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<br />I 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 /> <br />The primary problem at the Mountain Home Reservoir Is the Inadequate spillway <br />In conjunction with Inadequate freeboard on the dam for the spillway size. <br />Following Is a general list of deficiencies. <br /> <br />1. Inadequate spillway size In conjunction with the available freeboard <br />to allow filling to the maximum decreed gage height. <br />2. Poor condition of the spillway control section. <br />3. Seepage at the toe of the main dam. <br />4. Potential for sliding of the basalt blocks to the south of the <br />spillway If flood flows saturate the underlying silts and clays. <br /> <br />Due to the deflclencles of the emergency spillway, the State Engineer has placed <br />a restriction on the dam requiring storage be limited to Gage Height 87.5 feet <br />rather than the maximum storage of Gage Height 100 feet. <br /> <br />Following Is a summary of the "Alternatives" considered and the estimated <br />construction costs of each alternative. <br /> <br />MOUNTAIN HOME RESERVOIR - SPILLWAY ALTERNATIVES <br />CONSTRUCTION COST ESTIMATE <br /> <br />Alternative <br /> <br />Description <br /> <br />Estimated Cost <br /> <br />1. <br /> <br />Construct a 200 foot wide emergency spillway at <br />the left abutment with a 150 foot Roller Compacted <br />Concrete control section at Elevation 8202 feet. <br />Raise the main dam to Elevation 8216 feet and <br />construct a saddle dam In the existing spillway channel <br />to divert the spillway flows. <br /> <br />$681,350.00 <br /> <br />IA. <br /> <br />Same as No. 1 above except eliminate saddle dam In the <br />spillway channel and allow flows to enter Trlnchera <br />Creek 1000 feet downstream of dam. Provide rlprap <br />protection at the Hlghllne Canal. <br /> <br />$681,850.00 <br /> <br />2. Construct 400 foot wide Roller Compacted Concrete <br />spillway over the main dam crest. Raise dam to <br />Elevation 8212 feet. <br /> <br />$897,250.00 <br /> <br />2A. Construct 200 foot wide Roller Compacted Concrete <br />spillway over the main dam crest. Raise the main <br />dam crest to Elevation 8216 feet. <br /> <br />$749,150.00 <br /> <br />3. Construct a 200 foot wide spillway In the existing <br />spillway channel. Raise the main dam to elevation 8216 <br />feet and construct a saddle dam In the spillway channel <br />to divert flows. <br /> <br />$399,950.00 <br /> <br />3A. Same as No. 3 above except eliminate saddle dam In <br />spillway channel and allow flows to enter Trlnchera <br />Creek 1000 feet downstream of dam. Provide rlprap <br />protection at the IIIghllne Canal. <br /> <br />$366,150.00 <br /> <br />II. <br />