Yakima Basin groundwater supply study nears completion

Washington State Department of Ecology

Department of Ecology News Release - September 22, 2009

09-232

Yakima Basin groundwater supply study nears completion

YAKIMA – Today's release by the U.S. Geological Survey (USGS) 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 (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.

“While water levels in many aquifers are relatively stable, demands on that water have significantly increased over the last 50 years,” notes Slattery. “Since 1960, municipal demands doubled due to the growth of cities and towns. In the same time, irrigation demands quadrupled, due largely to the buildout of the U.S. Bureau of Reclamation Project.”

Increased demands and recent droughts have prompted water managers to take actions to protect existing uses and seek strategies to meet new demands in the future.

Agricultural demands on groundwater have been fairly stable because Ecology stopped issuing new groundwater rights for irrigation more than 15 years ago as a result of the settlement of a legal challenge by several senior water right holders. However, new residential developments relying on groundwater withdrawals under the state's permit exemption have proliferated in recent years, prompting an emergency halt on new groundwater withdrawals in Upper Kittitas County.

“A work group of high level stakeholders is moving forward with an integrated approach to solve water problems in the Yakima basin. For instance, we're looking for new storage opportunities and to improve the efficiency of water delivery systems,” explained Derek Sandison, with Ecology's Office of Columbia River. “Much of our success will hinge on our understanding of how surface water and groundwater move in the basin and how junior water users can offset their groundwater pumping and avoid impairing senior rights during future droughts.”

Aquifers are recharged by precipitation, snow melt, streamflows, irrigation return flows and other return discharges such as septic systems, reservoir flows etc. Pumping groundwater connected to surface water diminishes stream flows relied on by senior surface water right users for irrigation and municipal purposes, and can reduce flows for fish.

Two final USGS reports will provide detailed information on how water is exchanged between aquifers and rivers and streams. It will also simulate very specifically how ground water flows within the Yakima Basin.

When completed, the USGS study will provide a state-of-the art technical tool to help managers make sound decisions in the Yakima River Basin where surface water is fully appropriated.

###

Media Contact: Joye Redfield-Wilder, 509-575-2610; jred461@ecy.wa.gov