Sheltered Waters

Table of Contents
1	INTRODUCTION
1.1	Sheltered Waters Focused Study Group and Approach
1.2	Current FEMA Guidance on Sheltered Waters Flood Hazards
1.3	Suggested Improvements
2	CRITICAL TOPICS	
2.1	Critical Topic 6a  Provide definitions and develop a classification method for 
sheltered water studies as a framework for an approach
2.1.1	Description of the Topic 6a
2.1.2	Current FEMA Guidance on the Topic	
2.1.3	Alternatives for Improvement
2.1.4	Recommendations
2.2	Critical Topic 6b  Prepare guidance for reconstructing historic flood conditions 
to validate flood study results
2.2.1	Description of the Topic	
2.2.2	Current FEMA Guidance on the Topic
2.2.3	Alternatives for Improvement
2.2.4	Recommendations	
2.3	Critical Topic 6c  Seek peer input on new sheltered water guidelines needs
2.4	Critical Topic 6d  Prepare guidance for defining the 1-percent-chance flood 
event in sheltered water areas	
2.4.1	Description of the Topic
2.4.2	Current FEMA Guidance on the Topic
2.4.3	Alternatives for Improvement
2.4.4	Recommendations	
2.5	Critical Topic 6e  Prepare guidance for estimating stillwater elevations and 
currents in sheltered water areas
2.5.1	Description of the Topic	
2.5.2	Current FEMA Guidance on the Topic	
2.5.3	Alternatives for Improvement
2.5.4	Recommendations	
2.6	Critical Topic 6f  Prepare guidance for evaluating coastal flood protection 
structures in sheltered waters
2.7	Critical Topic 6g  Prepare guidance for identifying flood insurance risk zones 
in sheltered waters
2.8	Critical Topic 6h  Coordinate the preparation of sheltered waters guidelines 
with other Map Modernization objectives and multi-hazard planning initiatives	
2.8.1	Description of the Topic	
2.8.2	Current FEMA Guidance on the Topic
2.8.3	Alternatives for Improvement	
2.8.4	Recommendations	
3	AVAILABLE TOPICS	
4	IMPORTANT TOPICS	
5	ADDITIONAL OBSERVATIONS	
6	SUMMARY	20
7	REFERENCES

Tables

TABLE 1.  SUMMARY OF FINDINGS AND RECOMMENDATIONS FOR SHELTERED WATERS	
TABLE 2.  PRELIMINARY TIME ESTIMATE FOR GUIDELINE PREPARATION FOR 
SHELTERED WATER FLOOD HAZARDS	

Figures

Figure 1.  Seasonal wind patterns in Puget Sound, Washington
Figure 2.  Conceptual procedural flow chart for a sheltered water classification system.
Figure 3.  Representative sheltered water methodology.
Figure 4.  Sverdrup-Munk Bretschnieder diagram for wave forecasting in sheltered waters	

Acronyms

ACES	Automated Coastal Engineering Systems
CTP	Coordinating Technical Partners
DFIRM	Digital Flood Insurance Rate Map
FIS	Flood Insurance Study
FIT	Flood Information Tool
MAS	Mapping Activity Statement
NFIP	National Flood Insurance Program


1	INTRODUCTION
This report provides recommendations for a program leading to improvement of the current 
FEMA Guidelines related to Sheltered Waters Flood Hazards and develops preliminary time 
estimates to accomplish these improvements. One sheltered water category was developed at the 
December 2003 Workshop. This category was labeled Critical for the Pacific and Non-Open 
Coast and Helpful for the Atlantic and Gulf Coast.
  
This was the only focused study category initially established with one related topic; however, 
the nature of this focused study cuts across many other focused studies, as indicated by the 
number of ratings in the Non-Open Coast column of the original focused study table. Therefore, 
this single category has been subdivided into additional topics (needs).  The topics either provide 
detail for recommendations not captured under other focused studies or provide 
recommendations to refine open coast guidance prepared by other focused study groups, for 
application to sheltered water studies.  The topics were further refined during the February 2004 
Workshop. 

The preparation of guidance for many of the above topics will be coordinated with other 
appropriate focused study groups because of the interrelationship of these topics with similar 
topics found in other focused studies. The purpose of addressing these topics here in the 
Sheltered Waters Focused Study is to document aspects of the work that may have more 
relevance to sheltered water flood studies, as opposed to open coast studies.

1.1	SHELTERED WATERS FOCUSED STUDY GROUP AND APPROACH
The Sheltered Waters Focused Study group consisted of: Jeff Johnson, David Divoky, Darryl 
Hatheway, Ron Noble, and Kevin Coulton who served as Team Leader for this effort.
To provide structure to the team efforts and to avoid unnecessary duplication of work, the 
following approach was used: the Team Leader developed background material, reviewed 
available information, and developed draft write-ups, which were then distributed to the Team. 
All Team Members contributed information of which they were uniquely aware, critiqued and 
contributed to the draft write ups and accomplished specific components of the overall effort 
leading to this report. 

