The National Mitigation Framework (NMF) provides context for how the whole community works together and how mitigation efforts relate to all other parts of national preparedness. It covers the capabilities necessary to reduce the loss of life and property by lessening the impact of disasters, emphasizing the valuable role of local leadership, collaboration among various parts of the whole community and education. The NMF is one in a series of National Planning Frameworks outlining how the whole community can work together to achieve national preparedness.

More than two dozen Federal organizations participate in the Federal Support Toolbox for Integrated Water Resources Management. The Toolbox is an evolving "one-stop-shop" water resources data portal with direct links to databases, programs and initiatives, and models and tools. This website also serves as a resource for sharing ideas and water resources needs, best management practices, collaborations and partnerships, and more. 

A searchable "Federal Flood Risk Management Resources" website provides summaries of Federal programs across Federal agencies that relate in some way to flood risk management.  The website was developed by the USACE National Flood Risk Management Program in coordination with a variety of other Federal agencies.

U.S. Army Corps of Engineers

• The Corps works with local non-Federal sponsors in the planning, engineering and construction of flood risk reduction projects. These activities are supported by the Flood Risk Management Planning Center of Expertise, the Coastal Storm Damage Reduction Planning Center of Expertise and the engineering expertise of the Flood and Coastal Storm Damage Reduction Program.
• The Corps Rehabilitation Program (authorized under Public Law 84-99 (pdf, 28 KB)) provides emergency assistance to flood risk management projects that have been damaged by a flood event.
• Through the Inspection of Completed Works, the Corps performs reviews of flood risk management projects to ensure the projects are properly operated and maintained.
• The Corps Levee Safety Program inspects and assesses the reliability of the levees and floodwalls in the Corps portfolio and communicates risks to life, property and the environment to local communities (usually through non-Federal sponsors) including assessment of the level and nature of the risk.
• The Corps Dam Safety Program uses a risk-informed approach to manage its portfolio of 694 dams, with public safety the number one priority.
• The National Nonstructural Flood Proofing Committee promotes the development and use of nonstructural flood risk reduction measures within Corps programs and activities.
• The laboratories of the Corps’ Engineer Research and Development Center, including the Coastal and Hydraulics Laboratory, performs ocean, estuarine, riverine, and watershed regional scale systems analyses research support work.

Federal Emergency Management Agency

The Federal Emergency Management Agency supports our citizens and first responders to ensure that as a nation we work together to build, sustain, and improve our capability to prepare for, protect against, respond to, recover from, and mitigate all hazards. Some of its major programs that support community flood risk mitigation and preparedness include:

• FloodSMART  and The National Flood Insurance Program provides information on understanding and reducing the risk of flooding through the purchase of flood insurance for your home or business.
• FEMA's Flood Hazard Mapping activities identify flood hazards, assess flood risks, and partner with States and communities to provide accurate flood hazard and risk data to guide them to mitigation actions. FEMA's Mapping activities include the Risk Mapping, Assessment, and Planning Program (RiskMAP) and addresses special types of flood risk such as coastal and levee impacted areas.
• FEMA’s Hazards-United States (Hazus) software contains models for estimating potential losses from earthquakes, floods, and hurricanes. Hazus uses Geographic Information Systems (GIS) technology to estimate physical, economic, and social impacts of disasters. It graphically illustrates the limits of identified high-risk locations due to earthquake, hurricane, and floods. Users can then visualize the spatial relationships between populations and other more permanently fixed geographic assets or resources for the specific hazard being modeled, a crucial function in the pre-disaster planning process.
• FEMA’s “ready.gov” site covers various topics about planning and preparation for disasters and emergencies, and has a section focused on floods.
• Preparedness (Non-Disaster) Grants - FEMA provides state and local governments with preparedness program funding in the form of Non-Disaster Grants to enhance the capacity of state and local emergency responders to prevent, respond to, and recover from disasters.
• Hazard Mitigation Assistance Grant Programs - Hazard Mitigation Assistance (HMA) grant programs provide funding for eligible mitigation activities that reduce disaster losses and protect life and property from future disaster damages.

U.S. Fish & Wildlife Service

• The Coastal Barriers Resource Act  (CBRA) provides guidance and direction to coastal communities regarding limiting development in flood-prone areas.

National Oceanic and Atmospheric Administration

• The National Weather Service provides up-to-date information and forecasting for flood events.
• The Coastal Zone Management Program provides funding to 34 coastal states to help balance development and economic activity with natural resource management. Coastal storm and other types of flooding (e.g., sea level rise, subsidence, erosion) are core to this program.

US Department of the Interior

• The U.S. Geological Survey provides practical, unbiased information about the Nation's rivers and streams that is crucial in mitigating hazards associated with floods.
• U.S. Bureau of Reclamation Flood Hydrology and Consequences Group specializes in technical investigations, designs, reviews, and related work in flood hydrology and hydrometeorology.

U.S. Environmental Protection Agency

• EPA provides information for effective stormwater management, green infrastructure and low impact development techniques that help to reduce flood risk.

USDA Natural Resources Conservation Service

• NRCS has several programs that help take farmland out of active production or limit activities on agricultural lands. These programs can sometimes be involved in acquiring space for flood waters to go naturally without harming people or property.

The National Response Framework (NRF) outlines the roles, responsibilities, and organizational structures that enable a coordinated incident response by the Federal government.

There are several agencies that respond to community needs, including FEMA, the Department of Housing and Urban Development, Department of Health and Human Services, Environmental Protection Agency, Small Business Administration, etc. Actions that the Corps undertakes during an emergency include:

• Under Emergency Support Function #3 the Corps is responsible for critical public facility restoration, debris management, infrastructure assessments, ice and water delivery, urban search and rescue, and temporary power, housing, and roofing.
• Through its Levee Safety Program, the Corps inspects and assesses the reliability of the levees and floodwalls in its portfolio and communicates risks to life, property and the environment to local communities (usually through non-Federal sponsors) including assessment of the level and nature of the risk.
• The Corps Rehabilitation Program (authorized under Public Law 84-99 (pdf, 28 KB) ) provides emergency funds to address flood damages to flood risk management projects.
• The Dam Safety Program uses a risk-informed approach to manage its portfolio of 694 dams, with public safety the number one priority.

To assist communities recovering from a disaster, FEMA coordinates the National Disaster Recovery Framework which provides the principles, roles, responsibilities, and coordinating structure for recovery efforts. The Framework includes six Recovery Support Functions, each with a lead agency:

• Community Planning and Capacity Building: Federal Emergency Management Agency
• Economic: U.S. Department of Commerce
• Health and Social Services: U.S. Department of Health and Human Services
• Housing: U.S. Department of Housing and Urban Development
• Infrastructure Systems: U.S. Army Corps of Engineers
• Natural and Cultural Resources: U.S. Department of Interior

More generally, Federal agencies have several forums through which they coordinate activities related to flood risk management outside of the immediacy of a disaster, including:

• The Federal Interagency Floodplain Management Task Force (FIFM-TF) is comprised of 14 Federal government entities that promote the health, safety, and welfare of the public by encouraging programs and policies that reduce flood losses and protect the natural environment through improved coordination, collaboration, and transparency in floodplain management efforts.
• The Silver Jackets program supports teams at the state level to coordinate and collaboratively address risk management issues among state and Federal partners.
• Several Regional Task Forces have been established to address flood risk management at a regional scale. The task forces play an integral role in the post flood recovery process for their respective regions and generated many innovative strategies and products to ensure a highly communicative, effective and efficient flood recovery effort. Recent regional task forces include:
  • The Interagency Recovery Task Force was established in response to the May-June 2011 flooding centered largely in the Lower Mississippi River Basin and is comprised of representatives from seven states and ten Federal agencies.
  • The Missouri River Flood Task Force was established in response to the October 2011 floods and brought together Federal, state, local and tribal entities that cover eight states.
• Federal agencies also create bi-lateral partnerships to address water resource management.
  • The NRCS/USACE Partnership Handbook (pdf, 3.67 MB), is designed to stimulate and facilitate active cooperation and collaboration between NRCS and the Corps on water resource issues and challenges facing the nation.
  • The Corps, U.S. Geological Survey, and National Oceanic and Atmospheric Administration have signed a Memorandum of Understanding documenting their partnership in the Integrated Water Resources Science and Services (IWRSS) initiative.

TWO COASTAL FLOOD INUNDATION MAPS‐ WHICH SHOULD I USE?

December 2011

Storm surge is an abnormal rise of water generated by a storm, over and above the predicted tide level. Storm Surge Inundation Maps (SSIMs) and Flood Insurance Rate Maps (FIRMs) both identify areas that are subject to inundation from coastal storm surge. Often, community officials ask which of these products they should use and in what situations. The purpose of this paper is to explain the differences between these two products.

Hurricane Evacuation Study ‐ Storm Surge Inundation Maps:

SSIMs are created as part of a Hurricane Evacuation Study (HES), which are often conducted by the Federal Emergency Management Agency (FEMA) and the United States Army Corps of Engineers (USACE), in coordination with the state and local counties/municipalities. The SSIMs are an important component of the HES and are used as a basis for the identification of hurricane evacuation zones.

SSIMs are based on storm surge from hurricanes. Hurricane storm surge heights are influenced by many factors, including: hurricane intensity (categorized by the Saffir‐Simpson (SS) Hurricane Wind Scale, ranging from category 1 to category 5), size (radius of maximum winds), forward speed, the angle of approach to the shoreline, width and slope of the continental shelf, astronomical high tide level, and local geographic features.

The National Oceanic and Atmospheric Administration (NOAA) Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is used to calculate storm surge water surface elevation values used to create SSIMs. Since many factors influence storm surge heights, the maximum calculated surge heights are composited for thousands of different types of hurricanes within an SS category. Occurrence probabilities of these hurricanes are not considered.

The results from the simulations are used to identify possible areas of storm surge inundation and maximum surge heights from various combinations of hurricane forward speed, trajectory, storm size, and high tide level within each SS category. The surge height outputs from SLOSH are then compared to local high resolution ground elevation data to finalize the areas of possible storm surge inundation for each SS category. These areas of potential inundation are shown on the SSIM. The SLOSH output, and therefore the SSIM, does not include any impacts from wave action.

The inundation zone for an SS category shown on the SSIM does not depict the expected storm surge from any one particular type of hurricane with that SS category. Rather, the SSIM depicts areas of possible flooding from thousands of hypothetical hurricanes within an SS category. The map provides an upper threshold estimate of potential storm surge inundation during a high tide landfall, which is important for the purpose of developing hurricane evacuation zones for HES. The SSIM is intended to be used for long range hurricane planning and population protection, and is not intended to be used for regulatory or insurance purposes.

National Flood Insurance Program ‐ Flood Insurance Rate Maps:

FIRMs are produced by FEMA in support of the National Flood Insurance Program (NFIP). The FIRMs are regulatory documents that identify the Special Flood Hazard Areas (SFHA) where land use and building requirements of the NFIP need to be enforced, in order for a community to participate in the NFIP. The SFHAs identify areas of possible inundation due to both riverine flooding and coastal flooding. The FIRMs establish flood zones that are used for floodplain management regulations, to set flood insurance rates, and to identify where flood insurance is required as a condition of a federally insured mortgage. Flood inundation areas shown on the FIRMs for coastal areas are based on the storm surge and wave action (where applicable) from the flood that has a 1% chance of being equaled or exceeded in a given year (also known as the 100‐year flood or base flood). The regulatory and insurance requirements of the NFIP are based on the flood data shown on the FIRM. The maps may also show the extent of stillwater inundation (without consideration of wave height) from the flood that has a 0.2% chance of being equaled or exceeded in a given year (also known as the 500 year flood).

FEMA Region III is in the process of updating the coastal FIRMs within the Region III domain. This work is being completed by the USACE and private contractors. For this update the storm surge elevations are determined using the ADdvanced CIRCulation Model for Oceanic, Coastal, and Estuarine Waters (ADCIRC) coupled with the Simulating Waves Nearshore (SWAN) model. Historical extra‐tropical and tropical storms, along with a suite of hypothetical tropical storms representative of possible storms that could affect Region III, are simulated with the ADCIRC/SWAN models and other calculation methods to determine the 1% annual chance stillwater level. The Wave Height Analysis for Flood Insurance Studies (WHAFIS) model is then used to calculate base flood elevations that include the impacts of wave action.

The flood inundation areas shown on the FIRMs are created by comparing the calculated 1% annual chance stillwater elevation to local high resolution ground elevation data. The FIRM shows the area of the 1% annual chance floodplain, and within the floodplain it shows base flood elevations and flood risk zones that include the impacts of calculated wave action.

Although FIRMs can be a useful tool to assist with hurricane/coastal storm planning, they are intended to be used as a regulatory document for insurance, land use, and building requirements. Wave action is included due to the forces that waves and other high‐velocity flow impart on buildings and other structures located in the floodplain, therefore having a direct correlation to insurance, land use, and building requirements.

When a hurricane approaches, communities should rely on the SSIMs from the HES and storm surge forecast products from NOAA when making evacuation and other emergency management decisions. 

The Important Differences:

Storm Surge Inundation Maps are component of a Hurricane Evacuation Study. The areas of surge inundation shown on the maps reflect potential flooding from different types of hurricanes within a SS category, with no consideration of wave action or probability. The result is intended to be a conservative estimate of possible surge inundation from hurricanes within an SS category, which is used for long range hurricane planning purposes and population protection. The SSIM is not intended to be used for regulatory or insurance purposes.

Flood Insurance Rate Maps identify the areas subject to flooding associated with a water elevation that has a 1% chance of being equaled or exceeded in any given year. This FIRM identifies flood risk zones and base flood elevations that include the impacts of wave action. The FIRM is a regulatory and insurance product developed within a Flood Insurance Study and is used to support the NFIP.

Both maps can be looked at when determining where to build as each will help assess the overall flood risk in an area, from different categories of hurricanes and from the 1% annual chance flood with wave action, and the combination of the two will give a more complete picture. Both maps can also be useful for general coastal planning applications if the user understands their limitations.

A major difference between the two products is that the FIRMs are based on a flood with a certain probability of occurring, while the SSIMs are not. The 1% annual chance water level is a statistical measure and varies throughout a region. No single storm event would produce the 1% annual chance water level everywhere in that region. While certain types of hurricanes within a SS category may be capable of producing or exceeding a 1% annual chance water level in a given area, other types of hurricanes within that SS category may not. Additionally, there may be hurricane scenarios within multiple SS categories that have the potential to produce or exceed the 1% annual chance water level for an area. Therefore, the 1% annual chance water level for an area cannot be directly related to any particular category of hurricane.

Below is an example of a FIRM (top image) and an SSIM (bottom image) for the same area. On the FIRM, the 1% annual chance floodplain is shown in light blue, and a flood zone and base flood elevation are included. The red box on the FIRM represents the area shown on the SSIM. On the SSIM, the blue designates the areas of possible flooding from Category 1‐4 hurricanes, the purple from Category 2‐4 hurricanes, the yellow from Category 3‐4 hurricanes, and the pink from Category 4 hurricanes. Note that this area is not included in the 1% annual chance floodplain shown on the FIRM. This means that some types of Category 1‐4 hurricanes, with certain size, forward speed, and track trajectory characteristics , impacting at high tide, are expected to produce a water level higher than the 1% annual chance water level, and inundate a larger area than the 1% annual chance water level would inundate.

