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iJ028;J3 CHAPTER 4. ENVIRONMENTAL CONSEQUENCES ?rZ>>23'-::?,:$'~~:0";:,-:;:::~>>;:'W"~{;&;:.:.m,;:;*,W<<<W.Js:'/.'0.,<<~:m~;;:;.%.'<<".::;:;~3'3.-.'<:;:;:;:"'?':$;:m:>::;':;:;:~~~~~1"";W::t;..'>>."<<?l::~:':;;:X:~,%:;:;:l$m:z:-:(~};:;',*,'%.~%";::$;:;.,<:r<<<:;:;:~~':3i<:: Alternative B. Indirect downstream impacts, dlOUgh, would be less than those associated with Alternative B, due to a reduction in the storage capaCity of the reservoir. Peak flow discharges would increase to 80,400 cis (see Table 4-1). This represents a 17,200 cis increase over the No Action Alternative and a 55,800 cis decrease over the proposed reservoir expansion. A peak depth on Fish Creek at the water filtration plant would be 19 feet at 0.9 hours after dam failure. A flood wave of 23 feet would occur on Fish Creek at Highway 40 at 1.0 hour after dam failure. The peak depth on the Yampa River at Riverside Drive would be 11 feet at 1.5 hours after dam failure. 4.2.2.4 Borrow Sites, AcclISe Roads, and Power Supply As part of the construction of either Alternative B or C, one or more borrow sites would be utilized. Three borrow areas (A-l, A-2, and B) have been designed for development under Alternatives B or C. Short-term direct impacts which would occur during construction include lowering the shallow groundwater table, which is estimated to be 3 and 19 feet, through dewatering. Riprap requirementS would be satisfied with rock from Borrow Areas A-lor A-2. Blasting of the bedrock would be required to attain the proper rip rap size. Indirect impacts associated with blasting the riprap source would include the potential generation of flyrock, noise, and vibrations. Since the borrow areas would be submerged during operation, indirect impacts resulting from the operation of borrow sites during construction are considered negligible. Under Alternative B or C, one of the three optional dam access routes would have to be utilized during construction to carry materials to the construction site. The access road would also have to be utilized during dam inspections after construction is completed. A further discussion of road impacts is presented in Section 4.10, Transportation. Under Alternative B or C, one of three optional power sources would be utilized for construction and for the operation of the early warning and remote operational control systems. The underground electrical supply source is the most reliable of the three optional power sources. Power requirements are such that neither the propane nor the solar options could reliably produce sufficient power to operate the outlet valve and the early warning and remote operational control systems. 4.2.3 Cumulative Impacts Cumulative impacts to dam safety and flood hazards associated with Alternative A would occur as a result of future development within the flood inundation area identified in Section 3.2. Increased development downstream of the Fish Creek Reservoir would elevate the likelihood of loss of property and life in the event of dam failure. If Alternative B is combined with potential future development within the flood inundation area (See Section 3.2), cumulative impacts would include an increase in the potential downstream consequences involving loss of property and life. These impacts would be balanced to a certain degree, however, by the proposed increases in dam safety (including improved construction techniques and materials, and the installation of an early warning system). Cumulative impacts associated with Alternative C would be similar to those of Alternative B, although the volume of water which would be released in the event of a dam failure under Alternative C would be reduced. ~>:<:<::.:::::-:;::~~"'<m:.::~~<<=:>>>:*,~,,:<<~'<;'".-}~:-:::=~::::,<mM=":<:=m.~:~m-,>>>>,..::~::..-m;:.:::{::7,.;~:'}.,<:-~:~....~~,?;:S':;....,"m:~"(/~...L-'.lXv.>...'<<?~: Sepl<rnb<r 1993 Page 4.5