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Report Details How Groundwater Pumping In Yakima Basin Reducing Yakima River Flows
Posted on Friday, September 24, 2010 (PST)

The latest results of a comprehensive groundwater study reaffirm the need for water managers to work together to find long-term water supply solutions for the Yakima River Basin, the parties commissioning the report announced this week.


The long-awaited report ( and model presented this week by the U.S. Geological Survey provides a clearer picture of the significant interaction between surface water and groundwater in the Yakima River Basin, where competition over water has been escalating for more than 30 years.


The Yakima River Basin USGS groundwater study and computer model was commissioned by the Washington Department of Ecology, Yakama Nation, and the Bureau of Reclamation in a 1999 memorandum of agreement related to groundwater management in the Yakima Basin.


In public meetings held this week, the USGS shared preliminary results that confirm a substantial amount of water is lost to the river because of groundwater pumping and use.


The report estimates, on average, groundwater pumping reduces flows by 200 cubic feet per second by the time the Yakima River drains into the Columbia River. The impacts are significant when compared to federally mandated target streamflows at Sunnyside and Prosser dams, which range from 300 to 600 cfs depending on the amount of runoff the Yakima basin generates each year.


"The numbers are sobering. Groundwater pumping and depletion of this magnitude means there's less water available to meet federally mandated target streamflows and the irrigation delivery obligations in the basin," said Ken Slattery, Ecology's water resources program manager. "This certainly adds urgency to our efforts to tackle the basin's water supply needs, particularly for junior water users."


"The existing groundwater pumping is impairing senior water rights in the fully appropriated Yakima Basin. Any new pumping of groundwater would do more of the same. This impairment of the Yakama Nation's water rights cannot continue or increase. A permanent solution is needed to either stop the groundwater pumping or obtain mitigation to our satisfaction for that junior water use," said Philip Rigdon, the Yakama Nation's deputy director for Natural Resources.


The study demonstrates the connection between surface and groundwater, and will be used to estimate when and by how much groundwater pumping is reducing surface water supplies. The three parties are reaching out to others in the local area to provide input on developing a groundwater management program for the Yakima River basin.


Slattery added: "The study and computer model provide important information that was previously lacking to help quantify and meet current and future water needs. Building infrastructure that captures and stores more water will be a part of the solution, as will continuing to improve the efficiency of existing infrastructure and water use."


The Yakima River Basin Water Enhancement Project work group is factoring results of the study in its efforts to develop additional water supplies to meet both current and future water demands for agriculture, municipalities, groundwater pumping, including domestic wells, and improving stream flows.


The work group is comprised of state and federal agencies, commissioners from the three Yakima Basin counties, the city of Yakima, the Yakama Nation, irrigation districts, fisheries managers, and representation from the environmental organization American Rivers.


They are looking at surface and aquifer storage, water markets, modifications at existing facilities and operations, and other opportunities to bolster water supplies in the Yakima basin. The group is expected to make its recommendations to water managers by the end of 2010.


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