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Yakima Reservation Water Resources

Project Summaries

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WA335 - Quality of Ground Water in the Toppenish Basin, Yakima Indian Reservation - Completed FY1993

Problem - The Toppenish basin contains 627 square miles of land on the Yakima Indian Reservation in south-central Washington. Most of the land in the lower part of the basin is used for irrigated agriculture; the upper part of the basin is mostly forest or arid rangeland. The majority of the basin's population resides in the lower part and relies exclusively on ground water for their potable water supply. There are three main aquifers in the basin, the alluvium, the Ellensburg Formation, and the basalt, which underlies the other two. Most domestic supplies are taken from the upper two aquifers. The limited available ground-water-quality data indicate that some ground water is contaminated with nitrate. It is suspected that water supplies may also contain some contaminants that are derived from agriculture, domestic wastes, food processing, and a few light industries within the basin.

Objectives - The objectives of the study are to define ground-water quality in the lower Toppenish basin and identify existing and potential water-quality problems, relate ground-water quality conditions to geohydrology and attempt to identify source areas and flow paths of contaminants causing identified existing and potential water-quality problems, and to present results in a manner usable to managers responsible for the water resources of the Yakima Indian Reservation.

Approach - Within each one-square-mile section of each aquifer, data will be collected on population; land use; aquifers and their characteristics; population served by wells; and number and annual mean discharge of irrigation, stock, and industrial wells. About 600 wells and 50 surface-water sites with ground-water seepage will be sampled once during a synoptic survey for nitrate are bacteria. Twenty wells will be sampled over a one-year period to determine seasonal variations in water quality. Water from 15 wells will be analyzed once for a wide variety of organic compounds. Then water from 60 wells will be analyzed for the prevalent compounds. All data on water quality will be related to ground-water flow paths and land use.

WA147 - Water Resources of the Yakima Indian Reservation - Completed FY1983

Problem - Because of the increase in ground-water withdrawals locally from deep basalt aquifers in eastern washington, water levels have declined as much as 40 feet in some places and the rate of decline has been rapidly increasing. Unless natural recharge can be supplemented by some means, pumping will have to be reduced to avoid excessive mining of the resource.

Objectives - To determine whether artificial recharge of the deep basalt aquifers in eastern Washington would afford a means of at least partially offsetting the effects of heavy pumping.

Approach - Search all available literature on artificial recharge. make field reconnaissance and complete feasibility study. Determine best sites for experimental injection, auger monitoring network around test sites, construct injection sites, inject, monitor, test pump. Prepare methods report and final report.

WA217 - Comparison of Regulated and Unregulated Streamflow for the Yakima River At Union Gap, Washington - Completed FY1982

Problem - The Yakima Indian Tribe contends that non-Indians have reduced the quantity of streamflow available to the Tribe from the Yakima River by construction and operations of reservoirs and diversion canals for irrigation in the river basin upstream of the Reservation. The Tribe also contends that they are entitled by treaty to a quantity of the streamflow which night has been naturally available to support their fisheries, agriculture, and other uses. The U.S. Bureau of Indian Affairs, on behalf of the Yakima Tribe, has requested that the USGS investigate and determine the extent that the natural flow of the Yakima River has been changed by upstream storage and diversion.

Objectives - The objective is to produce a comparison of natural or unregulated flow with regulated flow for the Yakima at Union Gap. The USBR has synthesized unregulated strawflower for the Yakima R. near Parker for 1911-77, using the Corps of Engineers' SSARR (Streamflow Synthesis and Reservoir Regulation) digital-computer model. The accuracy of the data from the SSARR model predictions is not known. Therefore, this study is divided into 2 parts: a feasibility study to determine (1) if the error of estimate can be determined, (2) if statistical analyses can be used to compare natural flows prior to 1903 with regulated flows from 1904-77, (3) if another model would be better suited for the study, (4) if the model could be improved by incorporating data not presently used, and (5) if differences can be determined between natural flows and derived regulated flows for the 1886-1903 (natural flow) period. If the last 3 points are negative or indeterminate, the project will be concluded with an open-file report. If the USGS believes that some improvements can be made in the comparison, Phase II will be initiated. This phase will aim at greater accuracy in the comparisons.

Approach - Phase I of this investigation, conducted from 10/78 to 9/79 has been completed. In that phase, the SSARR model was applied to streamflow, reservoir-regulation, and diversion data in the Yakima basin. Results in sensitivity and statistical analyses indicate that the effects of reservoir storage and canal diversions on the flow of the river are substantial and that unregulated flows computed by the model contain large and undefined inaccuracies, but the reliability of these figures can be improved. In Phase II, the model will be reconfigured to take advantage of the numerous available gaging-station records not now in the model. Using this method the historic pre-1979 mean values of unregulated discharges will be determined.

WA173 - Water-Quality Investigation of the Yakima Indian Reservation - Completed FY1975

Problem - Few data are available on the quality of water on the Yakima Indian Reservation. Extensive surface-water irrigation and cattle and sheep grazing coupled with large logging operations have caused changes in water quality in both the surface and ground water. In some places there is water logging and alkali soils, and drains return water of increased temperature, turbidity and mineral content. Because of the water-quality differences and deficiencies in accurate data, the Yakima Indian Tribal Council needs current, factual information to guide them in the wise and efficient development and management of their water resources.

Objectives - To appraise the water-quality of surface and ground water on the Yakima Indian Reservation.

Approach - A surface-water-quality network will be established throughout the reservation. The sampling sites were selected to reflect the varied land uses. The analyses array will differ between sites because each site is affected by different conditions. Also, the diurnal do cycle will be investigated at 18 sites, and several sites downstream from logging operations will be sampled for suspended sediment. In the ground-water phase of the investigation over 500 wells will be sampled to better define the quality of the ground water. The sampling arrays on some wells will differ also depending on local conditions. All will have spec. cond., no(3), and fecal coliform determined and some will be analyzed for the "standard complete" array plus FE and MN.

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