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<br />aGGG <br /> <br />reservoir. For the purposes of this study, artificial recharge shall <br />be defined as any means of introducing surface water into the ground- <br />water system so as to augment the naturally available quantities of <br />ground water. <br /> <br />Recharge Method <br /> <br />For the purposes of this study, the method selected to induce <br />infiltration into the ground-water reservoir consists of a system of <br />diversion structures, canals, and shallow infiltration ponds. In <br />order to maintain high infiltration rates, scarification, sediment <br />removal, and alternate periods of wetting and drying would be <br />be necessary. <br /> <br />Geology <br /> <br />In the study area, which lies generally east and north of Fort Morgan, <br />Colorado, the South Platte River Valley is composed of sedimentary <br />rocks and deposits ranging in age from Late Cretaceous to Recent. The <br />geology of this area has been described by Bjorklund and Brown (1957). <br />Stratigraphically, from oldest to youngest, the formations and deposits <br />of interest are the Pierre shale, Chadron formation, Brule formation, <br />Ogallala formation, alluvium, and the surficial deposits of dune sands <br />and loess. <br /> <br />The youngest deposits of the area, from Pleistocene to Recent, consist <br />of alluvium deposited in the South Platte River Valley and the mantling <br />,dune sand and loess deposits. The alluvium consists of heterogeneous <br />mixtures of clay, silt, sand, and gravel deposits. Extensive lenses <br />of clay occur within the river valley, but are more characteristic of <br />the tributary valleys. Alluvial terrace deposits are characteristic <br />and up to six distinct terrace levels have been described. <br /> <br />In general, dune sands overlie only the outer edges of the alluvial <br />deposits and are present mostly south of the river. These deposits <br />consist primarily of fine to medium sand with some silt, clay, and <br />coarse sand. Loess, a deposit of silt and very fine sand, mantles <br />most of the alluvial deposits in the study area, <br /> <br />In the South Platte River Valley and tributary stream valleys, the <br />principal aquifer is the alluvium. The Cretaceous and Tertiary deposits <br />contain relatively small amounts of recoverable ground water and are <br />not considered as aquifers. The lithologic characteristics of these <br /> <br />38 <br />