Surface-Water-Quality Assessment of the Yakima River Basin in Washington : overview of major findings, 1987-91

Water-Resources Investigations Report 98-4113

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Surface-water-quality conditions were assessed in the Yakima River Basin, which drains 6,155 square miles of mostly forested, range, and agricultural land in Washington. The Yakima River Basin is one of the most intensively farmed and irrigated areas in the United States, and is often referred to as the ?Nation?s Fruitbowl.? Natural and anthropogenic sources of contaminants and flow regulation control water-quality conditions throughout the basin. This report summarizes the spatial and temporal distribution, sources, and implications of the dissolved oxygen, water temperature, pH, suspended sediment, nutrient, organic compound (pesticide), trace element, fecal indicator bacteria, radionuclide, and aquatic ecology data collected during the 1987?91 water years. The Yakima River descends from a water surface altitude of 2,449 feet at the foot of Keechelus Dam to 340 feet at its mouth downstream from Horn Rapids Dam near Richland. The basin can be divided into three distinct river reaches on the basis of its physical characteristics. The upper reach, which drains the Kittitas Valley, has a high gradient, with an average streambed slope of 14 feet per mile (ft/mi) over the 74 miles from the foot of Keechelus Dam (river mile [RM] 214.5) to just upstream from Umtanum. The middle reach, which drains the Mid Valley, extends a distance of 33 miles from Umtanum (RM 140.4) to just upstream from Union Gap and also has a high gradient, with an average streambed slope of 11 ft/mi. The lower reach of the Yakima River drains the Lower Valley and has an average streambed slope of 7 ft/mi over the 107 miles from Union Gap (RM 107.2) to the mouth of the Yakima River. These reaches exhibited differences in water-quality conditions related to the differences in geologic sources of contaminants and land use. Compared with the rest of the basin, the Kittitas Valley and headwaters of the Naches River Subbasin had relatively low concentrations and loads of suspended sediment, nutrients, organic compounds, and fecal indicator bacteria. There were very few failures to meet the Washington State dissolved oxygen standard or exceedances of the water temperature and pH standards in this reach. In general, these areas are considered to be areas of lessdegraded water quality in the basin. The pre- Tertiary metamorphic and intrusive rocks of the Cle Elum and Teanaway River Subbasins, however, were found to be significant geologic sources of antimony, arsenic, chromium, copper, mercury, nickel, selenium, and zinc. As a result, the arsenic, chromium, and nickel concentrations measured in the streambed sediment of the Kittitas Valley were 13 to 74 times higher than those measured in the Lower Valley. The Mid and Lower Valleys had similar water-quality conditions, governed by the intensive agricultural and irrigation activities, highly erosive landscapes, and flow regulation. Most of the failures to meet the Washington State standards for dissolved oxygen and exceedances of the standards for water temperature and pH occurred in the Mid and Lower Valleys. Agricultural drains in the Mid and Lower Valleys were found to be significant sources of nutrients, suspended sediment, pesticides, and fecal indicator bacteria. Downstream from the irrigation diversions near Union Gap, summertime streamflow in the Yakima River was drastically reduced to only a few hundred cubic feet per second. In the lower Yakima River, agricultural return flow typically accounts for as much as 80 percent of the main stem summertime flow near the downstream terminus of the basin. Therefore, the water-quality characteristics of the lower Yakima River resemble those of the agricultural drains. The highest fecal bacteria concentrations (35,000 colonies of Escherichia coli per 100 milliliters of water) were measured in the Granger/Sunnyside area, the location of most of the livestock in the basin. The east side area of the Lower Valley (area east of the Yakima River) was the predominant source area f

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Surface-Water-Quality Assessment of the Yakima River Basin in Washington : overview of major findings, 1987-91
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Water-Resources Investigations Report
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U.S. Geological Survey ; Branch of Information Services [distributor],
xii, 119 p. :ill., col. maps ;28 cm.