-chance flood arising from an extratropical storm.  The 
dominant conditions include speed and duration of sustained winds, along with the storm size 
controlling fetch along which waves may be generated.  
Where hurricanes are of primary importance, the 1-percent-annual-chance flood is likely 
associated with central pressure deficits having exceedance probabilities between 5 and 10 
percent (FEMA, August 1988).  That description generally corresponds to a major hurricane, 
where sustained winds exceed 120 mph.  Other meteorological characteristics are likely to be 
fairly typical for the study area and may be determined using the hurricane climatology 
documented in Hurricane Climatology for the Atlantic and Gulf Coasts of the United States (Ho, 
Su, Hanevich, Smith, & Richards, 1987).  That guidance includes localized probabilities for 
central pressure deficit, radius to maximum winds, and speed and direction of storm motion.


 


[February 2002]
D.2.2.7	Storm Wave Characteristics
The basic presumption in conducting coastal wave analyses is that wave direction must have 
some onshore component, so that wave hazards occur coincidentally with the 1-percent-annual-
chance flood.  That presumption appears generally appropriate for open coasts and along many 
mainland shores of large bays, where the 1-percent-annual-chance SWEL must include some 
contribution from direct storm surge and thus requires an onshore wind component.  However, an 
assumption of onshore waves coincident with a flood may require detailed justification along the 
shores of connecting channels, in complex embayments, near inlets, and behind protective 
islands.  Once it is confirmed that sizable waves likely travel onshore at a site during the 1-
percent-annual-chance flood, the storm wave condition must be defined for assessments of 
coastal structure stability, sand dune erosion, wave runup and overtopping, and overland 
elevations of wave crests.  
It is important to recognize that somewhat different descriptions of storm waves (Table D-2) can 
be appropriate in assessing each distinct flooding effect.  This depends mainly on the formulation 
of an applicable empirical or analytical treatment for each effect.  In FIS models and analyses, the 
different wave descriptions include the following:  
*	Various wave statistics (e.g., mean wave condition for runup elevations, but an extreme or 
controlling height for overland waves); 
*	Various dominant parameters (e.g., incident wave height for overtopping computation, but 
incident wave period for overland crest elevations); and 
*	Various specification sites (e.g., deep water for estimating runup elevations, but waves 
actually reaching a structure in shallow water for most stability or overtopping 
considerations). 
To proceed with general orientation, the Mapping Partner may develop storm wave conditions 
from actual wave measurements, from wave hindcasts or numerical computations based on 
historical effects, and from specific calculations based on assumed storm meteorology.  Where 
possible, the Mapping Partner shall pursue two or all three of these possibilities in estimating 
wave conditions expected to accompany the 1-percent-annual-chance flood at a study site.  Using 
all available information can improve the level of certainty in estimated storm wave 
characteristics. 
Wave measurements for many sites over various intervals have been reported primarily by the 
USACE and by the National Data Buoy Center.  Available data include records from nearshore 
gages in relatively shallow water (Thompson, 1977) and from sites further offshore in moderate 
water depths (Gilhousen, Meindl, Changery, Franks, Burgin, & McKittrick, 1990).  The potential 
sources of storm wave data also include other Federal agencies and some State or university 
programs.  


Table D-2.  Some Commonly Used Specifications of Irregular Storm Waves
SYMBOL
NAME
DESCRIPTION
Wave Heights (water depth must be given)
Hs
Significant
average over highest one-third of waves
Hc
Controlling
defined as (1.6 Hs) in NAS (1977)
 
Mean
average over all waves
Hmo
zero moment
defined by the variance of water surface, and about 
equal to Hs in deep water
Wave Periods (basically invariant with water depth)
Ts
significant
associated with waves at significant height
Tp
peak
represents the maximum in energy spectrum
 
mean
average over all waves

The USACE is the primary source for long-term wave hindcasts along open coasts.  That 
information is conveniently summarized as extreme wave conditions expected to recur at various 
intervals, for Atlantic hurricanes in Hurricane Hindcast Methodology and Wave Statistics for 
Atlantic and Gulf Hurricanes from 1956-1975 (Abel, Tracy, Vincent, & Jensen, 1989) and for 
extratropical storms in Hindcast Wave Information for the U.S. Atlantic Coast (Hubertz, Brooks, 
Brandon, & Tracy, 1993) and Southern California Hindcast Wave Information (Jensen, Hubertz, 
Thompson, Reinhard, Borup, Brandon, Payne, Brooks, & McAneny, 1992), as examples.  In 
some vicinities, other wave hindcasts may be available from the design activities for major 
coastal engineering projects.  
Either measurements or hindcast results pertain to some specific (average) water depth.  
However, the Mapping Partner may need to convert such wave information into an equivalent 
condition at some other water depth for appropriate treatment of flood effects.  The Mapping 
Partner shall consult the following publications for guidance regarding transformation of storm 
waves between offshore and nearshore regions, where processes to be considered include wave 
refraction, shoaling, and dissipation: the USACE Shore Protection Manual (USACE, 1984), 
Random Seas and Design of Maritime Structures (Goda, 1985), and Automated Coastal 
Engineering System, Version 1.07 (Leenknecht, Szuwalski, & Sherlock, 1992). 
The Mapping Partner may also consider determining local storm wave conditions by developing 
a specific estimate for storm meteorology taken to correspond to the 1-percent-annual-chance 
flood.  That can be done with relative ease for deep-water waves associated with a hurricane of 
specified meteorology, using the estimation technique provided in the USACE Shore Protection 
Manual (USACE, 1984).  For extratropical storms, the ACES program in Automated Coastal 
Engineering System, Version 1.07 (Leenknecht et al., September 1992) executes a modern 
method of wave estimation for specified water depth, incorporating some basic guidance from 
the Shore Protection Manual (USACE, 1984) and Random Seas and Design of Maritime 
Structures (Goda, 1985). The Mapping Partner may prepare an outline of important 
considerations to assist in developing a site-specific wave estimate.  
Major factors in wave generation are windspeed, wind duration, water depth, and fetch length. 
Fetch length is he over-water distance toward the wind along which waves arise (USACE, 1994).  
These factors determine flux of momentum and energy from the atmosphere into waves on the 
water surface.  For some cases, fetch length might be estimated as straight-line distance in the 
wind direction, but the current ACES guidance pertinent to many partially sheltered coastal sites 
indicates that a more involved analysis of restricted fetches must be performed for water basins 
of relatively complex geometry.  The effective fetch length is derived as a weighted average of 
over-water distance with angle from the wind direction.  With specified geometry for a restricted 
fetch, the ACES program carries out computations necessary for the desired estimates of 
representative wave height and wave period (Leenknecht et al., 1992).  
The resulting wave field is commonly summarized by the significant wave height and wave 
period; namely, average height of the highest one-third of waves and the corresponding time for a 
wave of that height to pass a point.  Another useful measure is wave steepness, the ratio of wave 
height to wavelength: in deep water, the wavelength is 0.16 times the gravitational acceleration, 
times the wave period squared, that is, (gT2/2?).  On larger water bodies and in relatively deep 
water, typical wave steepness is approximately 0.03 for extreme extratropical storms and 0.04 for 
major hurricanes.  The Mapping Partner may use these values for wave steepness to determine 
the wave period if only the wave height is known, and the wave height if only the wave period is 
known.
[February 2002]
D.2.2.8	Coastal Structures
The Mapping Partner shall obtain documentation for each coastal structure possibly providing 
protection from 1-percent-annual-chance flood.  That documentation shall include the following:
*	Type and basic layout of structure;
*	Dominant site particulars,(e.g., local water depth, structure crest elevation, ice climate);
*	Construction materials and present integrity;
*	Historical record for structure, including construction date, maintenance plan, responsible 
party, repairs after storm episodes; and.  
*	Clear indications of effectiveness or ineffectiveness.  
The Mapping Partner shall develop much of this information through office activity, including a 
careful review of aerial photographs.  In some cases of major coastal structures, site inspection 
would be advisable to confirm preliminary judgments.  
[February 2002]
D.2.2.9	Historical Floods
While not required as input to any of the FEMA coastal models, local information regarding 
previous storms and flooding can be very valuable in developing accurate assessments of coastal 
flood hazards and validation of storm surge models.  General descriptions of flooding are useful 
in determining what areas are subject to flooding and in obtaining an understanding of flooding 
patterns.  More specific information, such as the location of buildings flooded and damaged by 
wave action, can be used to verify the results of the coastal analyses.  Detailed information on 
pre- and post-storm beach or dune profiles is valuable in checking the results of the erosion 
assessment. 
When quantitative data are available on historical flooding effects, the Mapping Partner shall 
make a special effort to acquire all recorded water elevations and wave conditions for the 
vicinity.  That information can be used in estimating recurrence intervals for SWELs and for 
wave action in the event, assisting an appropriate comparison to the 1-percent-annual-chance 
flood.  
Local, county, and state agencies are usually good sources of historical data, especially more 
recent events.  It is becoming common practice for these agencies to record significant flooding 
with photographs, maps, and/or surveys.  Some Federal agencies (e.g., the USACE, USGS, and 
National Research Council) prepare post-storm reports for more severe storms.  Local libraries 
and historical societies may also be able to provide useful data.  
[February 2002]
D.2.3	Evaluation of Coastal Structures
The purpose of the evaluation is to determine whether each individual coastal structure appears 
properly designed and maintained in order to provide protection from the 1-percent-annual-
chance flood.  If a particular structure can be expected to be stable through the 1-percent-annual-
chance flood, the structure geometry may figure in all ensuing analyses of wave effects 
accompanying the flood: coastal erosion, runup and overtopping, and wave crest elevations.  
Otherwise, the coastal structure is considered to be destroyed during the 1-percent-annual-chance 
flood and removed from the transect representation before proceeding with analyses of wave 
effects.  
Criteria for Evaluating Coastal Flood-Protection Structures presents a technical review and 
recommends procedural criteria for evaluating coastal flood protection structures in regard to the 
1-percent-annual-chance flood (Walton, Ahrens, Truitt, & Dean, 1989).  The FEMA 
"Memorandum on Criteria for Evaluating Coastal Flood Protection Structures for National Flood 
Insurance Program Purposes" includes an account of the evaluation process (FEMA, 1990).  
FEMA has adopted that memorandum as the basis for NFIP accreditation of new or proposed 
coastal structures in reducing effective flood hazard areas and elevations.  Ideally, these 
evaluation criteria could be applied to existing coastal structures, but available information about 
older structures typically is not sufficient to complete the detailed evaluation.  Where complete 
information is not available for an existing structure, the Mapping Partner shall make an 
engineering judgment about its likely stability based on a visual inspection of physical conditions 
and any historical evidence of storm damage and maintenance.  
Criteria for Evaluating Coastal Flood-Protection Structures addressed coastal flood protection 
structures and identified the four primary types according to a functional standpoint: gravity 
seawalls, pile-supported seawalls, anchored bulkheads, and dikes or levees.  The report 
recommends as a general policy that "FEMA not consider anchored bulkheads for flood-
protection credit because of extensive failures of anchored bulkheads during large storms" 
(Walton et al., 1989, p. 100).
Flood protection structures can have a significant effect on the flood hazard information shown 
on a FIRM, perhaps directly justifying the removal of sizable areas from the coastal high hazard 
area.  The focus on flood protection structures in the FEMA memorandum cited above should not 
divert a recognition that similar considerations are appropriate in crediting the protection 
provided by structures in categories other than those named in the memorandum, and that such 
credit can be important.  In contrast to flood protection, a breakwater primarily may act to limit 
wave action and a revetment primarily may control shore erosion, but any stable coastal structure 
can notably affect results of various hazard analyses for the 1-percent-annual-chance flood, and 
the Mapping Partner shall take these effects into account.  The FEMA memorandum places the 
responsibility on local interests to certify new structures, but the primary consideration in an FIS 
must be that the structure evaluation yields a correct judgment based on available evidence.  This 
is necessary for accurate hazard assessments, because a structure might decrease flood effects in 
one area while increasing erosion and wave hazards at adjacent sites.  Of course, the greater the 
potential effects of a coastal structure, the more detailed should be the evaluation process.  
In areas where buildings conforming to V-Zone construction standards are elevated above the 
wave crest elevation, the Mapping Partner shall model the piles supporting the structure as 
obstructions in the wave height analysis.  The building itself, being elevated, shall not be 
modeled as an obstruction to wave propagation.  
[February 2002]
D.2.4	Erosion Assessment
Coastal sand dunes usually extend above the 1-percent-annual-chance SWEL, but such barriers 
to flooding may not be durable because of massive shorefront erosion occurring during a 1-
percent-annual-chance flood.  Storm-induced erosion will remove or significantly modify most 
frontal dunes on U.S. coasts.  This is particularly true on barrier islands known historically to be 
susceptible to storm overwash.  Therefore, the Mapping Partner shall assess coastal erosion 
before determining wave elevations and mapping V Zones for the 1-percent-annual-chance flood.  
Available procedures for computing erosion show limited precision in documented hindcasts of 
recorded erosion quantities and have questionable pertinence to the entire range of erosion effects 
possible on U.S. coasts.  Therefore, a rather schematic treatment of expected erosion quantities 
and geometries has been developed as an appropriate approach for treating erosion in FISs.  The 
overall rationale and level of detail in these erosion assessment procedures closely parallel the 
simple and effective NAS methodology for calculating wave action effects associated with storm 
surges (NAS, 1977).  
The procedures described here are empirically valid for treating dune erosion during the 1-
percent-annual-chance flood.  These procedures are meant to give schematic estimates of eroded 
profile geometry suitable for FEMA flood study purposes.  The simplified estimates are suitable 
erosion approximations for extreme storms at sandy sites with typical open-coast wave and flood 
climate.  The erosion assessment procedures that follow are intended for application to natural 
sites where there are no coastal structures such as breakwaters, groins, or revetments.  Scour in 
front of certified structures can account for eroded sand quantities and an adjustment of the shore 
profile.  
Quantitative considerations here are based on measured sand erosion accompanying extreme 
floods from hurricanes or extratropical storms on the U.S. Atlantic and Gulf coasts (FEMA, 
November 1988).  For the study site, the Mapping Partner may use storm meteorology along with 
associated flood and wave characteristics to assess whether such open-coast effects can be typical 
of anticipated local erosion for the 1-percent-annual-chance flood.  Of course, the Mapping 
Partner shall examine any local historical evidence on storm erosion in deciding applicability of 
the procedures below.  
[February 2002]
D.2.4.1	Basic Erosion Considerations
The primary factor controlling the basic type of dune erosion is the pre-storm cross section lying 
above the 1-percent-annual-chance SWEL (frontal dune reservoir).  The Mapping Partner shall 
determine this area to assess the stability of the dune as a barrier.  If the elevated dune cross-
sectional area is very large, erosion will result in retreat of the seaward duneface with the dune 
remnant remaining as a surge and wave barrier.  On the other hand, if the dune cross-sectional 
area is relatively small, erosion will remove the pre-storm dune leaving a low, gently sloping 
profile.  Different treatments for erosion are required for these two distinct situations because no 
available model of dune erosion suffices for the entire range of coastal situations.  
Figure D-3 introduces terminology for two representative dune types.  A frontal dune is a ridge or 
mound of unconsolidated sandy soil, extending continuously alongshore landward of the sand 
beach.  The dune is defined by relatively steep slopes abutting markedly flatter and lower regions 
on each side.  For example, a barrier island dune has inland flats on the landward side, and the 
beach or back beach berm on the seaward side.  The dune toe is a crucial feature and can be 
located as the junction between gentle slope seaward and a slope of 1:10 or steeper marking the 
front duneface.  The rear shoulder, as shown on the mound-type dune in Figure D-3, is defined 
by the upper limit of the steep slope on the dune's landward side.
The rear shoulder of mound-type dunes corresponds to the peak of ridge-type dunes.  Once 
erosion reaches those points, the remainder of the dune offers greatly lessened resistance and is 
highly susceptible to rapid and complete removal during a storm.  Figure D-3 shows the location 
of the "frontal dune reservoir," above 1-percent-annual-chance SWEL and seaward of the dune 
 



 peak or rear shoulder. The amount of frontal dune reservoir determines dune integrity under 
storm-induced erosion.  
To prevent dune removal during the 1-percent-annual-chance storm, the frontal dune reservoir 
must typically have a cross-sectional area of at least 540 square feet (or 20 cubic yards volume 
per foot along the shore) (FEMA, September 1986; FEMA, November 1988).  For more massive 
dunes, erosion will result in duneface retreat, with an escarpment formed on the seaward side of 
the remaining dune.  To compute the eroded profile in such cases, FEMA has adopted a 
simplified version of the dune retreat model developed by Delft Hydraulics Laboratory of the 
Netherlands.  This treatment is also appropriate in cases with sandy bluffs or headlands extending 
above the 1-percent-annual-chance SWEL.  The simplified treatment of duneface retreat is 
described in Subsection D.2.4.3.  
If a dune has a frontal dune reservoir less than 540 square feet, storm-induced erosion can be 
expected to obliterate the existing dune with sand transported both landward and seaward.  The 
Mapping Partner shall estimate the eroded profile using procedures presented in Subsection 
D.2.4.2.  Those procedures provide a realistic eroded profile across the original dune, but do not 
determine detailed sand redistribution by dune erosion, overwash, and breaching.  
Quantitative treatment of overwash processes is not feasible at present (Birkemeier, Kraus, 
Scheffner, & Knowles, June 1987), so the frontal dune is simply removed.  
The initial decision in treating erosion as duneface retreat or as dune removal is based entirely on 
the size of the frontal dune reservoir.  For coastal profiles more complicated than those in Figure 
D-3, the Mapping Partner shall use judgment to separate the sand reservoir expected to be 
effective in resisting dune removal from the landward portion of the pre-storm dune.  The 
Mapping Partner shall complete the erosion assessment for the shoreline conditions 
representative of either the summertime shore profile for hurricane effects or the wintertime 
shore profile for Northeaster storm effects, whichever is the appropriate and predominant source 
of coastal flooding that has been selected for use in the coastal hydraulic analyses and erosion 
assessment.
Figure D-4 presents a complete flowchart of necessary erosion considerations, outlining the 
major alternatives of duneface retreat and dune removal.  Figure D-5 provides schematic sketches 
of the different geometries of dune erosion arising in coastal flood hazard assessments.  


 
Figure D-4.  Flowchart of Erosion Assessment for a Coastal Flood Insurance Study


 


One additional factor complicating erosion assessment is the dissipative effect of wide sand 
beaches that shelter dunes from the full storm impact and retard retreat or removal.  If the 
existing slope between mean level and the 1-percent-annual-chance SWEL is 1:50 or gentler, 
overestimation of erosion is possible during the 1-percent-annual-chance flood; therefore, the 
Mapping Partner shall examine this carefully.  This effect and other variables, such as sand size, 
dune vegetation, and actual storm characteristics at a specific site, make thorough comparison of 
estimated erosion to documented historical effects in extreme storms necessary.  
[February 2002]
D.2.4.2	Treatment of Dune Removal
Determining the dune reservoir requires assessing the profile area located above the 1-percent-
annual-chance flood level and seaward of the crest of the primary dune (see Figure D-3).  Where 
the frontal dune reservoir is less than 540 square feet, construction of the eroded profile is 
extremely simple:  dune removal is effected by means of a seaward-dipping slope of 1:50 running 
through the dune toe.  The eroded profile is taken to be that slope across the pre-storm dune, 
simply spliced onto the flanking segments of a given transect.  This gives a gentle ramp across 
the extended storm surf zone adequate as a first approximation to the profile existing at the 
storm's peak.  This treatment simply removes the major vertical projection of the frontal dune 
from the transect.  
Construction of an eroded profile focuses on the usually distinct feature termed the dune toe.  
The dune toe is taken to be the junction between the relatively steep slope of the front duneface 
and the notably flatter seaward region of the beach or the backbeach berm (including any minor 
foredunes).  If a clear slope break is not apparent on a given coastal transect, its location should 
be taken at the typical elevation of definite dune toes on nearby transects within the study region.  
The alternative is to set the dune toe at the 10-percent-annual-chance SWEL in the vicinity: that 
appears to be a generally adequate approximation along the Atlantic and Gulf coasts.  In every 
case, the dune toe must be taken at an elevation above that of any beach berms on local shores.  
Figures D-6, D-7, and D-8 display examples of this treatment for a removed dune. These simple 
constructions give appropriate estimates for the limits of high ground removed during the 1-
percent-annual-chance flood, but cannot provide accurate representations of eroded profiles 
because of the complicated processes of dune failure.  One example of overly simplified results 
is that deeper scour appears to occur where the frontal dune reservoir is relatively large.  
The present viewpoint is consistent with this basic description of storm-induced erosion:  greater 
erosion occurs where the pre-storm barrier provides more resistance; that is, has a relatively large 
cross section but still is removed during the 1-percent-annual-chance flood.  Net shore erosion 
appears to be maximum for situations where the dune barrier apparently just failed, and the 
eroded cross section can be much greater than in cases of duneface retreat.  A slight opening to 
landward flow as an eroded dune becomes an overwash channel can result in much deeper scour 
than in cases of duneface retreat, where most shore erosion is above the SWEL as duneface sand 
is continuously deposited in shallow water during the storm.  


 
Figure D-6. Quantitative Example of Dune Removal Treatment for Alabama Profile 
Eroded by 1979 Hurricane Frederic.  Situation Is Profile B-35 in Baldwin County, 
Alabama


 

Figure D-7.  Case of Relatively Large Dune Removed by 1979 Hurricane Frederic in 
Baldwin County, Alabama


 
Figure D-8.  Erosion of Relatively Low Profile by 1957 Hurricane Audrey in Cameron 
Parish, Louisiana
[February 2002]
D.2.4.3	Treatment of Duneface Retreat
The procedure described here yields an eroded profile for duneface retreat in the 1-percent-
annual-chance flood, for cases where the frontal dune reservoir is at least 540 square feet.  
During such retreat, the frontal dune barrier remains basically intact and eroded sand is 
transported in the seaward direction.  The post-storm profile provides a balance between sand 
eroded from the duneface and sand deposited at lower elevations seaward of the dune.  
The following procedure for constructing the eroded profile constitutes a simplification of the 
dune retreat model developed by Delft Hydraulics Laboratory (DHL) of the Netherlands 
(Vellinga, 1986).  Erosion above 1-percent-annual-chance SWEL is fixed at 540 square feet, to 
guarantee an appropriate amount for the U.S. Atlantic and Gulf coasts (FEMA, 1986 and 
November 1988).  (In the DHL model, erosion is determined as the variable depending on 
specified storm and site conditions.)  
Figure D-9 summarizes the simple procedure adopted to treat cases of duneface retreat.  The 
eroded profile consists of three planar slopes:  uppermost is a retreated duneface slope of 1:1, 
joining an extensive middle slope of 1:40, which is terminated by a brief segment with a slope of 
1:12.5 at the limit to storm deposition.  Upper dune erosion is specified to be 540 square feet 
above the 1-percent-annual-chance SWEL and in front of the 1:1 slope.  Geometrical 
construction balances the nearshore deposition with the total dune erosion of somewhat more 
than 540 square feet by an appropriate seaward extension of the 1:40 slope.  The resulting eroded 
profile is spliced onto the unchanged landward and seaward portions of the pre-storm profile.  
This procedure gives a complete profile suitable for use with the Wave Runup Model in 
assessing an appropriate flood elevation on the dune remnant.  


 

Figure D-9.  Procedure Giving Eroded Profile in Cases of Duneface Retreat, and 
Simplification of Dune Retreat Model Developed by Delft Hydraulics Laboratory of the 
Netherlands)

Figure D-10 presents an example of duneface retreat according to the present procedure.  This 
simple construction of a retreated dune profile gives appropriate eroded slopes important to the 
wave runup analysis of the remaining barrier.  For this example, estimated erosion and deposition 
do not match well with those recorded, because there is a net sand loss shown on this profile and 
the event appears somewhat less extreme than a 1-percent-annual-chance flood (judging from 
reported characteristics of Hurricane Eloise).  Where historical data on duneface retreat are 
available for comparison, agreement of estimated erosion slopes with those recorded should be 
considered of primary importance in verifying the present treatment.  Actual quantities of dune 
erosion are subject to large variations in natural situations, and this procedure presumes a 
generally representative value for 1-percent-annual-chance flood conditions.  
The Mapping Partner shall apply the basic procedure illustrated in Figure D-9 in estimating 
erosion of high open-coast headlands or bluffs of sandy material.  
This modification to the DHL model eliminates potential problems associated with computation 
sensitivity to storm wave height and with uncertain capabilities for situations dissimilar to the 
Netherlands coast (Birkemeier et al., 1987; FEMA, November 1988).  The other modifications of 
the model and treatment of duneface retreat have been implemented in an attempt to simplify the 
treatment by ignoring the variation of sand size and approximating the planar slope to the curved 
segment of the DHL post-storm profile.
In such cases, parallel retreat of the existing face slope should be presumed, rather than using the 
typical 1:1 slope for the escarpment on an eroded sand dune, because that existing slope reflects 
actual consolidation properties of the headland or bluff material.  
[February 2002]
D.2.4.4	Finalizing Erosion Assessment
Based on measured erosion along the Atlantic and Gulf coasts, the demarcation between 
duneface retreat and dune removal in a 1-percent-annual-chance flood has been set at a frontal 
dune reservoir of 540 square feet (FEMA, 1986 and November 1988).  This quantitative criterion 
might appear too precisely stated, in view of potential inaccuracies in available dune topography, 
possible complications in delineating the effective frontal dune reservoir, and documented 
variability of dune erosion during extreme storms.  In fact, the likelihood of duneface retreat or 
dune removal cannot be assessed with full certainty, so that validating the present erosion 
assessment by means of available evidence for a specific site is advisable.  
At many sites, some historical evidence may be available regarding the extent of flooding, 
erosion, and damage in an extreme event comparable to the local 1-percent-annual-chance flood.  
Then the erosion treatment giving results more consistent with historical records must be selected 
as appropriate.  That choice may be relatively clear-cut, given potential differences in expected 
erosion and inland flood penetration for duneface retreat versus dune removal.  Where available 
historical evidence is not definitive, the decision between retreat and removal on a given transect 
should be based solely on size of the frontal dune reservoir.  Present procedures for erosion 
assessment are highly simplified, but provide an unbiased estimation and a level of detail 
appropriate to coastal FISs.
[February 2002]



D.2.4.5	Wave Overtopping for Cases of Duneface Retreat
Where the erosion assessment indicates duneface retreat, an eroded dune remnant persists as an 
appreciable barrier to the 1-percent-annual-chance flood.  However, storm wave action can result 
in occasional extreme runups overtopping that barrier, yielding floodwaters running off or 
ponding landward of the dune.  DHL has determined the mean overtopping rate with storm 
waves incident on a typical duneface retreat geometry determined by the DHL (1983) to be  
	 .	(1)
Here the overtopping rate  1 has units of cubic feet per second per foot alongshore (cfs/ft), and 
F is maximum height (in feet) of the dune remnant above SWEL.  


