The area in blue is not simply a new area that is in danger. There are many factors to consider such as location, shape of the waves, soil conditions, water drainage areas and so on. You are invited to check out the FEMA website, there is a great deal of material there. Geology is not my field but I hope that the readers to this blog will find some of this material helpful even though it is not transit related. Please see glossary below copied from the FEMA website.
Advisory Base (1% Annual Chance) Flood Elevation [ABFE]
The coastal water surface elevation of a flood having a 1% annual chance of being equaled or exceeded in any given year. It is expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88) and can reflect the elevation of an Advisory Flood Zone V or A. In New Jersey and New York, State and local officials, property owners, builders and others are encouraged to use ABFEs to make informed decisions about rebuilding, and to reduce the impact of future flood events. For more information about ABFEs being developed for some coastal New Jersey and New York communities in the aftermath of Hurricane Sandy, visit this website's Hurricane Sandy ABFE Homepage.Advisory 0.2% Annual Chance Flood Elevation
The coastal water surface elevation of a flood having a 0.2% annual chance of being equaled or exceeded in any given year. It is expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88).Advisory Base Flood Elevation (ABFE) Zones
A map layer which indicates whether a zone is designated as a V or A flood hazard zone and which provides the 0.2% Advisory Flood Elevation and the 1% Advisory Base Flood Elevation (ABFE) in feet referenced to the North American Vertical Datum of 1988 (NAV88) for the zone. Different ABFE zones are distinguished by yellow lines.
Advisory Flood Hazard Zones
Indicates the lettered Advisory flood hazard zone associated with the location:
• Advisory Zone V is comprised of the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. Zone V is subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
• Advisory Zone A is comprised of the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
• Advisory Shaded Zone X is comprised of areas of moderate coastal flood risk outside of Advisory Flood Hazard Zones V and A up to the 0.2% annual chance flood level.
• Advisory Zone V is comprised of the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. Zone V is subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
• Advisory Zone A is comprised of the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
• Advisory Shaded Zone X is comprised of areas of moderate coastal flood risk outside of Advisory Flood Hazard Zones V and A up to the 0.2% annual chance flood level.
Advisory Flood Hazard Zones V and A
The Advisory 1% annual chance floodplain includes both A and V Advisory flood hazard zones:
Advisory Zone V is comprised of the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. Zone V is subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
Advisory Zone A is comprised of the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
Advisory Limit of the 1% Annual Chance Flood Hazard Area
The limit of the Advisory 1% annual chance floodplain. The advisory 1% annual chance floodplain includes both V and A Advisory flood hazard zones.
Advisory Map Panels
The Advisory Map Panels layer on the FEMA Advisory Base Flood Elevations map shows the map paneling scheme used to produce the New Jersey and New York Advisory flood hazard information. The symbology shown for each map panel in this layer indicates its current availability:
• Green: Advisory information for the panel is currently available
• Yellow: Advisory information for the panel is partially available
• Diagonal hatching: Advisory information is not yet available for the panel.
• Yellow: Advisory information for the panel is partially available
• Diagonal hatching: Advisory information is not yet available for the panel.
If there is no panel outline shown on the map, currently there are no plans to produce Advisory flood hazard information for that area.
To download a .pdf version of a map panel from the interactive ABFE map showing the Advisory information (once available), simply click on the desired map panel while the Advisory Map Panel layer is turned on and click on the ‘PDF Map Hyperlink’ field in the pop up window. The .pdf map panels are produced at a scale of 1” = 1,000 feet.
Advisory Shaded Zone X
The Advisory Shaded Zone X map layer shows areas of moderate coastal flood risk outside the regulatory 1% annual chance flood but within the limits of the 0.2% annual chance flood level.
Advisory Zone V-A Boundary
The division between the Advisory flood hazard Zone V and Advisory flood hazard Zone A. This is where the high velocity wave action greater than 3 ft in height is anticipated to end for a coastal 1% annual chance flood. Zone V, also known as the coastal high hazard area, is subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
Area of MOderate Wave Action (MOWA)
The portion of the 1% annual chance coastal Advisory flood hazard area referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many National Flood Insurance Program (NFIP)-compliant structures on shallow or solid wall foundations.
B
Base Flood
A flood having a 1% chance of being equaled or exceeded in any given year. The base flood is the national regulatory standard used by the National Flood Insurance Program (NFIP) and all Federal agencies for the purposes of requiring the purchase of flood insurance and regulating new development. Base Flood Elevations (BFEs) are typically shown on Flood Insurance Rate Maps (FIRMs).
