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<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 />I <br /> <br />INTRODUcnON <br /> <br />Hourglass Dam is an earth embankment wtth a maximum height of 45 feet and a crest length of about <br />2,400 feet. The crest elevation is 9,372 feet above sea level (40 gage). The dam impounds 1,693 acre- <br />feet of storage at an elevation of 9.366.5 feet (34,5 gage), <br /> <br />The dam Is located in Larimer County on a small tributary to Beaver Creek some nine miles south of <br />Rustic, Colorado. Most of the resl!lVOir Inflow is supplied from Comanche Dam through a feeder canal. <br /> <br />The dam was originally constructed about 1898 and was enlarged about 1901. Reservoir use was <br />reduced and finally abandoned in the late 1940's because of outlet works deterioration, Rehabilttation <br />plans were drawn up In 1965 and the following improvements were made in 1966, <br /> <br />1. The existing outlet was removed and replaced by a 33-inch reinforced concrete outlet condutt <br />controlled by two parallel upstream control gates. A downstream stilling basin was provided, <br /> <br />2. Parts of the dam were reshaped and the crest was raised to a uniform level. <br /> <br />3, Riprap was provided at the upstream face of the maximum dam section. <br /> <br />4. A primary side channel spillway was provided in the inlet channel with its crest at elevation <br />9,366.5 (34,5 gage). <br /> <br />5, A secondary emergency spillway was provided a the right side of the dam wtth tts crest at <br />elevation 9,367.2 (35.2 gage). <br /> <br />Excessive seepage developed at the downstream toe of the dam adjacent to the stilling basin when the <br />reservoir was filled. The outlet was then extended about 72 feet downstream, the downstream dam <br />slope was flattened and the stilling basin was reconstructed. Excessive seepage persisted at high <br />reservoir levels following those improvements and the State Engineer's Office restricted storage levels <br />in the reservoir in the 1970's. <br /> <br />Runoff from a severe thunderstorm in August 1985 ran down the downstream face of the dam at the <br />left groin. The deep gully caused by this flow erosion extended from the top of the dam to tts <br />downstream toe, