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<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 /> <br />5.3 <br /> <br />Several areas of the embankment appear to be susceptible to erosion damage. Only the central <br />part of the main embankment is covered with riprap on the upstream face. The remaining <br />portions of the upstream lace of the main embankment show minor erosion damage in the form <br />of small wave scarps. In the past, the left groin of the downstream face of the main <br />embankment has eroded badly. The repairs which were made were not permanent and the <br />potential for erosion of the downstream face still exists. The emergency spillway is unlined, and <br />the left side is formed by an apparently uncompacted dike, In the event that the emergency <br />spillway would carry flow, this area could erode, allowing water along the downstream toe of <br />the embankment. <br /> <br />Several past inspections by the State Engineer's Office have noted possible low spots on the <br />crest of the embankment, and that the crest may need to be regraded to slope to the upstream <br />side, A State Engineer's Office inspection report, dated July 31, 1986, noted minor spalling of <br />concrete in the floor of the energy dissipator, and some exposure of reinforcing steel. <br /> <br />GEOTECHNICAL EVALUATION <br /> <br />5,3.1 GEOLOGY <br /> <br />5,3,1.1 Geomorphology <br /> <br />Hourglass Reservoir Is located within Beaver Creek drainage, an east treading drainage <br />on the eastern slope of the Rocky Mountains. The site is located approximately 31\ <br />miles northeast of Comanche Peak. Beaver Creek drainage is a U-shaped glacial valley. <br />Comanche Reservoir Is located approximately 1\ mile upstream of Hourglass Reservoir. <br />The valley slopes are steep In the vicinity of the reservoirs and become relatively less <br />steep downstream of Hourglass Reservoir which corresponds to a general widening of <br />the valley floor. In the vicinity of the reservoirs the surface of the valley floor is <br />relatively flat. Beaver Creek is located near the northern side of the valley and has <br />eroded into the flat valley bottom. Beaver Creek is approximately 75 feet In elevation <br />below the reservoir, Beaver Creek maintains a relatively flat gradient from Comanche <br />Reservoir to a point approximately '4 of a mile downstream of Hourglass Reservoir. At <br />this location, the stream gradient increases sharply and flows down the face of an east <br />facing terminal moraine, <br /> <br />5-6 <br />