DIGITAL FLOOD INSURANCE RATE MAP DATABASE, Washington COUNTY, NE

Resource lineage description

source

source description  Source Contribution: Spatial and attribute information, base flood elevations, floodplain widths, floodplain locations, and cross sections.Source Type paper

source citation

Title Flood Insurance Rate Map, Washington County, NE

publication  Date   2009-07-08

cited responsible party - originator

organisation Name  Federal Emergency Management Agency

source

source description  Source Contribution: Attribute information, Community information, Hydrology and Hydrologics, base flood elevations, firm panel layout, and general structures.Source Type paper

source citation

Title Flood Insurance Study, Washington County, NE

publication  Date   2009-07-08

cited responsible party - originator

organisation Name  Federal Emergency Management Agency

source

source description  Source Contribution: Kirkham Michael generated a new paneling scheme for the current effective Flood Insurance Rate Map data. The S_FIRM_PAN feature class was created according to FEMA specifications for DFIRM productionSource Type online

source citation

Title S_FIRM_Pan

publication  Date   2009-12-11

cited responsible party - originator

organisation Name  Kirkham Michael

source

source description  Source Contribution: Visual Bench Mark identification on the paper map provides the necessary relative location information for engineering professionals to establish tie-in identification. The online datasheet information provides the additional technical data for horizontal and vertical details.Source Type online

source citation

Title Permanent Bench Marks Data Sheets

publication  Date   2009-12-11

cited responsible party - originator

organisation Name  National Geodetic Survey

source

source description  Source Contribution: Public land survey information, quadrangle index, base index, river mile markers, and stream featuresSource Type online

source citation

Title Basemap for Washington County, Nebraska

publication  Date   2009-12-11

cited responsible party - originator

organisation Name  United States Geological Survey (USGS)

source

source description  Source Contribution: This data was used to reference corporate and county boundaries.Source Type CD-ROM

source citation

Title Political boundaries

publication  Date   2009-12-11

cited responsible party - originator

organisation Name  Washington County Revenue Commission

AbsoluteExternalPositionalAccuracy

name Of Measure Horizontal Positional Accuracy Report

evaluation Method Description  The DFIRM Database consists of community based 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.

AbsoluteExternalPositionalAccuracy

name Of Measure Vertical Positional Accuracy Report

evaluation Method Description  The DFIRM Database 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 FEMA's DFIRM database was also performed.

Completeness Commission

evaluation Method Description  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.

Completeness Omission

evaluation Method Description  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.

ConceptualConsistency

measure Description  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.