C150122 Feasibility Study - Laserfiche WebLink

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I I I I I I I I I I I I I I I I I I I alternative including evaluation of engineering issues is summarized in the following section. Site Description General A site map for the proposed reservoir is shown in Figure 3. The site slopes generally to the east and exhibits topographic relief all around. The immediate area within the reservoir is generally flat to gently rolling pastureland. The maximum relief on the site is 40 feet, with elevations ranging from 5160 feet to 5200 feet along both abutments. The site is drained by an unnamed tributary of Dry Creek which flows intermittently. A low area exists within the footprint of the proposed reservoir that ponds water during periods of heavy moisture. Present landforms on the site are the result of erosion and consist of remnants of alluvial deposits of clay and sand that cover residual sandstone and underlying shale. The proposed dam would be located across the unnamed tributary to Dry Creek and would be constructed in a NE-SW orientation with a maximum elevation of 5200 feet. The elevation of the valley floor is 5160 feet and the elevations of the north and south abutments are approximately 5205 feet and 5210 feet respectively. A typical cross-section and engineering details for the dam are shown on Figure 4. The reservoir would be bounded to the west by a ridge . which reaches an elevation in excess of 5360 feet. Geotechnical Evaluation Dam Site The soils on the site consist of interbedded alluvial sand, clay, sandstone, and claystone or weathered shale bedrock. These materials were distributed by various depositional and erosion processes and are erratic in distribution and thickness, varying from a few feet to over ten feet. The soil survey of Larimer County by the Soil Conservation Service indicates the basin of the reservoir is dominated by Heldt Clay Loam. Renohill Clay Loam appears on the north and south abutments with Longmont Clay also in the south abutment area. Kim Loam emerges on the western edge of the basin. Borings in the proposed dam area show overburden clay to depths ranging from approximately four to fourteen feet. Sand and sandstone extending to depths ranging from approximately nine to eighteen feet was encountered below the clay. The sand and sandstone layers could easily be cut off with a standard cutoff trench in the dam. Shale bedrock was encountered in each boring at depths ranging from nine to twenty-two feet. This material would provide an excellent foundation for the proposed dam. Boring information at the proposed dam location is shown on the dam centerline profile in Figure 5. Dry Creek Reservoir Feasibility Study 8