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NEED FOR THE PROJECT <br />The two reservoir owned by the HID have been inspected by Smith Geotechnical and are in need <br />of repair. Following is a summary of the deficient items that need repair. <br />Horsecreek Reservoir Dam: <br />The dam impounding Horsecreek Reservoir is a homogenous earth f 11 dam approximately 70 feet <br />in height, 4800 feet in length, with three 48-inch diameter steel outlet conduits. The outlet is <br />controlled by three hydraulicly operated slide gates located at the upstream end of the conduit. The <br />upstream face is at a slope of approximately 2.7H to 1 V ana is partially covered with riprap for slope <br />erosion protection. The downstream slope is at approximately a 2H to 1 V, is grass covered, and has <br />a 35 to 40 foot bench approximately %2 the way down the slope which has a downstream face slope <br />of approximately 3.4H to 1 V. <br />The dam was constructed in 1911 and failed due to piping in 1914. The maximum discharge of <br />reservoir water during the failure was 137,140 cfs and over 20,000 cubic yards of the earth <br />embankment was eroded. The failure was due to uncontrolled seepage along the line of saturation <br />of the downstream face. A report by Victor Miguel Ponce, San Diego State University,1982, states, <br />" The material underlying the dam consists of a sandy loam containing a considerable amount of <br />clay. Before the embankment was started, the entire area was ploughed, and the sod from the <br />upstream third was removed and replaced in the downstream toe. The material was deposited in <br />layers as thick as 4 ft, and spread by Fresno scrapers. The bottom 2 ft of the dam was placed moist. <br />The remainder of the material was very dry, and no effort was made to moisten it to aid compaction." <br />The dam also had a failure in the downstream slope near station 30 to station 40 in 1971. This was <br />repaired by installing a berm along the downstream face and a toe drain. However, the toe drain <br />location allows tne phreatic surface to remain high in this area. <br />Due to the problems of the past, the dam embankment has been modified several times. The dam <br />emba.nkments still experience some problems due to the original construction methods and the lack <br />of adequate seepage control. In the area of dam station 34 the dam has a bulge and piezometers in <br />the area indicate high phreatic water levels in the embankment at the downstream face. Water has <br />been recorded in piezometers P-10, P-11, P-12, and P-13 near the ground surface. Due to the <br />presence of high internal water levels, Smith Geotechnical has added additional piezometers and <br />plan to monitor the dam more closely during the 2007 irrigation season. Additional seepage control <br />measures are planned to lower the intemal water levels between station 30 and 40. <br />The outlet conduit is a cast-in-place concrete conduit that has been lined with a steel pipe and is in <br />need of repair or replacement in the near future. The conduit has not reached its safe or effective life <br />but is near it and we believe needs attention within the next five years. <br />The outlet is controlled by three hydraulicly operated slide gates that are positioned at the upstream <br />Horsecreek & Prospect Reservoirs - 06.014 <br />Henrylyn Irrigation District Page 6 <br />