1.2	CURRENT FEMA GUIDANCE ON SHELTERED WATER FLOOD HAZARDS
Sheltered waters are water bodies with shorelines that are not subjected to the direct action of 
undiminished ocean waves. Although similar processes contribute to flooding in sheltered water 
shorelines as along open coastlines, such as wave setup, runup, and overtopping, there are 
several aspects of sheltered water flood hazards not addressed in the current FEMA Guidelines. 
For example, wind-generated waves are highly dependent on the shape and orientation of the 
surrounding terrain to prevailing wind directions (Figure 1).

Wave generation and transformation in sheltered waters are typically limited by an open water 
fetch distance, complex bathymetry, and often the presence of structures.  See the Storm Wave 
Characteristics Focus Study Report for more information about seas in sheltered waters. 

A sheltering effect typically reduces wave energy and flood potential compared to open coast 
areas; however, wave runup and overtopping along sheltered water shorelines may present 
additional hazards from wave-cast debris and backshore flooding because insured buildings are 
often located closer to the shoreline than along the open coast. Hazard evaluations for these and 
other characteristics of sheltered waters require special methods not available in the Guidelines.

The existing Guidelines (FEMA, 2003) are generally written to provide guidance for coastal 
flood studies along the open coasts of the Atlantic Ocean and Gulf of Mexico. Several references 
to sheltered water areas are made in these Guidelines, but detailed guidance is not provided. The 
Great Lakes are very large sheltered water bodies and guidelines (Great Lakes G&S in Appendix 
D) are provided for flood studies; however, these guidelines are very specific to the storm 
meteorology and physiography of the Great Lakes and are assumed to not be applicable to 
Pacific Ocean sheltered water areas.

Figure 1.  Seasonal wind patterns in Puget Sound, Washington
(Figure from Downing, 1983)

The following listing provides a brief description of portions of the existing guidelines relevant 
to the topic of Sheltered Waters flood studies.  These items are expanded on in subsequent 
sections of this report.

	* Section D.1.2.4  Methods by which barriers, inlets and rivers have been treated are 
	required in documentation of the hydrodynamic storm surge model.  However, no 
	guidance is provided for methods to consider modeling for sheltered waters.  
	
	* Section D.2.2.7  The analysis of restricted fetches in sheltered coastal sites is 
	addressed in the existing guidelines and the ACES software is referred to; however, more 
	specific guidance can be provided on how to apply this software to fetch-limited 
	conditions.
	  
	* Section D.2.5.5  Wave runup in special situations addresses wave runup and 
	overtopping on shoreline barriers where overtopping flows discharge across landward-
	dipping or level backshore slopes to a bay, river, or backwater. These situations are 
	prevalent in sheltered water areas.  No additional guidance is provided.

The natural processes that result in flooding in sheltered water areas are complex and not 
adequately addressed in the current guidelines. Sheltered water areas often have unique flood 
hazards, due to the effects of fluvial drainages and modified tidal and surge hydrology, and 
relatively strong currents. Wave-cast debris from extreme wave runup and overtopping can be 
especially problematic, owing to the proximity to sources of such materials in many estuaries. 

Other unique flood-related characteristics include the complex geometry of the embayments, 
lack of coincident peak storm surge with peak winds, shallow water and restricted wind fetches 
for wave growth, and non-sandy shoreline types with special erosion and scour hazards.  These 
unique flood hazards are not adequately addressed in the current guidelines for sheltered water 
bodies.

New guidelines are needed to inform and guide Mapping Partners in the preparation of coastal 
flood insurance studies and flood hazard maps in sheltered water areas of the coastal floodplain. 

1.3	SUGGESTED IMPROVEMENTS
Flood hazards in sheltered waters are caused by physical processes that are also responsible for 
open coast flooding (e.g., tidal surge, wave runup and overtopping); however, the sheltering 
effect of high elevation upland terrain on wind wave development and the localized shallow 
water bathymetry influence on the inland propagation of ocean swell and waves may create flood 
hazards unique to sheltered water areas. 

At a basic level, definitions and descriptions of the physical conditions and physical processes 
associated with flood hazards in sheltered water areas need to be clearly described to Mapping 
Partners (and the public) through the guidelines. This information should be documented in the 
guidelines in a manner that establishes a framework for standardized, repeatable, and defendable 
flood study methods.

Given the lack of guidance for performing sheltered waters flood studies, Mapping Partners have 
developed methods to meet the needs of these unique studies over the years. Therefore, a 
concerted effort should be made to compile, review, and compare past methods that have been 
employed and approved by FEMA, and may be suitable for documentation in the new 
Guidelines.

It is proposed that new guidelines for sheltered water areas be developed as a separate section of 
the Guidelines to accompany the Pacific Ocean, Gulf of Mexico/Atlantic Ocean, and Great 
Lakes sections. This Sheltered Waters section would consist of methods unique to physical 
processes influenced by these sheltering effects. Cross-references would be provided to other 
sections of the guidelines to either instruct Mapping Partners on where and how to import 
parameters for use in the unique sheltered water methods or to export findings for use in 
subsequent methods to define final flood hazards.

An interim approach is to include a description of sheltered waters in the Pacific Coast 
Guidelines, which is to be written in Phase 2 of this project. It is anticipated that this section 
would also be useful for flood studies in other regions.

