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While this alternative has no immediate capital expenditures, the risk and potential costs can be very <br />great. A problem with the outlet or a slope failure in the dam embanlrnlent during the height of the <br />irrigation season would result in the loss of the reservoir for the at least two irrigation seasons. Thus <br />the cost of not providing for the dam repair can potentially very high even without failure of the dam. <br />A problem developing in the outlet during the irrigation season could result in restrictions that could <br />either require the reservoir be emptied or alternatively only allow limited discharges during the <br />irrigation season. <br />2. Construction Alternative 1- Repair <br />This alternative considered repairing the outlet conduit by lining the existing steel and concrete outlet <br />pipe using Insitu Form technology to insert a chemically stabilized liner in outlet. The Insitu Form <br />liner will add to the structural integrity and will seal the outlet from infiltration. <br />The concrete inlet and outlet structures will be patched and repaired as needed to maintain their <br />integrity. The control gate, stem, and operator will be checked for any problems and repaired to <br />reduce the potential for future problems or failure of the gate and control system. <br />The dam crest will be graded at a 1.0% slope toward the reservoir and 4 inches of roadbase placed <br />on the dam crest for erosion protection. <br />3. Construction Alternative 2- Complete Rehabilitation <br />This alternative considers a complete rehabilitation of the dam including breaching and removing <br />and replacing the outlet works, applying riprap bedding on the upstream face of the dam from the <br />dam crest to the upstream toe, and flattening the downstream slope to increase the dam stability and <br />to remove the storage restriction. A summary of the components considered is as follows. <br />a. Breach the dam at a 1.5 to 1 slope and remove the existing outlet works. <br />b. Replace the existing outlet conduit with one 48 inch diameter ductile iron pipe <br />encased in a minimum of 12 inches of concrete. <br />c. Gate operators will be hydraulicly operated and will be installed above the normal <br />water level in a gate control house. The gate stem will extend from the gate to the <br />operator and will be supported on an 18 inch by 24 inch deep concrete grade beam. <br />The reservoir gage rod will be supported on the grade beam. <br />d. The inlet structure will be concrete and will support the trash rack and one 48 inch <br />by 48 inch control gate. <br />e. The outlet Structure will be a USBR Type 7 baffled energy dissipater. <br />f. The existing concrete slab on the upstream face of the dam will be removed and <br />replaced with 8 inches of bedding and 24 inches of riprap (dso =12 inches) placed on <br />the bedding. <br />g. The downstream face of the dam will be flattened to 2,5 horizontal to 1 vertical and <br />a stability berm added to the downstream face.. <br />Horsecreek & Prospect Reservoirs - 06.014 <br />Henrylyn Irrigarion District Page 10 <br />