The District of Columbia

FldPlnPly_CrossSection

FldPlnPly_CrossSection

by Federal Emergency Management Agency on 20100927

Keywords
About: Hydrology, Environment, Inland Waters, Structure, Transportation, Elevation, FEMA Flood Hazard Zone, DFIRM Database, DFIRM, Special Flood Hazard Area, Digital Flood Insurance Rate Map, Riverine Flooding, NFIP, Base Flood Elevation, SFHA, Flood Insurance Rate Map, FIRM, Floodway
Taking place at: REGION 03, STATE DC, COUNTY DISTRICT OF COLUMBIA, COUNTY-FIPS 11001, COMMUNITY WASHINGTON, FEMA-CID 110001

Abstract

Cross Sections. The Digital Flood Insurance Rate Map (DFIRM) Database depicts flood risk information and supporting data used to develop the risk data. 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 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 FISs and FIRMs are published by the Federal Emergency Management Agency (FEMA). The file is georeferenced to earth's surface using the UTM projection and coordinate system. The specifications for the horizontal control of DFIRM data files are consistent with those required for mapping at a scale of 1:12000.

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 located or to be located in identified areas having special flood hazards," 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 DFIRM Database presents the flood risk information depicted on the FIRM in a digital format suitable for use in electronic mapping applications. The DFIRM database is a subset of the Digital FIS database that serves to archive the information collected during the FIS.

Access constraints

None

Use constraints

The hardcopy FIRM and DFIRM and the accompanying FISs are the official designation of SFHAs and Base Flood Elevations (BFEs) for the NFIP. For the purposes of the NFIP, changes to the flood risk information published by FEMA may only be performed by FEMA and through the mechanisms established in the NFIP regulations (44 CFR Parts 59-78). These digital data are produced in conjunction with the hardcopy FIRMs and generally match the hardcopy map exactly. However the hardcopy flood maps and flood profiles are the authoritative documents for the NFIP. Acknowledgement of FEMA would be appreciated in products derived from these data.

Point of contact


in Federal Emergency Management Agency

500 C Street, S.W.
Washington District of Columbia, 20472, USA

phone: 1-800-358-9616

Data accuracy

Accuracy
The DFIRM Database consists of countywide 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 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. 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 database 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 this DFIRM database. 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.

Logical consistency
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
Data contained in the DFIRM Database files reflect 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.

Horizontal positional accuracy
The DFIRM Database consists of countywide vector files and associated attributes produced in conjunction with the hardcopy FEMA FIRM. The published effective FIRM and DFIRM 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 FEMA's DFIRM database was also performed.

Vertical positional accuracy
The DFIRM Database consists of countywide 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 FEMA's DFIRM database was also performed.

Lineage / Sources

  • StreetCenterlineLn
    CD-ROM, Spatial and attribute information for information was created at a scale of 1:1000..
    BASE1
    by DC District Department of Transportation, 20050905
  • Permanent Bench Mark Data Sheets
    CD-ROM, Spatial and attribute information for permanent benchmarks.
    BASE2
    by National Geodetic Survey, 2002
  • DCBndyPly
    CD-ROM, Spatial and attribute information for information was created at a scale of 1:24000..
    BASE3
    by DC GIS, 20020610
  • ParkPly
    CD-ROM, Spatial and attribute information for information was created at a scale of 1:24000..
    BASE4
    by National Park Service, 20020610
  • RailRdLn
    CD-ROM, Spatial and attribute information for information was created at a scale of 1:1000..
    BASE5
    by National Capital Planning Commission, District of Columbia Department of Public Works, District of Columbia Office of the Chief Technology Officer, 20020701
  • WaterPly
    CD-ROM, Spatial and attribute information for information was created at a scale of 1:1000..
    BASE6
    by National Capital Planning Commission, District of Columbia Department of Public Works, District of Columbia Office of the Chief Technology Officer, 20020610
  • dc_aerial_mosaic_2002_utm18.sid
    CD-ROM, Spatial and attribute information for The original imagery came from true color stable-base aerial photography film flown at 7,500 feet above average ground elevation. The digital raster files for each orthoimage chip provide imagery used in the digital orthoimage..
    BASE7
    by U.S. Geological Survey, 2002
  • USGS 7.5-Minute Series Topographic Maps
    online, Spatial and attribute information for the index of USGS 7.5-Minute Series Topographic Map boundaries.
    BASE8
    by U.S.Geological Survey, 1989
  • Flood Insurance Study, WASHINGTON, DISTRICT OF COLUMBIA
    paper, Spatial and attribute information for floodplain widths, BFEs, cross sections, floodway widths, floodway locations, and floodplain location.
    FIS1
    by Federal Emergency Management Agency, 19851115
  • Hydraulic updates of D.C. streams for Map Modernization Study
    digital files, Spatial and attribute information for floodplains, floodways, cross sections, and BFEs..
    STUDY1
    by U. S. Army Corps of Engineers, 2005
  • Levees, floodwalls, and closure structures included in FEMA's Map Modernization MLI (Mid-term Levee Inventory).
    digital data, Spatial and attribute information for levees, floodwalls, and closure structures in S_GEN_STRUCT..
    STUDY2
    by Michael Baker Jr. Inc., 2007
  • Washington D.C. DEMs
    DVD-ROM, Spatial and attribute information for the DEMs was created from LiDAR data..
    STUDY3
    by National Geospatial-Intelligence Agency (NGA), 2004
Lineage / Processes