2	CRITICAL TOPICS
A series of focused study topics were identified to support the original Sheltered Waters issues in 
Topic 6, which was identified as being a critical need in Workshop 1. Following Workshop 1 
eight critical topics were identified, but as of Workshop 2 three topics from this focused study 
report were either removed entirely or included in another Category and Topic. The remaining 
five Sheltered Water topics are discussed in the following sections of this report. 

2.1	CRITICAL TOPIC 6A  PROVIDE DEFINITIONS AND DEVELOP A CLASSIFICATION 
METHOD FOR SHELTERED WATER STUDIES AS A FRAMEWORK FOR AN APPROACH 

2.1.1	Description of the Topic 6a
Definitions for coastal and riverine flood studies are provided in the NFIP regulations (44 CFR 
59.1).  These definitions are useful as they convey basic concepts related to flood insurance 
studies and they support the Guidelines and Specifications.  Sheltered waters is not currently 
defined in the NFIP regulations or the existing Guidelines.  One USACE definition of sheltered 
waters is shorelines that are not subjected to the direct action of undiminished ocean waves. 
There are likely additional definitions that should be reviewed and considered to clarify the terms 
used in the pending revised guidelines.  Examples of sheltered water bodies may also be 
appropriate to present in the guidelines to demonstrate the range of sheltered water conditions 
that can be encountered in coastal flood studies.

Pacific Coast examples of important sheltered water areas include Puget Sound (WA), San 
Francisco Bay (CA), and San Diego Bay (CA).  Siletz Bay (OR), Humboldt Bay (CA), Morro 
Bay (CA), and Newport Bay (CA), San Diego Bay (CA) are examples of smaller embayments 
which may exhibit similar characteristics of sheltered waters.

Gulf of Mexico examples of sheltered water include Galveston Bay (TX), Mobile Bay (AL), 
Tampa Bay (FL), and Charlotte Harbor, (FL).

Atlantic Ocean examples of sheltered water include Indian River Lagoon (FL), Albermarle and 
Pamlico Sounds (NC), Chesapeake Bay (MD-VA), Delaware Bay (DE-PA), Long Island Sound 
(NY-CT), Narragansett Bay (RI), Buzzards Bay (MA), and Cape Cod Bay (MA).

This focused study proposes the use of a classification system as a way to provide a framework 
for the sheltered waters guidelines.  Given the variety of coastal conditions a Mapping Partner 
could encounter along the shorelines of bays, river deltas, estuaries, etc. and the variety of 
coastal processes at work in sheltered water resulting in unique flood hazards, a classification 
system may assist a Mapping Partner to determine relevant issues and available methods for 
assessing potential flood hazards. Such an approach would benefit Study Contractors working on 
the open coast as well.
  
2.1.2	Current FEMA Guidance on the Topic
The following sections from the current FEMA Guidelines (2003) generally address this topic:

	* Section D.1  General guidance is primarily oriented to the Atlantic and Gulf Coasts; 
	however, a 1977 technical paper is referenced for Pacific Northwest open coast flood 
	study guidance. No references are provided for sheltered water flood studies in the 
	current Guidelines. 
	
	* Section D.1.2.1  The geographic setting of the flood study site is required as part of 
	the engineering report.  It is assumed that the general description of the geographic and 
	demographic conditions of the study area are prepared to satisfy this requirement, and 
	then is typically used as text for the FIS narrative report.  
	
	* Section D.1.2.4  Methods by which barriers, inlets and rivers have been treated are 
	required in documentation of the hydrodynamic storm surge model.  
	
	* Section D.2.1. and Section D.3.1  Typical shoreline types (Table D-1) are provided in 
	guidance for Atlantic and Gulf Coast studies and basic types of coastal topography 
	(Table D-14) are provided for Great Lakes studies.  No similar specific classification 
	system is provided for Pacific Coast or sheltered water areas.  
	
	* Section D.2.2. and Section D.2.2.2  Upland regions and Topographic data are 
	discussed in these sections in relation to data requirements for coastal flood hazard 
	analyses.  The discussion is primarily focused on shore topography and does not 
	encourage a broader view of regional topographic conditions.  
	
	* Section D.2.2.4  Land cover data are discussed in the current guidelines as related to 
	the immediate shoreline and backshore areas.  This information is used to establish 
	shoreline reaches with similar cultural features and define the nature of overland wave 
	obstructions caused by vegetation and buildings.  

2.1.3	Alternatives for Improvement
In lieu of changing the NFIP regulations and adding to the definitions provided in 44 CFR 59.1, 
a new section in Appendix D of the Guidelines for coastal flood study definitions (sheltered 
water and open coast) should be provided to augment those in 44 CFR 59.1.  It is understood that 
the Guidelines currently has a Glossary of Flood Hazard Mapping Terms following the 
appendices; however, it may be easier for users of the Guidelines to refer to definitions within 
the technical appendix itself.

There is an opportunity to expand existing guidance for defining the geographic setting of the 
flood study site.  Expanded guidance would be provided to assist the Mapping Partner in 
undertaking a systematic approach to quickly assess a project setting in order to better 
understand the regional and site specific characteristics of the study site.  With this 
understanding, the Mapping Partner would then be guided to a series of methods to best define 
flood hazards given the study site characteristics.  This approach would be embodied in a 
classification system.

Classification has been used in a variety of disciplines to order characteristics of systems into 
similar categories or relationships.  Classification systems have been used since the 1800s to 
describe rivers and streams.  Some examples of these classification systems include Montgomery 
and Buffingtons geomorphological classification of drainage channels in the Pacific coastal 
ecoregion (Montgomery and Buffington, 1993) and Rosgens classification of stream channels 
for restoration design (Rosgen, 1996).

Crafting an approach to the guidelines that helps orient the Mapping Partner to the physical 
characteristics and processes present at a given flood insurance study site location is an important 
consideration in planning the content of the new Guidelines.  Based on this information the 
Mapping Partner can work through the guidelines to determine the types and relative importance 
of coastal hazards to consider (erosion, setup, overtopping, drift logs, etc) and select the 
appropriate methods to properly define hazard zones. A coastal classification system (perhaps in 
a flow chart or table format) would be provided in the guidelines for this purpose. 

An example of a potential procedural flowchart that could assist Study Contractors to determine 
site history, conditions and relevant issues related to Sheltered Water areas is shown in Figure 2. 
The approach shown in the figure would encourage a Mapping Partner to systematically identify 
and understand the processes and the physiographic setting within, and beyond, a specific study 
 
Figure 2.  Conceptual procedural flow chart for a sheltered water classification system.

site at multiple spatial scales.  For example, seasonal wind patterns and the sheltering effect of 
surrounding terrain would be identified at a regional scale. Sediment and erosion characteristics 
would then be identified at the littoral cell scale and shoreline and backshore features at the 
project reach and transect scale. Site classification (determination of site conditions and relevant 
issues) is typically the first step in conducting a flood hazard assessment and it is an essential 
part of scoping a study to reduce the chance of missing important study needs specific to a 
projects location, setting and history.

Additional improvements to existing guidance in the G&S are as follows:

	* Section D.1  General guidance: New references to FEMA-accepted flood insurance 
	studies in sheltered water areas (Port Angeles 1995, Whatcom County 2001) should be 
	included in the references for all coasts.  Phase 2 efforts should involve a review of these 
	studies to determine their appropriateness to serve as references for guidance.
	
	* Section D.1.2.4  Methods by which barriers, inlets and rivers have been treated: 
	Where these methods involve sheltered water, specialized guidance should be referenced 
	in a separate section to explain how the storm surge model took into account sheltering 
	affects of high terrain, large forested vegetation stands, urban development, deep-cut 
	navigation channels, etc.
	
	* Section D.2.1. and Section D.3.1  Typical shoreline types: New guidance should be 
	provided to support the proposed classification system described in the next section.
	
	* Section D.2.2. and Section D.2.2.2  Upland regions and Topographic data: For 
	sheltered water studies, the wind sheltering and channeling effects of nearby upland 
	terrain on regional storm systems are important, as is the proximity of river mouths and 
	the associated terrain and land use characteristics within river watersheds. New 
	guidelines should provide guidance for evaluating these broader topographic data issues.
	
	* Section D.2.2.4  Land cover data: New guidelines should broaden the review of these 
	data to support the proposed geographic setting classification system and allow an 
	evaluation of sources of wave-cast floating debris.  In addition, if storm-induced erosion 
	is to be addressed in the new guidelines, then geology and soils data may be best 
	discussed in this section of the guidelines.

2.1.4	Recommendations
The recommendations for Topic 6a include:

	1.	Review previous sheltered water flood studies  Document how studies have been done 
	in the past and compare methods approved by the various FEMA Regions.
	
	2.	Define Sheltered Water (non-Open Coasts) for the purposes of FEMA flood insurance 
	studies - Compile a list of sheltered water flood study definitions and clarify terminology 
	used in guidelines.
	
	3.	Identify sheltered water physical processes and site characteristics - Identify physical 
	processes that may need to be considered to map the coastal flood hazard; consider 
	processes common to all coastal areas and those unique to the identified landform class.  
	Identify specific site characteristics (in this case sheltered water) that may need to be 
	considered, evaluated and quantified to map the coastal flood hazard within a certain 
	coastal class.
	
	4.	Review classification systems established by others and refine/adapt a system for 
	sheltered water areas  Provide a framework for standardizing an approach to coastal 
	flood studies and identifying the relative importance of certain physical characteristics 
	and processes to coastal flood hazards, based on the physical location of a flood study 
	project site.
	
	5.	Write Guidelines for Sheltered Water in the Pacific Coast Region with information useful 
	to the Atlantic, Gulf and Great Lakes Regions as appropriate. 
	Table 1 at the end of this report contains a summary of the key findings and recommendations 
	for Topic 46.  Table 2 at the end of this report presents estimates of times required to accomplish 
	the various tasks in this topic.