  
Figure D-10.  Example of  Duneface Retreat Treated by Simplified version of D.H.L. model, 
with erosion Above SWEL Fixed at 540 Square Feet.  Situation Is Profile R-105 in Walton 
County, Florida, Surveyed Before and After 1975 Hurricane Eloise



This result was measured in DHL tests scaled to reproduce a specific extratropical storm on the 
Dutch seacoast, with a significant deep-water wave height of 25 feet and a peak wave period of 
12 seconds.  Those wave conditions seem roughly representative for the 1-percent-annual-chance 
flood along U.S. seacoasts, although expected wave characteristics will differ between hurricanes 
and extratropical storms at various sites.  Recorded rates of overtopping can show sizable 
departures from the expected mean even with steady flood conditions (Goda, 1985; Owen, 1980).  
Despite uncertainties about actual overtopping rates for a dune remnant, the equation gives a 
useful basis for outlining expected effects.  The order of magnitude for severe overtopping may 
be taken as 1 cfs/ft, past allowable thresholds for structural integrity with bare soil behind steep 
barriers exposed to storm waves (Goda, 1985).  From Equation 1,  2 of  approximately 1 cfs/ft 
corresponds to F of approximately 7 feet, so retreated remnants with less relief above the 1-
percent-annual-chance SWEL certainly require consideration of possible flood hazards landward 
of the dune.  Appropriate treatments for ponding or runoff behind barriers are outlined in 
Subsection D.2.6.  
[February 2002]
D.2.5	Wave Runup, Setup, and Overtopping
Wave runup is the uprush of water from wave action on a shore barrier intercepting stillwater 
level.  The water wedge generally thins and slows during its excursion up the barrier, as residual 
forward momentum in wave motion near the shore is fully dissipated or reflected.  The notable 
characteristic of this process for present purposes is the wave runup elevation, the vertical height 
above stillwater level ultimately attained by the extremity of uprushing water.  Wave runup at a 
shore barrier can provide flood hazards above and beyond those from stillwater inundation and 
incident wave geometry, as illustrated in Figure D-11.  
Two additional phenomena, wave setup and wave overtopping, may require explicit 
consideration for adequate treatment of the coastal flood hazards linked to wave runup.  Wave 
setup generates a mean water surface elevated above the SWFL, caused by accumulation of water 
against a barrier exposed to wave heights attenuating in shallow water.  Wave overtopping 
consists of any wave-induced flow passing over the barrier crest, so that flood water may exhibit 
wave, sheet flow, or ponding characteristics over an inland area.  These phenomena and their 
quantitative evaluation will be addressed later in this Appendix.  
The extent of runup can vary greatly from wave to wave in storm conditions, so that a wide 
distribution of wave runup elevations provides the precise description for a specific situation.  
Current policy for the NFIP is that the mean runup elevation (rather than some occasional 
extreme) for a situation is appropriate in mapping coastal hazards of the 1-percent-annual-chance 
flood. 






[February 2002]
D.2.5.1	Wave Runup Model Description
The current version of the FEMA Wave Runup Model, RUNUP 2.0, may be run either on a 
minicomputer (e.g., DEC VAX 11/750) or on an IBM-compatible personal computer (PC or 
PC/AT).  Given the flood level, shore profile and roughness, and incident wave condition 
described in deep water, the program computes by iteration a wave runup elevation fully 
consistent with the most detailed guidance available (Stoa, 1978).  This determination includes 
an analysis separating the profile into an approach segment next to the steeper shore barrier, and 
interpolation between runup guidance for simple configurations bracketing the specified 
situation.  
Some additional description of the workings of the Wave Runup Model can assist informed 
preparation of input and interpretation of output.  The incorporated guidance gives runup 
elevation as a function of wave condition and barrier slope, for eight basic shore configurations 
distinguished by water depth at the barrier toe, along with the approach geometry.  Where those 
basic geometries do not appropriately match the specified profile, reliance is placed on the 
composite slope method (Saville, 1958); this assumes the input shore profile (composite slope) is 
equivalent to a hypothetical uniform slope, as shown in Figure D-12.  The runup elevations are 
derived from laboratory measurements in uniform wave action, rather than the irregular storm 
waves usually accompanying a flood event.  Runup guidance for uniform waves, however, also 
pertains to the mean runup elevation from irregular wave action with identical mean wave height 
and mean wave period.  Figure D-13 presents an overview of the basic computation procedure 
within RUNUP 2.0.  
Basic empirical guidance incorporated within this computer model generally does not extend to 
vertical or nearly vertical flood barriers.  For such configurations, RUNUP 2.0 usually will 
provide a runup elevation, but the result may be misleading because reliance on the composite-
slope method can yield an underestimate of actual wave runup with the abrupt barrier.  Where a 
vertical wall exists on a transect, the Mapping Partner shall develop a runup estimate using 
specific guidance in Figure D-14, taken from the Shore Protection Manual (USACE, 1984).  As 
within RUNUP 2.0, these empirical results for uniform waves should be utilized by specifying 
mean wave height and mean wave period for entry, and taking the indicated runup as a mean 
value in storm wave action.  Shore configurations with a vertical wall are also addressed 
separately in Subsection D.2.5.7.  
[February 2002]
D.2.5.2	Wave Runup Model Input Preparation
The input to the Wave Runup Model is done by transects.  As specified in Subsection D. 2.2, the 
Mapping Partner shall locate transects along the shoreline.  Because the runup results are very 
sensitive to shore slope or steepness, it is important to have at least one transect for each distinct 
type of shore geometry.  Often, areas with similar shore slopes are located throughout a 
community, and the results of one transect can be applied to all the areas that are similar.  This is 
especially typical of New England communities with rocky bluffs.  When the Wave Runup 
Model is being applied to dune remnants where eroded slopes are fairly uniform, transect 
location is governed by the upland land-cover characteristics, which are major considerations in










in the WHAFIS model.
The ground profile for the transect is plotted from the topography and bathymetry after the data 
have been referenced to the National Geodetic Vertical Datum (NGVD).  The profile must 
extend from an elevation below the breaker depth to an elevation above the limit of runup or to 
the maximum ground elevation.  An adequate vertical extent for the transect description will 
usually be 1.5 times the wave height above and below the SWEL.  If the landward profile does 
not extend above the computed runup (30 feet NGVD is commonly a maximum), it will be 
assumed that the last positive slope segment continues indefinitely.  This is very common with 
low barriers, so the Mapping Partner shall select the last slope carefully so it is representative.  
To complete the description, each slope segment of the profile will need a roughness coefficient, 
with some common values presented in Table D-3.  The roughness coefficient must be between 
zero (maximum roughness) and one (hydraulically smooth), and values for slope segments above 
the SWFL control the estimated runup.  The roughness coefficient (r) is used as a multiplier for 
runup magnitude (R) defined on a smooth barrier to estimate wave runup with a rough barrier.  
Table D-3.  Values for Roughness Coefficient in Wave Runup Computations
ROUGHNESS
COEFFICIENT
DESCRIPTION OF BARRIER SURFACE
1.00
Sand; smooth rock, concrete, asphalt, wood, fiberglass
0.95
Tightly set paving blocks with little relief
0.90
Turf, closely set stones, slabs, blocks
0.85
Paving blocks with sizable permeability or relief
0.80
Steps; one stone layer over impermeable base; stones set in cement
0.70
Coarse gravel; gabions filled with stone
0.65
Rounded stones, or stones over impermeable base
0.60
Randomly placed stones, two thick on permeable base; common rip-rap installations
0.50
Cast-concrete armor units:  cubes, dolos, quadripods, tetrapods, tribars, etc.  

Transects are approximated by the minimum adequate number of linear segments, up to a limit of 
20.  Segments may be horizontal, or higher at the landward end; portions with opposite 
inclination should be represented as horizontal when developing the transect approximation.  
Using many linear segments to represent a transect can be wasted effort, because the Wave 
Runup Model may combine adjacent segments in defining the appropriate approach and barrier 
extents.  With the runup computation procedure, the Mapping Partner shall apply engineering 
judgment to transect representation to assist in obtaining the most valid estimate of wave runup 
elevation.  
The input transect must reflect wave-induced modifications expected during the 1-percent-
annual-chance event, including erosion on sandy shores with dunes.  The Mapping Partner shall 
represent only coastal structures expected to remain intact throughout the 1-percent-annual-
chance event on a specific transect.  Besides the transect specification, other required input data 
for the Wave Runup Model are the 1-percent-annual-chance SWEL  and the incident mean wave 
condition described in deep water.  The specified SWEL should exclude any contributions from 
wind-wave effects.  If available elevations include wave setup, the Mapping Partner shall remove 
that component before using this model so that calculated runup elevations do not indicate a 
doubled wave setup.  Basic empirical guidance relates runup at a barrier to the water level in the 
absence of wave action and thus includes the wave setup component.  
The mean wave condition to be specified for valid results with the Wave Runup Model may be 
derived from other common wave descriptions by simple relationships.  Wave heights in deep 
water generally conform to a Rayleigh probability distribution, so that mean wave height equals 
0.626 times either the significant height based on the highest one-third of waves or the zero-
moment height derived from the wave energy spectrum.  No exact correspondence between 
period measures exists; but, mean wave period usually can be approximated as 0.85 times the 
significant wave period or the period of peak energy in the wave spectrum.  
Table D-4 lists a series of wave height and period combinations, of which one should be fairly 
suitable for runup computations at fully exposed coastal sites (depending on the local storm 
climate).  These mean wave conditions have wave steepness values typical of U.S. hurricanes or 
within 30 percent of a fully arisen sea for extratropical storms.  Commonly, the Mapping Partner 
may have some difficulty in specifying a precise wave condition as accompanying the 1-percent-
annual-chance flood.  In that case, is the Mapping Partner also shall consider  wave heights and 
periods both 5 percent higher and 5 percent lower than that selected (or whatever percentages suit 
the level of uncertainty) and shall run the model with all nine combinations of those values.  The 
average of computed runup values then provides a suitable estimate for mean runup elevation.  A 
wide range in computed runups signals the need for more detailed analysis of expected wave 
conditions or for reconsideration of the transect representation.  


Table D-4.  Appropriate Wave Conditions for Runup Computations Pertaining to 1-
Percent-Annual-Chance Event in Coastal Flood Insurance Studies
MEAN WAVE PERIOD
(SECONDS)
MEAN DEEP WATER WAVE HEIGHT
(FEET)
HURRICANES
8
12
9
15.5
10
19
11
23
12
27.5
EXTRATROPICAL STORMS
11
18
12
21.5
13
25
14
29
15
33.5

[February 2002]
D.2.5.3	Wave Runup Model Operation
The input to the FEMA Wave Runup Model consists of several separate lines specifying an 
individual transect and the hydrodynamic conditions of interest within particular columns.  All 
input information is echoed in an output file, which also includes computed results on wave 
breaking and wave runup.
The input format is outlined in Table D-5.  The first two lines of the input give the Name and Job 
Description, which must be included for each transect.  The next line of input is the Last Slope, 
which contains the cotangent of the shore profile continuing from the most landward point 
provided.  This is followed by the profile points, which define the nearshore profile in 
consecutive order from the most seaward point.  Each line gives the elevation and station of a 
profile point and the roughness coefficient for the segment between that point and the following 
point.  The roughness coefficient on the last profile line is for the continuation defined in the Last 
Slope line.  The number of profile points cannot exceed 20.  The final input is the series of 
hydrodynamic conditions of interest.  Each line here contains the SWEL along with a mean wave 
height in deep water and a mean wave period. 


 
Table D-5.  Description of Five Types of Input Lines for Wave Runup Model
	Name Line
This line is required and must be the first input line.  
	Columns	Contents
	1-2	Blank
	3-28	Client's Name
	29-60	Blank
	61-70	Engineer's Name
	71-80	Job Number
	Job Description Line
	Columns	Contents
	1-2	Blank
	3-76	Project description or run identification
	77-80	Run Number
	Last Slope Line
This line is required and defines the slope immediately landward of the profile actually specified 
in detail.  
	Columns	Contents
	1-4	Slope (horizontal over vertical or cotangent) 
of profile continuation
	5-80	Blank
	Profile Lines
These lines must appear in consecutive order from the most seaward point landward.  Each line 
has the elevation and station of a profile point and the roughness coefficient for the section 
between that point and the following point.  The roughness coefficient on the last profile line is 
for the continuation defined in the Last Slope Line.  The Mapping Partner shall ensure that at 
least one profile point with a ground elevation greater than the SWEL is specified.  The number 
of Profile Lines cannot exceed 20.  
	Columns	Contents
	1	Last point flag.  The most landward point on 
the profile is indicated by a 1.  If not the last 
point, leave blank.  
	2	Blank
	3-7	Elevation with respect to NGVD, in feet
	8	Blank
				9-14									Horizontal distance.  It is common to assign 	
														the shoreline (elevation 0.0) as Point 0 with 	
														seaward distances being negative and 			
														landward distances positive. 
	15	Blank


Table D-5.  Description of Five Types of Input Lines for Wave Runup Model (Cont'd).
	
	Columns	Contents 
	16-20	Roughness coefficient in decimal form 
between 0.00 (most rough) and 1.00 
(smooth). 
	21-80	Blank
	Water Level and Wave Parameter Lines
These lines specify hydrodynamic conditions for runup calculations on each profile.  Namely, 1-
percent-annual-chance SWEL along with mean wave height and period for deep water.  
Typically, SWEL remains constant for a given profile, while the selected wave conditions closely 
bracket that expected to accompany the 1-percent-annual-chance flood.  A maximum of 50 of 
these lines can be input for each profile.  
	Columns	Contents
	1	Last line, new transect flag.  A 1 indicates the 
last line for a given transect and notifies that 
another transect is following.  If not the last 
line, or if the last line of the last transect, 
leave blank.  
	2-6	SWEL with respect to NGVD, in feet.
	7	Blank
	8-12	Deepwater mean wave height,  3o, in feet, 
greater than 1 foot
	13	Blank
	14-18	Mean wave period,  4, in seconds
	19-80	Blank
The output as shown in Table D-6 has two parts.  The first page is a printout of the transect listed 
as a numbered set of profile points, cotangents (slopes) of the segments, and the roughness 
coefficient for each segment.  The second page is the output table of computed results for each 
set of conditions: the values of runup elevation and breaker depth, each with respect to the 
specified SWEL, along with an identification of the segment numbers giving the seaward limit to 
wave breaking and the landward limit to mean wave runup. 
[February 2002] 
D.2.5.4	Wave Runup Model Output Messages
Several output messages alert the user to specific problems encountered in running the program.  
All but the last three indicate that the program has stopped execution without completing runup 
calculations.  
*	"NEGATIVE RUN PARAMETER, PROGRAM STOPS"
	An input value of wave height or wave period is read as negative or zero.  Check that the 
input has been entered in the correct columns.  
*	"MORE THAN 20 POINTS IN PROFILE, PROGRAM STOPS"
	The program accepts a maximum input of 20 points defining the nearshore profile.  This 
encourages a profile approximation that is not overly detailed, because each transect is to 
represent an extensive area.  
*	"**** Ho/Lo LESS THAN 0.002 ****" or 
	"**** Ho/Lo GREATER THAN 0.07 ****"
	These limits on wave steepness pertain to the extent of incorporated guidance on breaker 
location.  They should be adequate to include appropriate mean wave conditions for extreme 
events and also conform to the usual limits in detailed guidance on wave runup elevations.  
*	"DATA EXCEEDED TABLE"
	An entry into subroutine LOOK of the program is not within the parameter bounds of the data 
table from which a value is sought.  
*	"SOLUTION DOES NOT CONVERGE"
	After 10 iterations, the current and previous estimates of runup elevation continue to differ by 
more than 0.15 foot, and both values are provided in the output table.  The calculation is 
usually oscillating between these two runup estimates when this occurs.  
*	"COMPOSITE SLOPE USED BUT WAVE MAY REFLECT, NOT BREAK"
	The output runup elevation relies to some extent on a composite-slope treatment, but the 
overall slope is steep enough that the specified wave may reflect from the nearshore barrier.  
Thus, the application of a calculated breaker depth in determining overall slope and runup 
elevation is questionable.  
*	"WARNING; COMPOSITE SLOPE USED, BUT INPUT PROFILE DOES NOT EXTEND 
TO BREAKER DEPTH"
	If the input profile does not extend seaward of the breaker depth, an incorrect breaker depth 
may be computed and the associated runup elevation will also be incorrect.  The input profile 
should include bathymetry to 30 or 40 feet in depth. 
[February 2002]
D.2.5.5	 Wave Runup in Special Situations
To interpret and apply the calculated results properly, the Mapping Partner shall examine the 
output of the Wave Runup Model carefully for each situation.  One important consideration is 
that a mean runup elevation below the crest of a given barrier does not necessarily imply the 
barrier will not occasionally be overtopped by floodwaters; the necessary supplementary 
examination of wave overtopping is addressed in Subsection D.2.5.7.  Other cases may yield 
 



results of more immediate concern, in that the Wave Runup Model may calculate a runup 
elevation exceeding maximum barrier elevation; this outcome can occur because the program 
assumes the last positive slope to continue indefinitely. For bluffs or eroded dunes with negative 
landward slopes, a general rule has been used that limits the wave runup elevation to 3 feet above 
the maximum ground elevation.  When the runup overtops a barrier such as a partially eroded 
bluff or a structure, the floodwater percolates into the bed and/or runs along the back slope until 
it reaches another flooding source or a ponding area.  The runoff areas are usually designated as 
Zone AO with a depth of 1, 2, or 3 feet.  Ponding areas are designated as Zone AH (depth of 3 
feet or less) with a BFE.  Standardized procedures for the treatment of sizable runoff and ponding 
are presented in Appendix E of these Guidelines.  
A fairly typical situation on the Atlantic and Gulf coasts is that wave runup exceeds the barrier 
top and flows to another flooding source such as a bay, river, or backwater.  It may not be 
necessary in this situation to compute overtopping rates and ponding elevations; only the flood 
hazard from the runoff must be determined.  Simplified procedures have been used to determine 
an approximate depth of flooding in the runoff area (Williams, 1983).  These procedures are 
illustrated in Figure D-15 and discussed below.  
When the runup computed on the imaginary extension of the last positive slope is greater than or 
equal to 3 feet above the maximum ground elevation, the maximum runup shall be 3 feet above 
the ground crest elevation.  This elevation decays to 2 feet above the ground profile at 50 feet 
behind the crest and continues at this depth until it encounters other flooding.  Computed runup 
is not adjusted if it is less than 3 feet above the ground crest.  In the same initial 50 feet, this 
elevation decays to 1 foot above the ground and continues at this depth until it encounters other 
flooding.  The runoff area from the ground crest to the limit of the other flooding is designated 
Zone AO with the appropriate depth of flooding.
A distinct type of overflow situation can occur at low bluffs or banks backed by a nearly level 
plateau, where calculated wave runup may appreciably exceed the top elevation of the steep 
barrier.  A memorandum entitled "Special Computation Procedure Developed for Wave Runup 
Analysis for Casco Bay, FIS - Maine, 9700-153" provides a simple procedure to determine 
realistic runup elevations for such situations, as illustrated in Figure D-16 (French, 1982).  An 
extension to the bluff face slope permits computation of a hypothetical runup elevation for the 
barrier, with the imaginary portion given by the excess height R' = (R-C) between calculated 
runup and the bluff crest.  Using that height R' and the plateau slope m, Figure D-17 defines the 
inland limit to wave runup, X, corresponding to runup above the bluff crest of (mX) or an 
adjusted runup elevation of Ra = (C + mX).  This procedure is based on a Manning's "n" value of 
0.04 with some simplifications in the energy grade line and is meant for application only with 
positive slopes landward of the bluff crest.  A different treatment of wave overflow onto a level 
plateau, for possible FIS usage, is provided in "Overland Bore Propagation Due to an 
Overtopping Wave" (Cox & Machemehl, 1986).

 











These runup assessment procedures are given for general guidance, but situations may exist 
where they are not entirely applicable.  For example, runup elevations need to be fully consistent 
with wave setup and wave overtopping assessments described in subsections that follow.  In 
problematic cases, the Mapping Partner shall use good judgment and rely on the historical data to 
reach a solution about realistic flood hazards associated with a shore barrier.  Subsection D.2.7 
considers the integration of separately calculated wave effects into coherent hazard zonations for 
the 1-percent-annual-chance flood.  When a unique situation is encountered, the Mapping Partner 
shall prepare a Special Problem Report and discuss it with the FEMA RPO.  
[February 2002]
D.2.5.6	Wave Setup
Nearshore wave action can increase mean water elevation in front of a shore barrier by the 
phenomenon called wave setup, which is related to wave attenuation by breaking in shallow 
water.  In treating the 1-percent-annual-chance flood, focus may be restricted to the cumulative 
setup effect in the immediate vicinity of the shore barrier.  Laboratory measurements of wave 
runup generally include the contribution due to wave setup, because runup elevations are defined 
relative to stillwater level in the absence of wave action.  
A separate calculation for wave setup can be appropriate even if a wave runup elevation has 
already been determined, in part because the changed mean water depth can increase wave 
heights and crest elevations to be expected near the shore.  In addition, empirical guidance within 
the Wave Runup Model is based on uniform laboratory wave action, so that incorporated setup 
might pertain to the field situation of swell waves from distant storms; setup effects may be much 
different in the local storm waves accompanying the 1-percent-annual-chance flood.  If storm 
wave setup is found to exceed the wave runup calculated for a particular situation, the Mapping 
Partner shall apply the setup estimate as a lower bound for actual wave runup in further analysis 
of wave effects and 1-percent-annual-chance flood elevations.
The USACE Shore Protection Manual provides straightforward empirical guidance on wave 
setup for various storm wave conditions and plane bottom slopes, as reproduced in Figure D-18 
(USACE, 1984).  Setup magnitude is given in dimensionless form, as normalized by incident 
significant wave height.  This guidance, given typical significant storm-wave steepness of 0.03 to 
0.04, indicates shore setups of 7 to 8 percent of incident wave height.  Incident wave conditions 
are specified in deep water as the significant wave height and the wave steepness, Hos/Lop), where 
 5 is wavelength in deep water.  Bottom slope may be taken as an overall 
average over the breaker zone between d = 2Ho and d=0, if the bottom geometry is relatively 
simple.  For other geometries, e.g., with a berm or reef in front of the shore barrier, the wave 
setup can be larger than given by Figure 18 and a more detailed examination may be required.
Wave setup also appears appreciably larger according to an independent treatment of storm 
waves on plane slopes, as outlined for a relatively narrow spectrum describing incident wave 
energy in Random Seas and Design of Maritime Structures (Goda, 1985).  If historical evidence 
indicates greater setup increases of mean water depth in extreme floods than Figure D-18 gives 
for the study site, the Mapping Partner shall develop a wave setup estimate based on that 
independent guidance through the ACES computer program provided in Automated Coastal 
Engineering System, Version 1.07 (Leenknecht, Szuwalski, & Sherlock, 1992).  The program 
does not permit direct calculation of wave effects at d=0; however, the Mapping Partner may 
linearly extrapolate setup results from about d=Ho to the shallow limit of computations to the 
stillwater shoreline.  
[February 2002]
D.2.5.7	Wave Overtopping
Wave overtopping results when a shore barrier does not contain incident wave action, so that 
floodwater penetrates to the protected area landward.  This process of a partial halt and 
dissipation to storm waves is more difficult to treat than wave runup or wave setup.  Important 
rates of wave overtopping can vary over several orders of magnitude, and can depend strongly on 
the detailed geometry of the barrier.  That complicates the development of empirical guidance on 
wave overtopping, but little demand exists for such guidance in coastal engineering practice.  
According to Criteria for Evaluating Coastal Flood-Protection Structures, the design process for 
a major coastal flood protection structure relies on site-specific model testing, rather than 
generalized overtopping guidance (Walton, Ahrens, Truitt, & Dean, 1989).  
Of course, the assessment of potential wave overtopping for present purposes must rely on 
readily available empirical guidance, historical effects, and engineering judgment.  Except for 
very heavy overtopping, useful guidance is derived from tests with irregular waves, because the 
intermittently large overtopping discharges in storm situations could not be reproduced 
otherwise.  Adding to the formal complexity of an adequate treatment for flood hazard 
assessment, overtopping effects may be cumulative so that the entire course of a flood event 
could require consideration, not just the peak conditions.  However, the Mapping Partner shall 
estimate only the order of magnitude of overtopping rates because there are clearly documented 
thresholds below which wave overtopping may be classified as negligible.    On the other hand, if 
a preliminary estimate indicates severe overtopping that threatens the stability of a given 
structure, that structure might be removed from the transect for analyses of the 1-percent-annual-
chance flood, and no further overtopping consideration would be required.  
Two publications, Design of Seawalls Allowing for Wave Overtopping (Owen, 1980) and 
Random Seas and Maritime Structures (Goda, 1985) appear to provide the most trustworthy and 
wide-ranging summaries of mean overtopping rates with storm waves.  The former publication 
addresses smooth plane or bermed slopes, and the latter publication considers vertical walls with 
or without a fronting rubble mound.  Before surveying those primary sources of overtopping 
guidance, however, some introductory considerations can help to determine whether detailed 
assessment is needed for 1-percent-annual-chance flood conditions at a specific shore barrier.  
The initial consideration is an interpretation of mean runup elevation already calculated ( 6), in 
terms of likely extreme elevations according to the Rayleigh probability distribution usually 
appropriate for wave runups.  To parallel the extreme wave height addressed in coastal studies 
(NAS, 1977), a controlling runup magnitude may be defined as 1.6 times significant runup, or 
 


