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News Release

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

Release: January 14, 2002
William Bidlake
253-428-3600, ext. 2641

Less than half of rainfall in northern Kitsap County makes it to ground water, study shows

A study of ground-water recharge in northern Kitsap County indicates that about half of the rainfall that falls over the area eventually is lost to evaporation, a bigger loss than by any other means, according to a report released by the U.S. Geological Survey (USGS).

The USGS examined precipitation, runoff, and evaporation in an 85-square-mile area, including Naval Submarine Base Bangor, in order to estimate ground-water recharge-the water that travels into the ground and down to the water table.

Because ground water is the primary source of drinking water for the Kitsap Peninsula, understanding ground-water recharge and what controls it is especially important for managing ground-water resources there. According to recent statistics, the population in Kitsap County increased about 117 percent over the last 25 years-about double the state average-which means increased demand for ground water.

Of the 38.9 to 52.1 inches of precipitation per year that fell during the study period (1994-96), annual recharge ranged from 11.9 to 16.6 inches per year. Estimated evaporation losses ranged from 19.6 to 24.2 inches per year, and runoff ranged from 5.7 to 17 inches per year, depending mostly on soil type and type of land cover. Evaporation losses include water on the soil surface that evaporates, transpiration of water by plants, and interception loss-the precipitation that wets the vegetation and evaporates back into the atmosphere without ever reaching the ground.

"A large portion of annual rainfall in northern Kitsap County is lost to evaporation," said Bill Bidlake, USGS hydrologist and the lead author of the report, "and yet there is much we need to learn about the processes that result in evaporation, which affects streams and ground-water recharge. The more you know about evaporative loss, the more accurate are your predictions of ground-water recharge."

The report, "Estimating Recharge to Ground Water from Precipitation at Naval Submarine Base Bangor and Vicinity, Kitsap County, Washington," by W.R. Bidlake and K.L. Payne, is published as U.S. Geological Survey Water-Resources Investigations Report 01-4110. Copies of the report are available for reading at the U.S. Geological Survey, 1201 Pacific Avenue, Suite 600, Tacoma, WA 98402. Copies can be purchased from the U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225-0286, telephone 303-202-4200.

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