2.2	CRITICAL TOPIC 6B  PREPARE GUIDANCE FOR RECONSTRUCTING HISTORIC 
FLOOD CONDITIONS TO VALIDATE FLOOD STUDY RESULTS

2.2.1	Description of the Topic
The current FEMA Guidelines provide limited guidance on methods that can be used to obtain 
past flood data, reconstruct historic flood conditions, and use the data to validate new flood study 
results.  This is an extremely important consideration because the complexity of coastal flood 
events can impart great uncertainty into the estimation of final Base Flood Elevations.  The 
ability to compare theoretical results of the 1-percent-annual-chance flood to observed flood data 
can greatly reduce the uncertainty involved. This effort can increase the credibility of FEMA 
studies and reduce the potential for appeals.
Therefore, an objective of this work will be to prepare guidance for using historic flood 
observations to validate new flood study results.  

2.2.2	Current FEMA Guidance on the Topic
The following section from the current FEMA Guidelines addresses this topic:

	* Section D.2.2.9  Historical floods and buildings flooded are discussed and general 
	guidance is provided encouraging acquisition of all available data related to high water 
	marks and tidal flooding from extreme coastal flood events.

2.2.3	Alternatives for Improvement
In sheltered water areas, many buildings and other features of the built environment are closer to 
the shoreline and often more exposed to flooding than along open coast areas. An opportunity 
exists to expand guidance on historical flood data acquisition to include methods for 
reconstructing past flood water elevations observed on these landmarks found in sheltered water 
areas (buildings, mailboxes, street signs, etc.) together with new survey data.  Reconstruction 
implies converting qualitative flood observations (e.g., homeowner account of flood water up to 
my deck) to a quantitative elevation using local survey methods employed on recent studies in 
Puget Sound (Whatcom County, WA - Sandy Point 2001 and Birch Bay 2002) can be reviewed 
and summarized for use as case study examples in the new guidelines.

Accordingly, expanded field reconnaissance guidance for sheltered water flood studies will be 
developed.  

This guidance may include the following:

	* Develop sample flood hazard questionnaire for Mapping Partners to edit and send out 
	to local government officials and property owners during the reconnaissance phase of a 
	flood study.
	
	* Develop field reconnaissance guidance on how to find and document coastal flood high 
	water marks and wave heights.
	
	* Develop guidance for historic flood reconstruction methods that convert qualitative 
	flood observations to more quantitative data for results validation.

2.2.4	Recommendations
The following recommendations for Topic 6b include:

	1.	Review previous sheltered water flood studies and document methods used for validating 
	flood study results  A summary of the review may include a checklist for results 
	validation.
	
	2.	Review of previous sheltered water flood studies and compare results of past flood 
	studies to actual damage and flood observations made by community officials and 
	residents.
	
	3.	Prepar
	e field reconnaissance guidance for reconstructing historic flood observations.

2.3	CRITICAL TOPIC 6C  SEEK PEER INPUT ON NEW SHELTERED WATER GUIDELINES NEEDS 
NOTE: This Topic was deleted during Work Shop 2.

2.4	CRITICAL TOPIC 6D  PREPARE GUIDANCE FOR DEFINING THE 1-PERCENT-ANNUAL-
CHANCE FLOOD EVENT IN SHELTERED WATER AREAS

2.4.1	Description of the Topic
The current guidance in Appendix D focuses on open coast areas and does not provide any 
recommended procedures for developing the 1-percent-annual-chance flood event in sheltered 
water areas.  Guidance needs to be provided for the unique conditions found in sheltered waters 
where high terrain obstructs and channels the winds associated with regional storm systems as 
they traverse sheltered water bodies. Some sheltered water areas also receive strong influences 
from seasonal fresh water inflows, often leading to the need for assessing the joint probability of 
such combined influences of coastal and terrestrial flood conditions.

This topic will be coordinated with Topic 51 addressed by the Storm Meteorology Focused 
Study Group.

2.4.2	Current FEMA Guidance on the Topic
The following sections from the current FEMA Guidelines generally address this Topic:

	* Section D.2.2.1 and Section D.2.2.7  The current guidelines state only the 1-percent-
	annual-chance SWEL is required for coastal analyses and the basic presumptionis 
	that wave hazards occur coincidentally with the 1-percent-annual-chance flood (flood 
	is assumed to mean stillwater).  
	
	* Section D.2.2.6 - The current 1-percent-annual-chance flood event guidance was 
	developed primarily for open-coast settings on the Atlantic and Gulf Coasts; e.g., 
	guidance refers to storm meteorology associated with Northeasters and hurricanes and 
	rules of thumb are provided for typical wind speed and surge conditions.  As 
	mentioned above, the current Guidelines appear to define the 1-percent-annual-chance 
	stillwater as the flood event.  
	
	* Section D.2.2.7  The analysis of restricted fetches in sheltered coastal sites is 
	mentioned in the existing guidelines and the Mapping Partner is referred to ACES user 
	manual for guidance.  
	
	* Section D.2.5.2  Wave height and period estimates suitable for runup computations at 
	fully exposed coastal sites are provided in Table D-4.

2.4.3	Alternatives for Improvement
Alternatives for improvement may be provided in sheltered water flood studies conducted for 
FEMA in Region X (CH2M Hill, 1989; PWA, 2002). These studies resulted in different methods 
that were approved by FEMA to estimate the 1-percent-annual-chance flood event for sheltered 
water areas of Puget Sound (Figure 3). A comparison of these methods to each other and to 
observed flood data would be informative to assess the sensitivity and accuracy of the methods. 
Based on the findings, more definitive guidance could be provided to Mapping Partners for 
estimating the 1-percent-annual-chance flood event for sheltered water areas. 

Where streams are tributary to sheltered water, definition of the 1-percent-chance flood event 
requires consideration of the joint probability effects of riverine and tidal flooding.  The 
dependence or independence of these two events in a flood frequency analysis is a complex 
issue, based on the size and speed of the regional storm system and the resulting coincidence or 
lag between peak occurrences of storm surge and river runoff.  Guidance could be provided to 
Mapping Partners to define and enable mapping of these complex flood hazards.
Additional improvements to existing guidance in the G&S are as follows:

	* Section D.2.2.1 and Section D.2.2.7: Recent sheltered water studies in Puget Sound 
	recognized the wind sheltering effect of high mountainous terrain on low-pressure storm 
	systems approaching the Pacific Coast and alternate methods were employed to estimate 
	the 1-percent flood event with restricted fetches limiting the wave growth regions 
	throughout Puget Sound.  The methods used in these studies involved the estimation of 
	the 1- through 100-year return period tides for use in joint probability statistical analyses.  
	Therefore, new guidelines may actually require Mapping Partners to consider more than 
	just the 1-percent-annual-chance flood (stillwater) elevation for estimation of the 1-
	percent-annual-chance flood event caused by the combination of wind waves and tide.
	
	* Section D.2.2.6:  Definition of the recurrence interval of this stillwater event is deemed 
	important for providing a basis from which to assign recurrence intervals to observed 
	historic extreme stillwater events and for assessing wave conditions likely associated 
	with this stillwater event.  These storm systems are addressed because of their potential 
	differences in duration of the surge event.  Therefore, new guidelines may need to 
	address the duration of the surge event and not just the peak elevation of the stillwater 
	event alone.  The duration, or time history, of the tidal surge event may become important 
	if more detailed guidance is provided on methods for determining the probability of the 
	simultaneous occurrence of two events, as opposed to the related occurrence of the events 
	within a broader time period.
	
	* Section D.2.2.7: New guidelines might expand on the fetch-limited wave height 
	calculations made through the use of the currently referenced ACES Windspeed 
	Adjustment and Wave Growth computer routine.
	 
	Figure 3.  Representative sheltered water methodology.
	
	* Section D.2.5.2: A similar table to Table D-4 or nomograph relating wind speed to fetch 
	length, such as the classic Sverdrup-Munk-Bretschnieder diagram (Figure 4), or 
	improved guidance, would be useful in the guidelines to describe wave growth for 
	sheltered water conditions based on fetch length, wind speed and duration.
	Figure 4.  Sverdrup-Munk Bretschnieder diagram for wave forecasting in sheltered waters

2.4.4	Recommendations
The following recommendations for Topic 6d include:

	1.	Review the methods used in previous FEMA-accepted sheltered water flood insurance 
	studies for possible adoption as methods to reference in the new guidelines. 
	
	2.	Prepare guidance on independent/dependent joint probability effects on the 1%-chance 
	event considering coastal watersheds and riverine-tidal flooding.
	
	3.	Expand discussion of existing guidance on wind data acquisition and analysis and fetch-
	limited wave forecasting.

2.5	CRITICAL TOPIC 6E  PREPARE GUIDANCE FOR ESTIMATING STILLWATER 
ELEVATIONS AND CURRENTS IN SHELTERED WATER AREAS

2.5.1	Description of the Topic 
Sheltered water areas encompass a variety of complex shorelines.  This complexity in geography 
and topography can result in unique circumstances where methods derived for open coast 
assessments may not be directly applicable to sheltered water coastal flood studies.  The 
objective of this work is to prepare guidance interactively with the Stillwater and Wave 
Transformation Focused Study Groups, refining appropriate open coast guidance (Item 8 and 55) 
into a reliable methodology for sheltered water areas.

2.5.2	Current FEMA Guidance on the Topic
The following sections from the current FEMA Guidelines and NFIP regulations generally 
address this topic:
	
	* D.2.2.1  Guidance on the estimation of stillwater elevations is provided with 
	recommendations for the use of measured water levels at gauge stations or storm surge 
	modeling.  Models are recommended for complex shorelines where gage records may 
	not represent true stillwater elevations.  
	
	* D.2.6.1  Various tidal datums (MLW, MTL, MHW) are referred to in Figure D-24 of the 
	existing Guidelines.  Tidal datums are also referred to in the NFIP regulations under 
	44CFR60.3(e)(3) Mean High Tide and normal high water is referred to in the 
	definition of reference feature in 44CFR59.1.  There is currently no guidance on how to 
	obtain these data or estimate these elevations.

