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<br />J <br /> <br />2.2 DESCRITION OF STRUCTURE <br /> <br />The spillway structure is a reinforced concrete uncontrolled side channel chute structure <br />with an overall length of approximately 175 feet. The inlet structure is 135 feet long and <br />the chute is about 30 feet wide. The inlet pas a depth of 10 feet at the upstream end and <br />22 feet at the downstream end and varies in width from 10 feet to 30 feet. The crest <br />length is 135 feet and is at elevation 95.1 (location site control). No as built drawings are <br />available; however, a field examination and a review of some old outdated design <br />drawings indicate that the inlet structure consists of a 12 inch thick concrete lining <br />reinforced with one layer of steel. Drainage behind the walls and under the floor slab <br />consists of a grid of 4-inch diameter pipe with a 6-inch diameter collector drain, which is <br />located along the centerline of the structure and exits at the downstream end of the chute. <br />The chute section has several 2-inch dia11leter weep holes near the base of the walls. <br />There is no evidence that foundation anchors were used. <br /> <br />Apparently the chute was not completed to its full design length, as the present chute <br />does not have sufficient length to retain the downstream slope of the designed <br />embankment. The downstream slope of the dam has been steepened adjacent to the wall. <br />In addition, reinforcement rebar protrude, from the downstream end of the concrete <br />chute, which indicates that an additionalleOgth of chute was planned. There is no riprap <br />in the outlet channel. <br /> <br />2.3 SPILL WAY DEFICIENCES <br /> <br />Much of the concrete in the inlet structure is cracked, has numerous spalls and displaced <br />portions of concrete. The downstream 80 feet of the floor slab and back wall (west wall) <br />have numerous cracks and show evidence of movement. Several pieces of wall concrete <br />have separated from the reinforcing mat arld are lying on the floor slab. The crest and <br />crest wall (east wall) are free of cracks or spalls, except where the concrete has cracked <br />and loosened along the construction joint ~d waterstop located at the base of the wall. <br />There is a large spall in the floor surface of the chute and a rock pocket at the base of the <br />west wall. <br /> <br />Drainage around and under the structure pas a number of deficiencies. The drainage <br />system may not be affective because the exit pipe has collapsed. Surface drainage around <br />and behind the west wall is direct toward the backside of the wall. In addition, there is a <br />small continuously flowing stream on the far side of the road that is located adjacent to <br />the west wall. Flows that exceed the channel capacity, flow over the road and are <br />directed toward the back of the wall. <br /> <br />Several factors haw been identified that may have contributed to the failure of the <br />spillway structure: <br /> <br />I) Design deficiencies <br />2) Construction deficiencies <br />3) Harsh climate, over 10,000 feet in elevation <br /> <br />2 <br />