2.5 times mean runup according to the Rayleigh distribution. If elevation of the barrier crest 
above 1-percent-annual-chance SWEL, or the barrier freeboard F, equals or exceeds (2.5  7), 
then the landward area is not subject to wave-induced discharges during the 1-percent-annual-
chance flood.  That requirement might be supplemented by consideration of F near (2  8), 
corresponding to 4.5 percent of the runup reaching the barrier crest according to the Rayleigh 
distribution.  If F ? (2 9), wave overtopping can certainly be appreciable during the 1-percent-
annual-chance flood, and the Mapping Partner shall assess ponding or runoff behind the barrier.  
The extreme runups introduced here, (2 10) and (2.5 11), bracket the elevation exceeded by 
the extreme 2 percent of wave runup, a value commonly considered in structure design.  
Once the need for quantitative overtopping assessment is established, wave runup considerations 
become inapplicable because a runup elevation generally cannot be converted to an overtopping 
estimate.  Also, the composite-slope method used in determining wave runup does not appear 
applicable for overtopping of barriers with composite geometry, because details of the wave 
transformation on a barrier influence the resultant overtopping rates.  Wave overtopping 
estimates for a specified situation generally must be based on measurements in a similar 
configuration.  Before considering some implications of quantitative guidance for idealized 
cases, an overview of overtopping magnitudes gives a useful introduction (Goda, 1985; Gadd, 
Potter, Safaie, & Resio, 1984).  
Wave overtopping is specified as a mean discharge: water volume per unit time and per unit 
alongshore length of the barrier, commonly cfs/ft.  By interpreting or visualizing a given 
overtopping rate, the Mapping Partner may take into account that the actual discharges generally 
are intermittent and isolated, being confined to some portion of occasional wave crests at 
scattered locations.  Distinct regimes of wave overtopping may be described as spray, splash, 
runup wedge, and waveform transmission, in order of increasing intensity.  Flood discharges 
corresponding to those regimes naturally depend on the incident wave size, but certain 
overtopping rates have been associated with various characteristics (Goda, 1985).  Among those 
rates, 0.01 cfs/ft seems to correspond to flooding that generally should be considered appreciable, 
and 1 cfs/ft appears to define an approximate threshold where structural stability of the shore 
barrier commonly becomes threatened by severe overtopping.  
Once the mean overtopping rate has been estimated for the 1-percent-annual-chance flood, 
determining resultant flooding may require a representative duration for the interval of 
overtopping.  That duration can vary widely depending on the coastal flood cause, from a fast-
moving hurricane to a nearly stationary extratropical storm. A minimum assumption for the 
duration of flood-peak overtopping would generally be 1 to 2 hours.  Durations of 10 hours or 
more could be appropriate for cumulative effects in an extratropical storm causing flooding over 
multiple high tides.  
Figure D-19 summarizes some empirical overtopping guidance for storm waves, in a schematic 
form meant to assist deciding the likely significance of flooding behind a coastal structure.  
Variables describing the basic situation are cotangent of the front slope for a smooth structure 
with ideally simple geometry, and freeboard of the structure crest above stillwater level, as 
normalized by incident significant wave height, F/Hs.  The mean overtopping rate,  12, is 
provided in dimensionless form as
	Q* =  13/(gH s3)0.5	(2)
with test results shown for structure slopes of 1:1, 1:2, and 1:4 (Owen, 1980) and for a smooth 
vertical wall (Goda, 1985).  These results pertain to: significant wave steepness of approximately 
2?Hs/gT2p= 0.035, fairly appropriate for extreme extratropical storms or hurricanes; water depth 
near the structure toe of approximately dt = 2Hs, so that incident waves are not appreciably 
attenuated; and moderate approach slopes of 1:30 for a vertical wall or 1:20 for other structures.  
The major feature of interpolated curves is fixed as a maximum in overtopping rate for structure 
slope of 1:2, corresponding to the gentlest incline producing (at this wave steepness) total 
reflection rather than breaking, and thus peak waveform elevations (Nagai & Takada, 1972).
These measured results for smooth and simple geometries clearly show severe or "green water" 
overtopping even at relatively high structures (F?Hs) for a wide range of common inclinations 
(cotangents between 0 and 4).  Also, for freeboards considered here, a vertical wall (cotangent 0) 
permits less overtopping than common sloping structures with cotangent less than approximately 
3.5.  Gentler barriers are uncommon because the construction volume increases with the 
cotangent squared, so steep coastal flood-protection structures usually face attenuated storm 
waves and/or have rough surfaces.  Basic effects of those differences can be outlined for use in 
simplified overtopping assessments.
For sloping structures sited within the surf zone (dt < 2Hs), Design of Seawalls Allowing for 
Wave Overtopping indicates that basic overtopping guidance in Figure D-19 can be used with 
attenuated rather than incoming wave height (Owen, 1980).  A simple estimate basically 
consistent with other analyses of the 1-percent-annual-chance flood is that significant wave 
height is limited to H' s = dt/2 at the structure toe.  The value of (2F/dt) describes the effectively 
increased freeboard in entering Figure D-19, and the indicated Q* value is then converted to   
using H's .  The presumed wave attenuation ignores any wave setup as a small effect with the 
partial barrier, and dt should always correspond to the scour condition expected in wave action 
accompanying the 1-percent-annual-chance flood. 
Figure D-19 might also be made applicable to rough slopes, using a roughness coefficient (r) 
from Table D-3 to describe the effectively increased freeboard with greater wave dissipation on 
the structure.  Design of Seawalls Allowing for Wave Overtopping proposed formulating effect of 
structure roughness as F/r, and Beach and Dune Erosion during Storm Surges confirmed a 
similar dependence of overtopping on roughness in measured results for irregular waves (Owen, 
1980; Vellinga, 1986).  The overtopping relation reported as reliable in "Wave Runup and 
Overtopping on Coastal Structures" is
	Q* = 8*10-5  exp[3.1(rR*  -  F / Hs)]	(3)	


 


where R* = [1.5 m/(Hs/Lop)0.5], up to a maximum value of 3.0, is an estimated extreme runup 
normalized by Hs, for a barrier slope given as the tangent m (de Waal & van der Meer, 1992).  
Equation 3 is meant to pertain to very wide ranges of test situations with moderate overtopping, 
but appears very approximate in comparison with specific results for r=1 shown in Figure D-19.  
It may be advisable to evaluate Equation 3 for both smooth and rough barriers, then to use the 
ratio to adapt a value from Figure D-19 for the case with roughness.  Design of Seawalls 
Allowing for Wave Overtopping (Owen, 1980) and "Wave Runup and Overtopping on Coastal 
Structures" (de Waal & van der Meer, 1992) provide further overtopping guidance on the effects 
of composite profiles, oblique waves, and shallow water with sloping structures.  
For overtopping of vertical walls, effects of wave attenuation appear relatively complex, but 
Random Seas and Design of Maritime Structures (Goda, 1985) provides extensive empirical 
guidance on various structure situations with incident waves specified for deep water.  Figure D-
20 converts basic design diagrams for wave overtopping rate at a vertical wall, to display wall 
freeboard required for rates of 1 cfs/ft and 0.01 cfs/ft with various incident wave heights. Goda 
(1985) also provides a convenient summary on the effect of appreciable fronting roughness in 
storm waves: the required freeboard of a smooth vertical wall for a given overtopping rate is 
approximately 1.5 times that which is needed when a sizable mound having concrete block armor 
is installed against the wall.  With this information, a specific vertical wall can be categorized as 
having only modest overtopping ( 14 < 0.01 cfs/ft), intermediate overtopping, or severe 
overtopping ( 15 > 1 cfs/ft) expected for the 1-percent-annual-chance flood.  Likely runoff or 
ponding behind the wall must then be identified; severe overtopping requires delineation of the 
landward area susceptible to wave action and velocity hazard.  Subsection D.2.7 outlines several 
common zonations of flood hazards near shore barriers in describing the integration of computed 
wave effects.
Considering Figure D-20 with respect to common wall and wave heights, wave overtopping 
dangerous to structural stability appears the usual case during the 1-percent-annual-chance flood.
 


  
An assessment of failure during the 1-percent-annual-chance flood for typical walls would be 
fully consistent with one recommendation of Criteria for Evaluating Coastal Flood-Protection 
Structures: that "FEMA not consider anchored bulkheads for flood-protection credit because of 
extensive failures" (Walton et al., 1989).
Interpretation of estimated overtopping rate in terms of flood hazards is complicated by the 
projected duration of wave effects, by the increased discharge possible under storm winds, by the 
varying inland extent of water effects, and by the specific topography and drainage landward of 
the barrier.  However, guidance is provided in Table D-7 as potentially applicable to typical 
coastal situations.  
Table D-7.  Suggestions for Interpretation of Mean Wave Overtopping Rates
 16 ORDER OF MAGNITUDE
FLOOD HAZARD ZONE BEHIND BARRIER
<0.0001 cfs/ft
Zone X
0.0001-0.01 cfs/ft
Zone AO (1 ft depth)
0.01-0.1 cfs/ft
Zone AO (2 ft depth)
0.1-1.0 cfs/ft
Zone AO (3 ft depth)
>1.0 cfs/ft*
30-ft width+ of Zone VE
(elevation 3 ft above barrier crest),
landward Zone AO (3 ft depth)
*With estimated  17 much greater than 1 cfs/ft, removal of barrier from transect representation may be appropriate.  
+Appropriate inland extent of velocity hazards should take into account structure width, incident wave period or 
wavelength, and other factors.  
For each coastal structure experiencing sizable wave runup in the 1-percent-annual-chance flood 
(for example,  18 > 2 ft), a brief report to the Project Officer should outline overtopping 
assessments and document conclusions consistent with historical evidence for the site.
[February 2002]
D.2.6	Analysis of Overland Wave Dimensions
As water waves propagate near the shore and over flooded land, they can undergo marked 
transformations due to local winds, interaction with the bottom, and physical features such as 
buildings, trees, or marsh grass.  Figure D-21 illustrates schematic effects on the wave crest 
elevations and on the type of flood zone.  The fundamental analysis of wave effects for an FIS is 
provided by the WHAFIS 3.0 computer program, entitled "Wave Height Analysis for Flood 
Insurance Studies" (FEMA, 1988).  This program or model calculates wave heights, wave crest 
elevations, flood hazard zone designations, and the location of zone boundaries along a transect.  
Wave description for NFIP purposes addresses the controlling wave height, equal to 1.6 times the 
significant wave height common as a representative wave description.  Significant wave height is 
the average height of the highest one-third of waves, and controlling wave height is 
approximately the average height of the highest one percent of waves in storm conditions.  The 
original basis for wave treatment under the NFIP was the NAS methodology, which accounted 
for varying fetch lengths, barriers to wave transmission, and the regeneration of waves over 
flooded land areas (USACE, 1975).  Because of the introduction of the NAS methodology, 
periodic upgrades have been made to incorporate improved or additional wave considerations.  
Technical details of the current WHAFIS model are fully documented (Technical Documentation 
for WHAFIS Program Version 3.0), but a brief overview indicates the level of wave treatment in 
WHAFIS 3.0 (FEMA, September 1988).  A wave action conservation equation governs wave 
regeneration due to wind and wave dissipation by marsh plants.  This equation is supplemented 
by the conservation of waves equation, which expresses the spatial variation of the wave period 
at the peak of the wave spectrum.  The wave energy (equivalently, wave height) and wave period 
respond to changes in wind conditions, water depths, and obstructions as a wave propagates.  
These equations are solved as a function of distance along the transect.  A predominant element 
in this wave treatment remains unchanged from the NAS methodology: controlling wave height 
is limited to 78 percent of the local mean water depth.
[February 2002]
D.2.6.1	Use of WHAFIS 3.0 Model
Careful preparation and input of required site data are necessary in using WHAFIS.  Like the 
other coastal treatments, the WHAFIS model considers the study area by representative transects.  
For WHAFIS, transects are selected with consideration given to major topographic, vegetative, 
and cultural features.  The ground profile is defined by elevations referenced to NGVD and 
usually begins at elevation 0.0 and proceeds landward until either the ground elevation exceeds 
the meanwater elevation for the 1-percent-annual-chance flood or another flooding source is 
encountered.  
Other fundamental specifications among WHAFIS input include the 1-percent-annual-chance 
mean water elevation and a description of waves existing at the transect start.  In the wave 
description, provision is made for an overwater fetch length, an initial significant wave height, or 
an initial period of dominant waves.  In most applications, the wave period is the input 
description, because that parameter is readily available from information about offshore storm 
waves and the period does not change during most wave transformations.  WHAFIS then 
computes an appropriate depth-limited wave height at the transect start.  The only check 
necessary is to confirm that incident waves likely exceed that height and a wave condition 
limited by water depth occurs.
 Different wave specifications can be appropriate for sites not on an open, straight coast.  Where 
land shelter or wave refraction may result in reduced incident waves, it is appropriate to specify 
an initial significant wave height for the transect.  Also, at sites on restricted water bodies, the 
overwater fetch length should be specified for likely wind direction at the flood peak.  WHAFIS 
then computes an appropriate incident wave condition for the transect, but such waves are 
limited and any fetch length exceeding 24 miles yield the same results.


 


In preparing WHAFIS input, transects are to be located on the work maps and the transect ground 
profile is to be plotted from the topographic data, adjusted for erosion.  Each transect is to have 
all the input data identified on the profile plot for ease of input coding.  The location, height, and 
extent of elongated manmade structures is to be identified and shown as part of the ground 
profile, after the structure's stability under forces of the 1-percent-annual-chance flood is 
confirmed as discussed in Subsection D.2.3.  When locating transects across barrier islands or 
sand spits, common practice is to continue the transect across the back bay and onto the 
mainland.  If there is a large and/or unusually shaped embayment behind the island, it may be 
necessary to place additional transects just along the mainland shore.  These transects may not 
parallel the transects from the open coast, and they may cross one another.  The Mapping Partner 
shall keep crossing transects to a minimum; however, where it is not possible to avoid this, the 
transect determining greatest flood hazards shall control in mapping the flood hazards.  
Once representative transects are located, the local 1-percent-annual-chance mean water levels 
can be defined for WHAFIS input.  Wave setup should be included in this water elevation, as a 
part of the appropriate mean depth controlling wave dimensions (FEMA, September 1988).  If 
wave setup was not calculated separately for the site, 1-percent-annual-chance SWEL is the 
appropriate specification.  WHAFIS also has an input field for a 10-percent-annual-chance 
SWEL; however, it is only employed to determine Flood Hazard Factors, which FEMA no longer 
uses.  Still, the Mapping Partner shall provide this input if it is readily available, because it could 
help in distinguishing between transects.  
When a transect covers two or more flooding sources, the Mapping Partner shall identify an area 
of transition between the different SWELs.  This is a common situation for barrier islands with 
ocean elevations on one side and bay elevations on the other side.  It is usually assumed that the 
higher ocean elevations extend inland to the highest point of the reduced ground profile.  
WHAFIS performs a linear interpolation within a transect segment where elevations differ at the 
end stations.  The interpolated elevations are compared to the ground elevations and adjusted, if 
necessary, to be above the ground elevations.  The Mapping Partner may have to input the SWEL 
a second time to identify areas of constant elevation and elevation transition.  
The proper transect representation of some land features, particularly buildings and vegetation, 
merits further discussion.  Buildings are specified on the transect as rows perpendicular to the 
transect.  Because buildings are not always situated in perfect rows, the Mapping Partner shall 
exercise judgment to determine which buildings can be represented by a single row.  The 
required input value for each row of buildings is the ratio of open space to total space.  This is 
simply the sum of distances between buildings in a row, divided by the total length of that row. 
The Mapping Partner shall examine whether the first row or two of buildings along the shoreline 
should be considered as obstructions.  During a 1-percent-annual-chance event, it is sometimes 
appropriate to assume that these buildings will be destroyed before the peak of the flood occurs if 
they are not elevated on pilings.  If they are elevated, the waves should propagate under the 
structure with minimal reduction in height.  It is useful to contact local officials to obtain typical 
construction methods and the lowest elevations of structures.  
The WHAFIS program has two separate routines for vegetation:  one for rigid vegetation that can 
be represented by an equivalent "stand" of equally spaced circular cylinders (NAS, 1977), and 
one for marsh vegetation that is flexible and oscillates with wave action (FEMA, 1984).  For 
either type, the Mapping Partner shall exercise considerable care in selecting representative 
parameters and in ruling out that the vegetation will be intentionally removed or that effects 
would be markedly reduced during a storm through erosion, uprooting, or breakage.  
For the areas of rigid vegetation located on the transect, the required input values are the drag 
coefficient, CD; mean wetted height, h; mean effective diameter, D; and mean horizontal spacing, 
b.  The value of CD should vary between 0.35 and 1.0, with 1.0 being used in most cases of wide 
vegetated areas.  When the vegetation is in a single stand, the Mapping Partner shall use a value 
of 0.35.  The Mapping Partner may obtain representative values for h, D, and b from stereoscopic 
aerial photographs or by field surveys.  Various guides for terrain analysis can provide advice on 
estimating values from aerial photographs.  Table D-8 provides a useful process developed from 
Terrain Analysis Procedural Guide for Vegetation (Messmore, Vogel, & Pearson, 1979).
For marsh vegetation, a more complicated specification is required for completeness.  The eight 
parameters used to describe the dissipational properties of a specific type are explained in Table 
D-9.  However, WHAFIS incorporates considerable basic information on the eight common 
types of seacoast marsh plants listed in Table D-10 (FEMA, 1984).  That information can be used  
either by specifying the Table D-10 abbreviation or a geographical region as indicated in Figure 
D-22.  Figure D-22 shows the coastal wetland regions of the Atlantic and Gulf coasts, along with 
the identifying number used in WHAFIS.  If the site is near a region border, the likely plant 
parameters can be interpolated using an input weighting factor.  Although the South Texas region 
has insignificant amounts of marsh grass, it is included for usage in spatial interpolation. 
Climate affects the geographic range of each marsh plant type, so that some plant types are not 
found in all regions.  Table D-11 lists the dominant plant type in each region, where the term 
"dominant" refers to the plant types that cover the largest amount of area in the marshes.  Table 
D-12 shows the significant plant types in each region, where the term "significant" refers to the 
plant types that occur in large enough patches (at least 10,000 square feet) to significantly affect 
waves.  For marsh plants, simply the coastal wetland region, plant type, and area or percent of 
coverage may be specified.  Given this information, WHAFIS will supply default values for the 
other marsh plant parameters appropriate to the site (FEMA, 1984).  
Following the identification of the marsh plant types present, the area and fraction of coverage, 
Fcov, for each plant type must be calculated.  For each transect, the total area of marsh vegetation 
coverage is determined.  The different types of vegetation within this area usually occur in 
patches.  Fcov is defined for each plant type as the ratio of the patch area for that type to the total 
marsh area.  Using the above data, a fairly good determination can be made of the plant types 
present, but an attempt should be made to confirm these plant types.  Local, county, or state 
officials may provide some assistance, and a site visit can be very useful.




 


	Table D-9.  Marsh Plant Parameters
PARAMETER
EXPLANATION
CD
Effective drag coefficient.  Includes effects of plant flexure and modification of the 
flow velocity distribution.  Default value is 0.1, usually appropriate for marsh plants 
without strong evidence to the contrary.
Fcov
Fraction of coverage.  A default value is calculated by the program so that each plant 
type in the transect is represented equally, and the sum of the coverage for the plant 
types is equal to 1.0.
h
Unflexed stem height (feet).  The stem height does not include the flowering head of 
the plant, the inflorescence.
N
Number density.  Expressed as plants per square foot.  The relationship to the average 
spacing between plants, b, can be expressed as N = 1/b2.
D1
Base stem diameter (inches).  Default value may be determined from stem height and 
regression equations built into the program.
D2
Mid stem diameter (inches).  Default value may be determined from plant type and 
base stem diameter.
D3
Top stem diameter (inches), at the base of the inflorescence.  Default value may be 
determined from plant type and base stem diameter.
CAb
Ratio of the total frontal area of the cylindrical portion of the leaves to the frontal area 
of the stem below the inflorescence.  Default value may be determined from the plant 
type.

Table D-10.  Abbreviations of Marsh Plant Types used in WHAFIS
SPECIES OR SUBSPECIES
ABBREVIATION
Cladium jamaicense (saw grass)
CLAD
Distichlis spicata (salt grass)
DIST
Juncus gerardi (black grass)
JUNM
Juncus roemerianus (black needlerush)
JUNR
Spartina alterniflora (medium saltmeadow cordgrass)
SALM
Spartina alterniflora (tall saltmeadow cordgrass)
SALT
Spartina cynosuroides (big cordgrass)
SCYN
Spartina patens (saltmeadow grass)
SPAT






Table D-11.  Dominant Marsh Plant Types by Region and Habitat
REGION
NUMBER
REGION NAME
HABITAT
DOMINANT SPECIES
1
North Atlantic
salt1
brackish2
*S. alterniflora (medium, tall)
Spartina patens
2
Mid-Atlantic
salt
brackish
S. alterniflora (medium, tall)
*Juncus roemerianus/S. patens
3
South Atlantic
salt
brackish
*S. alterniflora (medium, tall)
J. roemerianus
4
South Florida
salt
brackish
S. alterniflora (medium, tall)
*C. jamaicense
5
Northeastern Gulf
salt
brackish
---
*J. roemerianus
6
Delta Plain
salt
brackish
*S. Alterniflora (medium, tall)
S. patens
7
Chenier Plain
salt
brackish
S. alterniflora (medium, tall)
*S. patens
8
South Texas
salt
brackish
---
---
 Salt concentration is greater than 20 parts per thousand (ppt)
2Salt concentration is between 5 and 20 ppt
*When more than one dominant plant type occurs within the region, the indicated type covers the largest geographic area (acreage)
--- Insignificant amounts of marsh plants within the given habitat in the region  



Table D-12.  Significant Marsh Plant Types in Each Seacoast Region and WHAFIS Default Regional Plant Parameter Data
REGION NO.
1
2
3
4
5
6
7
8
REGION NAME:
NORTH
ATLANTIC
MID-
ATLANTIC
SOUTH
ATLANTIC
SOUTH
FLORIDA
NORTHEASTERN
GULF
DELTA
PLAIN
CHENIER
PLAIN
SOUTH
TEXAS
CLAD
---
---
---
7.50(+)
0.0656
6
6.00(2)
0.0260
6
---
---
---
DIST
---
0.78(1)
0.0039
211
1.00(1)
0.038
243
1.00(+)
0.0038
248
---
---
1.08(4)
0.0035
102
1.08(+)
0.0035
102
---
JUNM
1.23(1)
0.0042
300
1.23(+)
0.0042
300
---
---
---
---
---
---
JUNR
---
2.95(+)
0.0095
147
2.95(+)
0.0095
147
---
2.95(3)
0.0095
147
3.00(4)
0.0106
83
2.95(+)
0.0095
147
---
SALM
1.39(1)
0.0184
45
1.06(1)
0.0103
36
1.63(1)
0.0141
12
1.63(+)
0.0141
12
---
1.67(4)
0.0141
21
2.62(5)
0.0211
16
---
SALT
1.86(1)
0.0175
37
2.21(1)
0.0169
18
3.20(1)
0.0183
10
3.20(+)
0.0183
10
---
3.20(4)
0.0183
10
3.20(+)
0.0183
10
---
SCYN
---
---
8.29(+)
0.0492
6
---
---
4.00(4)
0.0267
7
---
---
SPAT
1.03(1)
0.0025
409
0.85(1)
0.0019
327
1.65(1)
0.0019
236
---
2.58(2)
0.0026
236
1.88(4)
0.0016
333
1.88(+)
0.0019
333
---
Data arranged in vertical triplets:

Parenthetical references indicate data source: 





h, stem height below inflorescence, in feet

1 = Hardisky and Reimold, 1977
5 = Turner and Gosselink, 1975, Diameters extrapolated
D, base diameter, in feet

2 = Monte, August 1983
+ = Extrapolated Data
N, number density, in inverse square feet

3 = Kruczynski, Subrahmanyam, Drake, 1978
--- = Insignificant amounts of this plant type in the region


4 = Hopkinson, Gosselink, Parrondo, 1980, Diameters extrapolated



				
	 






[February 2002]
D.2.6.2	Input Coding for WHAFIS
After all the necessary input data have been identified on the transect, the Mapping Partner shall 
divide the transect into contiguous segments, each representing a continuous open fetch or a 
single obstruction.  Fetches are flooded areas with no obstruction, while obstructions include 
dunes, manmade barriers, buildings, and vegetation. The Mapping Partner shall subdivide the 
fetches at points where the ground elevation abruptly changes and in the transition area of 
changing SWELs.  The Mapping Partner shall subdivide obstructions into smaller segments at 
the transect's seaward edge to model the wave dissipation more accurately.  Rigid vegetation 
shall have two to three seaward segments extending 10 to 50 feet, and the first two or three rows 
of buildings shall have a segment for each row.  Marsh vegetation will be subdivided within 
WHAFIS, so segmented input from the Mapping Partner is not necessary.  
The Mapping Partner shall enter the necessary data using 11 line types, including the Title line.  
The ten remaining lines, each describing a certain type of fetch or obstruction, are listed as 
follows: 
*	The IE (Initial Elevation) line describes the initial overwater fetch and the initial SWELs.  
*	The IF (Inland Fetch) and OF (Overwater Fetch) lines define the endpoint stationing and 
elevation of inland and overwater fetches, respectively.  
*	Obstructions are categorized either as buildings (BU line), rigid vegetation (VE line), marsh 
vegetation (VH and MG lines), dunes and other natural or manmade elongated barriers (DU 
line), or areas where the ground elevation is greater than the 1-percent-annual-chance SWEL 
(AS line).  
*	The ET (End of Transect) line enters no data but indicates the end of the input data.  
Each line has an alphanumeric field describing the type of input for that line, followed by ten 
numeric fields describing the parameters.  
To ensure proper modeling, the Mapping Partner shall enter all segments of each transect either 
as fetches or obstructions, with one input line required for each fetch or obstruction segment.  
The first two columns of each line identify the type of fetch or obstruction.  The remaining 78 
columns consist of one field of six columns followed by nine fields of eight columns.  The 
Mapping Partner shall right-justify the numbers in any data field only if no decimal point is used. 
Decimal points are permitted but not required.  The end point of one fetch or obstruction is the 
beginning of the next.  The first two numeric fields of each line are used to read in the stationing 
(measured in feet from the beginning of transect) and elevation (in feet) of the end point.  The 
last two fields used on each line are for entering new SWELs.  An interpolation is performed 
within a transect segment starting at the closest station with an input SWEL.  This interpolation 
uses the new SWEL input at the end point of the segment and the SWEL input at a previous 
segment.  If these fields are blank or zero, the SWELs remain unchanged.  
The input data requirements are summarized below for each line type.  The Title line must be the 
first line, followed by the IE line, followed by any combination of the various fetch and 
obstruction lines.  The ET line must be the last card entered for the transect.  A blank line must 
follow to signify the end of the run.  If multiple transects are being run, the Title line for the next 
transect will follow the blank line.  All units are in feet unless otherwise specified.  
TITLE Line (Title)
This line is required and must be the first input line.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
Blank
1-10
3-80
Title information centered about column 40

IE Line (Initial Elevations)
This line is required and must be the second input line.  This line is used to begin a transect at the 
shoreline and compute the wave height arising through the overwater fetch.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
IE
1
3-8
Stationing of end point of initial overwater fetch in feet (zero at beginning of 
transect)
2
9-16
Ground elevation at end point in feet (usually zero at beginning of transect)
3
17-24
Overwater fetch length (miles), if wave condition is to be calculated.  Values of 
24 miles or greater yield identical results.
4
25-32
10-percent-annual-chance SWEL in feet
5
33-40
1-percent-annual-chance SWEL in feet
6
41-48
Initial wave height in feet; a blank or zero causes a default to a calculated wave 
height
7
49-56
Initial wave period (seconds); a blank or zero causes a default to a calculated 
wave period.  The period is usually the most convenient wave specification for 
open coasts.
8-10
57-80
Not used

AS Line (Above Surge)
This line is used to identify the end point of an area with ground elevation greater than the 1-
percent-annual-chance SWEL (such as a high dune or other land mass).  This is used when the 
ground surface temporarily rises above the 1-percent-annual-chance SWEL.  The line 
immediately preceding the AS line must enter the stationing and elevation of the point at which 
the ground elevation first equals the 1-percent-annual-chance SWEL.  SWEL on the inland side 
may differ from SWEL on the seaward side.  The ground elevation entered on the AS line must 
equal the SWEL that applies to the inland side of the land mass.  Computer calculations will be 
terminated if a ground elevation greater than the 1-percent-annual-chance SWEL is encountered.  

DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
AS
1
3-8
Stationing at end point in feet of area above 1-percent-annual-chance SWEL
2
9-16
Ground elevation in feet at end point
3
17-24
A blank or zero indicates no change to the 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to the 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used

BU Line (Buildings)
This line enters information needed to compute wave dissipation at each group of buildings.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
BU
1
3-8
Stationing of end point in feet of group of buildings
2
9-16
Ground elevation at end point in feet
3
17-24
Ratio of open space between buildings to total transverse width of developed 
area
4
25-32
Number of rows of buildings
5
33-40
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
6
41-48
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
7-10
49-80
Not used

DU Line (Dune)
This line enters information necessary to compute wave dissipation over flooded sand dunes and 
other natural or manmade elongated barriers (e.g., levees and seawalls).  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
DU
1
3-8
Stationing at top of dune or barrier in feet
2
9-16
Elevation at top of dune or barrier in feet
3
17-24
A blank or zero indicates a dune or other natural barrier; any other number 
indicates a seawall or other manmade barrier
4
25-32
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
5
33-40
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
6-10
41-80
Not used

IF Line (Inland Fetch)
This line enters the parameters necessary to compute wave regeneration through somewhat 
sheltered fetches and over shallow inland water bodies.  The IF regeneration is computed using a 
sustained wind speed of 60 mph.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
IF
1
3-8
Stationing at end point of fetch in feet
2
9-16
Ground elevation at end point in feet
3
17-24
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used

OF Line (Overwater Fetch)
This line enters the parameters necessary to compute wave regeneration over large bodies of 
water (i.e., large lakes, bays) using a sustained wind speed of 80 mph.  If an inland body of water 
is sheltered and has a depth of ten feet or less, the IF line calling for reduced wind speed should 
be used.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
OF
1
3-8
Stationing at end point of fetch in feet
2
9-16
Ground elevation at end point in feet
3
17-24
A blank or zero indicates no change to the 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used







VE Line (Vegetation)
This line enters parameters necessary to compute wave dissipation due to rigid vegetation stands.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
VE
1
3-8
Stationing at end point of vegetation in feet
2
9-16
Ground elevation at end point in feet
3
17-24
Mean effective diameter of equivalent circular cylinder in feet
4
25-32
Average actual height of vegetation in feet
5
33-40
Average horizontal spacing between plants in feet
6
41-48
Drag coefficient; a blank or zero causes a default to 1.0
7
49-56
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
8
57-64
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
9-10
65-80
Not used

VH Line (Vegetation Header for Marsh Grass)
Marsh grass is often part of a plant community that may consist of several types.  The VH line is 
used to enter data that apply to all plant types modeled in the transect segment.  To enter data for 
each plant type, MG lines for each plant type must follow the VH line.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
VH
1
3-8
Stationing at end point of marsh vegetation segment in feet
2
9-16
Ground elevation at end point in feet
3
17-24
Regp, number of the primary seacoast region for default plant parameters.  See 
Figure 22.
4
25-32
Wtp, weighting factor for the primary seacoast region.
5
33-40
Regs, number of secondary seacoast region.  See Figure D-22.
6
41-48
Np1, number of plant types; range is 1 to 10, inclusive.  One MG line is required 
for each plant type.
7
49-56
A blank or zero indicates no change to the 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
8
57-64
A blank or zero indicates no change to the 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
9
65-72
Not used
10
73-80
This field is for overriding the default method of averaging flood hazard factors 
in A Zones; if 1 in column 80, averaging process begins or ends at end of 
vegetation segment; otherwise, default averaging method is used



MG Line (Marsh Grass)
This line is used to enter data for a particular plant type.  The first MG line must be preceded by a 
VH line.  For the common seacoast marsh grasses listed in Table D-10, some potentially useful 
default values are supplied in Table D-12, and the program can provide additional default values 
(FEMA, October 1984).  If a plant type not listed in the table is used, then appropriate data must 
be developed for Fields 2-9.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
MG
1
5-8
Marsh plant type abbreviation (see Table 10)
2
9-16
CD, effective drag Coefficient; default value is 0.1
3
17-24
Fcov, decimal fraction of vegetated area to be covered by this plant type; a blank 
or zero causes a default to be calculated so that each plant type is represented 
equally
4
25-32
h, mean unflexed height of stem (feet); for marsh plants, the inflorescence is not 
included
5
33-40
N, number of plants per square foot
6
41-48
D1, base stem diameter (inches)
7
49-56
D2, mid stem diameter (inches)
8
57-64
D3, top stem diameter (inches)
9
65-72
CAb, ratio of the total frontal area of cylindrical part of leaves to frontal area of 
main stem
10
73-80
Not used

ET Line (End of Transect)
This line is required and must be the last input card because it identifies the end of input for the 
transect.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
ET
3-10
3-80
Not used

[February 2002]
D.2.6.3	Error Messages
The error messages that may appear when running the model are described below.
*	"AS card ground elevation less than SWEL, should use other type card, job dumped."
	Only use AS (above surge) line when the ground elevation is above the SWEL.  Can 
otherwise use IF, OF, BU, DU, VE, or VH.  
*	"Ground elevation greater than surge elevation encountered, job dumped."  
	If ground elevation is above surge elevation, AS card should be used.  
*	"Average depth less than or equal to zero, job dumped."
	The water depth must be greater than zero or a wave height cannot be computed.  Check the 
SWEL and the ground elevation if point of job dump is not the last point along the transect 
profile.  
*	"The above card contains illegal data in the first 2 columns."
	Check input data for incorrect values or input within wrong columns.  Aside from the title 
line, the first two columns in each line should contain the card identifiers.  
*	"Transmitted wave height at last fetch or obstruction = ______ which exceeds 0.5."
	Code the transect profile up to the inland limit where ground elevation intersects the SWEL 
so that wave height should decrease to zero.  If the scope of work ends at the corporate limits 
before the ground elevation meets the SWEL, this message can be ignored.  
*	"Array dimensions exceeded.  Job dumped."
	Size of the array is limited and the number of input parameters has exceeded the array.  
Check the number of input parameters at the location where the job dumped.  
*	"Invalid data in field 1 of IF card," etc.
	Check input data to make sure that data are in correct columns.  
*	"Wave period less than or equal to zero in subroutine fetch.  Abort run."  
	Either a fetch length or a wave period must be input for the program to run properly.  Check 
input data.  
*	"Invalid data in field 3 or field 5 of VH card."
	Check input data.
*	"Invalid data in field 4 of VH card."
	Check input data.  
*	"Invalid data in field 3 of MG card."
	Check input data.  The fraction of vegetated area covered by the stated plant type should be a 
decimal number between 0.0 and 1.0.  
*	"Missing MG card or incorrect data in field 6 of VH card."
	A MG card must always follow the VH card.  Field 6 of the VH card pertains to the number 
of plant types, and one MG card is required for each plant type.  
*	"Invalid input data."
	Check input data for invalid characters, such as an O instead of a zero.  Check to be sure that 
all data are in their correct columns.  
*	"Fcov was found to be negative for plant type = _______."
	Check input data to be sure that the decimal fraction of the vegetated area covered by the 
plant type is not negative.  
*	"Ncov is .LE. zero in Sub.Lookup when it should be .GT. zero.  Abort run."  
	Check input for number of plants covering the area.  
*	"The first card is not an IE card, this transect is aborted.  Continued to next transect."  
	The first card after the title line must always be an IE card.  Check input data.  
*	"****  The surge elevation at this station (stationing ____), which is ____ card, is less than 
the ground elevation.  The interpolation process is continued.  ***  Please double check the 
surge and ground elevations in the vicinity of this station"
	The surge elevation should not be below the ground elevation.  If the interpolated surge 
elevation is interpolated below the ground elevation, insert additional cards to specify surge 
and ground elevations and use an AS card if necessary.  
*	"Interpolation line cuts off more than two portions of high ground ridge.  This transect is 
aborted, re-assign 1-percent-annual-chance elevations at high ground stations."
	When the interpolated value falls below the ground elevation, insert additional cards to better 
model the area and set the SWEL equal to the ground elevation where appropriate.  Insert AS 
cards as necessary.  
*	"****  Unreasonable high ground elevation at station ____ which is ____ card.  This transect 
is aborted, continued to next transect.  ****  Double check the surge and ground elevations in 
the vicinity of this station.  If the ground elevations are correct, either assign a higher surge 
elevation or use AS cards."  
	Add additional input data as necessary to better define the ground elevation and surge 
elevation in this area.  
[February 2002]
D.2.6.4	Output Description
The output of the program provides all the data necessary for plotting the BFEs and flood 
insurance risk zones along the transect.  The output is in six parts:  
Part 1 - Input
This is a printout showing all input data lines and the parameters assigned to each line, both 
manually and by default.  This is followed by a more detailed printout with column headings for 
each input data line.  When VH and MG Lines are used, a separate insert will be printed directly 
beneath the MG Line showing any default values supplied by the computer.  
Part 2 - Controlling Wave Heights, Spectral Peak Wave Period, and Wave Crest Elevations
This is a list of the calculated controlling wave heights, spectral wave peak periods, and wave 
crest elevations at the end point of each fetch and obstruction of the input, and at calculation 
points generated between the input stations.  
Part 3 - Location of Areas Above 1-Percent-Annual-Chance Surge
This is a list of the locations of areas where the ground elevation is greater than the 1-percent-
annual-chance stillwater (surge) elevation.  Only areas identified by AS lines are listed.  
Part 4 - Location of Surge Elevations  
This is a list of the 10- and 1-percent-annual-chance stillwater (surge) elevations and the 
stationing of the points where each set of SWELs first becomes fully effective.  
Part 5 - Location of V Zones  
This is a list of the locations of the V/A Zone boundary and locations of the V Zone areas relative 
to these boundaries.  The stationing is given for each V/A Zone boundary.  The locations of the V 
Zone areas in relation to these boundaries are given as windward or leeward of the boundary.  
Part 6 - Numbered A Zones and V Zones  
This is a list of the zone data needed to delineate the flood hazard boundaries on the FIRM.  The 
location of a flood zone boundary and the wave crest elevation at that boundary are given on the 
left.  Between the boundary listings are the zone designations and FHFs.  Under FEMA's Map 
Initiatives Procedure guidelines, all numbered V and A Zones should be changed to VE and AE 
Zones, respectively (elevations will not change), and the FHFs can be ignored (FEMA, 1991).  
When the same zone and elevation are repeated in the list, they should be treated as a single 
zone.
[February 2002]
D.2.7	Mapping of Flood Elevations and Zones
Requirements for reviewing the initial model results and identifying flood insurance risk zones, 
guidance and examples for determining transects, and guidance for depicting the analysis on the 
FIRM are presented in this subsection.
[February 2002]
D.2.7.1	Review and Evaluation of Basic Results
Prior to mapping the flood elevations and zones, the Mapping Partner shall review results from 
the models and assessments from a common-sense viewpoint and compare them to available 
historical data.  When using these models, there is the potential to forget that the transects 
represent real shorelines of sandy beaches, rocky or cohesive bluffs, wetlands being subjected to 
extremely high water, waves, and winds.  Familiarity and experience with the coastal area being 
modeled or similar areas should provide an idea of what is a "reasonable" result.  
Use of the historical data is also very important in evaluating whether the results are reasonable.  
It would be very convenient if data from a storm closely approximating the 1-percent-annual-
chance event were available, but this is seldom the case.  Although most historical flood data are 
for storms less intense than a 1-percent-annual-chance event, these data will still indicate, at a 
minimum, what areas should be in flood zones.  For instance, if a storm that produced an 
extreme flood below the 1-percent-annual-chance SWEL generally caused structural damage to 
houses 100 feet from the shoreline, a "reasonable" Zone VE width must be at least 100 feet.  
Similarly, houses that collected flood insurance claims for the same storm should be at least in a 
Zone AE, AH, or AO.  If the analyses of the 1-percent-annual-chance flood produce flood zones 
and elevations indicating lesser hazards than those recorded for a more common storm, the 
analyses should be reevaluated.  One possible explanation can be that a new coastal structure acts 
to reduce flood hazards locally.  
If there are indications that a reevaluation is needed, the Mapping Partner shall determine 
whether the results of the erosion assessment are appropriate. The Mapping Partner shall attempt  
to compare the eroded profile to past effects, whether in the form of profiles, photographs, or 
simply descriptions.  A general idea of what happened previously can be sufficient. The Mapping 
Partner shall use judgment and experience to project previous storm effects to the 1-percent-
annual-chance conditions and to ensure that the eroded profile is consistent with previous events.  
The Mapping Partner shall examine other data input to the assessments of wave effects.  This 
includes checking that the SWELs, wave heights, wave periods, and fetch lengths were used 
correctly and are consistent with the historical data.  Further consideration might be given to 
examining if the buildings or structures modeled would be destroyed by the storm or if the 
buildings are on pilings above the flooding.  
The main point to be emphasized here is that the results should not be blindly accepted.  There 
are many uncertainties and variables in coastal processes during an extreme flood and many 
possible adjustments to methodologies for treating such an event.  The validity of any model is 
demonstrated by its success in reproducing recorded events.  Therefore, the model results must 
be in basic agreement with past flooding patterns, and historical data must be used to evaluate 
these results.  
[February 2002]
D.2.7.2	Identification of Flood Insurance Risk Zones
The Mapping Partner shall identify the flood insurance zones and BFEs including wave heights 
be identified on each transect plot before delineating the flood insurance zones on the work 
maps, because of additional wave effects along with the 1988 redefinition of Coastal High 
Hazard Area to include the primary frontal dune.  The existing topography, eroded transect, 
combination of shore effects in the wave envelope, and other results from wave overtopping 
assessment are all important to the proper identification of flood insurance risk zones.  
Specifically, as discussed in Subsection D.2.1.2, the existing ground profile defines an 
appropriate extent of the primary frontal dune, as a ridge of sand bounded by relatively steep 
slopes.  As discussed in Subsection D.2.4.5, the eroded transect for cases of duneface retreat may 
imply that flood hazards due to wave overtopping extend into an area landward of the WHAFIS 
results.  In addition, as discussed in Subsection D.2.5.7, wave overtopping of stable shore 
barriers can result in flooding to areas above the mean elevation of wave runup.  However, the 
main consideration for integrated treatment of wave-controlled flood elevations is to define the 
wave envelope joining height and runup effects.  
This wave envelope is a combination of representative wave runup elevation with the controlling 
wave crest profile determined by WHAFIS.  The wave crest profile is plotted on the transect 
from the data in Part 2 of the WHAFIS output.  A horizontal line is extended seaward from the 
wave runup elevation to its intersection with the wave crest profile to obtain the wave envelope, 
as shown in Figure D-25.  If the runup elevation is greater than the maximum wave crest 
elevation, the wave envelope will be a horizontal line at the runup elevation.  Conversely, if the 
wave runup is negligible or was not modeled, the wave crest profile becomes the wave envelope.  
Flood insurance risk zones are defined basically by the wave envelope along with the general 
zone descriptions in Table D-13.  Those results are supplemented by runup and overtopping 
considerations, as introduced previously.  The following material outlines the process of flood 
insurance risk zone identification, with specific examples presented in the next section to 
illustrate some usual results.  
Table D-13.  Descriptions of Coastal Flood Insurance Risk Zones
Zone VE	Coastal High Hazard Areas where wave action and/or high-velocity water can 
cause structural damage in the 1-percent-annual-chance flood.  These areas are 
primarily identified by: (1) the area where 3-foot or greater wave height could 
occur (this is the area where the WHAFIS wave crest profile is 2.1 feet or more 
above the SWEL), (2) the area where the eroded ground profile is 3 feet or more 
below the representative runup elevation, and (3) the entire primary frontal dune, 
by definition.  Subdivided into elevation zones with BFEs assigned.  
Zone AE 	Areas of inundation by the 1-percent-annual-chance flood, including wave heights 
less than 3 feet and runup elevations less than 3 feet above the ground.  These 
areas are also subdivided into elevation zones with BFEs assigned.  
Zone AH 	Areas of shallow flooding or ponding, with water depths of 1 to 3 feet.  These 
areas are usually not subdivided, and a BFE is assigned.  
Zone AO 	Areas of sheet-flow shallow flooding where overtopping water flows into another 
flooding source.  These areas are designated with 1-, 2-, or 3-foot depths of 
flooding.  
Zone X 	Areas above 1-percent-annual-chance flood inundation.  On the FIRM, shaded 
Zone X is inundated by the 0.2-percent annual chance flood, unshaded Zone X is 
above the 0.2-percent annual chance flood.
For a complete listing of flood insurance risk zones, refer to Section 1.4.2.7.1 of Volume 1 of 
these Guidelines.


 


The first step in identifying the flood insurance risk zones on the transect is locating the inland 
extent of the VE Zone, also known as the VE/AE boundary.  The VE-Zone limit for each of the 
three criteria is identified, and the VE/AE boundary placed at the one furthest landward, as 
shown in Figure D-26.  The Mapping Partner may need to move that boundary further inland in 
the vicinity of a wave barrier where severe overtopping is indicated for the 1-percent-annual-
chance flood, so high-velocity impacts occur over a limited landward area.  
The Mapping Partner shall extend the Zone AE from the VE/AE boundary to the inland limit of 
1-percent-annual-chance inundation, which is a ground elevation equal to the representative 
runup elevation, or the 1-percent-annual-chance SWEL if runup is negligible.  The Mapping 
Partner may designate additional areas of shallow flooding or ponding for the 1-percent-annual-
chance event as Zone AH or Zone AO.  In cases of severe wave overtopping effects, a VE Zone 
may abut areas designated as Zone AH or Zone AO.  The Mapping Partner shall label all areas 
above the 1-percent-annual-chance inundation as Zone X.  
The Mapping Partner shall then subdivide the Zone AE and VE areas into elevation zones with 
whole-foot BFEs assigned according to the wave envelope.   Ideally, the Mapping Partner would 
establish an elevation zone for every BFE in the wave envelope; but because these zones are 
mapped on the FIRM so that buildings or property can be located in a flood insurance risk zone, 
the Mapping Partner shall use a minimum width for the mapped zone to provide a usable FIRM.  
For coastal areas, the minimum zone width is 0.2 inch on the FIRM.  For identifying elevation 
zones on the transect, the minimum width is 0.2 times the final FIRM scale; for example, a width 
of 80 feet for a FIRM at a scale of 1 inch equals 400 feet, or a width of 100 feet for a FIRM at a 
scale of 1 inch equals 500 feet.
The Mapping Partner shall not subdivide the horizontal runup portion of the wave envelope, if 
any; the runup elevation, rounded to the nearest whole foot, is the BFE.  The Mapping Partner 
shall subdivide the WHAFIS wave crest profile.  Generally, the VE Zone is subdivided first.  
Initially, the Mapping Partner shall mark the location of all elevation zone boundaries on the 
transect.  Because whole-foot BFEs are being used, these should always be at the location of the 
half-foot elevation on the wave envelope.
The Mapping Partner shall combine elevation zones that do not meet the minimum width with an 
adjacent zone or zones to yield an elevation zone wider than the minimum.  The BFE for this 
combined zone is a weighted average of the combined zones.  Often, in subdividing VE Zones, 
the maximum BFE is located just inside the mapped shoreline, and the remainder of the VE Zone 
is then subdivided into elevation zones of the minimum width.  
The Zone AE, if wide enough, shall be subdivided in the same manner.  If the total AE Zone is 
less than the minimum width, the lowest elevation VE Zone is usually assigned to that area.  This 
situation typically occurs for steep or rapidly rising ground profiles, and it is not unreasonable to 
designate the entire inundated area as a VE Zone.  In some cases, however, it may be appropriate 
for the Mapping Partner to extend the AE Zone slightly into the next zone seaward in order to 
satisfy the minimum width requirement.  


 


Relatively low areas inland of zones with assigned wave elevations may be subject to shallow 
flooding or ponding of flood water; the Mapping Partner shall designate these areas as Zone AH 
or Zone AO.  Such designations can be relatively common landward of coastal structures and 
dunes, where wave overtopping occurs.  Identifying appropriate zones and elevations may require 
particular care for dunes, given that the entire primary frontal dune is defined as Coastal High 
Hazard Area.  Although the analyses may have determined a dune will not completely erode and 
wave action should stop at the retreated duneface with only overtopping possibly propagating 
inland, the Mapping Partner shall designate the entire dune as Zone VE.  The Mapping Partner 
shall assign the BFE at the duneface for the remainder of the dune.  
It may seem unusual to use a BFE that is lower than the ground elevation, although this is 
actually fairly common.  Most of the BFEs for areas where the dune was assumed to be eroded 
are also below existing ground elevations.  In these cases, it is the VE Zone designation that is 
most important to the NFIP, under current regulations, structures in VE Zones must be built on 
pilings and prohibits alterations to the dune.  
[February 2002]
D.2.7.3	Transect Examples
Figure D-26 provides a schematic summary for the three criteria potentially defining the 
landward limit to the Coastal High Hazard Area.  The examples discussed below depict idealized 
transects of typical types to illustrate common flood hazard zonations in a quantitative way.  
Coastal erosion is a dominant consideration for the first set of examples.  The second set of 
examples addresses some usual effects at stable shore barriers exposed to extreme wave action.  
Figure D-27 presents an example of dune removal with appreciable runup occurring on the 
eroded profile.  For this transect, the VE Zones with BFEs of 13, 14, and 15 feet are too narrow 
to be mapped, so they are averaged to a BFE of 14 feet.  The Zone VE, elevation 12 feet, is 
enlarged slightly to include some of the elevation 13-foot area so that the boundary would be 
located at the dune toe or 5-foot contour line, a feature easily identified on the work map.  The 
boundary between the Zone VE, elevation 14 feet and the Zone VE, elevation 16 feet is located 
just landward of the shoreline.  The Zone AE, elevation 12 feet, in Figure D-27 is only 70 feet 
wide, slightly less than the minimum mapping width.  In this example, the Mapping Partner 
would have to examine the work map to determine if this zone might be wider or narrower in the 
contiguous area.  If wider, the Zone AE should be used; if narrower, the designation extended 
through this area should be Zone VE, elevation 12 feet.  
Figure D-28 illustrates an example of a relatively high retreated duneface.  A mean runup 
elevation of 13 feet is calculated for the eroded duneface.  This elevation is assigned through the 
dune, all of which is designated as Zone VE.  Because the dune remnant extends more than 7 feet 
above the SWEL, no flooding landward of the dune is indicated by designating the area as Zone 
X.  Note that the retreated dune profile shifts the 0.0 foot elevation shoreline 65 feet seaward.  
Because the existing 0.0 foot elevation shoreline is used on the work map, the Zone VE, 
elevation 16 feet, is located just landward of the existing shoreline.  


 


 


Figure D-29 illustrates an example of a retreated duneface with a relatively small remnant having 
low relief.  A mean runup elevation of 12 feet is calculated for the eroded profile, and this flood 
elevation is assigned through the dune, all of which is designated as Zone VE .  The division into 
separate map zones is similar to the division in Figure D-28.  Because the dune remnant extends 
less than 7 feet above the SWEL, appreciable wave overtopping is expected during the 1-percent-
annual-chance flood.  An area landward of the dune of about the minimum mapping width is 
designated as a Zone AO, depth 1 foot.  
Figure D-30 illustrates an example of dune removal where there is some runup and overtopping 
of the remaining stub.  As in Figure D-27, the VE Zone with a runup elevation of 11 feet is 
extended to the dune toe and the Zone VE, elevation 16 feet, is located just landward of the 
shoreline.  Although elevation 14 feet is shown on Figure D-30 for the intermediate VE Zone, 
elevation 13 feet could also be used; adjacent transects should be examined and a compatible 
BFE should be selected.  Also note that the boundary between the Zone AO, depth 1 foot, and the 
Zone AE, elevation 7 feet, is at the intersection of the SWEL and ground profile.  
An eroded bluff is shown in Figure D-31.  The angle of the bluff face remains the same while the 
seaward extension from the toe is a 1:40 slope.  The computed runup elevation slightly exceeds 
the bluff crest and is higher than the maximum wave crest elevation.  The area is designated 
Zone VE, elevation 18 feet, until the difference between the runup elevation and the ground is 
less than 3 feet.  In this figure, the Zone AE, elevation 18 feet, is slightly narrower than the 
minimum mapping width.  As was recommended for the example in Figure D-27, the 
neighboring area on the work map should be examined to determine if this zone should be 
mapped.  AE Zones are usually not mapped for bluffs unless computed runup exceeds the bluff 
crest, as shown in Figure D-31.  (Note: Figures D-16 and D-17 outline another flooding treatment 
of bluffs where computed runup is well above the crest.)
On sandy shores, transects usually are extended across barrier islands, marshes, inland water 
bodies, etc., such that at least two VE Zones can be identified.  Procedures in these cases are the 
same, with elevation averaging also very common.  With a little practice, identification of the 
flood zones and elevations becomes fairly routine using the wave envelope and transect profile.  
With shore structures having steep slopes, runup elevations are relatively high and a wide range 
of wave hazards can occur, including erosion or scour near the structure.  These circumstances 
may result in a variety of distinct and compact situations, where appreciable engineering 
judgment can be required for appropriate assessment of flood hazards.


