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Fish Creek Reservoir Expansion EIS ww~~~-m~~~...$W.J,.;~'>i&"":~Y/.-=mn-.%.~~~"$'..m;:;::~mw<<:..~&:;t::::>>:$::;:;~"i,~>>: Water Ouality - As stated previously, the City and Mt. Werner would have to develop additional water supplies under Alternative A. These additional water supplies would not be equal to the Fish Creek supply in terms of water quality. Dependent upon the quality of the supply, extensive treatment might be required. Under Alternative A, the erosional damage to Puppy Dog Lake drainage, and the subsequent downstream sedimentation, would continue unless corrective action is taken by the Forest Service. Cumulative water quality impacts associated with increased recreational use of Fish Creek Reservoir are discussed in Section 4.3.3 4.3.2.2 Alternetive B . Propossd RUlrvoir Explnsion Physical Characteristics - Alternative B is a 2,280 AF expansion of the present Fish Creek Reservoir. The total capacity of the reservoir under Alternative B would be 4,122 AF covering 140 acres. This represents an increase in surface area of approximately 50 acres. The main dam length would be 830 feet (an increase of 180 feet), and the height would be 75 feet (an increase of 20 feet). The saddle dam would be increased in length to 1,060 feet (an increase of 660 feet), and the height would be 40 feet (an increase of 24 feet). Water supply from the Upper Middle Fork of Fish Creek and Granite Creek would be sufficient to fill the proposed reservoir expansion during average years. However, during a 25-year low-flow period, the 3,570 AF available as inflow would fall 550 AF (or approximately 13 percent) short of filling the 4,122 AF reservoir, assuming that the reservoir was totally empty prior to spring runoff. Construction Plan - Construction under Alternative B is anticipated to occur over two construction seasons. During the first construction season activities would include mobilization, borrow area drainage, excavation of borrow materials, removal of the saddle dam, partial construction of the main dam raise, modifications to the existing outlet works, construction of the high level outlet works, and stream diversion for the upper tributaries (WCC, 1992a). The saddle dam would be breached after the spring runoff flows occur in May and early June, and after the reservoir is drawn down to the base of the existing saddle dam. When the saddle dam is breached, stream flow from the Upper Middle Fork of Fish Creek and Granite Creek would be diverted through the breached dam into the Puppy Dog Lake drainage. Average monthly flows that occur in the summer months after spring runoff O"uly through September) in the Upper Middle Fork of Fish Creek over the period of record October, 1984 to September, 1991 range from 0.35 cis during September to 2.34 cis during July. Average monthly flows during July through September in Granite Creek over the same period of record range from 0.92 cis in September to 6.24 cis during July. Flows of this magnitude would not result in additional erosional damage to the Puppy Dog Lake drainage. The Applicant would finance a Forest Service position to oversee the implementation of this alternative and monitor the project during construction. During the second construction season, the existing outlet and the high level outlet works would be operational so that the diversion channel would be removed and flow would be directed through the main stem of the Middle Fork of Fish Creek. Work would then be completed on the saddle dam. Erosion and sedimentation control measures, utilizing best management practices, would be required throughout the construction period by both the Forest Service and the WQCD. Additionally, stream monitoring would be required. ~r.~::?:";.:~w::..~"SSS:<z : 7~::>>;~~":;~~~~:m:w..ffi'~;.':;.>>':<<:::>>:$~:;,:s:i:':':Sm:::w~h.~':.'::t.~':3;W:~;::~~,:$i~':;'::&:;;.'>>~~~~~~...;~~ Page 4-8 September 1993