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<br />Fish Creek Reservoir Expansion EIS <br />~:~~X;:?"""'"("'~~:<<y:.,..;..:","'?/...:W.w.:*"....@"~~"::i~;:;;,~~~m.%~;<<:AAW..>>~~ZW~:;:;-'::m:"'~,~~~~ <br /> <br />4.2.4 Mitigation and Enhancements Summary <br /> <br />Essentially, the mitigation necessary to ensure dam safety and reduce potential flood hazards would <br />be incorporated into the final designs of Alternatives B or C. <br /> <br />4.2.5 Unavoidable Adverse Impacts <br /> <br />Unavoidable adverse dam safety/flood hazard impactS associated with the implementation of <br />Alternative A include the continued operation of the dam in the absence of early warning and <br />remote operational control systems. The downstream consequences of a dam failure would remain <br />the same. <br /> <br />If Alternative B or C is implemented, the current reservoir would be expanded. This expansion <br />would increase the storage capacity of the reservoir and would, therefore, increase the downstream <br />consequences associated with a dam failure. The downstream consequences of a dam failure would <br />be greater under Alternative B than under Alternative C since the proposed reservoir storage <br />capacity is greater under Alternative B. This unavoidable adverse impact would be balanced to a <br />cenain degree, however, by the improved dam design and construction techniques, and by the <br />installation of an early warning system which is proposed under both Alternatives B and C. <br /> <br />4.3 WATER RESOURCES <br /> <br />4.3.1 Introduction <br /> <br />Alternatives A, B and C are described below in terms of the physical characteristics of the dam and <br />reservoir, the availability of water to fill the reservoir annually, construction sequencing, operational <br />differences between alternatives, problems associated with erosion and sedimentation, and water <br />rights. Additionally, impacts associated with water quality, water demand, and reservoir storage <br />requirements are discussed. <br /> <br />4.3.2 Direct and Indirect Impacts <br /> <br />4.3.2.1 Allernetive A . No Action <br /> <br />Alternative A, the No Action Alternative, assumes that the City would continue to operate Fish <br />Creek Reservoir as it is presently operated. Section 3.3, Water Resources describes the physical <br />characteristics of the reservoir, and its operation. <br /> <br />Physical Characteristics - Under the No Action Alternative, the physical characteristics of the <br />reservoir would remain the same. To summarize, the existing Fish Creek Reservoir has a storage <br />capacity of 1,842 AF and a surface area of approximately 90 acres. The main dam is 650 feet in <br />length, and has an embankment crest elevation of 9,874 (55 feet high). The saddle dam is 400 feet <br />in length, and has an embankment crest of 9,871.5 feet (16 feet high). Water supply from the Upper <br />Middle Fork of Fish Creek and Granite Creek is sufficient to fill the reservoir at its present capacity <br />(1,842 AF) in both an average flow year t! ,723 to 8,560 AF) and during a 25-year low flow year <br />(3,570 AF). See Section 3.3, for a description of how available water supply flows were estimated. <br /> <br />Construction Plan - There would be no construction activities under Alternative A. <br /> <br />$..~~~~~.m:t::~~~~~~'-'?i;:;&"",,";-:~~~:;:.;':3~:<.::w;:;:;:.:':3~:Y,:.;':::;:';::<<0i~W>>: <br /> <br />Pose 4.6 <br /> <br />September 1993 <br />