Base Flood Elevation (BFE)
The elevation shown on the Flood Insurance Rate Map (FIRM) for Zones AE, AH, A1-30, or VE that indicates the water surface elevation resulting from a flood that has a 1-percent chance of occurring in any given year. In coastal areas, BFEs are calculated using 4 components: 1) the storm surge stillwater elevation, 2) the amount of wave setup, 3) the wave height above the storm surge stillwater elevation, and 4) the wave runup above the storm surge stillwater elevation (where present).
Bathymetry
The measurement of water depths in oceans, seas, and lakes; also information derived from such measurements.
Breakaway Wall
A wall that is not part of the structural support of a building and is intended through its design and construction to collapse under specific lateral loading forces, without causing damage to the elevated portion of the building or supporting foundation system.
Breakwater
A structure protecting a shore area, harbor, anchorage, or basin from waves.
Bulkhead
A structure or partition built to retain or prevent sliding of the land.
C
Coastal A/AE Zone
The portion of the Special Flood Hazard Area landward of a V zone (i.e., areas where wave heights are computed as less than 3 feet) that is mapped as an A or AE zone on the FIRM. While the wave forces in coastal A zones are not as severe as those in V zones, the capacity for the damage or destruction of buildings is still present.
Coastal Barrier Resources Act (CBRA) Zones
The Coastal Barrier Resources Act (CBRA) established the John H. Chafee Coastal Barrier Resources System (CBRS), a defined set of geographic units along the Atlantic, Gulf of Mexico, Great Lakes, U.S. Virgin Islands, and Puerto Rico coasts. Most new Federal expenditures and financial assistance (including flood insurance) are prohibited within the CBRS, with some exceptions. The U.S. Fish and Wildlife Service is responsible for administering CBRA. CBRS boundaries shown on FEMA mapping products are for informational purposes only. For the best available CBRS boundary data, visit: http://www.fws.gov/cbra/Maps/Mapper.html. For additional information on the CBRA and the CBRS, visit: http://www.fws.gov/cbra.Coastal Erosion
The wearing away of land and the removal of beach or dune sediments by wave action, tidal currents, wave currents, or drainage. Waves, generated by storms, wind, or fast moving motor craft, cause coastal erosion, which may take the form of long-term losses of sediment and rocks or a temporary redistribution of coastal sediments; erosion in one location may result in the buildup of sediment in other places nearby.
Coastal High Hazard Areas (V/VE Zones)
The Special Flood Hazard Area (SFHA) 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. Typically, this is the area where the computed wave heights for the base flood are 3 feet or more. V zones are subject to more stringent building requirements and different flood insurance rates than other zones shown on the FIRM because these areas are exposed to a higher level of risk than other coastal flooding areas.
Community Rating System (CRS)
A FEMA initiative, established under the National Flood Insurance Program (NFIP), to recognize and reward communities that have implemented floodplain management measures beyond the minimum NFIP requirements. Under the CRS, those communities that choose to participate may reduce the flood insurance premium rates for property owners in the community by taking these additional actions.
Compliance/ Adoption Period
The 6-month period in the FIRM update process that begins with the issuance of a Letter of Final Determination and ends when a new or revised FIRM becomes effective, during which a community must enact and adopt new or revised floodplain management ordinances required for participation in the National Flood Insurance Program.
Cooperating Technical Partners (CTP) Program
An innovative FEMA program to create partnerships between FEMA and participating NFIP communities, regional agencies, and State agencies that have the interest and capability to become more active participants in the FEMA flood hazard mapping program.
Critical Facilities
Facilities that, if damaged, would present an immediate threat to life, public health, and safety. Critical and essential facilities include, but are not limited to, hospitals, emergency operations centers, water systems, and utilities.
D
Development
Any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation or drilling operations or storage of equipment or materials.
Duration
In wave forecasting, the length of time the wind blows in nearly the same direction over the fetch, or "generating area."
E
Effective Flood Hazard Zone
Indicates the lettered flood zone associated with the location shown on the effective Flood Insurance Rate Map and will be usually be populated with one of the following lettered zones described below. Effective FIRM data in the 'What is My ABFE' tool report is derived from FEMA's National Flood Hazard Layer.
• Zone V: the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. V zones are subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
• Zone A: the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
• Zone X: Areas of moderate coastal flood risk outside the regulatory 1% annual chance flood up to the 0.2% annual chance flood level.
