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3. Dam Layouts I I I I II I I I I The preliminary design of the dams will require geologic and geotechnical investigations. Topographic and geologic maps should be prepared of the dam alignments and the reservoir area. Particular attention should be paid to the landslide on the south side of the southern damsite. The dam alignments should be drilled for core and the formation tested for permeability. Material suitable for construction of earthen or rollercrete dams are probably available in the area but mapping, sampling and testing will be required to define quantities and qualities. Three dam and reservoir layouts were completed for the site near the USGS gaging station. The largest, an estimate of the maximum reasonable size, was laid out first (See Figure IV-S). The other two layouts were then completed so as to provide 2/3 and 1/3 of the storage available for the largest. The resulting three storage volu. mes ranged from 16,200 acre-feet to 5,400 acre-feet wi th an inter- mediate volume of 10,800 acre-feet. Quantities and costs were then calculated based on these three layouts for both earth embankment and roller compacted concrete (RCC) type dams. 4. Flood Hydrology and Spillway Layouts I I I I I I I I Spillway design floods were developed, and reservoir routing was completed according to the methods described in Section IV, A, 4, Hydrologic and Hydraulic Criteria. The peak inflow of the design flood is 14,200 cis. Routing this flood through each of the three reservoir sizes results in a maximum spillway width of 130 feet for the two smaller reservoirs and a spillway width of 90 feet for the large reservoir. Spillway sizes are the same for both RCC and earth embankment dams. S. Outlet Works Design The criteria used for the outlet works design are presented in Section IV, A, 4. The two smaller dams utilize a 36 inch concrete outlet pipe. The largest dam requires a 48 inch concrete outlet pipe. Flow control for all three layouts is provided by hydraulically operated sluice gates at the upstream inlet of the outlet pipe. Controls for the gates will be located on the dam crest in all cases. A standard USBR impact type stilling basin is included in the quantity and cost estimates for each dam. IV-20 I I