 


 
 


 


Figures D-32, D-33, and D-34. illustrate schematic effects for a few basic configurations, 
presuming the structures remain intact through the 1-percent-annual-chance flood and no 
appreciable shore erosion occurs
Figure D-32 illustrates an example of moderate structure overtopping expected for waves 
accompanying the 1-percent-annual-chance flood.  The structure crest has sufficient freeboard 
above the 1-percent-annual-chance SWEL to contain a calculated mean runup of 6 feet, but 
extreme wave runups are likely to overtop the structure intermittently.  The entire extent of shore 
structure is treated as a unit and designated as a VE Zone, and is assigned the mean runup 
elevation of 16 feet.  Landward of the structure, an area with at least the minimum mapping 
width is appropriate for designation as Zone AO, depth 1 foot, with the extent of the zone 
depending on ground profile.  
Figure D-33 illustrates an example of a structure extending above the 1-percent-annual-chance 
SWEL but heavily overtopped by wave action.  The calculated mean runup elevation is 5 feet 
above the seaward face, but that is reduced to the maximum excess runup of 3 feet in assigning a 
flood elevation of 16 feet for the shorefront VE Zone.  That zone extends through the entire 
structure and over an additional 30 feet landward, because likely wave impact area reaches 
beyond the structure during the 1-percent-annual-chance flood.  Cumulative wave overtopping 
yields ponding within an additional landward area that is 100 feet wide, which is designated as 
Zone AO, depth 2 feet.  
Figure D-34 illustrates an example of a structure covered by 3 feet of water during the 1-percent-
annual-chance flood.  Flood depth is not sufficient for waves 3 feet in height to propagate inland 
of the structure, but the V Zone must extend to 30 feet landward of the structure, in view of likely 
wave effects through the flood's course.  The shore structure is too narrow for multiple V Zones 
to be delineated, so there is one designation of Zone VE, elevation 13 feet.  Landward of that 
zone, further wave hazards occur in the Zone AE, elevation 11 feet.  
In examining Figures D-32, D-33, and D-34, it may seem surprising that relatively high 
structures can result in higher flood elevations, compared to an inundated structure.  However, a 
structure with more freeboard can deflect incident wave action to greater elevations during the 1-
percent-annual-chance flood, so the present zonations are physically appropriate.  The hazard 
zonations landward of coastal structures generally have more importance, and they reflect the 
greater protection provided by higher but durable structures.  
[February 2002]
D.2.7.4	Mapping Procedures
Properly integrated delineation of the results of flooding analyses involves judgment and skill in 
reading topographic and land cover maps.  The time and effort put forth to determine the flood 
elevations and extents will be negated if the results of these analyses are not properly delineated 
on the FIRM.  The FIRM is usually produced from the work maps described in Subsection D.2.2. 
Therefore, the Mapping Partner shall transfer the flood zones and elevations identified on the 
transects to the work maps and interpolate boundaries between transects.  The Mapping Partner 
shall set up the work maps with contour lines, buildings, structures, vegetation, and transect lines 
clearly located.  Because roads are often the only fixed physical features shown on the FIRM, the
 



 


 


Mapping Partner shall ensure that other features and the flood zone boundaries are properly 
located on the work maps in relation to the centerline of the roads as they will appear on the 
FIRM.  
For each transect, the Mapping Partner shall transfer the identified elevation zones from the 
transect to the work maps, marking the location of the boundaries along the transect line so that 
boundary lines can be interpolated between transects.  The Mapping Partner shall ensure that 
boundaries are marked at the correct location.  Because of erosion assumptions, the location of 
the elevation 0.0 shoreline changes on the transect but not the work maps.  
Using the transect profile, the Mapping Partner shall determine the location of the zone change in 
relation to a physical feature (e.g., ground contour, back side of a row of houses, 50 feet into a 
vegetated area) and delineate the boundary line for the area represented by that transect along this 
feature.  The Mapping Partner shall measure the widths of the zones carefully; zones that narrow 
to less than 0.2 inch must be tapered to an end.  Likewise, if the zone becomes much wider, it 
may be possible to break an averaged elevation zone into two mapped elevation zones.  
One of the more difficult steps in delineating coastal flood zones and elevations is the transition 
between transect areas.  Good judgment and an understanding of typical flooding patterns are the 
best tools for this job.  Initially, the Mapping Partner shall locate the area of transition (an area 
not exactly represented by either transect) on the work maps.  The Mapping Partner shall then 
delineate the floodplain boundaries for each transect up to this area.  The Mapping Partner shall 
examine how a transition can be made across this area to connect matching zones and still have 
the boundaries follow logical physical features.  Other transects similar to this area could give an 
indication of flooding.  Sometimes the elevation zones for the two contiguous transects are not 
the same; in such cases, the Mapping Partner may have to taper the zones to an end or enlarge the 
zones and subdivide them in the transition area.  
Communities with significant flooding hazards from wave runup may have one transect 
representing more than one area because the areas have similar shore slopes.  In this case, the 
Mapping Partner shall identify the different areas and delineate the results of the typical transect 
in each area.  Transition zones may be necessary between areas with high runup elevations to 
avoid large differences in BFEs and to smooth the change in flood boundaries.  These zones are 
to be fairly short and cover the shore segment with a slope not exactly typical of either area.  The 
Mapping Partner shall determine the transition elevation using judgment in examining runup 
transects with similar slopes.  The Mapping Partner shall not use transition zones if there is a 
very abrupt change in topography, such as the end of a structure.  
Lastly, Mapping Partner shall map the Zone X areas.  The Mapping Partner shall show areas 
below the 0.2-percent annual chance SWEL that are not covered by any other flood zone as Zone 
X  (shaded) on the FIRM.  Often the maximum runup elevation is higher than the 0.2-percent-
annual-chance SWEL; in such cases, the Zone X (shaded) designation will be used in that area.  
All other areas are designated Zone X without shading.  
Because flood elevations are rounded to the nearest whole foot, the Mapping Partner does not 
need to spend hours resolving a minor elevation difference.  Also, because structures or proposed 
structures must be located on the FIRM, the Mapping Partner shall attempt whenever possible to 
smooth the boundary lines and to follow a fixed feature such as a road.  In preparing the FIRM, 
the Mapping Partner shall ensure that the mapped results are technically correct and but the 
FIRM is easy for the local insurance agent, building inspector, or permit officer to use.  
[February 2002]
D.2.8	Required Documentation
The Mapping Partner shall fully document the coastal flood hazard determination for each 
affected community.  Because FIS Reports and FIRMs form the basis of Federal, State, and local 
regulatory and statutory enforcement mechanisms and are subject to administrative appeal and 
litigation, Mapping Partners shall ensure that all technical processes and decisions are recorded 
and documented.  The FIS Report may not contain all the documentation that would be needed 
for a response in the event that the study results are questioned.  Therefore, the Mapping Partner 
shall prepare an engineering report for each study.  This report will provide detailed data needed 
by FEMA or the community to reconstruct or defend the study results on technical grounds.  The 
minimum information required for the engineering report is summarized below.
Basic Data. 
In this section, the Mapping Partner shall include all contacts made to obtain data for the study.  
All basic data used must be fully referenced and, if possible, reproduced in the report.  All 
historical flood information must be documented in this section, even if the Mapping Partner did 
not use the information in quantitative analyses.  
Transects  
The Mapping Partner shall show all transects on a transect location map.  Each transect must be 
plotted separately and show the erosion assessment, input data for wave models, wave envelope, 
and zone determination.  
Model Input and Output 
The Mapping Partner shall provide computer printout listings for input and output data for both 
the Wave Runup and Wave Height Models for all the transects.  These listings must be keyed to 
the transect location map and transect plots.  
Study File  
During the course of the study, the Mapping Partner shall maintain a file containing records of all 
coordination, activities, and decisions.  This is especially important where nonstandard 
approaches were used and engineering judgment played a significant role.  The Mapping Partner 
shall ensure this file meets the requirements for a Technical Support Data Notebook as 
documented in Appendix M of these Guidelines.  
[February 2002]


D.3	Wave Elevation Determination and V Zone Mapping: 
Great Lakes
Methodologies for determining coastal flood elevations and flood insurance risk zones have been 
adopted and refined over a period of time, as recounted in Section D.2 and in FEMA's Guidelines 
and Specifications for Wave Elevation Determination and V Zone Mapping (1995).  Standard 
treatments for U.S. seacoast sites address wave heights, wave crest elevations, wave runup, and 
coastal erosion accompanying the 1-percent-annual-chance flood (FEMA, 1995).  The effects of 
such waves determine flood elevations and the extent of Coastal High Hazard Areas (V Zones). 
Until recently, wave effects were not taken into account along Great Lakes shores, but storms 
during the high water levels from 1985 to 1987 prompted reconsideration of this omission.  A 
USACE study in 1989 concluded that recent significant storm damage at New York, Michigan, and 
Illinois sites confirmed the importance of wave runup contributions to actual coastal flooding on the 
Great Lakes.  That finding led to specific calculation procedures to determine runup elevations 
appropriate to Great Lakes coasts with barriers to wave propagation (FEMA, 1991).  Later, the 
standard NFIP seacoast model for wave height analysis was modified to apply to the lower wind 
speeds typical of Great Lakes events, and a detailed review addressed wave conditions and coastal 
erosion processes and quantities accompanying extreme floods at various U.S. lake sites (Dewberry 
& Davis, 1995).  All necessary guidance has now been developed for treating wave effects in 
communities located along the Great Lakes 
This subsection unifies the technical policies, procedures, and methodologies relevant to 
conducting a flood hazard study for a Great Lakes coastal community.  In addressing coastal studies 
for specific geographical regions, these Guidelines and FEMA's Guidelines and Specifications for 
Wave Elevation Determination and V Zone Mapping (1995) serve as user guides.  Appropriate 
application of this guidance, along with an understanding of coastal engineering principles, will 
assist Mapping Partners in determining coastal flooding elevations and hazards and presenting this 
information on the FIRM. 
[February 2002]
D.3.1	Appropriate Treatments
The  methodologies that shall be used to treat all the wave hazards possibly associated with a 1-
percent-annual-chance flood are summarized in Table D-14.  However, Mapping Partners must  
recognize that not every wave effect that occurs on the Great Lakes must be addressed for every 
flood hazard study or for every lakeshore community.  To minimize unnecessary effort, it is useful 
early in the study process to identify those wave effects that can contribute noticeably to the BFEs 
and thus should be analyzed.  Whether or not a wave treatment is appropriate depends primarily on 
the basic type of coastal topography, as outlined in Table D-14.  


Table D-14.  Important Wave Treatments for Typical Coastal Topographies
COASTAL TOPOGRAPHY
IMPORTANT WAVE TREATMENTS

EROSION
RUNUP
WHAFIS
Rocky bluff

x
x
Sediment bank or bluff
x
x
x
Sandy beach, small dunes
x

x
Sandy beach, large dunes
x
x
x
Open wetlands


x
Shore protection structure

x
x

The objective of a coastal study is to provide legible and accurate flood hazard maps with 
appropriate BFEs including wave contributions.  Although procedures to define V Zones are 
fully documented in these Guidelines, mapping V Zones may not be appropriate in some Great 
Lakes areas.  Both engineering and practical judgment are required for a proper decision on this 
matter.  The typical study finding is a narrow V Zone, making its usefulness uncertain on maps at 
usual scales. Also, relatively small numbers of existing coastal buildings are likely to be affected 
by possible V-Zone designations along some Great Lakes.
V Zones are to be mapped only when the Regional Project Officer (RPO) approves such action.  
Some common exceptions to required approval might include coastal areas lakeward of sizable 
bluffs or designated as primary frontal dunes, so that the V Zone can be clearly delineated.
A flowchart with the basic study procedures for defining flood hazards in the Great Lakes region 
is presented in Figure D-35. 



 


[February 2002]
D.3.2	Data Requirements for Coastal Flood Hazard Analyses
A coastal flood hazard analysis begins with collecting the data and information required for the 
ensuing analyses, including the input needed for the computer models.  The coastal models 
discussed here are executed along transects, which, as discussed earlier in this Appendix, are 
cross sections taken perpendicular to the mean shoreline to represent a segment of coast with 
similar characteristics.  Thus, collected data are compiled primarily for use in developing 
transects and for locating and detailing the results on work maps.  Work maps are to show the 
topography and land cover at a scale with sufficient detail to properly delineate the results of the 
analyses and interpolate between transects.
Data collection is to start at the community level and proceed with inquiries to appropriate 
county, State, and Federal agencies.  To pursue any suggestions provided by government 
agencies, private firms specializing in topographic mapping or aerial photography may also be 
contacted.
This subsection describes the data requirements for coastal flood hazard analyses.
[February 2002]
D.3.2.1	Stillwater Elevations
The USACE's Revised Report on Great Lakes Open-Coast Flood Levels  (1988) is FEMA's 
source for SWELs on the Great Lakes, at recurrence intervals of 10, 50, 100, and 500 years 
(reflecting 10-, 2-, 1-, and 0.2-percent-annual-chance flood elevations, respectively).  
Documented flood elevations pertain to specific U.S. reaches of open coast, defined as "lake 
shoreline which is unprotected by the presence of islands and which is uninterrupted by bays."  
These elevations are based on a standardized analysis of maximum annual water levels from 
long-term gage records (1900 to 1986) and are referenced to NGVD.
The USACE report on Great Lakes flood levels is divided into Phase I and Phase II reports.  The 
Phase I report provides SWELs for most of the U.S. shoreline of Lake Superior (divided into five 
separate reaches), Lake Michigan (nine reaches), Lake Huron (eight reaches), Lake St. Clair (one 
reach), Lake Erie (24 reaches), and Lake Ontario (five reaches).  In Subsection D.3.9, charts 
identifying separate reaches and the flood elevations on each lake are reproduced; except on Lake 
Erie, flood elevations usually remain constant over tens of miles along the shore.  The Phase II 
report provides the flood levels for connecting channels and addresses general methods for 
developing flood levels in other areas, such as bays, inlets, and sheltered shorelines.  For some of 
these areas, separate reports such as the "Saginaw Bay Flood Levels Report" for Lake Huron, 
have been prepared to document the SWELs (USACE, September 1989).
[February 2002]
D.3.2.2	Transect Locations
Transects for coastal flood hazard analyses are to be located with careful consideration given to 
the physical and cultural characteristics of the land so that they will closely represent conditions 
in the vicinity of the transect.  If they are carefully placed, excessive mapping interpolation of the 
BFEs between transects, as well as unnecessary study effort, can be avoided.  The transects are to 
be placed more closely together in areas of complex topography, dense development, and unique 
flooding, and where computed wave heights and runup may be expected to vary significantly.  
Wider spacing may be appropriate in areas having more uniform characteristics.  For example, a 
stretch of developed shoreline with various building densities, protective structures, and 
vegetation may require a transect every 1,000 feet or so, whereas a long stretch of undeveloped 
shoreline with a continuous dune or bluff of fairly constant height and shape, and similar 
landward features may require a transect only every 1 to 2 miles.
In areas where runup is significant, the location of transects is governed by variations in shore 
slope or steepness.  In other areas where dissipation of wave heights is significant to the 
computation of flood hazards, transect location is based on variations in land cover, such as 
buildings and vegetation.  Often, areas with similar characteristics may be scattered throughout a 
community, and the results from one transect are also representative of other locations and can be 
delineated accordingly.
The Mapping Partner performing the coastal flood hazard study shall locate transects on the work 
map to be submitted with the analysis, and shall compile the input data and displayed the data on 
individual profiles for each transect.  The Mapping Partner shall take the data (e.g., topography, 
development, vegetation) not only at the transect site, but for the entire area or length of shoreline 
represented by the transect so that the input data depict average characteristics of the area.  The 
Mapping Partner may divide the work map into transect areas to help in compiling the data.
[February 2002]
D.3.2.3	Topographic Data
Topographic data must have a contour interval of equal or greater detail than that used for the 
effective FIS, and a minimum interval of 5 feet or 1.5 meters.  While more detailed information, 
such as spot elevations or a smaller contour interval, can be useful in defining the dune or bluff 
profile and in delineating floodplain boundaries, it is required only when a map revision request 
with new coastal analyses is based on new detailed topographic data.   As discussed in Volume 2, 
the data, usually in the form of maps, shall be certified and shall reflect current conditions in the 
area of the analysis or, at a minimum, conditions at a time more recent than the topographic data 
used in the effective FIS.
Topography must extend lakeward at least to the Low Water Datum defined for each Great Lake, 
as listed in Table D-14.  The Low Water Datum corresponds to extremely low annual means of 
lake level during the 1900s and is described in terms of the International Great Lakes Datum of 
1985 (IGLD85).  The relation of NGVD29 to IGLD85 needs to be defined for each coastal flood 
hazard analysis site.  NGVD29 is required as the datum for the topographic map.  
If possible, the Mapping Partner shall check the shore topography to note any changes caused by 
construction, erosion, or other causes and document any significant erosion by location with 
descriptions, drawings, and/or photographs.  The Mapping Partner is not required to field survey 
transects unless available topographic data are unsuitable or incomplete.  
The community, county, and state are usually the best sources for topographic data. The Mapping 
Partner shall examine USGS 7.5-minute series topographic maps.  The USGS maps may have a 
5-foot contour interval, and if not, they are still often useful as a reference for planimetric 
features in the study area.  
Table D-14.  Elevations of Low Water Datum on the Great Lakes
LOCATION
LOW WATER DATUM ELEVATION:

FEET ABOVE
IGLD85
FEET ABOVE NGVD29
(APPROXIMATE)
Lake Superior
601.1
601
Lake Michigan
577.5
578
Lake Huron
577.5
578
Lake St. Clair
572.3
573
Lake Erie
569.2
570
Lake Ontario
243.3
244

[February 2002]
D.3.2.4	Land-Cover Data
The land-cover data include information on structures and vegetation.  Stereoscopic aerial 
photographs can provide the required data on structures and some of the data on vegetation.  The 
aerial photographs must not be more than 5 years old unless they are updated by surveys.  A 
local, county, or State agency may have the coastline photographed on a periodic basis.  That 
agency may provide the photographs or give permission to obtain them from its contractor.  
Because topographic maps are often developed from aerial photographs, the Mapping Partner 
also shall contact the mapping contractor for the topographic maps for data.
Aerial photographs can provide the required data on tree- and bush-type vegetation and can be 
used to identify areas although not the specific type of grass-like vegetation.  National Wetland 
Inventory maps from the U.S. Fish and Wildlife Service and color infrared aerial photographs 
can provide more specific data required for marsh plants.  Ground-level photographs and surveys 
also are useful in providing information on the plants (e.g., density, species).  State offices of 
coastal zone management, park and wildlife management, and/or natural resources should be 
able to provide information on significant vegetation types.  Also, the Mapping Partner shall 
contact local universities with coastal studies and/or Sea Grant programs.  The Mapping Partner 
may conduct field surveys in lieu of the above sources, but these are more cost effective when 
used only to verify some of the data obtained from these sources.  
[February 2002]
D.3.2.5	Bathymetric Data
It is not possible to provide precise guidance on the extent of bathymetry needed for a Great 
Lakes FIS.  In some cases, only typical water depths in the vicinity of shore structures will be 
required in the analysis of wave effects.  For sand beaches, bathymetry out to water depths of 
approximately 30 feet is required for wave treatments.  Bathymetry further offshore may be 
useful for interpreting likely differences between nearshore and offshore wave conditions. (See 
Subsection D.3.2.6).  An advisable procedure for studies of Great Lakes sites is to gather any 
readily available bathymetric data, but to defer all data reduction or analysis until the need is 
firmly established.  Bathymetric data can be acquired from National Ocean Survey nautical 
charts, although any reliable source can be used.  
[February 2002]
D.3.2.6	Offshore Wave Characteristics
One basic assumption in conducting coastal wave analyses is that wave direction must have some 
onshore component, so wave hazards occur coincidentally with the 1-percent-annual-chance 
flood.  That assumption appears generally appropriate on open coasts and bay shores of the Great 
Lakes, where the 1-percent-annual-chance SWEL must include some contribution from storm 
surge and usually requires an onshore wind component.  However, the assumption of onshore 
waves along the shores of connecting channels, near inlets, and behind protective islands may 
require detailed examination.
Once the Mapping Partner has confirmed that sizable waves travel onshore during the 1-percent-
annual-chance flood, the most important specification is wave period rather than wave height.  
This is because wave heights are severely limited by shallow water at sites where the models 
described in Subsections D.3.5 and D.3.6 are applied.  Wave treatments within those models 
provide depth-limited wave heights controlled by the wave period, so that the specified period 
influences the results of coastal wave analyses.  The specified wave period can pertain to 
offshore storm waves in deep water, because dominant or spectral peak period is commonly 
unchanged during complex wave transformations near the shore.  The most notable sources of 
suitable storm-wave information along Great Lakes coasts are the USACE Coastal Engineering 
Research Center (CERC) Wave Information Studies (WIS) Nos. 22, 23, 24, 25, and 26, with one 
report for each Great Lake on computed wave conditions in deep water from 1956 to 1987 
(Driver, Reinhard, & Hubertz, 1991 and 1992; Hubertz, Driver, & Reinhard, 1991; Reinhard, 
Driver, & Hubertz, 1991).  Maps locating approximately 300 sites for which computed wave 
information is available, one map for each lake, are included in Subsection D.3.9. 
The draft of "Basic Analyses of Wave Action and Erosion with Extreme Floods on Great Lakes 
Shores" (Dewberry & Davis, 1995) concluded from historical evidence that extreme floods were 
usually accompanied by the local 1/2-year wave condition on Lake Ontario, or by the 3-year 
wave condition on Lakes Erie, Huron, Michigan, and Superior.  Those wave heights can be 
determined using the simple treatment illustrated by Figure D-36.  Tabulated significant wave 
heights in the CERC WIS reports include the extremes for each month/year at every calculation 
site, and the median of each set of results gives the 2-month/2-year wave height.  Extreme wave 
heights at various recurrence intervals usually are well approximated by an exponential 
distribution, so those two known values on a semi-logarithmic graph define other significant 
wave conditions of interest, as demonstrated in Figure D-36.

 


Once a suitable offshore wave height is specified from the CERC WIS reports, the Mapping 
Partner shall determine the wave period crucial to coastal analyses in one of two ways.  The more 
rigorous determination examines the electronic file of calculated conditions for 1956 to 1987, 
extracting cases with the specified wave height and with wave direction toward shore; prevalent 
wave period in those cases should be appropriate to the flood.  Section D.3.9 includes examples 
of appropriate wave conditions derived for several sites on each of the Great Lakes.  An 
alternative procedure considers wave steepness, or ratio of wave height to wavelength, with these 
typical values for storm waves: 0.035 for Lake Ontario or Lake Erie, 0.04 for Lake Huron or 
Lake Michigan, and 0.045 for Lake Superior.  In deep water, the wavelength is 0.16 times the 
gravitational acceleration times the wave period squared, so specified wave steepness and wave 
height imply a suitable wave period for the site.
The hindcast wave study of the CERC WIS reports provides no information for Lake St. Clair, or 
within major embayments and connecting channels of the Great Lakes.  Such sites require an 
independent assessment to define likely wave characteristics associated with the 1-percent-
annual-chance flood.  Fundamental information for such an assessment includes the water basin 
geometry at a site and the meteorology of storms potentially yielding the 1-percent-annual-chance 
SWEL, i.e., capable of generating the surge magnitude needed in addition to a high mean lake 
level.  
Major factors in wave generation are windspeed and duration, local water depth, and fetch 
length.  Fetch length is the over-water distance along which waves arise (USACE, 1984).  In the 
Great Lakes vicinity, a windspeed of 40 mph sustained for several hours is usually appropriate to 
the 1-percent-annual-chance flood.  For some cases, fetch length might be estimated as straight-
line distance in the wind direction, but current guidance specified in the USACE ACES manual 
(USACE, 1992) pertinent to many Great Lakes sites indicates that a more involved analysis of 
restricted fetches must be performed for water basins of relatively complex geometry.  The 
effective fetch length is derived as a weighted average of available distance with angle from the 
wind direction, as outlined in Figure D-37.  A PC-compatible computer program included with 
the ACES manual is convenient for evaluating restricted fetch geometries and provides estimates 
of representative wave height and wave period based upon recommendations by CERC on wave 
generation.  
[February 2002]
D.3.2.7	Coastal Structures
Documentation gathered for each coastal structure that may provide protection from 1-percent-
annual-chance flood hazards should include the following:
*	Type and basic layout of structure;
*	Dominant site particulars (e.g., local water depth, structure freeboard, ice climate); etc.
*	Construction materials and present integrity;