• Zone V: the area subject to high velocity wave action (a 3-foot breaking wave) from the 1% annual chance coastal flood. V zones are subject to more stringent building requirements than other zones because these areas are exposed to a higher level of risk.
• Zone A: the area subject to storm surge flooding from the 1% annual chance coastal flood. These areas are not subject to high velocity wave action but are still considered high risk flooding areas.
• Zone X: Areas of moderate coastal flood risk outside the regulatory 1% annual chance flood up to the 0.2% annual chance flood level.
Effective Flood Insurance Rate Map (FIRM) Panel
The FIRM issued by FEMA that is in effect as of the date shown in the title block of the map as "Effective Date", "Revised", or "Map Revised" and is to be used by the community and others for flood insurance and floodplain management purposes. The map area shown on each Advisory Map panel overlays exactly with the boundary of the respective effective FIRM panels for ease of comparison between the two products. Typically, the effective FIRM panels are at a scale of 1”=500’ scale, so four effective FIRM panels will fit within one Advisory Map panel shown at 1”=1000.’
Effective Flood Insurance Rate Map (FIRM) Panel Number
This field indicates the current effective community FIRM panel number which applies to the particular location in the What is my ABFE? address lookup tool. To view the entered location and effective and advisory information layers through FEMA's interactive Advisory Base Flood Elevation map, click the 'Link to FEMA ABFE Web Map for This Location' shown. FIRMs can also be accessed directly through FEMA’s Map Service Center webpage by clicking on the ‘Flood Maps’ link, selecting your community and navigating to the FIRM panel number specified.
Elevated Building
For insurance purposes, a non-basement building which has its lowest elevated floor raised above ground level by foundation walls, shear walls, posts, piers, pilings, or columns.
Erosion
See 'Coastal Erosion'.
Back to topF
Federal Emergency Management Agency (FEMA)
FEMA is the part of the Department of Homeland Security working to support 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. FEMA employees work all over the country – at FEMA Headquarters, the ten regional offices, the National Emergency Training Center, Center for Domestic Preparedness/Noble Training Center, and other locations – to support the larger emergency management team.
The FEMA Region II office supports New York, New Jersey, Puerto Rico and the U.S. Virgin Islands.
Federal Register
The document, published daily by the Federal Government, which presents regulation changes and legal notices issued by Federal agencies. FEMA publications related to the National Flood Insurance Program that are published in the Federal Register include Proposed and Final flood hazard determination notices and Final Rules concerning community eligibility for the sale of flood insurance.
Flood
A condition of partial or complete inundation of normally dry land areas from: (1) the overflow of inland or tidal waters, (2) the unusual and rapid accumulation or runoff of surface waters from any source, or (3) Mudslides. To learn more about flood hazards and ways to keep safe from floods, visit FEMA’s disaster preparedness site, Ready.gov.
Flood Insurance Rate Map (FIRM)
Official map of a community on which FEMA has delineated the 1% annual chance (base) floodplain or Special Flood Hazard Area, the Base Flood Elevations (BFEs), and the risk premium zones applicable to the community. The FIRM is used to determine who must buy flood insurance and where floodplain development regulations apply. Once effective, FIRMs are available through the local community map repository and online through the FEMA Map Service Center.
FIRM Database
A database containing digital flood hazard information shown on the FIRM, designed for use with specialized Geographic Information System (GIS) software. Users can integrate local data sets with the information in the FIRM database in order to assist with floodplain management or mitigation planning measures. The FIRM database is provided to your community once a FIRM becomes effective and will also available for download through the FEMA Map Service Center.
Flood Insurance Study (FIS) report
The official report which usually accompanies the Flood Insurance Rate Map (FIRM), provided by FEMA that contains additional technical information on the flood hazards identified on the FIRM.
Floodplain
Any land area susceptible to being inundated by water from any source.
Floodplain Management Regulations
Zoning ordinances, subdivision regulations, building codes, health regulations, special purposes ordinances (such as a floodplain ordinance, grading ordinance and erosion control ordinance) and other applications of police power. The term describes such state or local regulations, in any combination thereof, which provide standards for the purpose of flood damage prevention and reduction.
Floodproofing
Any combination of structural and nonstructural additions, changes, or adjustments to structures which reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures and their contents.
Floodway / Regulatory Floodway
The channel of a river or other watercourse and the adjacent land areas that must be reserved in order to discharge the base (1%-annual-chance) flood without cumulatively increasing the water surface elevation more than a designated height.