For more information:

NOAA Storm Surge and SLOSH Model: www.nhc.noaa.gov/surge/slosh.php; www.hurricanes.gov/surge

ADCIRC Model: https://www.erdc.usace.army.mil/Media/Fact-Sheets/Fact-Sheet-Article-View/Article/476698/advanced-circulation-model/ 

WHAFIS Model: www.fema.gov/plan/prevent/fhm/dl_wfis4.shtm

SWAN Model: www.swan.tudelft.nl

Saffir‐Simpson Hurricane Wind Scale: https://www.nhc.noaa.gov/aboutsshws.php

FEMA Region III Coastal Analysis and Mapping Study

FEMA Map Service Center: https://msc.fema.gov/portal

Flood Insurance Rate Maps: www.fema.gov/hazard/map/firm.shtm

This paper was produced through a collaborative effort between the US Army Corps of Engineers‐National Planning Center of Expertise for Coastal Storm Damage Reduction, FEMA, NOAA, and the Maryland Silver Jackets partnership.

TWO COASTAL FLOOD MAPS

Flood Insurance Rate Maps vs. Storm Surge Inundation Maps

Storm surge is an abnormal rise of water generated by a storm, over and above the predicted tide level. Storm Surge Inundation Maps (SSIMs) and Flood Insurance Rate Maps (FIRMs) both identify areas that are subject to flooding from coastal storm surge. The difference between these two coastal flood map products is described below:

National Flood Insurance Program- Flood Insurance Rate Maps (FIRMs)

FIRMs are regulatory documents produced to support the National Flood Insurance Program. FIRMs establish Special Flood Hazard Areas (SFHAs), flood risk zones and flood elevations. This data is used to set flood insurance rates, to identify where flood insurance is required as a condition of a federally insured mortgage, and for floodplain management and building regulations. Flood inundation areas shown on the FIRMs for coastal areas are based on the storm surge and wave action (where applicable) from the flood level that has a 1% chance of being equaled or exceeded in a given year (also known as the 100-year flood or base flood). In coastal areas, FIRMs are not intended to be used for evacuation planning and population protection. Unlike the SSIMs, FIRMs are based on the inundation area for the 1% annual chance flood level, and do not provide a depiction of the overall flood risk area that includes the impacts of more intense events.

Hurricane Evacuation Study – Storm Surge Inundation Maps (SSIMs)

SSIMs are a component of a Hurricane Evacuation Study (HES). The HES identifies areas at risk of storm surge flooding from hurricanes, establishes evacuation zones based on those areas of risk, identifies the amount of people living in the at-risk area, predicts the evacuation behavior of people in the at-risk areas, and calculates how long it will take to evacuate the at-risk area during different hurricane scenarios. Unlike the FIRM, the purpose of the HES and the SSIM is not to support insurance or regulatory requirements. Rather, the HES is a tool to support the efforts of government officials to prepare for and respond to a hurricane threat, and to take actions to protect the at risk population. The SSIMs provide the basis for the HES by depicting a conservative estimate of the possible area of storm surge inundation from different categories of hurricanes, without considering probability of occurrence. The SSIMs incorporate the storm surge potential from the simulation of hurricane events covering a wide range of intensities, and can therefore be used for long range hurricane planning purposes and population protection. SSIMs do not establish flood risk zones or flood elevations.

SSIMs provide an overview of all areas that could potentially flood during different categories of hurricanes. Probability of occurrence is not considered. The SSIM is not a regulatory document and is intended to be used to support hurricane planning, preparedness, and population protection.

FIRMs are regulatory documents produced to support the National Flood Insurance Program. They establish flood risk zones and flood elevations for the flood that has a 1% chance of being equaled or exceeded in a given year. The FIRMs are intended to be used for flood insurance rating and regulating building development.

This factsheet was developed through a collaborative effort by the Federal Emergency Management Agency (FEMA), the U.S. Army Corps of Engineers (USACE), and the National Oceanic and Atmospheric Administration (NOAA). For a more detailed description of the methodologies and procedures used to develop FIRMs and SSIMs, please see the “Coastal Flood Maps White Paper” available from USACE, FEMA and NOAA.

Division boundaries typically follow watershed boundaries, in contrast to some other Federal agencies.

USACE Boundaries

(Click on the image to enlarge)

FEMA Regions

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