*	


*	Historical record for structure, including construction date, maintenance plan, responsible 
party, and repairs after storm episodes; and 
*	Clear indications of effectiveness/ineffectiveness.
The Mapping Partner may develop much of this information through office activity, including a 
careful review of aerial photographs.  In some cases of major coastal structures, site inspection 
could be advisable to confirm preliminary judgments.
[February 2002]
D.3.2.8	Historical Erosion Accounts
Coastal erosion can occur during any major storm; however, the most significant erosion events 
for the purpose of a coastal FIS are those that occur with major storms during historical periods 
of high lake levels.  Ideal information documenting storm-eroded cross sections will seldom be 
available because studies including repetitively surveyed profiles appear rare, except at some 
Lake Michigan sites.  Although quantitative data may not be available, qualitative information 
can be valuable in confirming that reasonable results are obtained from the erosion assessment.  
The Mapping Partner shall conduct a search for erosion descriptions in newspaper articles or 
other publications, focusing on recent intervals of high mean lake levels.  In addition, State 
agencies may be able to provide long-term recession rates over the study area.  These are helpful 
in demonstrating local susceptibilities to storm-induced erosion.  
[February 2002]
D.3.2.9	Historical Flood Information
Information from previous storms and floods can be valuable in developing proper assessments 
of coastal flood hazards.  This is particularly true on the Great Lakes, because many notably 
extreme events occurred on the four western lakes during 1985, 1986, and 1987 and ample 
information should be readily available for many study sites.  
General descriptions of flooding are useful in determining what areas are subject to flooding and 
in obtaining an understanding of flooding patterns.  More specific information, such as erosion 
associated with the event or the location of buildings damaged by wave action, can be used to 
verify the results of the coastal analyses.  When quantitative data on the effects, recorded water 
elevations, and offshore wave conditions are available, the Mapping Partner shall check those 
data  for proximity to the coastal site and impact on the evaluation.  Those data can be used to 
estimate recurrence intervals for SWEL and wave action during the event and assist in the 
appropriate comparison to the 1-percent-annual-chance flood conditions and SWELs established 
by the USACE for the specific recurrence intervals (1988).  
Local, county, and State agencies are usually good sources for historical data, especially during 
the more recent events.  It is becoming common practice for these agencies to record significant 
flooding with photographs, maps, and/or surveys.  Federal agencies such as the USACE, USGS, 
and NRC prepare post-storm reports for the more severe storms.  Local libraries, newspapers, 
and historical societies may also be able to provide some useful data.  
Additional criteria and submittal requirements for historical information are identified in the 
certification forms package for Study Contractors (SC-1) and the application/certification forms 
package (MT-2) for map revision requests.
[February 2002]
D.3.3	Evaluation of Coastal Structures
The crucial first consideration in evaluating a coastal structure is whether it was properly 
designed and has been maintained to provide protection during the 1-percent-annual-chance 
flood.  If it can be expected to survive the 1-percent-annual-chance flood, the structure should 
figure in all ensuing analyses of wave effects (erosion, runup, and wave height).  Otherwise, it 
should be considered destroyed before the 1-percent-annual-chance flood and removed from 
subsequent transect representations.  
The USACE technical report entitled Criteria for Evaluating Coastal Flood-Protection 
Structures (Walton, Ahrens, Truitt, & Dean, 1989) recommends specific criteria for evaluating 
coastal flood-protection structures in regard to the 1-percent-annual-chance flood.  A FEMA 
memorandum dated April 23, 1990, entitled "Criteria for Evaluating Coastal Flood Protection 
Structures for National Flood Insurance Program Purposes," based on the USACE report, 
provides a self-contained account of the evaluation process.  The criteria in the memorandum 
have been adopted as the basis for NFIP accreditation of new or proposed coastal structures to 
reduce the flood hazard areas and elevations designated on the current NFIP maps.  Ideally, these 
evaluation criteria could be applied to existing coastal structures, but for older structures, design 
and construction information sufficient to complete the formal evaluation is typically 
unavailable.  For these structures, engineering judgment based on visual inspection and any 
historical evidence should be used.  
In general, for evaluation of coastal structures on the Great Lakes the Mapping Partner shall rely 
on engineering judgment firmly based on experience regarding structural stability at sites with 
similar flood and wave climate.  Because extreme floods have been relatively common over the 
past decade on the Great Lakes, the Mapping Partner shall consider historical information about a 
particular structure in its evaluation.  Construction date and damage history of a structure permit 
a performance record to be accumulated for events potentially comparable to the 1-percent-
annual-chance flood.  
Analysis based on historical information and past performance may be complicated by one 
unique aspect of Great Lakes design considerations.  The 1990 FEMA memorandum  specifies 
that representative analyses be carried out at a range of water levels, usually from the Low Water 
Datum to the 1-percent-annual-chance SWEL for Great Lakes sites.  However, incident wave 
conditions associated with the 1-percent-annual-chance flood may be markedly less extreme than 
those expected for lower but more persistent water levels near long-term Mean Lake Level.  
Nevertheless, even where water depth at the structure site strongly limits local wave heights, the 
most severe conditions for design could still occur during the 1-percent-annual-chance flood; 
therefore, the Mapping Partner must consider these conditions.
The USACE technical report identifies the four primary functional types of coastal flood 
protection structures: gravity seawalls, pile-supported seawalls, anchored bulkheads, and dikes or 
levees.  The report recommends as a general policy that "FEMA not consider anchored bulkheads 
for flood-protection credit because of extensive failures of anchored bulkheads during large 
storms" (p. 100).  However, the report provides no examples for the Great Lakes.  Seacoast storm 
conditions are possibly quite different from the 1-percent-annual-chance flood on the Great 
Lakes; therefore, this structure type cannot be completely discredited.
The FEMA memorandum focuses on structures designed for flood protection.  Such structures 
can have a significant impact on the information shown on a FIRM, perhaps directly justifying 
the removal of sizable areas from the Coastal High Hazard Area.  However, structures in other 
categories also are to be considered.  Although a breakwater may act primarily to limit wave 
action, and a revetment primarily to control shore erosion, these structures also can provide 1-
percent-annual-chance flood protection.  The FEMA memorandum places the responsibility on 
local interests to certify new structures; however, it is crucial that the Mapping Partner evaluate 
the structure accurately and consider its effects.  For example, a structure might decrease flood 
impacts in one area, yet increase erosion or wave hazards at adjacent sites.  Of course, the greater 
the potential effects of a coastal structure, the more detailed the evaluation process should be.
As discussed in Volume 2, additional requirements regarding coastal structures are included on 
Form 10 of the Application/Certification forms package (MT-2) for map revision requesters.
[February 2002]
D.3.4	Erosion Assessment
Along many Great Lakes shores, erosion accompanying the 1-percent-annual-chance flood may 
change the location and alter the form of an existing sedimentary barrier extending above the 
local 1-percent-annual-chance SWEL.  Mapping Partners must assess the likely erosion before 
proceeding to determination of additional flood effects dependent on topography, such as wave 
runup or overtopping, or overland wave heights.  Procedures described here are meant to give 
schematic estimates of eroded transect geometry suitable for the purposes of a coastal FIS or map 
revision request on the Great Lakes.
In an erosion assessment relating to the 1-percent-annual-chance flood, Great Lakes coasts may 
be separated into three basic site categories:
1.	Sandy shores with backing dunes or banks;
2.	Backshore bluffs of cohesive material; and
3.	Other shore situations more resistant to erosion during extreme floods, with bedrock, 
wetlands, shore protection, and other conditions.  
For the third category, erosion is usually not too important a consideration, so the major 
distinction for present purposes is between sand dunes and cohesive bluffs.  Besides up-to-date 
coastal topography, information about the basic shore type is crucial for an appropriate erosion 
assessment pertaining to the 1-percent-annual-chance flood.  Also, documented erosion effects 
during a historical flood at the study site can be useful in a valid assessment of 1-percent-annual-
chance flood effects, but such evidence requires careful interpretation, as discussed below.  
Detailed examination of recent record episodes of lake levels (Dewberry & Davis, 1995) 
provides several notable findings:
	Extreme Great Lakes floods usually involve rather moderate storms during relatively brief 
intervals when mean lake level is significantly higher than the long-term average.
	The storm situation for an extreme flood on Lake Ontario is markedly different than on Lake 
Erie, Lake Huron, Lake Michigan, Lake Superior.
	Coastal erosion on the Great Lakes exhibits extreme geographical and temporal variability 
during intervals of high mean lake level.  
Quantitative analysis establishes that Great Lakes erosion cross sections expected during the 1-
percent-annual-chance flood are 270 square feet on Lake Erie, Lake Huron, Lake Michigan, and 
Lake Superior and 190 square feet on Lake Ontario.
These amounts refer to the flood episode alone and lie entirely above the local 1-percent-annual-
chance SWEL.  The stated results derive from Great Lakes verification of an analysis similar to 
that which was performed for Atlantic Ocean and Gulf of Mexico regions for the 540-square-feet 
erosion cross section in seacoast 1-percent-annual-chance floods.  Appropriate application of this 
erosion guidance can depend on basic type of shore morphology, as illustrated in Figures D-38 
(bluff) and D-39 (sand dune).  
The cases consider no shore features lakeward of the basic flood barrier, because any distinct 
topography presumably will be removed by storm erosion before the peak effects to be 
considered.  For the bluff case in Figure D-38, erosion projection is based on a retreated profile 
parallel to the existing bluff, but with a potential adjustment to the eroded face governed by soil 
stability considerations for the site.  For the dune case in Figure D-39, erosion projection makes 
use of an escarpment slope of 45?, corresponding to the usual duneface geometry for storm 
conditions.  In each case, the barrier is presumed to be appreciably more sizable than the 
specified erosion cross section, even though that usually is more appropriate for bluff erosion 
where the barrier in effect is unlimited.  Erosion analysis may be unnecessary for very large 
coastal dunes, extending 20 feet or more above the SWEL; such sand accumulations may be 
considered resistant to notable storm erosion and to wave overtopping on the Great Lakes.
These quite simplified depictions of eroded profile geometry for Great Lakes shores may require 
modification in accordance with site-specific factors, engineering judgment, or the more detailed 
erosion considerations usually appropriate on seacoasts (FEMA, 1995).  Comparison of present 
assessment results to historical effects for notable local floods must recognize the extreme 
variability evident in Great Lakes shore erosion during a given storm.  Documented large or 
small amounts of erosion during a notable historical storm or flood at a particular Great Lakes 
site do not imply that similar effects should be expected for the 1-percent-annual-chance 


 


 


flood.  The only appropriate conclusion to be based directly on historical effects is that if a Great 
Lakes site has experienced no erosion over the past ten years, one should not assume that erosion 
will accompany the 1-percent-annual-chance flood.
The present evaluation guidelines outlined in Figures D-38 and D-39 lead to appropriate flood 
hazard identification, given that sizable wave effects on Great Lakes shores seldom penetrate 
inland past an erodible flood barrier in accordance with the geometrical consideration outlined in 
Figure D-40.  In a Great Lakes FIS, the major result of an erosion assessment is a barrier profile 
both convenient and appropriate for ensuing wave analyses.  
[February 2002]
D.3.5	Wave Runup and Overtopping
Wave runup and overtopping constitute coastal hazards beyond those associated with stillwater 
coastal flooding and incident wave geometry.  Wave runup is the uprush of water on a shore 
barrier intercepting the stillwater level.  The water wedge both thins and slows during its 
excursion up the barrier, as residual momentum from wave motion near the shore is fully 
dissipated.  The most significant characteristic of this process for present purposes is wave runup 
elevation: the vertical height above stillwater level ultimately attained by the extremity of 
uprushing water.  Likely runup must be assessed for wave conditions expected to accompany the 
1-percent-annual-chance flood.  The extent of runup can vary greatly from wave to wave in storm 
conditions, so that a wide distribution of wave runup elevations provides the precise description 
of a specific situation.  Wave overtopping occurs when an individual runup impulse surpasses the 
barrier crest and flood water penetrates inland of the shore barrier, perhaps with wave-like effects 
or with ponding of the flood waters behind the barrier.
Current NFIP policy is that the mean runup elevation (rather than some occasional extreme) for a 
situation is appropriate in mapping coastal hazards of the 1-percent-annual-chance flood.  The 
FEMA Great Lakes Wave Runup Model (GLWRM), which is based on methodologies 
recommended by the USACE, Detroit District, can be used to compute the mean runup elevation, 
as discussed in Subsection D.3.5.1.  Although the GLWRM provides an entirely suitable runup 
elevation, it can treat only the three types of shore situation judged to be most frequently 
encountered on the Great Lakes.  Therefore, adjustment or modification to computed results may 
be needed in applications at some sites.  Section D.3.5.2 introduces some methods for extending 
the applicability of the GLWRM and also discusses other considerations potentially important for 
a Great Lakes coastal flood hazard evaluation.
[February 2002]
D.3.5.1	Use of Great Lakes Wave Runup Model
The runup analysis begins with the determination of significant wave conditions near the shore.  
The site must be categorized as one of three shore types typical of the Great Lakes: smooth 
vertical wall, rip-rap revetment having a single face slope, or sloping sand beach.  For a 
revetment or beach, the characteristic slope, considered the grade of the slope from the mean lake 
 


level up to the 1-percent-annual-chance SWEL, must be determined.  For a vertical structure or a 
sloping revetment, the wave conditions must be determined at the specified water depth of the 
structure toe and at a water depth of 26 feet for a sand beach.  The depths to be used in analyzing 
wave conditions should be the depths of water below the local 1-percent-annual-chance flood 
level.
The wave runup elevation for the shore barrier can be estimated using the GLWRM, which is 
available from FEMA in digital format.  The program executes step-by-step procedures for runup 
computation at Great Lakes sites, following the recommendations from the Great Lakes Wave 
Runup Methodology Study (USACE, June 1989).  The interactive format occasionally prompts 
the user for input or review of hydraulic and topographic descriptions of a site, including the 
shore barrier specification, the 1-percent-annual-chance SWEL (see Subsection D.3.2.1), and 
offshore storm-wave characteristics (see Subsection D.3.2.6).
Tables D-15, D16, and D-17 present examples of computation input and output for the three 
distinct situations, namely, a vertical structure, a sloping revetment, and a sand beach.


 


 


 


[February 2002]
D.3.5.2	Additional Considerations
As mentioned earlier in this Appendix, the GLWRM treats three shore configurations: smooth 
vertical wall, rip-rap revetment having a single face slope, or sloping sand beach.  For some 
studies, the Mapping Partner may be required to evaluate other shore situations (e.g., grass or 
gravel shore slopes, mounds formed of other material or with a compound front slope).  
Although other methods and models for determining wave runup elevations could be used (see 
USACE, 1984 and 1992; Dewberry & Davis, 1991), the GLWRM runups can be adjusted to 
analyze these other shore situations.  Using the GLWRM will provide consistency of results 
within a single study.
One parameter frequently used in NFIP coastal assessments is a roughness coefficient measuring 
barrier surface effects along the runup excursion (Dewberry & Davis, 1995; Stone & Webster, 
1981).  Table D-18 presents typical values of the roughness coefficient, usually designated as r, 
for common barrier materials.  Wave runup elevation is assumed to vary directly with roughness 
coefficient, given no other difference in the geometrical configuration.  Thus, GLWRM results 
for a sand beach (having a situation otherwise identical to that shown in Table D-13) may be 
multiplied by 0.90 to apply with grass, or by 0.70 to apply with gravel.  For relatively steep 
slopes common to manmade shore structures, GLWRM results for a rip-rap revetment might be 
adjusted for application with other construction materials, using the appropriate ratio between 
roughness coefficients.  Expressed formally, the runup on a rough surface is given as r times 
runup for a smooth surface, so that for rip-rap
	R1 = r1 R 	(1)	
and for some other rough barrier material
	Ro = ro R = ro R1/r1  	(2)
where the value R1 is obtained directly from the GLWRM.  
Another simplification long employed in NFIP coastal assessments is the composite-slope 
method (Saville, 1958), where a hypothetical uniform slope is taken to represent the segmented 
barrier profile (Figure D-41).  That equivalent slope customarily extends from the water depth 
with initial wave breaking to the limit of wave runup, or from a water depth equal to incident 
wave height when waves do not break (at a very steep shore).  For a man-made structure, the 
GLWRM assumes a clearly identifiable toe or seaward limit to the wave barrier, so it is 
appropriate to start the equivalent uniform slope at that point.  Because the landward limit 
assumed for the uniform slope is at the runup limit, some manual computation may be needed in 
iterative adjustment of the input slope to attain suitable consistency with calculated runup 
elevation.

Table D-18.  Appropriate Values for Roughness Coefficient in Wave Runup Calculations
ROUGHNESS
COEFFICIENT
DESCRIPTION OF BARRIER SURFACE
1.00
Sand; smooth rock, concrete, asphalt, wood, fiberglass
0.95
Tightly set paving blocks with little relief
0.90
Turf, closely set stones, slabs, blocks
0.85
Paving blocks with sizable permeability or relief
0.80
Steps; one stone layer over impermeable base; stones set in cement
0.70
Coarse gravel; gabions filled with stone
0.65
Rounded stones, or stones over impermeable base
0.60
Randomly placed stones, two thick on permeable base
0.50
Cast-concrete armor units:  cubes, dolos, quadripods, tetrapods, tribars, etc.  



Once a definite runup elevation has been obtained for the shore situation, the Mapping Partner  
must compare it with barrier crest elevation to assess the possibility of wave overtopping.  The 
examination takes into account that calculated runup elevation refers to common rather than 
extreme water excursions on the barrier, whereas all expected hazards of the 1-percent-annual-
chance flood must be projected.  If wave runup elevation reaches more than halfway from the 
stillwater level to the barrier crest, the Mapping Partner shall perform an overtopping assessment 
for flood hazards because likely wave runups occasionally will proceed over the shore barrier.  
Overtopping discharges in storm conditions may be estimated using empirical results in Random 
Seas and Design of Maritime Structures (Goda, 1985) for vertical walls, in "Design of Seawalls 
Allowing for Wave Overtopping" (Hydraulics Research Station, 1980) for sloping structures, and 
in "Wave Runup and Overtopping at Dunes during Extreme Storm Surge" (Delft Hydraulics 
Laboratory, 1983) for sand dunes with common erosion geometry.  The Mapping Partner shall 
evaluate the effects of the discharge in terms of potential wave impacts, runoff depths, or 
ponding areas on ground landward of the shore barrier. 
A distinct type of overflow situation can occur at low bluffs or banks backed by a nearly level 
plateau, where calculated wave runup may appreciably exceed the top elevation of the steep 
barrier.  A memorandum entitled "Special Computation Procedure Developed for Wave Runup 
Analysis for Casco Bay, FIS - Maine, 9700-153" provides a simple procedure to determine 
realistic runup elevations for such situations, as illustrated in Figure D-42 (French, 1982).  An 
extension to the bluff face slope permits computation of a hypothetical runup elevation for the 
barrier, with the imaginary portion given by the excess height R' = (R-C) between calculated 
runup and the bluff crest.  Using that height R' and the plateau slope m, Figure D-43 defines the 
inland limit to wave runup, X, corresponding to runup above the bluff crest of (mX) or an 
adjusted runup elevation of Ra = (C + mX).  This procedure is based on a Manning's "n" value of 
0.04 with some simplifications in the energy grade line and is meant for application only with 
positive slopes landward of the bluff crest.  A different treatment of wave overflow onto a level 
plateau, for possible FIS usage, is provided in "Overland Bore Propagation Due to an 
Overtopping Wave" (Cox & Machemehl, 1986).
A less common situation on the Great Lakes is that calculated wave runup exceeds a relatively 
high barrier crest backed by negative slopes.  In such cases, a general rule limits the appropriate 
runup elevation to 3 feet above maximum ground elevation.  Floodwaters overtopping the barrier 
percolate into the bed, or run along the back slope until encountering another flooding source or a 
ponding area.  A runoff area is usually designated as Zone AO, with depth of flooding of 1, 2, or 
3 feet; a ponding area may be designated as Zone AH, with a flood elevation.  Standardized NFIP 
procedures have been developed for the treatment of sizable runoff and ponding, but are beyond 
the scope of this presentation; see Guidelines and Specifications for Wave Elevation 
Determination and V Zone Mapping (FEMA, 1995).
Aside from these considerations relating to the inland limit of flooding from wave runup and 
overtopping, the Mapping Partner must integrate the runup elevation at the shore barrier with 
calculated wave crest elevations near the shore.


 


 
[February 2002]
D.3.6	Nearshore Wave Dimensions
As waves propagate near the shore and over a flooded area, they undergo transformations caused 
by local winds, interaction with the bottom, and physical features such as buildings, trees, or 
marsh grass.  Figure D-44 illustrates the effects at a transect of obstructions on the wave crest 
elevations and the flood zone.  For Great Lakes coasts, the effects must be calculated objectively 
along each transect, from the Low Water Datum to the flooding limit.  Fundamental analysis of 
wave effects for an FIS is provided by the FEMA computer program Wave Height Analysis for 
Flood Insurance Studies (WHAFIS).  The program calculates wave heights, wave crest 
elevations, flood hazard zone designations, and the location of zone boundaries along a transect.  
The current program version for the Great Lakes region, WHAFIS 3.0 GL, incorporates 
windspeeds appropriate to Great Lakes events (40 mph over fully exposed waters and 30 mph for 
inland waters or marsh).
Wave description for an FIS addresses the controlling wave height, equal to 1.6 times the 
significant wave height common as a basic wave description, with the dominant (or spectral 
peak) wave period.  Significant wave height is the average height of the highest one-third of 
waves, and controlling wave height is slightly less than average height of the highest one percent 
of waves in storm conditions.  The wave condition of interest is that expected to accompany the 
1-percent-annual-chance flood.
Within WHAFIS, a wave action conservation equation governs wave regeneration caused by 
wind and wave dissipation caused by marsh plants.  This equation is supplemented by the 
conservation of waves equation, which expresses the spatial variation of the wave period at the 
peak of the wave spectrum.  The wave energy (i.e., wave height) and wave period respond to 
changes in wind conditions, water depths, and obstructions as a wave propagates.  These 
equations are solved as a function of distance along the transect.  Technical details are fully 
documented in the WHAFIS program documentation (FEMA, September 1988).
The current NFIP treatment of wave dimensions has resulted from periodic upgrades of technical 
procedures, with the original basis being the NAS methodology documented in Methodology for 
Calculating Wave Action Effects Associated with Storm Surges (NAS, 1977).  The NAS 
methodology, which was developed to be suitable for manual computations, accounts for varying 
fetch lengths, barriers to wave transmission, and the regeneration of waves over flooded land 
areas.  Several aspects of usual Great Lakes situations suggest that simplified analysis, 
considering only water depth and thin vertical barriers, might give a useful outline of wave 
effects for some sites.



[February 2002]
D.3.6.1	Simplified Wave Height Analysis
The potential usefulness of the simplified wave analysis method for treating 1-percent-annual-
chance flood waves is suggested by certain aspects of the Great Lakes situation: the relatively 
low windspeeds, reducing the intensity of wave regeneration; the relatively simple eroded 
geometries, which are generally featureless lakeward of the ultimate flood barrier; the absence of 
barrier islands and back bays so that another flood source or elevation is seldom encountered; 
and the typical narrowness of the Coastal High Hazard Area.  This method would not be 
appropriate where the transect includes coastal wetlands, other land cover providing appreciable 
flow resistance, or an extensive lowland area liable to flooding.  Before any wave analysis, there 
must be confirmation that sizable waves likely propagate towards shore during the local 1-
percent-annual-chance flood.  
All elements of this treatment are extracted from the basic NAS methodology (Dawdy & 
Maloney, 980; FEMA, February 1981; NAS, 1977), with wave heights entirely regulated by local 
water depth.  The estimated flood elevation (Z) is defined by wave action accompanying the 
flood, with the majority of the waveform in the crest above the 1-percent-annual-chance SWEL 
(S):  
	Z = S + 0.7 H	(3)
where H is the local controlling wave height.  A bound to H is given by wave breaking in shallow 
water, with the upper limit
	H* = 0.78 d	(4)
where local water depth (d) equals (S-G), G being ground elevation.  Combining these relations, 
local ground elevation constrains the flood elevation to an upper limit of
	Z* = S + 0.55 d	(5)
Equation (4) implies that a minimum water depth of 3.85 feet is required for the 3-foot wave 
height characterizing a V Zone.  
An obstruction on the transect may conveniently be treated as a thin barrier if flooding occurs to 
the same S on each side.  Wave transmission is assumed to occur only if the barrier top elevation 
(C) is below S plus one-half the incident wave height (Hi).  Transmitted wave height is
	Ht = 0.5 Hi + B	(6)
where B = 1/2[0.78 (S-C)] if the barrier is submerged, but B=[(S-C)] otherwise; the upper limit of 
Ht = Hi occurs when Hi is less than [0.78 (S-C)], requiring that Hi is not depth-limited.  
Transmitted wave height beyond the barrier remains limited by ground elevation on the landward 
side of the barrier (Gt), through Equation (2), just as incident wave height is limited by ground 
elevation on the lakeward side (Gi).  With engineering judgment, wave obstructions other than 
walls might be represented by proper choices of Gi, C, and Gt in this procedure.
Figure D-45 presents an idealized numerical example demonstrating estimated wave heights, 
flood elevations, and flood zones.  Note that varying elevations of depth-limited wave crests 
mirror the ground slopes.
[February 2002]
D.3.6.2	Use of WHAFIS 3.0 GL Model
Careful preparation and input of required site data are necessary in using WHAFIS.  Like the 
other coastal treatments, the WHAFIS model considers the study area by representative transects.  
For WHAFIS, transects must be defined considering major topographic, vegetative, and cultural 
features.  The transect, referenced to NGVD29, begins at the local elevation of Low Water 
Datum (Table D-13) and proceeds landward until either the ground elevation exceeds the SWEL 
or another flooding source is encountered.
Fundamental specifications for WHAFIS input include the 1-percent-annual-chance flood SWEL 
and a description of waves existing at the transect start.  The wave description provides for an 
overwater fetch length, an initial significant wave height, or an initial period of dominant waves.  
In most Great Lakes applications, the wave period should be the input description, because that 
parameter is readily available from information about offshore waves (see Subsection D.3.2.6).
The Mapping Partner shall locate transects on the work maps and plot the transect ground profile 
from the topographic data, adjusted for erosion. The Mapping Partner shall ensure that each 
transect has all the input data identified on the profile plot for ease of input coding.  The 
Mapping Partner also shall identify the location, height, and width of elongated manmade 
structures and show them as part of the ground profile, after confirming the structure's stability 
under forces of the 1-percent-annual-chance flood (see Subsection D.3.3).
Buildings are specified on the transect as rows perpendicular to the transect.  Because buildings 
are not always situated in perfect rows, the Mapping Partner shall exercise judgment  to 
determine which buildings can be represented by a single row.  The required input value for each 
row of buildings is the ratio of open space to total space.  This is simply the sum of distances 
between buildings in a row, divided by the total length of that row.  
 


The first row or two of buildings along the shoreline is not always to be considered as 
obstructions.  During a 1-percent-annual-chance flood, it is sometimes appropriate to assume that 
if they are not elevated on pilings, these buildings will be destroyed before the peak of the flood 
occurs.  If they are elevated, the waves should propagate under the structures with minimal 
reduction in height. The Mapping Partner shall contact local officials to obtain typical 
construction methods and the lowest elevations of structure. 
The WHAFIS program has two routines for vegetation: one for rigid vegetation that can be 
represented by an equivalent "stand" of equally spaced circular cylinders (NAS, 1977) and one 
for marsh vegetation that is flexible and oscillates with wave action (FEMA, 1984).  For either 
type, considerable care is required in selecting representative parameters and in ruling out that the 
vegetation will be intentionally removed or that effects during a storm would be markedly 
reduced through erosion, uprooting, or breakage.
For the areas of rigid vegetation located on the transect, the required input values are the drag 
coefficient, CD; mean wetted height, h; mean effective diameter, D; and mean horizontal 
spacing, b.  The value of CD should vary between 0.35 and 1.0, with 1.0 being used in most 
cases of wide vegetated areas.  When the vegetation is in a single stand, a value of 0.35 should be 
used.  Representative values for h, D, and b can be obtained from stereoscopic aerial photographs 
or by field surveys.  Various guides for terrain analysis can provide procedures for estimating 
these values from aerial photographs.  Table D-19 provide a useful procedure developed from 
Terrain Analysis Procedural Guide for Vegetation (Messmore, Vogel, & Pearson, 1979).
For marsh vegetation, a more complicated specification is required for completeness, and the 
eight parameters used to describe the attenuation properties of a specific vegetation type are 
explained in Table D-20.
WHAFIS includes considerable basic information on eight common types of seacoast marsh 
plants listed in Table D-21 (FEMA, 1984; FEMA, 1989), but among these, apparently only the 
Juncus species are likely to occur in the freshwater marshes on the Great Lakes.  For vegetation 
not listed in Table D-21, the Mapping Partner shall input the geometrical parameters to 
WHAFIS.
At lakeshore elevations that are seldom flooded and thus are important for the 1-percent-annual-
chance flood, a great diversity of wetland vegetation can occur along with upland vegetation 
species.  Prevalent marsh plants at relatively high elevations (Levels Reference Study Board) 
may include combinations of grasses (Phalaris arundinacea, Calamagrostis canadensis), sedges 
(Carex lacustris, C. rostrata, C. stricta, C. lasiocarpa), rushes (Juncus canadensis, J. effusus), or 
cattails (Typha varieties). The Mapping Partner shall specify each existing type of vegetation s, 
along with its fractional coverage in any sizable patch; a patch of at least 10,000 square feet (0.09 
hectare) can affect wave heights appreciably.


 


 


Table D-20.  Marsh Plant Parameters
PARAMETER
EXPLANATION
CD
Effective drag coefficient.  Includes effects of plant flexure and modification of the 
flow velocity distribution.  Default value is 0.1, usually appropriate for marsh plants 
without strong evidence to the contrary.  
Fcov
Fraction of coverage.  A default value is calculated by the program so that each plant 
type in the transect is represented equally, and the sum of the coverage for the plant 
types is equal to 1.0.  
h
Unflexed stem height (feet).  The stem height does not include the flowering head of 
the plant, the inflorescence.  
N
Number density.  Expressed as plants per square foot.  The relationship to the average 
spacing between plants, b, can be expressed as N = 1/b2.  
D1
Base stem diameter (inches).  Default value may be determined from stem height and 
regression equations built into the program.  
D2
Mid stem diameter (inches).  Default value may be determined from plant type and 
base stem diameter.  
D3
Top stem diameter (inches), at the base of the inflorescence.  Default value may be 
determined from plant type and base stem diameter.  
CAb
Ratio of the total frontal area of the cylindrical portion of the leaves to the frontal area 
of the stem below the inflorescence.  Default value may be determined from the plant 
type.  