Freeboard
A factor of safety usually expressed in feet above a flood level for purposes of floodplain management.
G
Geographic Information System (GIS)
A system of computer hardware, software, and procedures designed to support the capture, display, management, analysis, and modeling of spatially referenced geographic data.
H
HAZUS-MH
A nationally applicable standardized methodology, developed by FEMA under contract with the National Institute of Building Sciences for estimating potential losses from earthquakes, hurricane winds, and floods. HAZUS-MH uses GIS software to map and display hazard data and the results of damage and economic loss estimates for buildings and infrastructure. It also allows users to estimate the impacts of earthquakes, hurricane winds, and floods on populations.
Hurricane
A tropical cyclone, formed in the atmosphere over warm ocean areas, with a well-defined counter-clockwise circulation and sustained winds of 74 miles per hour or higher. Hurricanes can cause catastrophic damage to coastlines and even several hundred miles inland. Hurricanes can create storm surges along the coast and cause extensive damage from heavy rainfall. Floods and flying debris from the excessive winds are often the deadly and destructive results of these weather events. To learn more, including ways to prepare and keep safe from hurricanes, visit the Ready.gov Hurricanes webpage.
Hydraulic Analysis
An engineering analysis of a flooding source developed to provide estimates of the elevations of floods of selected recurrence intervals.
Hydrologic Analysis
An engineering analysis of a flooding source developed to establish peak flood discharges and their frequencies of occurrence. The results of the hydrologic analysis will be used when developing the hydraulic analysis performed to estimate flood elevations of selected recurrence intervals.
J
Jetty
A structure built out into the water to restrain currents and/or stabilize a shoreline. Jetties are commonly built at the mouths of rivers or tidal inlets to help deepen and stabilize the channel.
L
Letter of Map Amendment (LOMA)
An official amendment, by letter, to an effective FIRM. A LOMA establishes a property's location in relation to the Special Flood Hazard Area (SFHA). LOMAs are usually issued because a property has been inadvertently mapped as being in the floodplain, but is actually on natural high ground above the Base Flood Elevation (BFE).
Letter of Map Revision (LOMR)
An official revision, by letter, to an effective FIRM and sometimes the accompanying Flood Insurance Study (FIS) report. A LOMR may change flood insurance risk zones, flood zone boundary delineations, planimetric features, and/or Base Flood Elevations (BFEs). LOMRs are generally based on the implementation of physical measures that affect the hydrologic or hydraulic characteristics of a flooding source and thus result in the modification of the existing regulatory floodway, the effective BFEs, or the Special Flood Hazard Area (SFHA) or flood zone designations. The LOMR is generally accompanied by an annotated copy of the affected portions of the FIRM and FIS report.
Levee
A man-made structure, usually an earthen embankment, designed and constructed in accordance with sound engineering practices to contain, control, or divert the flow of water so as to provide protection from temporary flooding. While levees can help reduce the risk of flooding, they do not eliminate the risk. For additional information on levees and levee risk, visit FEMA’s Living With Levees Homepage.
Light Detection and Ranging (LiDAR)
LiDAR is a state-of-the-art method for collecting accurate elevation information using an instrument that measures distance to a reflecting object by emitting timed pulses of laser light and measuring the time between emission and reception of reflected pulses. Additional information on LiDAR, including a free online training module, can be found at NOAA’s Digital Coast website.
Limit of Advisory Base Flood Elevations
The Limit of Advisory Base Flood Elevations depicts the location at which the dominant flood hazard transitions from the 1% annual chance coastal Advisory Base Flood Elevation (ABFE) to the riverine flood hazard, as presented on the effective Flood Insurance Rate Map (FIRM). Users should access the Effective FIRM to get further information on their flood hazard beyond this limit.
Limit of Moderate Wave Action (LiMWA)
The LiMWA depicts the limit of the Area of Moderate Wave Action (MOWA), the portion of the 1% annual chance coastal Advisory flood hazard area referenced by building codes and standards, where base flood wave heights are between 1.5 and 3 feet, and where wave characteristics are deemed sufficient to damage many National Flood Insurance Program (NFIP)-compliant structures on shallow or solid wall foundations.
M
Mitigation
The effort to reduce loss of life and property by lessening the impact of disasters. For more information on hazard mitigation, visit FEMA’s Mitigation Homepage.
