Yakima River Basin Groundwater Study Background

September 2010 - Yakima River Basin USGS groundwater study

Preliminary 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 report and model presented by the U.S. Geological Survey (USGS) on Sept. 21, 2010, provide 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 Ecology, Yakama Nation, and the Bureau of Reclamation in a 1999 Memorandum of Agreement (MOA) related to groundwater management in the Yakima Basin.

In public meetings the USGS shared preliminary results that confirm the river loses a substantial amount of water to groundwater pumping.  The report estimates flows are reduced by as much as 200 cubic- feet- per- second (cfs) by the time the Yakima River drains into the Columbia River, due to groundwater withdrawals.  The impact is significant when compared to federally mandated target flows at Sunnyside and Prosser dams, which range from 300 to 600 cfs.

The Yakima River Basin USGS groundwater study and computer model was commissioned by Ecology, Yakama Nation, and the Bureau of Reclamation in a 1999 Memorandum of Agreement (MOA) related to groundwater management in the Yakima Basin.

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 to help when making groundwater permitting decisions.  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 exempt wells, and improving stream flows.

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

Long-term groundwater study: background, purpose and organization

Yakima River Basin Groundwater Study

Bureau of Reclamation News Release  - December 30, 2009 - Yakima River Basin Study to Move Forward in 2010.  The Bureau of Reclamation and Washington State Department of Ecology (Ecology) announced today that the Yakima River Basin Water Enhancement Project Workgroup has reached consensus to move forward with a preliminary Integrated Water Resource Management Plan intended to address water supply and aquatic resource problems of the basin.

The 10th study report on groundwater in the Yakima River Basin was released on September 22, 2009 by the U.S. Geological Survey (USGS).  This signals the near-completion of the largest study of groundwater resources conducted in the region.  Started in 2000, the final report is due in early 2010.  The Sept. 2009 report indicates that 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 past 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 uses 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,” said Ecology’s Water Resources Program Manager, Ken Slattery. “Since 1960, municipal demands doubled due to the growth of cities and towns. In the same time period, irrigation demands have quadrupled.”

Two final USGS reports will provide detailed information on how water is exchanged between aquifers and rivers and streams. The study will simulate very specifically how groundwater flows in the Yakima Basin.

When completed, the model will provide a state-of-the-art technical tool to help water managers make sound decisions in the Basin, where water shortages are a chronic problem.

News releases:

The report:

The Sept. 2009 study report is one of a series of reports issued by the U.S. Geological Survey (USGS) since the study began in 2000. In 1999, the Department of Ecology, the U.S. Bureau of Reclamation and the Yakama Nation agreed to study groundwater resources in the Yakima River Basin and to develop a groundwater model to be used as a tool for water planning and management. The study is being done by USGS.

The Yakima River Basin is one of the most intensively irrigated areas in the U.S. There are increasing demands for water for municipal, fisheries, agricultural, industrial, and recreational uses which must be met by groundwater withdrawals and by changes in the way water resources are distributed and used. The Yakima surface water adjudication is close to completion. It is timely and essential to have a better understanding of the groundwater flow system and its relation to rivers and streams to effectively manage the basin's water resources.

The study includes data collection, mapping of hydrogeologic units and groundwater levels, and a computer numerical model to bring together all the information.

Study being done in three phases

The study includes three phases. The first phase included (1) project planning and coordination, (2) compiling, documenting, and assessing available data, and (3) initial data collection.

The second phase consists of data collection to support the following Phase 2 work elements: (1) mapping of hydrogeologic units, (2) estimating groundwater pumpage, (3) developing estimates of groundwater recharge, (4) assessing ground water-surface water interchanges, and (5) constructing maps of groundwater levels. Together, these five elements provide the information needed to describe the groundwater flow system, the conceptual model, and provide the building blocks for the hydrogeologic framework.

In the third phase, six structural basin models and one regional model of the groundwater flow system will be constructed in order to integrate the available information. The numerical models will be used to gain a further understanding of the flow system and its relation to surface water, and to test management strategies. The models will be developed and maintained in such a fashion that it will be available and open to others.

September 2006 USGS report: Estimates of Ground-Water Pumpage from the Yakima River Basin Aquifer System, Washington, 1960-2000

September 18, 2006 - Yakima Basin Groundwater Use Estimated

Information on groundwater withdrawals in the Yakima River Basin is presented in the Sept. 2006 report published by the USGS. The report features data for over 3,000 wells, making it the largest study of its kind ever in the state.

The quantities of groundwater pumped in the basin were estimated for 1960 to 2000 for eight categories of water use. Pumpage estimates were based on methods that varied by the category and primarily represent pumpage for wells with groundwater rights.

"In 1960, total annual pumpage in the basin was about 115,776 acre-feet," said John Vaccaro, USGS hydrologist and lead author of the report. "By 2000, total annual pumpage was estimated to have nearly tripled, to 312,284 acre-feet."

Irrigation accounts for about 60 percent of the pumpage, followed by public water supply at about 12 percent. Groundwater is the principal source of drinking water in the basin and supplies about 330,000 people in the three-county area.

Water managers in the Yakima River Basin will incorporate the pumpage estimates into computer models to boost their understanding of the groundwater flow system and to test water management strategies.

News release:

The report:

June 2006 USGS Report: Hydrogeologic Framework of Sedimentary Deposits in Six Structural Basins, Yakima River Basin, Washington

June 13, 2006 - New Maps Show Yakima Basin Geology, Aquifers

Hydrogeologic information needed to model groundwater flow in the Yakima River Basin is available in a report published June 13, 2006 by the USGS.

Using information from about 4,700 wells, USGS scientists mapped the sedimentary deposits in six structural basins within the overall Yakima River Basin. The maps show where the deposits are and how thick they are, and identifies their water-bearing units. The sedimentary deposits were thickest in the Kittitas Basin, reaching a depth of greater than 2,000 ft, with Roslyn Basin the thinnest at about 700 feet.

USGS News Release June 13, 2006

The report, “Hydrogeologic framework of sedimentary deposits in six structural basins, Yakima River Basin, Washington,” by M.A. Jones, J.J. Vaccaro, and A.M. Watkins, is published as U.S. Geological Survey Scientific Investigations Report 2006-5116.

The report:

For more information

U.S. Geological Survey


Central Region Water Resources Program
Phone: (509) 575-2597