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News Release

U.S. Department of the Interior
U.S. Geological Survey

Release: November 12, 2002
Joseph Jones
253-428-3600, ext. 2684

Mapping a Flood-Before It Happens

[Note: The report can be viewed on the Web at]

A new U.S. Geological Survey mapping method can produce flood inundation maps as much as three to five days ahead of a forecasted storm, giving flood-response officials and others precious time to respond. The high-tech method is described in a report released today by the USGS.

At the heart of the new method is high-accuracy elevation data and a powerful, new computer flow model. They are combined with a computerized geographic information system to produce maps that are then served up on the Internet.

"The new flood forecast maps fill a critical information gap," said USGS hydrologist Joseph Jones, lead author of the report. "The maps show computer-generated predictions of flooded areas and flood depths for a specific storm and forecast."

Existing forecasts are limited to predicting river levels or flows only at specific points, without area or depth information.

The high-accuracy elevation data is gathered by an airborne laser system called LIDAR (Light Detection And Ranging). From an aircraft, tens of thousands of laser light pulses per second are emitted and bounce off the ground. The pulses are collected and combined with navigation and positioning systems to give highly accurate elevation data.

The new computer flow model uses automatically retrieved National Weather Service river forecast information to simulate the forecasted area of a flood. A geographic information system combines the results from the model with the high-accuracy elevation data to produce maps of flood extent, depth, arrival time, and peak time.

The maps are then served up on the Internet using advanced map-server technology. The maps are produced in nearly real-time and can quickly give emergency managers and others an accurate picture of flooding from as much as three to five days before a specific storm.

The report detailing the new method, "Near-Real-Time Simulation and Internet-Based Delivery of Forecast-Flood Inundation Maps Using Two-Dimensional Hydraulic Modeling--A Pilot Study for the Snoqualmie River, Washington," by J.L. Jones, J.M. Fulford, and F.D. Voss, is published as U.S. Geological Survey Water-Resources Investigations Report 02-4251. The USGS report is available on the Web at The report can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Denver, Colorado 80225, telephone 303-202-4200.

The USGS, a bureau within the Department of the Interior, 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 the quality of life.

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