Coastal Services Center

Mapping Techniques for Flood Forecasting

The NOAA Coastal Services Center has used river gage data, collected by the U.S. Geological Survey (USGS) during the intense rainfall associated with Hurricane Floyd in September 1999, to create time-series inundation maps at select locations along the Tar River. These maps were created using the latest in geographic information system (GIS) technologies.

The purpose of this project is to demonstrate a prototype application for flood forecast mapping. The project uses existing data as a model to illustrate the concept of mapping gage and water surface time-series data in an interactive GIS environment over the Internet. In this interactive format the user can pan, zoom, and identify data, as well as print maps and view metadata.

Pilot Project

This prototype shows time-series inundation maps at three urban areas that were most affected by Hurricane Floyd flooding on the Tar River: Rocky Mount, Tarboro, and Greenville.

The display of inundation maps associated with Hurricane Floyd is being used to illustrate how flood forecast data, distributed by the National Weather Service will be able to be displayed on the Internet. This will ultimately result in an enhanced flood forecast system that will be yet another part of the NCFMP, while serving as a pilot for a new suite of products and services of the National Weather Service's Advanced Hydrologic Prediction Services (AHPS) program.

Example of a flood gage text report converted to a map product

Map Creation Process

Each inundation map was created by using a water surface elevation from the USGS stage data and subtracting it in a GIS using spatial analysis techniques from the ground surface, represented by a 5 x 5 ft. Digital Elevation Model (DEM). The DEM was created from bare earth mass points and break line data taken from a LIDAR elevation data set collected by the North Carolina Flood Mapping Program (NCFMP). This is an effort to improve flood insurance rate maps (FIRMs) for six river basins in the eastern portion of the state. For more information on LIDAR elevation data, visit the FAQ section.

Examples of a high resolution DEM and a flood inundation map

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