	Table D-21.  Abbreviations of Marsh Plant Types Used in WHAFIS
SPECIES OR SUBSPECIES
ABBREVIATION
Cladium jamaicense (saw grass)
CLAD
Distichlis spicata (salt grass)
DIST
Juncus gerardi (black grass)
JUNM
Juncus roemerianus (black needlerush)
JUNR
Spartina alterniflora (medium saltmeadow cordgrass)
SALM
Spartina alterniflora (tall saltmeadow cordgrass)
SALT
Spartina cynosuroides (big cordgrass)
SCYN
Spartina patens (saltmeadow grass)
SPAT

[February 2002]
D.3.6.3	Input Coding 
After all the necessary input data have been identified on the transect, the Mapping Partner shall 
divide the transect into continuous segments, each representing a single open fetch or 
obstruction.  Fetches are flooded areas with no obstructions, such as dunes, manmade barriers, 
buildings, and vegetation. The Mapping Partner shall subdivide fetches at points where the 
ground elevation abruptly changes and in the transition area of changing SWELs.  The Mapping 
Partner shall subdivide obstructions at the transect's seaward edge to more accurately model the 
wave dissipation.  Rigid vegetation is to have two to three seaward segments extending 10 to 50 
feet, and the first two or three rows of buildings are to have a segment for each row.  Marsh 
vegetation will be subdivided by the WHAFIS model, and thus segmented input is not necessary.
The Mapping Partner shall enter the necessary data using 11 line types, including the Title line.  
The ten remaining lines each describe a certain type of fetch or obstruction, listed as follows:  
*	The IE (Initial Elevation) line describes the initial overwater fetch and the initial SWELs.  
*	The IF (Inland Fetch) and OF (Overwater Fetch) lines define the endpoint stationing and 
elevation of inland and overwater fetches, respectively.  
*	Obstructions are categorized either as buildings (BU line), rigid vegetation (VE line), marsh 
vegetation (VH and MG lines), dunes and other natural or manmade elongated barriers (DU 
line), or areas where the ground elevation is greater than the 1-percent-annual-chance SWEL 
(AS line).  
*	The ET (End of Transect) line enters no data but indicates the end of the input data.  
Each line has an alphanumeric field describing the type of input for that line, followed by ten 
numeric fields describing the parameters.  
To ensure proper modeling, the Mapping Partner shall enter all segments of each transect either 
as fetches or obstructions, with one input line required for each fetch or obstruction segment.  
The first two columns of each line identify the type of fetch or obstruction.  The remaining 78 
columns consist of one field of six columns followed by nine fields of eight columns.  The 
Mapping Partner shall right-justify the numbers in any data field only if no decimal point is used. 
Decimal points are permitted but not required.  The end point of one fetch or obstruction is the 
beginning of the next.  The first two numeric fields of each line are used to read in the stationing 
(measured in feet from the beginning of transect) and elevation (in feet) of the end point.  The 
last two fields used on each line are for entering new SWELs.  An interpolation is performed 
within a transect segment starting at the closest station with an input SWEL.  This interpolation 
uses the new SWEL input at the end point of the segment and the SWEL input at a previous 
segment.  If these fields are blank or zero, the SWELs remain unchanged.
The input data requirements are summarized below for each line type.  The Title line must be the 
first line, followed by the IE line, followed by any combination of the various fetch and 
obstruction lines.  The ET line must be the last card entered for the transect.  A blank line must 
follow to signify the end of the run.  If multiple transects are being run, the Title line for the next 
transect will follow the blank line.  All units are in feet unless otherwise specified.
TITLE Line (Title)
This line is required and must be the first input line.  

DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
Blank
1-10
3-80
Title information centered about column 40

IE Line (Initial Elevations)
This line is required and must be the second input line.  This line is used to begin a transect at the 
shoreline and compute the wave height arising through the overwater fetch.
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
IE
1
3-8
Stationing of end point of initial overwater fetch in feet (zero at beginning of 
transect)
2
9-16
Ground elevation at end point in feet (usually Low Water Datum at 
beginning of transect)
3
17-24
Overwater fetch length (miles), if wave condition is to be calculated.  
Values of 24 miles or greater yield identical results.
4
25-32
10-percent-annual-chance SWEL in feet
5
33-40
1-percent-annual-chance SWEL in feet
6
41-48
Initial wave height; a blank or zero causes a default to a calculated wave 
height
7
49-56
Initial wave period (seconds); a blank or zero causes a default to a 
calculated wave period.  The period is usually the most convenient wave 
specification for Great Lakes cases.
8-10
57-80
Not used

AS Line (Above Surge)
This line is used to identify the end point of an area with ground elevation greater than the 1-
percent-annual-chance SWEL (such as a high dune or land mass).  It is used when the ground 
surface temporarily rises above the 1-percent-annual-chance SWEL.  The line immediately 
preceding the AS line must enter the stationing and elevation of the point at which the ground 
elevation first equals the 1-percent-annual-chance SWEL.  The SWEL on the leeward side may 
be different from the SWEL on the windward side.  The ground elevation entered on the AS line 
must equal the SWEL that applies to the leeward side of the land mass.  The computer 
calculations will be terminated if a ground elevation greater than the 1-percent-annual-chance 
SWEL is encountered.


DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
AS
1
3-8
Stationing at end point in feet of area above 1-percent-annual-chance SWEL
2
9-16
Ground elevation in feet at end point
3
17-24
A blank or zero indicates no change to the 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to the 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used

BU Line (Buildings)
This line enters information needed to compute wave dissipation at each group of buildings.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
BU
1
3-8
Stationing of end point in feet of group of buildings
2
9-16
Ground elevation at end point in feet
3
17-24
Ratio of open space between buildings to total transverse width of developed 
area
4
25-32
Number of rows of buildings
5
33-40
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
6
41-48
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
7-10
49-80
Not used

DU Line (Dune)
This line enters information necessary to compute wave dissipation at substantial sand dunes and 
other natural or manmade elongated barriers (e.g., levees, seawalls).  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
DU
1
3-8
Stationing at top of dune or barrier in feet
2
9-16
Elevation at top of dune or barrier in feet
3
17-24
A blank or zero indicates a dune or other natural barrier; any other number 
indicates a seawall or other manmade barrier
4
25-32
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
5
33-40
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
6-10
41-80
Not used


IF Line (Inland Fetch)
This line enters the parameters necessary to compute wave regeneration through inland fetches 
and over shallow inland waterbodies.  The IF regeneration is computed using overland wind 
speed of 30 mph for Great Lakes floods.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
IF
1
3-8
Stationing at end point of fetch in feet
2
9-16
Ground elevation at end point in feet
3
17-24
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used

OF Line (Overwater Fetch)
This line enters the parameters necessary to compute wave regeneration over large bodies of 
water (i.e., large lakes, bays) using overwater wind speed of 40 mph for Great Lakes floods.  If an 
inland waterbody is sheltered and has a depth of ten feet or less, the IF line calling for overland 
wind speeds should be used.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
OF
1
3-8
Stationing at end point of fetch in feet
2
9-16
Ground elevation at end point in feet
3
17-24
A blank or zero indicates no change to the 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
4
25-32
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
5-10
33-80
Not used

VE Line (Vegetation)
This line enters parameters necessary to compute wave dissipation due to rigid vegetation stands.  



DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
VE
1
3-8
Stationing at end point of vegetation in feet
2
9-16
Ground elevation at end point in feet
3
17-24
Mean effective diameter of equivalent circular cylinder in feet
4
25-32
Average actual height of vegetation in feet
5
33-40
Average horizontal spacing between plants in feet
6
41-48
Drag coefficient; a blank or zero causes a default to 1.0
7
49-56
A blank or zero indicates no change to 10-percent-annual-chance SWEL; 
otherwise new 10-percent-annual-chance SWEL
8
57-64
A blank or zero indicates no change to 1-percent-annual-chance SWEL; 
otherwise new 1-percent-annual-chance SWEL
9-10
65-80
Not used

VH Line (Vegetation Header for Marsh Grass)
Marsh grass is often part of a plant community that may consist of several plant types.  The VH 
line is used to enter data that apply to all plant types modeled in the transect segment.  To enter 
data for each plant type, MG lines for each plant type must follow the VH line.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
VH
1
3-8
Stationing at end point of marsh vegetation segment in feet
2
9-16
Ground elevation at end point in feet
3
17-24
Regp, number of the primary seacoast region for default plant 
parameters.  Leave blank for Great Lakes computations.  
4
25-32
Wtp, weighting factor for the primary seacoast region.  Not 
applicable for Great Lakes analyses. 
5
33-40
Regs, number of secondary seacoast region.  Not applicable for 
Great Lakes analyses.
6
41-48
Np1, number of plant types; range is 1 to 10, inclusive.  One MG 
line is required for each plant type.  
7
49-56
A blank or zero indicates no change to the 10-percent-annual-
chance SWEL; otherwise new 10-percent-annual-chance SWEL
8
57-64
A blank or zero indicates no change to the 1-percent-annual-
chance SWEL; otherwise new 1-percent-annual-chance SWEL
9
65-72
Not used
10
73-80
This field is for overriding the default method of averaging flood 
hazard factors in A Zones; if 1 in column 80, averaging process 
begins or ends at end of vegetation segment; otherwise, default 
averaging method is used


MG Line (Marsh Grass)
This line is used to enter data for a particular plant type.  The first MG line must be preceded by a 
VH line.  For the common seacoast marsh grasses listed in Table D-21, potentially useful default 
values are supplied in Table D-22.  If a plant type not listed in the table is used, then appropriate 
data must be developed for Fields 2-9.  
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
MG
1
5-8
Marsh plant type abbreviation (see Table 10)
2
9-16
CD, effective drag Coefficient; default value is 0.1
3
17-24
Fcov, decimal fraction of vegetated area to be covered by this plant type; a blank 
or zero causes a default to be calculated so that each plant type is represented 
equally
4
25-32
h, mean unflexed height of stem (feet); for marsh plants, the inflorescence is not 
included
5
33-40
N, number of plants per square foot
6
41-48
D1, base stem diameter (inches)
7
49-56
D2, mid stem diameter (inches)
8
57-64
D3, top stem diameter (inches)
9
65-72
CAb, ratio of the total frontal area of cylindrical part of leaves to frontal area of 
main stem
10
73-80
Not used

ET Line (End of Transect)
This line is required and must be the last input card because it identifies the end of input for the 
transect.  
	
DATA FIELD
COLUMNS
CONTENTS OF DATA FIELDS
0
1-2
ET
3-10
3-80
Not used



Table D-12.  Significant Marsh Plant Types in Each Seacoast Region and WHAFIS Default Regional Plant Parameter Data
REGION NO.
1
2
3
4
5
6
7
8
REGION NAME:
NORTH
ATLANTIC
MID-
ATLANTIC
SOUTH
ATLANTIC
SOUTH
FLORIDA
NORTHEASTERN
GULF
DELTA
PLAIN
CHENIER
PLAIN
SOUTH
TEXAS
CLAD
---
---
---
7.50(+)
0.0656
6
6.00(2)
0.0260
6
---
---
---
DIST
---
0.78(1)
0.0039
211
1.00(1)
0.038
243
1.00(+)
0.0038
248
---
---
1.08(4)
0.0035
102
1.08(+)
0.0035
102
---
JUNM
1.23(1)
0.0042
300
1.23(+)
0.0042
300
---
---
---
---
---
---
JUNR
---
2.95(+)
0.0095
147
2.95(+)
0.0095
147
---
2.95(3)
0.0095
147
3.00(4)
0.0106
83
2.95(+)
0.0095
147
---
SALM
1.39(1)
0.0184
45
1.06(1)
0.0103
36
1.63(1)
0.0141
12
1.63(+)
0.0141
12
---
1.67(4)
0.0141
21
2.62(5)
0.0211
16
---
SALT
1.86(1)
0.0175
37
2.21(1)
0.0169
18
3.20(1)
0.0183
10
3.20(+)
0.0183
10
---
3.20(4)
0.0183
10
3.20(+)
0.0183
10
---
SCYN
---
---
8.29(+)
0.0492
6
---
---
4.00(4)
0.0267
7
---
---
SPAT
1.03(1)
0.0025
409
0.85(1)
0.0019
327
1.65(1)
0.0019
236
---
2.58(2)
0.0026
236
1.88(4)
0.0016
333
1.88(+)
0.0019
333
---
Data arranged in vertical triplets:

Parenthetical references indicate data source: 





h, stem height below inflorescence, in feet

1 = Hardisky and Reimold, 1977
5 = Turner and Gosselink, 1975, Diameters extrapolated
D, base diameter, in feet

2 = Monte, August 1983
+ = Extrapolated Data
N, number density, in inverse square feet

3 = Kruczynski, Subrahmanyam, Drake, 1978
--- = Insignificant amounts of this plant type in the region


4 = Hopkinson, Gosselink, Parrondo, 1980, Diameters extrapolated



[February 2002]
D.3.6.4	Error Messages
While using the WHAFIS program, the Mapping Partner may encounter the error messages listed 
below.
*	"AS card ground elevation less than SWEL, should use other type card, job dumped."
	Only use AS (above surge) line when the ground elevation is above the SWEL.  Can 
otherwise use IF, OF, BU, DU, VE, or VH.  
*	"Ground elevation greater than surge elevation encountered, job dumped."  
	If ground elevation is above surge elevation, AS card should be used.  
*	"Average depth less than or equal to zero, job dumped."
	The water depth must be greater than zero or a wave height cannot be computed.  Check the 
SWEL and the ground elevation if point of job dump is not the last point along the transect 
profile.  
*	"The above card contains illegal data in the first 2 columns."
	Check input data for incorrect values or input within wrong columns.  Aside from the title 
line, the first two columns in each line should contain the card identifiers.  
*	"Transmitted wave height at last fetch or obstruction = ______ which exceeds 0.5."
	Code the transect profile up to the inland limit where ground elevation intersects the SWEL 
so that wave height should decrease to zero.  If the scope of work ends at the corporate limits 
before the ground elevation meets the SWEL, this message can be ignored.  
*	"Array dimensions exceeded.  Job dumped."
	Size of the array is limited and the number of input parameters has exceeded the array.  
Check the number of input parameters at the location where the job dumped.  
*	"Invalid data in field 1 of IF card," etc.
	Check input data to make sure that data are in correct columns.  
*	"Wave period less than or equal to zero in subroutine fetch.  Abort run."  
	Either a fetch length or a wave period must be input for the program to run properly.  Check 
input data.  
*	"Invalid data in field 3 or field 5 of VH card."
	Check input data.
*	"Invalid data in field 4 of VH card."
	Check input data.  
*	"Invalid data in field 3 of MG card."
	Check input data.  The fraction of vegetated area covered by the stated plant type should be a 
decimal number between 0.0 and 1.0.  
*	"Missing MG card or incorrect data in field 6 of VH card."
	A MG card must always follow the VH card.  Field 6 of the VH card pertains to the number 
of plant types, and one MG card is required for each plant type.  
*	"Invalid input data."
	Check input data for invalid characters, such as an O instead of a zero.  Check to be sure that 
all data are in their correct columns.  
*	"Fcov was found to be negative for plant type = _______."
	Check input data to be sure that the decimal fraction of the vegetated area covered by the 
plant type is not negative.  
*	"Ncov is .LE. zero in Sub.Lookup when it should be .GT. zero.  Abort run."  
	Check input for number of plants covering the area.  
*	"The first card is not an IE card, this transect is aborted.  Continued to next transect."  
	The first card after the title line must always be an IE card.  Check input data.  
*	"****  The surge elevation at this station (stationing ____), which is ____ card, is less than 
the ground elevation.  The interpolation process is continued.  ***  Please double check the 
surge and ground elevations in the vicinity of this station!!!!!!"
	The surge elevation should not be below the ground elevation.  If the interpolated surge 
elevation is interpolated below the ground elevation, insert additional cards to specify surge 
and ground elevations and use an AS card if necessary.  
*	"Interpolation line cuts off more than two portions of high ground ridge.  This transect is 
aborted, re-assign 1-percent-annual-chance elevations at high ground stations."
	When the interpolated value falls below the ground elevation, insert additional cards to better 
model the area and set the SWEL equal to the ground elevation where appropriate.  Insert AS 
cards as necessary.  
*	"****  Unreasonable high ground elevation at station ____ which is ____ card.  This transect 
is aborted, continued to next transect.  ****  Double check the surge and ground elevations in 
the vicinity of this station.  If the ground elevations are correct, either assign a higher surge 
elevation or use AS cards."  
	Add additional input data as necessary to better define the ground elevation and surge 
elevation in this area.  
[February 2002]
D.3.6.5	Output Description
The output of the program provides all the data necessary for plotting the BFEs and flood 
insurance risk zones along the transect.  The output is in six parts:
Part 1 - Input
This is a printout showing all input data lines and the parameters assigned to each line, both 
manually and by default.  This is followed by a more detailed printout with column headings for 
each input data line.  When VH and MG Lines are used, a separate insert will be printed directly 
beneath the MG Line showing any default values supplied by the computer.  
Part 2 - Controlling Wave Heights, Spectral Peak Wave Period, and Wave Crest Elevations
This is a list of the calculated controlling wave heights, spectral wave peak periods, and wave 
crest elevations at the end point of each fetch and obstruction of the input, and at calculation 
points generated between the input stations.  
Part 3 - Location of Areas Above 1-Percent-Annual-Chance Surge
This is a list of the locations of areas where the ground elevation is greater than the 1-percent-
annual-chance stillwater (surge) elevation.  Only areas identified by AS lines are listed.  
Part 4 - Location of Surge Elevations  
This is a list of the 10- and 1-percent-annual-chance stillwater (surge) elevations and the 
stationing of the points where each set of SWELs first becomes fully effective.  
Part 5 - Location of V Zones  
This is a list of the locations of the V/A Zone boundary and locations of the V Zone areas relative 
to these boundaries.  The stationing is given for each V/A Zone boundary.  The locations of the V 
Zone areas in relation to these boundaries are given as windward or leeward of the boundary.  
Part 6 - Numbered A Zones and V Zones  
This is a list of the zone data needed to delineate the flood hazard boundaries on the FIRM.  The 
location of a flood zone boundary and the wave crest elevation at that boundary are given on the 
left.  Between the boundary listings are the zone designations and FHFs.  Under FEMA's Map 
Initiatives Procedure guidelines, all numbered V and A Zones should be changed to VE and AE 
Zones, respectively (elevations will not change), and the FHFs can be ignored (FEMA, 1991).  
When the same zone and elevation are repeated in the list, they should be treated as a single 
zone.  
[February 2002]
D.3.7	Mapping of Flood Elevations and Zones
This subsection discusses procedures for reviewing the initial model results and identifying flood 
insurance risk zones, and provides guidance for depicting the analysis on the FIRM.
[February 2002]
D.3.7.1	Review and Evaluation of Basic Results
The results of the technical analyses performed for the FIS or map revision determine the special 
flood hazards shown on the FIRM.  The coastal hazards mapped on the FIRM depict the effects 
of erosion on overland wave propagation, the impact of steep beach slopes and bluffs on wave 
runup elevation, and the areas subject to high velocity wave hazards (V Zones).  Because the 
FIRM is used for floodplain management and flood insurance determination, the Mapping 
Partner shall ensure the SFHAs are mapped with as much accuracy as possible.  
With the results of the various analyses at hand, the Mapping Partner shall place flood elevations 
and zones on the work map or up-to-date topographic survey map, after first reviewed them for 
their consistency with the terrain and conditions they represent and with historical data.  In using 
the models, it is possible to forget that the transects represent real shorelines of sandy beaches, 
rocky or cohesive bluffs, wetlands, etc., being subjected to extremely high water, waves, and 
winds.  The Mapping Partner shall review the results of the analyses to determine if they are a 
reasonable representation of the coastal areas being modeled.
Although historical data from a storm closely approximating the base (1-percent-annual-chance) 
flood are seldom available, flood data for less intense storms will still indicate, at a minimum, 
what areas should be in flood zones.  For instance, if a storm produced an extreme flood that 
caused structural damage to houses 100 feet from the shoreline, yet the flood was below the 1-
percent-annual-chance flood SWEL, a reasonable Zone VE width would be at least 100 feet.  
Similarly, houses more than 100 feet from the shoreline that are flooded but not structurally 
damaged by the same storm must be at least in a Zone AE, AH, or AO.  If the analyses of the 1-
percent-annual-chance flood produce flood zones and elevations indicating lesser hazards than 
those recorded for a more common storm, the Mapping Partner shall reevaluate the analyses.  
There may be an explanation for the inconsistency (other than an error in the input data); for 
instance, a new coastal structure may act to reduce flood hazards locally or a big storm may have 
significantly altered the terrain.  A field check should be undertaken to determine whether such 
an explanation exists.
If no explanation for the inconsistency is apparent, the Mapping Partner shall examine the data 
input to the models including checking that the SWELs, wave heights, wave periods, and fetch 
lengths were input correctly and are consistent with the historical data.  A further field check 
could examine whether buildings or structures modeled would be destroyed by the storm or 
whether the buildings are on pilings above the flooding. 
The Mapping Partner also shall evaluate the results of the erosion assessment by comparing the 
eroded profile to past effects, whether in the form of profiles, photographs, or simply 
descriptions.  A general idea of what happened previously can be sufficient.  Judgment and 
experience must be used to project previous storm effects to the 1-percent-annual-chance flood 
conditions and to ensure that the eroded profile is consistent with previous events.
The main point emphasized here is that the results are not to be blindly accepted.  Many 
uncertainties and variables in coastal processes may occur during an extreme flood, and many 
possible adjustments to methodologies for treating such an event may be appropriate.  The 
validity of any model is demonstrated by its success in reproducing recorded events.  Therefore, 
the model results must be in basic agreement with past flooding patterns and results, and 
historical data must be used to evaluate these results.
[February 2002]
D.3.7.2	Identification of Flood Insurance Risk Zones
Interpretation and accurate delineations of the hazards on the maps are the final critical elements 
in a coastal flood hazard study.  The transect used in the wave elevation determination and the 
resulting wave analyses, whether for wave height or wave runup, is the tool by which the results 
can be mapped.   Mapping Partner shall identify the  flood zones and BFEs should be identified 
on each of the transect plots before transferring the information and delineating the hazard zones 
and BFEs on the work maps.  It should be noted that because of changes in the NFIP in 1988 that 
redefined the Coastal High Hazard Area and incorporated wave runup hazards, Part 6 of the 
WHAFIS output, discussed in Section D.3.6, is no longer used to plot zones on the work maps.
It is important to understand the interrelationship of the three key elements in determining the 
flood hazard zone and BFE.  These elements are the existing transect ground profile, the eroded 
transect ground profile, and the wave envelope.  The existing transect ground profile may be 
modified by the presence of erosion forces along the shoreline, if appropriate, in which case the 
flood hazard zone depicted by the transect and wave analyses results may not appear to reflect the 
topography shown for existing conditions with ground elevations higher than the BFE.  The 
eroded transect ground profile, developed using treatment described in Subsection D.3.4, must be 
used in the wave analyses described in Subsections D.3.5 and D.3.6.  The BFEs and the 
topography shown on the work maps may differ from those produced by the erosion treatments 
for a shoreline reach and the wave analyses.  This is because the topography of the work maps 
does not reflect the erosion of the shoreline determined as part of the coastal FIS or map revision 
request.  To clarify areas where these discrepancies exist, the Mapping Partner shall provide a 
description of the areas subject to erosion treatments either in the coastal FIS Report or in the 
supporting engineering report for a map revision request.
The wave envelope is the most important of the three elements for identifying the flood hazard 
zone.  The wave envelope is a combination of representative wave runup elevation and the wave 
crest profile determined by the wave results computed using the WHAFIS program.  The wave 
crest profile is plotted on the final transect ground profile (with or without the effects of erosion) 
based on the results computed and shown in Part 2 of the WHAFIS output. For wave runup 
elevation results, a horizontal line is extended seaward from the computed runup elevation to its 
intersection with the wave crest profile.  This determines the wave envelope profile for the 
results combined from the WHAFIS wave height analysis and the RUNUP 2.0 wave runup 
analysis, as shown in Figure D-46.  If the runup elevation is greater than the maximum wave 
crest elevation, the wave envelope will be a horizontal line at the runup elevation.  Conversely, if 
the wave runup is negligible or was not modeled because of coastal processes and shoreline 
conditions that prevent significant runup from occurring, the wave crest profile alone will 
become the wave envelope.
Before transferring the established wave envelope information from each transect onto the work 
maps, it is important to understand the NFIP coastal flood zones and how to determine their 
location along the transect plot.  The descriptions are as follows:
Zone VE - Coastal High Hazard Areas where wave action and/or high velocity water can cause 
structural damage in the base (1-percent-annual-chance) flood.  The three criteria for determining 
a Zone VE area are:  (1) the area where 3 foot or greater wave height could occur (this is the area 
where the WHAFIS wave crest profile is 2.1 feet or more above the SWEL), (2) the area where 
the eroded ground profile is 3 feet or more below the representative runup elevation, and (3) the 
primary frontal dune, by definition.  Subdivided into elevation zones with BFEs assigned.  
Zone AE - Areas of inundation by the base (1-percent-annual-chance) flood, including wave 
heights less than 3 feet and runup elevations less than 3 feet above the ground.  Also subdivided 
into elevation zones with BFEs assigned.  
Zone AH - Areas of shallow flooding or ponding, with water depth equal to 3 feet or less.  
Usually not subdivided, but a BFE is assigned.  
Zone AO - Areas of "sheet-flow" shallow flooding where overtopping water flows into another 
flooding source.  Assigned with 1-, 2-, or 3-foot depth of flooding.  
Zone X - Areas above base (1-percent-annual-chance) flood inundation.  On the FIRM, shaded 
Zone X is inundated by the 0.2-percent annual chance flood, unshaded Zone X is above 0.2-
percent annual chance flood.  


