C150163 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 cursory map study, no physical features exist that would complicate the construction of a dam. Mineral Resources Northeastern Colorado contains various economical mineral resources including petroleum, natural gas, uranium, gravel and crushed-rock aggregate, and limestone. Gravel and crushed-rock aggregates are currently mined from various localities in Northern Colorado, but only small amounts exist on this site. Currently there are no mineral resources being extracted from this site and it does not appear that the site contains sufficient resources to be mined econom ically. Hydrologic Evaluation Dam Classification Detailed dam classification studies for the proposed reservoirs are beyond the scope of this feasibility study. Based on conservative assumptions, Drury Reservoir can be classified as a Class II, Small dam, Cornish Plains Reservoir can be classified as a Class II, Intermediate dam, and Barnesville Equalizer can be classified as a Class III, Small dam. HvdroloQic ModelinQ Preliminary hydrologic modeling was conducted using HEC-HMS from the U.S. Army Corps of Engineers. A runoff coefficient, Kn, of 0.06 was assumed for the basins based on topographic and land-use conditions. Uniform infiltration rates were determined for the soil conditions in the basins as determined from Soil Conservation Service Maps. Infiltration rates of 0.16 in/hr and 0.22 in/hr were used for the Drury Reservoir and Cornish Reservoir basins respectively. Because the Barnesville Equalizer basin is so small, no infiltration was used in the model. Synthetic unit hydrographs were determined based on the USBR's Flood Hydrology Manual. Spillway discharge was modeled as a trapezoidal weir with 6: 1 side slopes and a weir coefficient of 2.63. Results of the hydrologic studies are summarized below. Complete details and results of the hydrologic modeling are contained in Appendix D. Drury Reservoir The Drury Reservoir Dam can conservatively be classified as a Class II, Small dam. The required design storm for a Class II, Small dam is 50% of the Probable Maximum Precipitation (PMP). The required spillway length for Drury Reservoir based on the design storm would make the project unfeasible. However, due to the large size of the drainage basin, small reservoir size, and remote location, an incremental damage analysis should allow the reservoir to be designed for the New Cache Feasibility Study 21