C153629 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 I determined that the project would consist of a RCC dam at the down- stream site (Site B) forming a reservoir with a total storage capacity of 50,900 acre-feet. The reservoir will have a surface area of 1070 acres at the maximum normal pool at El. 8681 (full supply level) and will extend upstream about 3 miles from the dam. The total storage capacity includes a 500 acre-feet reservation for silt accumulation as determined by sedimentation studies discussed in Section 3.5. Exhibits 3-2, 3-3 and 3-4 show reservoir topography. The reservoir area is underlain by relatively impermeable materials and no significant leakage is expected. The reservoir will inundate a short section of Highway 134, a Forest Service access road, a 138-kV power transmission line, and a historic stagecoach stop building. Relocation of these features is discussed in Section 3-7. 3.3 GEOTECHNICAL INVESTIGATIONS A geologic report and surficial geologic mapping was prepared for the Rock Creek Site A and reservoir by Western Engineers, Inc. in conjunc- tion with consulting geologist, R.J. Irish, however, no subsurface investigations were made. Preliminary visual inspections and evalua- tions indicated a more favorable site downstream labeled Site B, in a location not covered by the geologic mapping. The geotechnical inves- tigations that were carried out and are described in this section consisted of surficial geologic mapping in the vicinity of Site B, seismic refraction surveys at Site A and Site B and three rotary bore- holes drilled at Site B. In addition test pits were excavated in the potential borrow areas for ReC aggregate and samples were obtained from these pits for physical characterization in the laboratory and prepara- tion of trial RCC test mixes. 3 - 7 68l9W/502OW