USGS Washington Water Science Center
|U.S. Department of the Interior
U.S. Geological Survey
Release: October 1, 2001
253-428-3600, ext. 2684
A new mapping method developed by the USGS can produce updated flood inundation maps with greater detail and accuracy at a much lower cost than traditional hand-drawn flood maps.
Flood inundation maps show areas that would be under water in various sizes of floods. The maps provide the details that planners, engineers, and others need to keep out of harm's way critical assets like roads, bridges, buildings, and schools. Because the method uses geographic information system (GIS) computer programs, digital map information such as the location of roads and buildings can also be easily added to flood maps.
Most of the flood maps produced for the National Flood Insurance Program in the 1970s and early 1980s now need updating. Since the original maps were drawn, more flood level data have accumulated, which can significantly change calculations of flood estimates, and new, very-high-accuracy elevation data are now available. The new USGS method is a quick, affordable way to include the new data and calculations while also providing greater detail and more flexible analysis capabilities.
"Many of the aging flood maps were based on now-outdated flood flow estimates, as well as on paper maps that lack sufficient detail," said Joseph L. Jones, USGS hydrologist and lead developer of the new method.
"With our new digital method, we can cut map-updating costs by up to 80 percent over the traditional methods while producing maps with improved accuracy and much greater detail. We can quickly update maps as new flood probability estimates and very-high-accuracy elevation data become available."
The method uses results from existing detailed Flood Insurance Studies conducted by the Federal Emergency Management Agency (FEMA), eliminating the expensive, time-consuming field collection of elevation and structures data. Very-high-accuracy elevation data collected by local governments are also used in the method that contributes greatly to lowering the costs while increasing the accuracy of the flood maps. Local and Federal agencies are already aggressively collecting this kind of elevation data for a variety of uses.
The report detailing the new method, "Updating Flood Maps Efficiently Using Existing Hydraulic Models, Very-High-Accuracy Elevation Data, and a Geographic Information System-A Pilot Study on the Nisqually River, Washington," by Joseph L. Jones, Tana L. Haluska, and David L. Kresch, is published as U.S. Geological Survey Water-Resources Investigations Report 01-4051. Copies of the report are available for reading at the U.S. Geological Survey, 1201 Pacific Avenue, Suite 600, Tacoma, Washington 98402. The report can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Denver, Colorado 80225, telephone 303-202-4200.
The USGS serves the nation by providing reliable scientific information to describe and understand the Earth; minimize loss of life and property from natural disasters; manage water, biological, energy, and mineral resources; and enhance and protect our quality of life.
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