2.5.3	Alternatives for Improvement
Given the concentration of development and insured structures that are typical within sheltered 
water areasthose adjacent to low gradient shoreline beaches and estuarine wetlandsthere is a 
need to better understand the true natural variation of tide, in addition to the hypothetical 1-
percent-annual-chance stillwater elevation. These tidal variations are commonly documented at 
tidal gauging stations as tidal datums. Vertical tidal datum references are often used in the 
more densely populated sheltered water areas to demarcate natural and human boundaries; e.g., 
legal property boundaries are often establish based on the Ordinary High Water Mark along 
shorelines and rivers.  Guidance should be provided 1) on where and how to obtain tidal datum 
information, 2) how tidal datums can be developed  from tide gauge data or derived in 
conjunction with field investigations, and 3) how tide data and tidal datums should be validated 
prior to usage.

Recurrence interval stillwater data are typically derived from tidal gauging stations.  These 
stations are normally located within a sheltered water body with open communication to the 
ocean.  For flood study sites located in a nearby ungauged sheltered water body, the direct 
transfer of tide gauge elevations, or interpolation of data between two gauging stations may not 
be appropriate.  For example, the morphology of an embayment with a narrow tidal inlet may 
result in tidal choking, resulting in stillwater elevations higher than predicted from adjacent 
gauge data. A sheltered bay influenced by large seasonal fresh water discharges from inland 
drainage areas are certain to have unique tidal characteristics (datums) during periods of high 
runoff. Guidance should be provided to Mapping Partners for transferring tide gauges data to 
ungauged locations.  This guidance could be similar to the standard hydrologic methods 
available for transferring stream gauge data from a gauged to ungauged watershed location.

Tidal, riverine and other nearshore currents may have an effect on wave shoaling and shoreline 
erosion under flood conditions.  The Guidelines should discuss these conditions and provide 
methods for assessing the significance of these physical processes on flood hazards. This topic 
should be coordinated with the Wave Transformations Study Group, owing to the effects of 
currents on wave refraction and shoaling. The key issue is that currents are often stronger in 
sheltered waters, and hence current effects on waves should not necessarily be neglected.

2.5.4	Recommendations
The following recommendations for Topic 6e include:

	1.	Review scientific literature and resource management practices related to stillwater, tidal 
	currents and tidal datums in sheltered water areas.
	
	2.	Prepare guidance for the transfer of tide gauge data to ungauged sheltered water bodies.
	
	3.	Prepare guidance for the assessment of tidal and riverine nearshore currents and their 
	significance to flood hazards.
	
	4.	Coordinate guideline development with appropriate Focused Study Groups.

2.6	CRITICAL TOPIC 6F  PREPARE GUIDANCE FOR EVALUATING COASTAL FLOOD 
PROTECTION STRUCTURES IN SHELTERED WATERS
NOTE: This Topic was assigned for coverage under Topic 21a during Work Shop 2. 

2.7	CRITICAL TOPIC 6G  PREPARE GUIDANCE FOR IDENTIFYING FLOOD INSURANCE 
RISK ZONES IN SHELTERED WATERS
NOTE: This Topic was assigned for coverage under Topic 17 during Work Shop 2. 

2.8	CRITICAL TOPIC 6H  COORDINATE THE PREPARATION OF SHELTERED WATER 
GUIDELINES WITH OTHER MAP MODERNIZATION OBJECTIVES AND MULTI-HAZARD 
PLANNING INITIATIVES

2.8.1	Description of the Topic 
The development of new coastal guidelines is one of many Map Modernization objectives 
identified by FEMA.  The sheltered water guidelines should reference other appropriate Map 
Modernization objectives and multi-hazard planning initiatives.  This coordination can broaden 
the use of the new guidelines to assist Mapping Partners with other hazard mitigation activities.  

For example, the utility of new guidelines may be enhanced if the methods for riverine-tidal 
flood assessments in sheltered water areas also provide guidance for incorporating future 
conditions riverine hydrology into coastal flood hazard maps.

2.8.2	Current FEMA Guidance on the Topic
The current FEMA Guidelines reference past coastal guidelines, that have been incorporated into 
the document, and other documented methodologies that are available as supporting guidance 
(Section D.1.1).  However, the current Guidelines do not reference other FEMA guidelines and 
initiatives Mapping Partners may consider when they start a flood insurance study.  For example, 
Mapping Partners may want to plan a flood study so that data can be subsequently used for the 
Coastal Flood Information Tool (FIT) for eventual HAZUS modeling. 

2.8.3	Alternatives for Improvement
As the draft guidelines for sheltered water flood hazards are being defined, a nominal effort 
should be made to understand how these guidelines may interrelate to other FEMA initiatives to 
identify potential benefits that could be relayed to Mapping Partners.  The new guidelines may 
simply include a listing of other FEMA initiatives for the Mapping Partners reference. Example 
of related FEMA initiatives may include:

	* Mapping future conditions  FEMA has provided guidance for mapping riverine 
	floodplains due to future conditions hydrology.  Similar guidance may be appropriate for 
	future hazards in sheltered water areas due to relative sea level changesea level rise 
	together with local tectonic uplift or subsidenceeither separately or in combination 
	with future riverine guidance for flood studies in areas of combined riverine  tidal 
	flooding. The focused study team believes consideration and mapping of long-term 
	changes are technically feasible, but problematic, given unresolved NFIP policy and 
	implementation issues.  These topics have received considerable attention by others (at 
	federal, state and local levels), but time and budget constraints prevented this team from 
	contributing to the topic beyond reiterating its importance.
	