N
National Flood Insurance Program (NFIP)
The Federal Program under which floodprone areas are identified and flood insurance is made available to the owners of the property in participating communities. For more information on the NFIP, visit Floodsmart.gov.
National Geodetic Vertical Datum (NGVD) of 1929
National standard reference datum for elevations, formerly referred to as Mean Sea Level (MSL) of 1929. NGVD 1929 may be used as the reference datum on some Flood Insurance Rate Maps (FIRMs).
Nor’easter
A nor’easter is a cyclonic storm that moves along the east coast of North America. It’s called “nor’easter” because the winds over coastal areas blow from a northeasterly direction. Nor’easters may occur any time of the year, but are most frequent and strongest between September and April. These storms usually develop between Georgia and New Jersey within 100 miles of the coastline and generally move north or northeastward.
Nor’easters typically become most intense near New England and the Canadian Maritime Provinces. In addition to heavy snow and rain, nor’easters can bring gale force winds greater than 58 miles per hour. These storms can produce rough seas, coastal flooding and beach erosion. (Source: National Oceanic and Atmospheric Administration)
Nor’easters typically become most intense near New England and the Canadian Maritime Provinces. In addition to heavy snow and rain, nor’easters can bring gale force winds greater than 58 miles per hour. These storms can produce rough seas, coastal flooding and beach erosion. (Source: National Oceanic and Atmospheric Administration)
North American Vertical Datum (NAVD) of 1988
The vertical control datum established for vertical control surveying in the Unites States of America based upon the General Adjustment of the North American Datum of 1988. It replaces the National Geodetic Vertical Datum of 1929. All New Jersey and New York Advisory flood hazard elevations are referenced to NAVD 88.
O
Overland Wave Modeling
In conjunction with storm surge modeling, overland wave modeling is conducted to determine Base Flood Elevations (BFEs) and to delineate coastal flood hazards. Overland wave modeling consists of the determination of wave heights, wave setup values, simulations of inland wave propagation, as well as computing wave runup scenarios. Typically, the Wave Height Analysis for Flood Insurance Studies (WHAFIS) model is used to perform overland wave modeling for FEMA flood studies.
Overwash
The mass of water representing the part of the wave advancing up a beach that runs over the highest part of a berm or other structure and that does not flow directly back to the sea or lake in which the wave originated.
P
Preliminary Flood Insurance Rate Map (FIRM)
A FIRM that is not yet effective that reflects the initial results of a flood map project performed by or for FEMA. The Preliminary FIRM is provided to the Chief Executive Officer (e.g., Mayor, County Commissioner, etc.) and floodplain administrator for each affected community and is available to all citizens both online or through the local community map repository (often the community planning or zoning office).
Primary Frontal Dune (PFD)
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. The PFD is used to delineate the limit of the coastal high hazard area.
Provisional Hurricane Sandy Storm Surge Elevation
Observed storm surge flood elevations from Hurricane Sandy, collected by the U.S. Geological Survey (USGS). These elevations, expressed in feet referenced to the North American Vertical Datum of 1988 (NAVD88), represent provisional USGS high water marks and storm tide sensors. These elevations are provided as a point of context between the Advisory Base Flood Elevations (ABFEs) and the storm surge elevation from Hurricane Sandy.
R
Risk Mapping, Assessment, and Planning (Risk MAP)
The FEMA program that provides flood information and tools that can be used by communities to enhance flood hazard mitigation planning efforts and to take action to better protect their citizens. Through more precise flood mapping products, risk assessment tools, and planning and outreach support, Risk MAP strengthens local ability to make informed decisions about reducing risk. For more information on Risk MAP, visit the FEMA Risk MAP homepage.
S
Sea, Lake, and Overland Surge from Hurricanes (SLOSH)
SLOSH is a computerized model developed by FEMA, the U.S. Army Corps of Engineers (USACE), and the National Weather Service (NWS) to estimate storm surge depths resulting from historical, hypothetical, or predicted hurricanes by taking into account a storm's pressure, size, forward speed, forecast track, wind speeds, and topographical data. SLOSH is used to evaluate the threat from storm surge, and emergency managers use this data to determine which areas must be evacuated. SLOSH output is used by the National Hurricane Program (NHP) when conducting Hurricane Evacuation Studies as a hazard analysis tool for assisting with the creation of state and local hurricane evacuation plans or zones.
Sea Level Rise
An increase in sea level caused by a change in the volume of the world’s oceans due to temperature increase, deglaciation (uncovering of glaciated land because of melting of the glacier), and ice melt (Source: NOAA).
