Ridenbaugh Press/Water Rights

Release by the U.S. Geological Survey of a 10th study report on groundwater in the Yakima River Basin signals that the largest study of aquifer resources conducted in the region is nearing completion. The study was funded by the USGS in partnership with the Washington Department of Ecology, Yakama Nation and the U.S. Bureau of Reclamation.

Due in early 2010 , the final report will help water managers estimate the potential impact new groundwater withdrawals would have on surface water supplies and allow managers to analyze ways water users may offset the effects of their groundwater withdrawals on senior water rights and stream flows.

“Understanding how, when and where groundwater pumping affects surface water is essential for water managers to make sound water resource decisions,” said Ken Slattery, Water Resources manager for Ecology. “This report will play a key role as we seek overall solutions to the long-term water supply concerns in the basin.”

Water shortages are a chronic problem in the Yakima River Basin. Demand for water to irrigate crops, to provide drinking water, and to ensure the survival of salmon and steelhead often exceeds supply.

Built over the last 10 years using actual well and water data, the Yakima Basin groundwater study will characterize the hydraulic connection between groundwater and surface water for all aquifers in the Yakima River Basin, including sedimentary aquifers of upper Kittitas County.

Groundwater movement in the higher elevation bedrock areas of upper Kittitas will be the subject of a separate study authorized by the Legislature. That narrower study is expected to commence soon.

The latest report from the USGS indicates groundwater levels in some areas have declined by 10 to 20 feet and in deeper confined aquifers, pumping has reduced water levels by as much as 300 feet. Groundwater levels in sedimentary aquifers have remained fairly steady over the last 50 years, largely due to recharge from surface water and irrigation seepage, but according to the report, that water cannot be considered available for new use because it is relied on to meet existing downstream water rights.

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