News Release

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

Release: February 5, 2008

Contact:
Mark Mastin
253-552-1609

John Clemens
253-552-1635

New Peak Flow For Record Chehalis Flood

[Editors: Photos of the damaged gaging station and graphs showing 12/03/07 streamflow for select Chehalis River stations are available at ftp://ftpext.usgs.gov/pub/wr/wa/tacoma/jclemens/Chehalis/ .]

A new record was set in peak streamflow in the upper watershed of the Chehalis River, according to preliminary calculations made after the December 3, 2007, storm event. The streamflow indicates a pattern resulting from a very intense rainstorm, according to the U.S. Geological Survey (USGS).

USGS scientists determined that the peak streamflow at their gaging station on the Chehalis River near Doty, Wash., occurred on December 3, with a flow of 63,100 cubic feet per second (cfs). The gaging station had transmitted in real-time, via satellite telemetry, a flow of 51,100 cfs before floodwaters swamped the instruments and destroyed equipment at the site. By comparison, the previous record peak flow was 28,900 cfs, reached during the February 1996 flood.

At the Doty gaging station, floodwaters rose quickly—within a few hours—to reach the peak flow, then tapered off gradually, a typical pattern of streamflow during an intense rainstorm. The force of the moving water was great enough to scour out a 37,000-lb concrete anchor block at the Doty gaging station and move it from one side of the river to the other.

Scientists made the calculations using a field survey technique in which they identified high-water marks and determined the channel geometry with surveying equipment. Usually, USGS scientists measure streamflow directly with current meters, but during a flood, it is often impossible or unsafe to use this measurement method, so a post-flood field survey technique is used.

USGS river gaging stations form the backbone of flood-warning systems in the state. Federal agencies, such as the U.S. Army Corps of Engineers and NOAA National Weather Service, as well as state, county, and local emergency management agencies use real-time streamflow data from USGS river gaging stations to closely monitor the height and flow of rivers in order to protect lives and mitigate damage to property.

USGS provides science for a changing world. For more information visit http://www.usgs.gov/ .

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