Sea Wall
A solid barricade, often concrete or stone, built at the water’s edge to protect the shore and to prevent inland flooding. Generally built parallel to the shore, a sea wall is typically more massive and capable of resisting greater wave forces than a bulkhead.
Simulating WAves Nearshore (SWAN) Model
A computer model that is often used to estimate wave generation and propagation in conjunction with the ADCIRC model when modeling the effects of coastal storm surge.
Special Flood Hazard Area (SFHA)
The land area covered by the floodwaters of the base (1%-annual-chance) flood on the FIRM. The SFHA is the area where the National Flood Insurance Program’s (NFIP's) floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The SFHA includes Zones A, AO, AH, A1-30, AE, A99, AR, AR/A1-30, AR/AE, AR/AO, AR/AH, AR/A, VO, V1-30, VE, and V.
Static Base Flood Elevation
The effective static coastal water surface elevation of a flood having a 1% annual chance of being equaled or exceeded in any given year shown on the community Flood Insurance Rate Map (FIRM) for A or Z flood hazard zones. On effective FIRMs, these elevations may either be referenced to the National Geodetic Vertical Datum of 1929 (NGVD 29) or the North American Vertical Datum of 1988 (NAVD 88). All BFEs and Advisory BFEs listed in the 'What is My ABFE' tool report are referenced to NAVD 88; in cases where elevations are actually referenced to NGVD 29 on the effective FIRM, a conversion factor has been applied so that these elevations are also referenced to NAVD 88. Effective FIRM data in the 'What is My ABFE' tool report is derived from FEMA's National Flood Hazard Layer.
Stillwater Elevation (SWEL)
The projected elevation of floodwaters in the absence of waves resulting from wind or seismic effects. In coastal areas, stillwater elevations are determined when modeling coastal storm surge; the results of overland wave modeling are used in conjunction with the stillwater elevations to develop the coastal Base Flood Elevations.
Storm surge
Storm surge is the water, combined with normal tides, that is pushed toward the shore by strong winds during a storm. This rise in water level can cause severe flooding in coastal areas, particularly when the storm coincides with the normal high tides. The height of the storm surge is affected by many variables, including storm intensity, storm track and speed, the presence of waves, offshore depths, and shoreline configuration. To model the effects of coastal storm surge, sophisticated computer models, such as ADCIRC and SWAN, are needed to handle the complexities of integrating these large quantities of data and performing the necessary simulations. To learn more about coastal storm surge, visit the Coastal Mapping Basics page of this website or NOAA’s State of the Coast website.
Subsidence
A gradual settling or sudden sinking of the Earth's surface owing to subsurface movement of earth materials. Subsidence is a global problem, and in the United States, more than 17,000 square miles in 45 states, an area roughly the size of New Hampshire and Vermont combined, have been directly affected by subsidence. (Source: NOAA)
Swale
The depression between beach ridges.
T
Transect
A surveyed cross section taken perpendicular to the shoreline to represent a segment of coast with similar characteristics. Transect data is used when performing overland wave modeling and mapping for a coastal flood study.
Tropical Storm
A tropical cyclone with maximum sustained (1-minute average) winds of 39 to 73 miles per hour.
W
Watershed
The area of land where all of the water that is under it or drains off of it goes into the same place (Source: Environmental Protection Agency).
Wave Height Analysis for Flood Insurance Studies (WHAFIS)
The WHAFIS model has been used to perform coastal flood studies since 1980, to incorporate the effects of wind-bourne wave action on FIRMs for communities along the Atlantic and Gulf Coasts. WHAFIS uses various input data to calculate wave heights, wave crest elevations, flood insurance risk zone designations, and flood zone boundaries along transects (cross sections of the shoreline) in a study area. Additional information on WHAFIS is available in FEMA’s Atlantic Ocean and Gulf of Mexico Guidelines Update.
Wave Propagation
The transmission of waves through water.
Wave Runup
The rush of water that extends inland when waves come ashore. Wave runup effects are computed as a part of the overland wave analysis and are added to the stillwater elevations computed from the storm surge model.
Wave Setup
The increase in the water level caused by the onshore mass transport of water that occurs due to waves breaking during a storm. Wave setup is affected by the wave height, the speed at which waves approach shore, and the nearshore slope.
Back to top
Get Plug-Ins
Back to top
Get Plug-Ins
No comments:
Post a Comment