 


The first step in identifying the flood insurance risk zones on the transect is locating the inland 
extent of the VE Zone, also known as the VE/AE boundary.  Once the Mapping Partner has 
identified the VE Zone limits for each of the three criteria described above, the Mapping Partner 
shall place the VE/AE boundary at the location that is furthest landward.  The AE Zone will 
extend from the VE Zone limit to the inland limit of the 1-percent-annual-chance flood 
inundation, which is a ground elevation equal to the representative runup elevation, or the 1-
percent-annual-chance SWEL if runup is negligible or not included in the wave analyses.  
Additional areas of shallow flooding or ponding for the 1-percent-annual-chance flood event can 
be designated as Zone AH or Zone AO.  All areas above the 1-percent-annual-chance flood 
inundation are Zone X.  
The Mapping Partner shall then subdivide the AE and VE Zones into elevation zones with 
whole-foot BFEs assigned.  Ideally, to help in floodplain management and insurance 
determinations for buildings and property, the Mapping Partner shall establish an elevation zone 
for every BFE in the wave envelope.  However, the FIRM scale may limit the number of zones 
that can be mapped.  For the FIRM to be legible, there must be a minimum width for the zones.  
For coastal areas, the minimum zone width is 0.2 inch.  For identifying elevation zones on the 
transect, the minimum width is 0.2 times the final FIRM scale; for example, 80 feet for a FIRM 
at a scale of 1 inch equals 400 feet, 100 feet for a FIRM at a scale of 1 inch equals 500 feet.  
The Mapping Partner shall not subdivide the horizontal runup portion of the wave envelope, if 
any; the runup elevation, rounded to the nearest whole foot, is the BFE. However, the Mapping 
Partner shall subdivide the WHAFIS wave crest profile.  Generally, the VE Zone is subdivided 
first.  Initially, the Mapping Partner shall mark the location of all the elevation zone boundaries  
on the transect.  Because whole-foot BFEs are being used, these must always be at the location of 
the half-foot elevation on the envelope.  
The Mapping Partner shall combine elevation zones that do not meet the minimum width 
criterion with an adjacent zone or zones to yield an elevation zone that is wider than the 
minimum.  The BFE for this combined zone is a weighted average of the combined zones.  Often 
in subdividing VE Zones, the maximum BFE is located just inside the mapped shoreline, and the 
remainder of the VE Zone is then subdivided into minimum width elevation zones.
The Mapping Partner shall subdivide the AE Zone, if it is wide enough, in the same manner.  If 
the total AE Zone is less than the minimum width, the lowest elevation VE Zone is usually 
assigned to that area.  This situation typically occurs for steep or rapidly rising ground profiles, 
and it is not unreasonable to designate the entire inundated area as a VE Zone.
Relatively low areas inland of the AE Zone may be subject to shallow flooding or ponding of 
flood water and designated as AH or AO Zone.  Such designations can be relatively common 
landward of coastal structures and dunes, where wave overtopping occurs.
Identifying appropriate zones and elevations may require particular care for dunes, given that the 
entire primary frontal dune is defined as Coastal High Hazard Area.  Although the analyses may 
have determined a dune will not completely erode and wave action should stop at the retreated 
duneface with only overtopping possibly propagating inland, the entire dune is still designated as 
a VE Zone.  The BFE at the duneface is assigned for the remainder of the dune.  
It may seem unusual to use a BFE that is lower than the ground elevation, although this is 
actually fairly common.  Most of the BFEs for areas where the dune was assumed to be eroded 
are also below existing ground elevations.  In these cases, it is the VE Zone designation that is 
most important to the NFIP; current regulations require structures to be built on pilings and 
prohibit alterations to the dune.
[February 2002]
D.3.7.3	Mapping Procedures
The final work maps prepared from the results of the coastal FIS or map revision request will be 
used to produce a new or revised FIRM for the affected community.  The work map is essentially 
the base map selected for the study area, as described in Subsection D.3.2, and the depiction and 
delineation of the coastal flood hazards that reflect the results of the wave elevation 
determinations and flood zones established for each respective area.  The Mapping Partner shall 
seta the work map  up with contour lines, buildings, structures, vegetation, and transects used in 
the wave analyses clearly and accurately located.  
The Mapping Partner shall transfer the flood zones and wave elevations identified on the 
transects to the work maps and interpolate the boundaries  between the transects.  The 
interpolation of the results at the transects and between the transects for the results of the wave 
height and wave runup analyses involves judgment and skill in reading the topographic and land 
cover information shown on the work maps.  The time and effort put forth to determine the wave 
elevations will be negated if the results cannot be properly delineated on the work maps and 
shown on the FIRM.  Because roads are the only fixed physical features shown on the FIRM, it is 
very important that other features and the flood zone boundaries are properly located on the work 
maps in relation to the centerline of the roads as they will appear on the FIRM.  Other important 
considerations for mapping the results of the coastal FIS or map revision request discussed below 
include shoreline fluctuations, flood zone widths, interpolation of the transitions between zones 
for the represented transects, and the depiction and delineation of the Zone X shaded special 
flood hazard areas in areas subject to wave runup hazard.
An important but potentially ambiguous map feature is the depicted shoreline in the study area.  
Great Lakes shorelines are subject to large position changes, given shore erosion or accretion 
along with the considerable range in mean lake levels.  The shoreline location may vary among 
the transects analyzed because of historical erosion or accretion not shown or accounted for on 
existing maps, but some clearly designated shoreline should be used for the work maps.  For 
Great Lakes studies, the Mapping Partner shall ensure the depicted shoreline corresponds to the 
land intercept of Low Water Datum, as given in Table D-12 and usually shown on USGS maps.  
(It is customary to delineate flood zones only landward of the shoreline.)
The Mapping Partner shall transfer the identified elevation zones for each transect to the work 
maps, locating the boundaries along the transect line so that boundary lines can be interpolated 
between transects, assuring that the boundaries are marked at the correct location.  Because of the 
erosion assumptions, the location of the elevation 0.0 NGVD shoreline changes on the transect 
but not the work maps.  The transect profile is used to determine the location of the zone change 
in relation to a physical feature, such as a ground contour, road, the back side of a row of houses, 
50 feet into a vegetated area, etc.  The boundary line along this feature for the area represented by 
that transect is then delineated.
The Mapping Partner shall check the widths of the zones being delineated  carefully; if they 
narrow to less than 0.2 inch, they should be tapered to an end.  Likewise, if an averaged elevation 
zone becomes much wider, it may be possible to break it into two elevation zones, both wider 
than 0.2 inch.  Consideration of the final map scale of the FIRM to be produced from the work 
maps will help in determining how the zones should be combined and averaged.
One of the more difficult steps in delineating coastal flood zones and elevations is the 
interpolation and  transition between transect results.  Good judgment and an understanding of 
typical flooding patterns are the best tools for this job.  The first step is to locate on the work 
maps any area of transition that is not exactly represented by either transect.  The next step is to 
delineate the flood boundaries for each transect up to this area.  Then consideration should be 
given to how a transition can be made across this area to connect matching zones, and still have 
the boundaries follow logical physical features.  If there are other transects that are similar to this 
area, they could give an indication of flooding.  Sometimes the elevation zones for the two 
contiguous transects are not the same; thus, some zones may have to be tapered to an end, or 
enlarged and divided in the transition area.
Communities with significant flooding hazards from wave runup may have one transect 
representing more than one area because the areas have similar shore slopes.  In this case, the 
different areas are identified, and the results of the typical transect delineated in each area.  
Transition zones may be necessary between areas with high runup elevations to avoid large 
differences in BFEs and to smooth the change in flood boundaries.  These zones, which should 
be fairly short, should cover the shore segment with a slope not exactly typical of either area.  
The transition elevation is determined by examining runup transects with similar slopes and 
using good judgment.  Transition zones should not be used if there is a very abrupt change in 
topography, such as is found at the end of a structure.
Lastly, Mapping Partner shall map the  Zone X (shaded) areas.  Areas below the 0.2-percent 
annual chance SWEL and not covered by any other flood zone are designated Zone X shaded and 
shown on the FIRM.  Often the maximum runup elevation is higher than the 0.2-percent annual 
chance elevation; thus, there will be no shaded Zone X in that area. The Mapping Partner shall 
designate all other areas as Zone X without any shading.
These Guidelines were compiled to give guidance in the preparation of coastal FISs and map 
revision requests.  The collection of accurate and representative data, the correct application of 
the models, the evaluation and comparison of the results to historical data, and the proper 
delineation of flood elevations and zones will produce a FIRM that is both technically correct 
and directly usable for the intended purposes.  
During all steps of the study, especially the mapping, the final product and its purposes should be 
remembered: the FIRM is used to determine flood insurance premiums and regulate building 
standards.  
Because flood elevations are rounded to the nearest whole foot, there is no reason for spending 
hours to resolve a minor elevation difference.  Also, because structures or proposed structures 
must be located on the FIRM, an attempt should be made whenever possible to smooth the 
boundary lines and to follow a fixed feature such as a road.  In preparing the FIS, not only must 
the mapped results be technically correct, but the FIRM must be easy for the local insurance 
agent, building inspector, or permit officer to use.
Additional criteria and submittal requirements are documented in the Certification forms for 
Study Contractors (SC-1) and Application/Certification form 5 (MT-2) for map revision requests.
[February 2002]
D.3.8	Required Documentation
The Mapping Partner shall fully document the coastal flood hazard determination for each 
affected community.  Because FIS Reports and FIRMs form the basis of Federal, State, and local 
regulatory and statutory enforcement mechanisms and are subject to administrative appeal and 
litigation, Mapping Partners shall ensure that all technical processes and decisions are recorded 
and documented.  The FIS Report may not contain all the documentation that would be needed 
for a response in the event that the study results are questioned.  Therefore, the Mapping Partner 
shall prepare an engineering report for each study.  This report will provide detailed data needed 
by FEMA or the community to reconstruct or defend on technical grounds the study results.  The 
minimum information required for the engineering report are summarized below.
Basic Data. 
In this section, the Mapping Partner shall include all contacts made to obtain data for the study.  
All basic data used must be fully referenced and, if possible, reproduced in the report.  All 
historical flood information must be documented in this section, even if the Mapping Partner did 
not use the information in quantitative analyses.  
Transects  
Each transect must be plotted separately and show the erosion assessment, input data for wave 
models, wave envelope, and zone determination.  
Model Input and Output 
The Mapping Partner shall provide computer printout listings for input and output data for both 
the Wave Runup and Wave Height Models for all the transects.  These listings must be keyed to 
the transect location map and transect plots.  


Study File  
During the course of the study, the Mapping Partner shall maintain a file containing records of all 
coordination, activities, and decisions.  This is especially important where nonstandard 
approaches were used and engineering judgment played a significant role.  The Mapping Partner 
shall ensure this file meets the requirements for a Technical Support Data Notebook as 
documented in Appendix M of these Guidelines.  
[February 2002]
D.3.9	Open Coast Flood Elevations and Wave Information
As discussed in Subsection D.3.2, the draft of "Basic Analyses of Wave Action and Erosion with 
Extreme Floods on Great Lakes Shores" (Dewberry & Davis, 1995) concluded from historical 
evidence that extreme floods were usually accompanied by the local 1/2-year wave condition on 
Lake Ontario, or by the 3-year wave condition on Lakes Erie, Huron, Michigan, and Superior.  
Examples of appropriate wave conditions derived for numerous sites on each of the Great Lakes 
are presented in Figures D-47 through D-56 and in Tables D-23 through D-27.





 


Table D-23.  Three-Year Wave Conditions as Hindcast for Selected Nearshore Sites on 
Lake Superior
HINDCAST SITE ID
WAVE HEIGHT (METERS)
WAVE PERIOD (SECONDS)
SUPER-05
6.0
10.0
SUPER-13
5.8
10.0
SUPER-15
3.7
7.1
SUPER-23
4.3
--
SUPER-29
5.0
9.1
SUPER-35
5.9
--
SUPER-42
5.2
--
SUPER-47
7.7
11.1
SUPER-54
6.2
--
SUPER-60
4.5
7.7



 


 


	Table D-24.  Three-Year Wave Conditions as Hindcast for Selected Nearshore Sites on 
Lake Michigan
HINDCAST SITE ID
WAVE HEIGHT (METERS)
WAVE PERIOD (SECONDS)
MICH-01
4.4
9.1
MICH-03
4.6
9.1
MICH-09
4.7
8.3
MICH-14
3.9
--
MICH-19
4.0
8.3
MICH-22
3.7
7.7
MICH-26
3.3
8.3
MICH-30
3.4
8.0
MICH-34
3.7
--
MICH-41
4.1
--
MICH-46
4.7
9.1
MICH-48
5.2
9.1
MICH-54
5.2
9.1
MICH-60
4.5
8.3


 


 


Table D-25.  Three-Year Wave Conditions as Hindcast for Selected Nearshore Sites on 
Lake Huron
HINDCAST SITE ID
WAVE HEIGHT (METERS)
WAVE PERIOD (SECONDS)
HURON-01
6.1
9.1
HURON-02
6.2
10.0
HURON-07
5.6
9.1
HURON-11
6.3
9.1
HURON-12
6.2
9.5
HURON-15
6.1
9.1
HURON-20
5.0
--
HURON-25
4.1
7.7
HURON-26
4.3
9.1


 


 


Table D-26.  Three-Year Wave Conditions as Hindcast for Selected Nearshore Sites on 
Lake Erie
HINDCAST SITE ID
WAVE HEIGHT (METERS)
WAVE PERIOD (SECONDS)
ERIE-01
2.0
6.2
ERIE-04
1.9
6.2
ERIE-07
3.3
--
ERIE-10
3.6
7.7
ERIE-12
4.0
8.3
ERIE-15
4.2
--
ERIE-18
4.6
9.1
ERIE-21
4.9
9.1
ERIE-24
4.2
9.1
ERIE-47
1.8
5.6



 


 


Table D-27.  One-Half-Year Wave Conditions as Hindcast for Selected Nearshore Sites on 
Lake Ontario
HINDCAST SITE ID
WAVE HEIGHT (METERS)
WAVE PERIOD (SECONDS)
ONT-04
2.7
--
ONT-06
2.9
6.7
ONT-07
3.0
7.1
ONT-11
3.2
7.1
ONT-14
2.6
--
ONT-17
3.2
7.1
ONT-21
2.4
5.9

[February 2002]



D.4	Wave Elevation Determination and V Zone Mapping: 
Pacific Ocean
No FEMA guidance documents have been published for Pacific Ocean coastal flood studies.  
Guidance is to be developed based on existing methodologies recommended by FEMA and 
coastal states for coastal analyses in the Pacific Ocean.  Mapping Partners that are undertaking a 
flood hazard analysis of a Pacific coast site should consult with the FEMA RPO for that area.
[February 2002]




D.5	Erosion Hazard Study, Identification, and Mapping
No FEMA guidance documents have been published for erosion hazard studies and mapping.  
Guidance is to be developed based on new or existing methodologies recommended by FEMA 
and coastal states for erosion hazard studies and mapping in all coastal areas.

[February 2002]


D.6	References
Abel, C. E., Tracy, B. A., Vincent, C. L., & Jensen, R. E.  (1989).  Hurricane Hindcast 
Methodology and Wave Statistics for Atlantic and Gulf Hurricanes from 1956-1975.  WIS 
Report 19.  Coastal Engineering Research Center.  Vicksburg, Mississippi.
Birkemeier, W. A., Kraus, N. C., Scheffner, N., & Knowles, S. C.  (1987).  U.S. Army Corps of 
Engineers, Coastal Engineering Research Center, Technical Report CERC-87-8.  Feasibility 
Study of Quantitative Erosion Models for Use by FEMA in the Prediction of Coastal Flooding. 
Vicksburg, Mississippi
Cox, J. C. & Machemehl, J.  (1986).  "Overland Bore Propagation Due to an Overtopping 
Wave."  Journal of Waterway, Port, Coastal and Ocean Engineering, Vol. 112, pp. 161-163.
Dawdy, David & Maloney, M. David.  (1980).  Method of estimating on-shore propagation of 
storm waves.  Geophysical Research Letters.  Vol. 7.  (pp. 845-847).  
de Waal, J. P. & van der Meer, J. W.  (1992).  Wave Runup and Overtopping on Coastal 
Structures.  Proceedings 23rd Coastal Engineering Conference, pp. 1758-1771.
Delft Hydraulics Laboratory.  (1983).  Wave Runup and Overtopping at Dunes During Extreme 
Storm Surge Report M1819, Part II.  (in Dutch).  Delft, The Netherlands.
Dewberry & Davis.  (1990).  Investigation and Improvement of the Capabilities of the FEMA 
Wave Runup Model (Technical Documentation for RUNUP 2.0), Report and Computer Program.  
Fairfax, Virginia.
Dewberry & Davis.  (1991).  Technical Documentation for RUNUP 2.0.  Report and computer 
program,  Fairfax, Virginia 
Dewberry & Davis.  (1995).  Basic Analyses of Wave Action and Erosion with Extreme Floods 
on Great Lakes Shores, draft prepared for Federal Emergency Management Agency.  Fairfax, 
Virginia.
Driver, D. B., Reinhard, R. D., & Hubertz, J. M.  (1991).  Hindcast Wave Information for the 
Great Lakes: Lake Erie, WIS Report 22, USACE, Coastal Engineering Research Center. 
Vicksburg, Mississippi.
Driver, D. B., Reinhard, R. D., & Hubertz, J. M.  (1992).  Hindcast Wave Information for the 
Great Lakes: Lake Superior, WIS Report 23, USACE, Coastal Engineering Research Center. 
Vicksburg, Mississippi.
Federal Emergency Management Agency.  (January 1981).  Computer Program for Determining 
Wave Height Elevations for Flood Insurance Studies, revised.  Washington, D.C.
Federal Emergency Management Agency.  (February 1981).  Users Manual for Wave Height 
Analysis, revised.  Washington, D.C.
Federal Emergency Management Agency.  (1984).  Procedures for Applying Marsh Grass 
Methodology.  Washington, D.C.
Federal Emergency Management Agency.  (1986).  Assessment of Current Procedures Used for 
the Identification of Coastal High Hazard Areas (V Zones). Washington, D.C.
Federal Emergency Management Agency.  (September 1988).  Wave Height Analysis for Flood 
Insurance Studies (Technical Documentation for WHAFIS Program Version 3.0).  Washington, 
D.C.
Federal Emergency Management Agency.  (August 1988).  Coastal Flooding Hurricane Storm 
Surge Model, Volumes 1, 2, and 3.  Washington, D.C.
Federal Emergency Management Agency.  (November 1988).  Basis of Erosion Assessment 
Procedures for Coastal Flood Insurance Studies.  Washington, D.C.
Federal Emergency Management Agency, Federal Insurance Administration.  (1989).  Guidelines 
and Specifications for Wave Elevation Determination and V Zone Mapping, Third draft report.  
Washington, D.C.
Federal Emergency Management Agency.  (1990).  "Memorandum on Criteria for Evaluating 
Coastal Flood Protection Structures for National Flood Insurance Program Purposes."  
Washington, DC, dated April 23, 1990.
Federal Emergency Management Agency, Federal Insurance Administration. (1991).  Guidelines 
for Great Lakes Wave Runup Computation and Mapping.  Washington, D.C.
Federal Emergency Management Agency, Federal Insurance Administration.  (August 1994).  
Basic Analyses of Wave Action and Erosion with Extreme Floods on Great Lakes Shores, draft 
report.  Washington, D.C.
Federal Emergency Management Agency.  (1994).  Guidelines and Specifications for Flood 
Hazard Mapping at Coastal Sites on the Great Lakes, draft. Washington, D.C.  
Federal Emergency Management Agency, Federal Insurance Administration. (1995.)  Guidelines 
and Specifications for Wave Elevation Determination and V Zone Mapping, final report.  
Washington, D.C.
French, J.  (1982).  Memorandum on Special Computation Procedure Developed for Wave 
Runup Analysis for Casco Bay, FIS - Maine, 9700-153.  Camp Dresser & McKee.
Gadd, P. E., Potter, R. E., Safaie, B. & Resio, D.  (1984).  Wave Runup and Overtopping:  A 
Review and Recommendations.  OTC 4674.  Proceedings 1984 Offshore Technology 
Conference, pp. 239-248.
Gilhousen, D. B., Meindl, E. A., Changery, M. J., Franks, P. L., Burgin, M. G., & McKittrick, D. 
A. (1990).  Climatic Summaries for NDBC Buoys and Stations:  Update 1.  National Data Buoy 
Center, National Space Technology Laboratory.  Mississippi.
Goda, Yoshima.  (1985).  Random Seas and Design of Maritime Structures.  University of Tokyo 
Press.  Japan.
Hardisky, M.A. & Reimold, R. J.  (1977).  Nondestructive Assessment of Salt Marsh Plant 
Biomass, unpublished report.  University of Georgia:  Athens, Georgia.
Hopkinson, C. W., Gosselink, J. G., & Parrondo, R. T.  (1980).  Production of Coastal Louisiana 
Marsh Plants Calculated from Phenometric Techniques.  Ecology, 61(5),  1091-1098.
Ho, F. P., Su, J. C., Hanevich, K. L., Smith, R. J., & Richards, F. P.  (1987).  Hurricane 
Climatology for the Atlantic and Gulf Coasts of the United States.  NOAA Technical Report 
NWS 38.  National Weather Service. Silver Spring, Maryland.
Hubertz, J. M., Driver, D. B., & Reinhard, R. D. (1991).  Hindcast Wave Information for the 
Great Lakes: Lake Michigan, WIS Report 24, USACE, Coastal Engineering Research Center. 
Vicksburg, Mississippi. 
Hubertz, J. M., Brooks, R. M., Brandon, W. A., & Tracy, B. A. (1993).  Hindcast Wave 
Information for the U.S. Atlantic Coast.  WIS Report 30. Coastal Engineering Research Center.  
Vicksburg, Mississippi.
Hydraulics Research Station.  (1980).  Design of Seawalls Allowing for Wave Overtopping.  
Report no. ex. 924. Wallingford, United Kingdom.
Jensen, R. E., Hubertz, J. M., Thompson, E. F., Reinhard, R. D., Borup, B. J., Brandon, W. A.,  
Payne, J. B., Brooks, R. M., & McAneny, D. S.  (1992).  Southern California Hindcast Wave 
Information.  WIS Report 20.  Coastal Engineering Research Center.  Vicksburg, Mississippi.
Knutson, P. L. & Woodhouse, W. W. Jr.  (1983).  Shore Stabilization with Salt Marsh 
Vegetation.  Special Report 9.  Coastal Engineering Research Center.  Fort Belvoir, Virginia.
Kruczynski, W. L., Subrahmanyam, C. B., & Drake, S. H.  (1978).  Studies on the Plant 
Community of a North Florida Salt Marsh:  Part I:  Primary Production.  Bulletin of Marine 
Science.  28(2),  316-334.
Leenknecht, D. A., Szuwalski, A., & Sherlock, A. R.  (1992).  Automated Coastal Engineering 
System, Version 1.07.  Coastal Engineering Research Center.  Vicksburg, Mississippi.
Levels Reference Study Board.  (1993).   Levels Reference Study: Great Lakes - St. Lawrence 
River Basin.  Annex 2 to report submitted to International Joint Commission.  Ottawa, 
Ontario/Washington, D.C.
Messmore, J. A., Vogel, T. C., & Pearson, A. R. (1979).  U.S. Army Corps of Engineers, 
Engineer Topographic Laboratories.  Terrain Analysis Procedural Guide for Vegetation.  ETL-
0178.  Fort Belvoir, Virginia.
Monte, J. A.  (1983).  Field Data from the Florida Panhandle, unpublished report.  Greenhorne & 
O'Mara, Inc.  Greenbelt, Maryland.
Nagai, S. & Takada, A. (1972).  Relations Between the Runup and Overtopping of Waves.  
Proceedings 13th Coastal Engineering Conference, pp. 1975-1992.
National Academy of Sciences.  (1977).  Methodology for Calculating Wave Action Effects 
Associated with Storm Surges.  Washington, D.C. 
Owen, M. W.  (1980).  Design of Seawalls Allowing for Wave Overtopping.  Report Ex. 924.  
Hydraulics Research Station.  Wallingford, United Kingdom.
Reinhard, R. D., Driver, D. B., Hubertz, J. M. (1991).  Hindcast Wave Information for the Great 
Lakes: Lake Huron, WIS Report 26, USACE, Coastal Engineering Research Center. Vicksburg, 
Mississippi. 
Saville, T., Jr.  (1958).  Wave Runup on Composite Slopes.  Proceedings of the Sixth Conference 
on Coastal Engineering.  ASCE.  Council on Wave Research.
Stoa, P. N.  (1978).  Reanalysis of Wave Runup on Structures and Beaches. Technical Paper 78-
2.  Coastal Engineering Research Center.  Fort Belvoir, Virginia.
Stone & Webster Engineering Corporation.  (1978).  Development and Verification of a 
Synthetic Northeaster Model for Coastal Flood Analysis.  Boston, Massachusetts.
Stone & Webster Engineering Corporation.  (1981).  Manual for Wave Runup Analysis, Coastal 
Flood Insurance Studies.  Boston, Massachusetts.
Suhayda, J. N.  (1984).  Attenuation of Storm Waves Over Muddy Bottom Sediments. Baton 
Rouge, Louisiana.
Thompson, E. F.  (1977).  Wave Climate at Selected Locations Along U.S. Coasts.  Technical 
Report 77-1.  Coastal Engineering Research Center.  Fort Belvoir, Virginia.
Turner, R. E. & Gosselink, J. G. (1975).  A Note on Standing Crops of Spartina alterniflora in 
Texas and Florida.  Contributions in Marine Science, University of Texas. 
U.S. Army Corps of Engineers, Galveston District.  (1973).  General Guidelines for Identifying 
Coastal High Hazard Zone, Flood Insurance Study - Texas Gulf Coast Case Study.  Galveston, 
Texas.  
U.S. Army Corps of Engineers, Galveston District. (1975).  Guidelines for Identifying Coastal 
High Hazard Zones.  Galveston, Texas.
U.S. Army Corps of Engineers, Coastal Engineering Research Center.  (1984).  Shore Protection 
Manual, Volumes I and II, 4th Edition, Washington, D.C.  
U.S. Army Corps of Engineers, Detroit District.  (1988).  Revised Report on Great Lakes Open-
Coast Flood Levels, Phase I/Phase II.  Detroit, Michigan.
U.S. Army Corps of Engineers, Detroit District. (June 1989). Great Lakes Wave Runup 
Methodology Study.  Detroit, Michigan.
U.S. Army Corps of Engineers, Detroit District. (September 1989).  Saginaw Bay Flood Levels 
Report, Detroit, Michigan.
U.S. Army Corps of Engineers, Coastal Engineering Research Center.  (1992).  Automated 
Coastal Engineering System Version 1.07.  Computer Programs and Documentation.  Vicksburg, 
Mississippi.
Vellinga, P.  (1986).  Beach and Dune Erosion During Storm Surges.  Communication No. 372.  
Delft Hydraulics Laboratory.  Delft University of Technology.  Delft, The Netherlands.
Walton, T. L., Jr., Ahrens, J. P., Truitt, C. L., & Dean, R. G.  (1989).  Criteria for Evaluating 
Coastal Flood-Protection Structures.  Technical Report CERC-89-15.  U.S. Army Corps of 
Engineers, Coastal Engineering Research Center.  Vicksburg, Mississippi.
Williams, P.  (1983).  Interoffice Correspondence on Wave Runup Methodology, Massachusetts 
and Rhode Island Flood Insurance Studies. PRC Harris, Inc.
[February 2002]
Guidelines and Specifications for Flood Hazard Mapping Partners

Section D.1	D-14	February 2002 Edition

Section D.2	D-111	February 2002 Edition

Section D.3	D-177	February 2002 Edition
D-1

Section D.4	D-187	February 2002 Edition

Section D.5	D-188	February 2002 Edition

Section D.6	D-193	February 2002 Edition