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<br />Fish Creek Reservoir Expansion EIS <br />~~::::::0>>:~;W-.:>>:""~:$~;t~,~~$;.;<<~~"".;3,*m0.:mr->>~~~::::;?-,~'i;..;.~,~~:;:>>:;;*:X:~~$m:.::mis;*~~~~~. <br /> <br />A high level outlet has also been proposed under Altern~tive B to allow a greater volume of water <br />to be discharged from the reservoir. This outlet would be founded on bedrock near the left <br />abutment and water would be discharged through a baffled outlet near the base of the dam. This <br />outlet struaure could be utilized to maximize the release of water from storage during potentially <br />dangerous, high-flow situations. Also under Alternative B, the saddle dam would be removed and <br />re-construaed to allow for a better foundation and to improve seepage control, thus improving the <br />safety and integrity of the saddle dam. In addition, a new spillway would be construaed in bedrock <br />on the right abutment of the new saddle dam, which would channel flows into the Puppy Dog Lake <br />drainage during peak runoff periods. This is discussed further in Sea ion 4.3, Water Resources. <br /> <br />During construaion, short-term impaas would occur and would generally be associated with the <br />draining of the reservoir. Aaivities such as dewatering for foundation excavations, earthwork <br />construaion, and struaure foundations, would result in direa impaas to the shallow groundwater <br />conditions. Seepage conditions and flood hazard conditions, however, would be eliminated during <br />the short-term construaion stage because Fish Creek Reservoir would be drained and would have <br />no storage during this period. <br /> <br />Flood hazard potential downstream of the proposed dam enlargement due to catastrophic dam failure <br />has been analyzed by Woodward-Clyde (WCC, 1992c) and is presented in Appendix F. Peak flow <br />discharges immediately downstream of Fish Creek Reservoir would be 136,200 cis, an increase of <br />73,000 cis over the No Aaion Alternative. As a result of this increase, the downstream <br />consequences associated with a dam failure would be increased. The peak depth on Fish Creek at <br />the water filtration plant would be 23 feet at 0.9 hours after dam failure. A flood wave of 28 feet <br />would occur on Fish Creek at Highway 40 at 1.0 hour after dam failure. The peak depth on the <br />Yampa River at Riverside Drive would be 13 feet at 1.4 hours after dam failure. Table 4-1, Results <br />of Dambreak Analysis for Fish Creek Reservoir, presents the peak flow, peak depth and elapsed time <br />from dambreak for each of the three alternatives. <br /> <br />However, due to improved construaion techniques and materials, the dam would have improved <br />static and dynamic stability, and therefore, would be a safer struaure. Alternative B includes the <br />installation of an early warning monitoring system that would use survey monuments, piezometers, <br />and weirs installed in the main and saddle dams to monitor and check the design criteria. This <br />instrumentation would be incorporated into the early warning and automated data acquisition system <br />(WCC, 1992b). This system would provide the information to alert City officials of direa impaas <br />to the dam embankments so that conditions, which might otherwise go undeteaed, could be <br />addressed before a catastrophic failure occurred. By responding early to dam conditions, correaive <br />dam maintenance measures could be taken, and/or the Emergency Preparedness Plan (Appendix E) <br />could be implemented. <br /> <br />Due to the relatively high density of the embankment materials and shallow foundation soils, the <br />deformation due to static and dynamic (earthquake) loads is expeaed to be small and within <br />acceptable limits. <br /> <br />4.2.2.3 Alternetive C . Smeller R8Iervair Expenlian <br /> <br />In the early 1980's the City of Steamboat Springs evaluated three alternative increases in the storage <br />capacity of the existing Fish Creek Reservoir, which included a 908 AF increase, a 2,000 AF increase, <br />and a 3,050 AF increase (D&D, 1983). The 908 AF increase is referred to as Alternative C, Smaller <br />Reservoir Expansion. According to a review of the conceptual design elements of this alternative <br />(D&D,1983), Alternative C would have similar direa and indirea impaas as those discussed under <br /> <br />~$:;:~"W~~~~~~'$'~~~~~~lW-~~?;:::>>::;.~.:::m~;:w.~':::1i=;:&>>:~~ <br /> <br />Page 4-4 <br /> <br />September 1993 <br />