Scientific Investigations Report 2006–5116
U.S. GEOLOGICAL SURVEY
Scientific Investigations Report 2006–5116
The Yakima River Basin aquifer system located in south-central Washington encompasses about 6,200 square miles. The six structural sedimentary basins delineated, from north to south are: Roslyn, Kittitas, Selah, Yakima, Toppenish, and Benton. Information was collected, interpreted, and combined from simplified surficial geology maps, hydrogeologic contour maps from previous studies, and from about 4,700 well logs. This information was used to delineate the thicknesses of the hydrogeologic units in the basin-fill deposits in each of the six basins.
All data types were entered into a Geographical Information System software program in order to construct a gridded, 3D digital hydrogeologic framework for each basin using a 10-m cell size. Data types for each basin included a digital elevation model, simplified surficial geology, previously constructed hydrogeologic unit contour maps (where available), mapped extents of hydrogeologic units, well-log point values of the tops and thicknesses of a hydrogeologic unit, and interpretations from sections that were constructed for each basin. The original data interpretations were honored as much as possible in developing the 3D framework. The calculated top and thickness cell values and/or mapped contours for the hydrogeologic units were compared to the original well and/or mapped contour data and adjusted to most accurately reflect the original interpretations.
The hydrogeologic framework defines the physical, lithologic, and hydrogeologic characteristics of the hydrogeologic units that comprise the ground-water system in the individual basins. The hydrogeologic units vary by basin and the thickness, extent, and total basin thicknesses were described.
The Roslyn Basin basin-fill deposits, which total about 700 ft thick, were divided and mapped into three hydrogeologic units and a total basin thickness. The hydrogeologic units consist of an upper coarse-grained unit, a clay unit, and a productive gravel unit.
The basin-fill deposits in the Kittitas, Selah, and Yakima Basins, which total about 2,000, 1,900, and 1,800 ft thick, respectively, were divided and mapped into three hydrogeologic units and total basin thickness. The hydrogeologic units consist of alluvial, unconsolidated, and consolidated deposits.
The Toppenish Basin basin-fill deposits, which total about 1,200 ft thick, were divided and mapped into five hydrogeologic units based on previous work compiled by Campbell (unpub. maps produced for Yakama Nation, 2001). The five hydrogeologic units consist of fine-grained and coarse-grained unconsolidated deposits, consolidated deposits of the upper Ellensburg Formation, a blue clay deposit of the top of the Rattlesnake Ridge unit, and a coarse-grained deposit of the basal Rattlesnake Ridge unit.
The Benton Basin basin-fill deposits, which total about 870 ft thick, were divided and mapped into two hydrogeologic units and a total basin thickness. The hydrogeologic units consist of unconsolidated and consolidated deposits. The unconsolidated deposits in the northeastern area of the basin were further divided into six subunits based on information compiled from previous investigations.
For more information about USGS activities in Washington, visit the USGS Washington Water Science Center home page.
U.S.
Department of the Interior | U.S. Geological
Survey
Persistent URL: https://pubs.water.usgs.gov/sir20065116
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