	* HAZUS-MH and the Coastal Flood Information Tool (FIT)  Analysis at Levels 2 and 3 
	using the FIT will likely rely on flood hazards determined from detailed coastal studies 
	performed using the new guidelines.
	
	* Letters of Map Change, Amendment and Revision MT Forms
	
	* Mapping Activity Statement (MAS) Template for Cooperating Technical Partners (CTP) 
	Program
	
	* DFIRM standards

Lastly, Volumes 1 to 3 and the remaining appendices of the FEMA Guidelines should be 
reviewed to determine if changes to the G&S will affect content elsewhere in the document.

2.8.4	Recommendations
The following recommendations for Topic 6h include:

	1.	Identify and assess interrelationships of new guidelines to other Map Modernization 
	objectives and related FEMA initiatives.
	
	2.	Review state floodplain management policies related to sheltered water.
	
	3.	Review Volumes 1-3 and other appendices of current Guidelines  
	
	4.	Document and disseminate the findings to the other Focused Study Groups and integrate 
	into the new Guidelines as appropriate.

3	AVAILABLE TOPICS
(Not Applicable)

4	IMPORTANT TOPICS
(Not Applicable)

5	ADDITIONAL OBSERVATIONS
Seiching may contribute to flood hazards in sheltered water. Seiching involves the movement of 
long waves that move rhythmically back and forth within an enclosed water body such as a lake 
or bay.  The waves can be caused by a sudden air pressure change from the passage of an intense 
storm system or a long period wave train entering an embayment from the ocean. The resulting 
wave period is a function of the size and depth of the water body. Flood hazards from seiching 
are limited, but could be significant if the wave period of a tsunami entering a sheltered 
embayment is an even multiple of the natural period of the embayment; in this case the seiching 
would be amplified and could potentially result in coastal flood hazards. The significance of this 
physical process should be considered in future Tsunami Studies.

6	SUMMARY
The Sheltered Waters Focused Study involves a unique effort because sheltered water aspects are 
included in many of the other Focused Studies. Accordingly, the preparation of guidance for 
many of the topics identified in this report will be coordinated with other appropriate focused 
study groups because of the interrelationship of the sheltered water and open coast topics. 
Five sheltered water topics are addressed in this report.  The first topic addresses the need to 
establish a framework for performing coastal studies and proposes the use of a classification 
system, to guide Mapping Partners through the scoping and execution of a coastal flood study 
project, and the need to simply define sheltered waters for FEMA flood study purposes.  The 
second topic will expand current guidance for documenting and using data on observed flood 
conditions to provide validation of flood study results.  The third topic will result in guidance 
specific to defining the 1-percent-annual-chance flood event involving dependent and 
independent joint probability occurrences of riverine and tidal flooding in sheltered water areas. 

Existing guidance on wind data acquisition and analysis and fetch-limited wave forecasting in 
sheltered waters will also be expanded.  The fourth topic addresses guidance for estimating 
stillwater elevations in sheltered waters and evaluating the effects of tidal and riverine currents 
on wave propagation.  The last topic addresses the benefits of referencing other appropriate Map 
Modernization objectives and multi-hazard planning initiatives.  This coordination can broaden 
the use of the new guidelines to assist Mapping Partners with other hazard mitigation activities.  
These topics and recommendations for preparing associated guidelines are summarized in 
Table 1.

An additional observation was made to include guidance on defining flood hazards caused by 
seiching in sheltered water bodies. 

7	REFERENCES
CH2M Hill.  1998.  Coastal Flood Insurance Study, Port Angeles, Clallam County, WA.

Downing, J. 1983. The Coast of Puget Sound: Its Processes and Development, Puget Sound 
Books, A Washington Sea Grant Publication, University of Washington Press, Seattle 
WA, 126 p.

Federal Emergency Management Agency (FEMA).  2003 (April).  Guidelines and Specifications 
for Flood Hazard Mapping Partners.  Appendix D: Guidance for Coastal Flooding 
Analyses and Mapping.

Gornitz, V. M., T.W. Beaty, and R.C. Daniels.  1997.  A coastal hazards data base for the U.S. 
West Coast, Oak Ridge National Laboratory, ORNL/CDIAC-81, NDP-043C, December.

Montgomery, D.R., and J.M. Buffington.  1993.  Channel classification, prediction of channel 
response, and assessment of channel condition, TFW-SH10-93-002, Timber, Fish and 
Wildlife Agreement, Department of Natural Resources, Olympia, Washington, 84 pp.

Phillip Williams & Associates, Ltd.  2002.  Coastal Flood Insurance Study, Sandy Point, 
Whatcom County, WA.

Rosgen, D.  1996.  Applied Geomorphology, Wildland Hydrology.  Pagosa Springs, CO