![]() ![]() Independent quality control testing of FEMA's DFIRM database was also performed. Attribute accuracy was tested by manual comparison of source graphics with hardcopy plots and a symbolized display on an interactive computer graphic system. 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. As with any engineering analysis of this type, variation from the estimated flood heights and floodplain boundaries is possible. Provisions exist in the regulations for public review, appeals and corrections of the flood risk information shown to better match real world conditions. For these purposes they are authoritative. As such they are adopted by local communities and form the basis for administration of the NFIP. The published effective FIRM and DFIRM maps are issued as the official designation of the SFHAs. Typically, only drainage areas that are greater than one square mile are studied.Īttribute accuracy report: The DFIRM Database consists of countywide vector files and associated attributes produced in conjunction with the hard copy FEMA FIRM. For areas where little or no development is expected to occur, FEMA uses approximate analyses to generate flood risk data. Generally, detailed analyses are used to generate flood risk data only for developed or developing areas of communities. Both detailed and approximate analyses are employed. 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. Flood risk data are developed for communities participating in the NFIP for use in insurance rating and for floodplain management. However, older information is often transferred from existing maps where some generalization has taken place. With new mapping, FEMA plans to maintain full detail in the spatial data it produces. Features may have been eliminated or generalized on the source graphic, due to scale and legibility constraints. The DFIRM database is a subset of the Digital FIS database that serves to archive the information collected during the FIS.Ĭompleteness report: Data contained in the DFIRM Database files reflect the content of the source materials. The DFIRM Database presents the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. 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. 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 located or to be located in identified areas having special flood hazards," Section 2 (b) (4) of the Flood Disaster Protection Act of 1973. Insurance applications include enforcement of the mandatory purchase requirement of the Flood Disaster Protection Act, which ". Purpose: The FIRM is the basis for floodplain management, mitigation, and insurance activities for the National Flood Insurance Program (NFIP). The specifications for the horizontal control of DFIRM data files are consistent with those required for mapping at a scale of 1:12,000. The file is georeferenced to earth's surface using the State Plane projection and coordinate system. The FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA). The DFIRM Database is 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 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 DFIRM Database depicts flood risk information and supporting data used to develop the risk data. More current data may be available from the Federal Emergcy Management Agency (FEMA). See below for time period of each county DFIRM Database included in this statewide XS layer. Abstract: Includes location and attributes for Cross-Section Lines (XS) shown on Digital Flood Insurance Rate (DFIRM) maps available for five Connecticut counties. ![]()
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