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WONT eTab Ri` re but � P aft Rtarer <br />-� <br />Slough <br />r <br />;. R1 t' R3 R7 R8 <br />r R6 5 <br />' R5 , <br />g �x . •fro , {S k S h,3, cif iR ,y W_ €Ye ° s .'Y ° 1� 8� ° `- <br />Figure 1 - Location of existing pumping wells, slough channels, and South Platte <br />River at the Tamarack Managed Recharge Project in Eastern Colorado. R1, R2, <br />R3, R5, R6, R7, and R8 are pumping wells. <br />The complex and dynamic nature of the Tamarack research site was noticed as <br />early as the mid- 1980s. The United States Geological Survey and the Division of <br />Wildlife entered into a cooperative study to investigate the hydrologic properties of the <br />site (Burns, 1985). Burns (1985) illustrates many of the important characteristics of the <br />site, including the breakdown of the system into component areas: South Platte River, <br />flood plain (river bottom), valley meadow, and rising sand dunes. The alluvial aquifer <br />consists of an underlying layer of relatively impermeable shale overlain by alluvial <br />deposits of relatively high permeability. The alluvial deposits are characterized as <br />braided stream deposits with interbedded deposits of clay, silt, sand, and gravel. Depths <br />to impermeable shale range from approximately 50 -200 ft. Burns (1985) documents the <br />alluvial aquifer characteristic of the area as high conducting sand, with an estimated <br />aquifer hydraulic conductivity, K, of 190 ft -d -1. Several recent pump test investigations <br />at the site have determined that more appropriate ranges of the aquifer hydraulic <br />conductivity may be between 200 to 700 ft -d- . <br />The South Platte River can be characterized as a shallow river of considerable <br />horizontal width variation. Several secondary channels, or backwater sloughs, are <br />present within the floodplain. These sloughs are expected to play influential roles in both <br />the depletion of the river by the groundwater wells and the return flows toward the river. <br />While the South Platte River is generally wide in horizontal dimension, most of the <br />sloughs have less horizontal width. The slough channel is estimated to have an average <br />width, W, of approximately 5 -7 m. <br />2 <br />