CRWR Online Report 2001-2

 
 

Developing Digital Flood Insurance Rate Maps for Lago Vista

By Kevin Michael Donnelly and David R. Maidment

ABSTRACT

Flood Insurance Rate Maps (FIRMs), managed by the Federal Management Agency, display flood hazards and are used to calculate insurance premiums for the National Flood Insurance Program. This research presents an approach for developing new data included in a DFIRM database, as well as converting existing map data into digital format. A raster base map combining USGS Digital Orthophoto Quadrangles (DOQs) and community developed digital orthophotos was created. Flood hazard zones were redelineated based upon previously determined 100-year and 500-year water surface elevations and recently developed, detailed contour data. This study also demonstrates how a DFIRM data model can be developed to run off an existing geodatabase model. The ArcGIS Hydro data model was extended to contain DFIRM features based upon FEMA's Standard DFIRM Spatial Database. An evaluation of the 100-year floodplain developed using "approximate" study methods (FEMA's Zone A) and a procedure for converting contour data between the vertical datums, NGVD29 and NAVD88, are also presented. The methodology is applied to a study area surrounding Lago Vista, Texas. The results of this research indicate that GIS is an effective environment for developing, utilizing, and storing Flood Insurance Rate Maps.

CRWR Online Report 2001-2

 

Developing Digital Flood Insurance Rate Maps for Lago Vista

By Kevin Michael Donnelly and David R. Maidment

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