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<br />Chapter IV - Formulation of Alternatives <br /> <br />There are three basic structural alternatives (with several variations each) and one <br />nonstructural alternative to providing the required additional spillway capacity at Left Hand Valley <br />Reservoir. The first structural alternative is to widen the existing spillway sufficiently to pass the <br />design flood. The second structural alternative is to construct an additional spillway which in <br />concert with the existing spillway would provide a total capacity sufficient to pass the design flood. <br />The third structural alternative is to lower the top of the north dam and make it overtoppable. The <br />nonstructural alternative is essentially a "do nothing" alternative leaving the existing spillway in <br />place and not providing any additional spillway capacity. Each plan is described in detail in the <br />following sections. <br /> <br />A. Plan A - No Action <br />A non-structural alternative to providing additional spillway capacity is to do nothing. If <br />ordered improvements to the spillway capacity are not completed the SEO would impose a storage <br />restriction on the reservoir. Because of the magnitude of the design storm the storage restriction <br />could effectively require the complete breach of the dam and loss of the storage reservoir. <br /> <br />B. Plan B - Widening the Existing Spillway <br />The existing spillway is located in a cut through the south abutment of the north dam <br />forming Left Hand Valley Reservoir. It is trapezoidal in shape with a bottom width of <br />approximately 30-40 feet and side slopes of 2: I horizontal to vertical. The south abutment of the <br />north dam, which is also the north abutment of the south dam is a bedrock knob approximately 450 <br />feet across from one dam to the other. The knob has an elevation at the top of 5,376 feet, or 18 feet <br />above the tops of the dams and 25 feet above the spillway crest. Figure IV-I shows the two dams <br />and the knob between them. <br /> <br />13 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />