Identification Information

Title Flood Control Structures

Date 2009-08-03

Date Type Publication

Cited Responsible Party

Organization Name Federal Emergency Management Agency

Role identify

Presentation Form vector digital data

Abstract The National Flood Hazard Layer (NFHL) data incorporates all Digital Flood Insurance Rate Map(DFIRM) databases published by FEMA, and any Letters Of Map Revision (LOMRs) that have been issued against those databases since their publication date. The DFIRM Database is the digital, geospatial version of the flood hazard information shown on the published paper Flood Insurance Rate Maps(FIRMs). The primary risk classifications used are the 1-percent-annual-chance flood event, the 0.2-percent-annual-chance flood event, and areas of minimal flood risk. The NFHL data are derived from Flood Insurance Studies (FISs), previously published Flood Insurance Rate Maps (FIRMs), flood hazard analyses performed in support of the FISs and FIRMs, and new mapping data where available. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA). The specifications for the horizontal control of DFIRM data are consistent with those required for mapping at a scale of 1:12,000. The NFHL data contain layers in the Standard DFIRM datasets except for S_Label_Pt and S_Label_Ld. The NFHL is available as State or US Territory data sets. Each State or Territory data set consists of all DFIRMs and corresponding LOMRs available on the publication date of the data set.

Purpose The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP). Insurance applications include enforcement of the mandatory purchase requirement of the Flood Disaster Protection Act, which "... requires the purchase of flood insurance by property owners who are being assisted by Federal programs or by Federally supervised, regulated or insured agencies or institutions in the acquisition or improvement of land facilities" (Section 2 (b) (4) of the Flood Disaster Protection Act of 1973). In addition to the identification of Special Flood Hazard Areas (SFHAs), the risk zones shown on the FIRMs are the basis for the establishment of premium rates for flood coverage offered through the NFIP. The NFHL data present the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. The NFHL database is a subset of the information created for the FIS and serves as a means to archive a portion of the information collected during the FIS.

Status In work

Point of Contact

Individual Name

Organization Name Federal Emergency Management Agency

Position Name

Role Point of contact

Voice 1-877-FEMA-MAP

Facsimile

Address

Delivery Point 500 C Street, S.W.
City Washington
Administrative Area District of Columbia
Postal Code 20472
Country USA

Electronic Mail Address fema-mscservice@dhs.gov

Maintenance and Update Frequency Monthly

Descriptive Keywords DFIRM, FIRM, FEMA Flood Hazard Zone, DFIRM Database, Special Flood Hazard Area, Digital Flood Insurance Rate Map, CBRS, Coastal Barrier Resources System, Riverine Flooding, Coastal Flooding, NFIP, Base Flood Elevation, SFHA, Flood Insurance Rate Map, Floodway

Access Constraints None

Use Constraints Acknowledgement of FEMA would be appreciated in products derived from these data.

Language English

Topic Category environment

Extent

Geographic Bounding Box

West Bound -107.53851372998
East Bound -103.190211779282
North Bound 36.0824478263115
South Bound 32.1198815210703

Temporal Extent

DateTime 2009-01-16

Data Quality Information

Attribute Accuracy Report

Report The National Flood Hazard Layer (NFHL) data incorporates all Digital Flood Insurance Rate Map(DFIRM) databases published by FEMA, and any Letters Of Map Revision (LOMRs) that have been issued against those databases since their publication date. The DFIRM Database consists of community based vector files and associated attributes produced in conjunction with the hard copy FEMA FIRM. The published effective FIRM and DFIRM maps are issued as the official designation of the Special Flood Hazard Areas (SFHAs). As such they are adopted by local communities and form the basis for administration of the National Flood Insurance Program (NFIP). For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners. Attribute accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of FEMA's DFIRM databases was also performed. To obtain more detailed information in areas where Base Flood Elevations (BFEs) and/or floodways have been determined, users are encouraged to consult the Flood Profiles and Floodway Data and/or Summary of Stillwater Elevations tables contained within the FIS report that accompanies the individual components of the DFIRM data. Users should be aware that BFEs shown in the S_BFE table represent rounded whole-foot elevations. These BFEs are intended for flood insurance rating purposes only and should not be used as the sole source of flood elevation information. Accordingly, flood elevation data presented in the FIS report must be used in conjunction with the FIRM for purposes of construction and/or floodplain management. The 1-percent-annual-chance water-surface elevations shown in the S_XS table match the regulatory elevations shown in the FIS report.