Distribution

Distribution liability
No warranty expressed or implied is made by FEMA regarding the utility of the data on any other system nor shall the act of distribution constitute any such warranty. FEMA will warrant the delivery of this product in a computer-readable format, and will offer appropriate adjustment of credit when the product is determined unreadable by correctly adjusted computer input peripherals, or when the physical medium is delivered in damaged condition. Requests for adjustment of credit must be made within 90 days from the date of this shipment from the ordering site.

Distributed by

in FEMA, Map Service Center

P.O.Box 1038
Jessup Maryland, 20794-1038, USA

phone: 1-800-358-9616

Entity

FldPlnPly_CrossSection / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for base flood elevations lines shown on the DFIRM

Attributes

  • SHAPE_LEN / ESRI
    Internal feature number.
  • VELOCITY / ESRI
    Internal feature number.
  • OBJECTID / ESRI
    Internal feature number.
  • Shape / ESRI
    Feature geometry.
  • XS_LN_ID
  • XS_LTR
  • START_ID
  • STREAM_STN
  • XS_LN_TYP
  • WTR_NM
  • WSEL_REG
  • LEN_UNIT
  • V_DATUM
  • SOURCE_CIT
  • BED_ELEV
  • TOP_WIDTH
  • XS_AREA
  • AREA_UNIT
  • VEL_UNIT / ESRI
    Feature geometry.
  • SHAPE / ESRI
    Feature geometry.

Entity

S_FIRM_Pan / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for DFIRM hardcopy map panels

Attributes










Entity

S_Fld_Haz_Ar / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for flood insurance risk zones on the DFIRM

Attributes










Entity

S_Fld_Haz_Ln / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for boundaries of flood insurance risk zones on the DFIRM

Attributes










Entity

S_Gen_Struct / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for flood control structures shown on the DFIRM

Attributes










Entity

S_Perm_Bmk / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for bench marks on the DFIRM

Attributes










Entity

S_Pol_Ar / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for political jurisdictions shown on the DFIRM

Attributes










Entity

S_Pol_Ln / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for political boundaries shown on the DFIRM

Attributes










Entity

S_Quad_Index / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for USGS quadrangle maps covering the DFIRM area

Attributes










Entity

S_Trnsport_Ln / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for roads, railroads and other transportation features shown on the DFIRM

Attributes










Entity

S_Wtr_Ln / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for hydrography features shown on the DFIRM

Attributes










Entity

S_XS / FEMA Guidelines and Specifications for Flood Hazard Mapping Partners, Appendix L: Guidance for Preparing Draft Digital Data and DFIRM Databases (available at http://www.fema.gov/fhm/dl_cgs.shtm)
Location and attributes for cross-section lines in the area covered by the DFIRM

Attributes










Metadata

FGDC Content Standards for Digital Geospatial Metadata / FGDC-STD-001-1998 as of 20100727

Provided by
FEMA Representative
in Federal Emergency Management Agency

500 C Street, S.W.
Washington District of Columbia, 20472, USA

phone: 1-800-358-9616