Quantitative Attribute Accuracy Assessment

Attribute Accuracy Value
Attribute Accuracy Explanation

Horizontal Positional Accuracy Report

Report The National Flood Hazard Layer data consists of community based vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and DFIRM maps are issued as the official designation of the SFHAs. As such they are adopted by local communities and form the basis for administration of the NFIP. For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners. Horizontal accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of the individual DFIRM data sets was also performed.

Quantitative Horizontal Positional Accuracy Assessment

Horizontal Positional Accuracy Value
Horizontal Positional Accuracy Explanation

Vertical Positional Accuracy Report

Report The National Flood Hazard Layer data consists of community based vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and DFIRM maps are issued as the official designation of the SFHAs. As such they are adopted by local communities and form the basis for administration of the NFIP. For these purposes they are authoritative. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Details of FEMA's requirements for the FISs and flood mapping process that produces these data are available in the Guidelines and Specifications for Flood Hazard Mapping Partners. Vertical accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. Independent quality control testing of the individual DFIRM data sets was also performed.

Quantitative Vertical Positional Accuracy Assessment

Vertical Positional Accuracy Value
Vertical Positional Accuracy Explanation

Logical Consistency Report When FEMA revises an FIS, adjacent studies are checked to ensure agreement between flood elevations at the boundaries. Likewise flood elevations at the confluence of streams studied independently are checked to ensure agreement at the confluence. The FIRM and the FIS are developed together and care is taken to ensure that the elevations and other features shown on the flood profiles in the FIS agree with the information shown on the FIRM. However, the elevations as shown on the FIRM are rounded whole-foot elevations. They must be shown so that a profile recreated from the elevations on the FIRM will match the FIS profiles within one half of one foot.

Completeness Report Information contained in the National Flood Hazard Layer data reflects the content of the source materials. Features may have been eliminated or generalized on the source graphic, due to scale and legibility constraints. With new mapping, FEMA plans to maintain full detail in the spatial data it produces. However, older information is often transferred from existing maps where some generalization has taken place. Flood risk data are developed for communities participating in the NFIP for use in insurance rating and for floodplain management. Flood hazard areas are determined using statistical analyses of records of river flow, storm tides, and rainfall; information obtained through consultation with the communities; floodplain topographic surveys; and hydrological and hydraulic analysis. Both detailed and approximate analyses are employed. Generally, detailed analyses are used to generate flood risk data only for developed or developing areas of communities. For areas where little or no development is expected to occur, FEMA uses approximate analyses to generate flood risk data. Typically, only drainage areas that are greater than one square mile are studied. The National Flood Hazard Layer data reflects the most current information available when the distribution data set was created.

Lineage

Source Information

Source Citation

Source Scale Denominator

Type of Source Media digital tape media

Source Time Period of Content

DateTime 2009-01-16
Source Currentness Reference Available effective DFIRMs and LOMRs issued against those DFIRMs.

Source Citation Abbreviation NFHL

Source Contribution Spatial and attribute information, floodplain widths, BFEs, floodplain location.

Process Step

Process Description The individual components of the National Flood Hazard Layer data are compiled in conjunction with the hardcopy FIRM and the final FIS report. The specifics of the hydrologic and hydraulic analyses performed are detailed in the FIS reports available for each community. The results of these studies are submitted in digital format to FEMA. These data and unrevised data from effective FIRMs are compiled onto the base map used for DFIRM publication and checked for accuracy and compliance with FEMA standards. As new DFIRM data sets are received the individual DFIRM layers are sewn into the nationwide layers of the NFHL. LOMRs for the DFIRMs in the NFHL are cut directly into the NFHL data layers as they are being produced and finalized.
Process Date 2009-01-16
Process Time
Process Contact

Flood Control Structures

Metadata from the RGIS Metadata Repository

Identification Information

Distribution Information

Spatial Reference Information

Data Quality Information

Metadata Reference Information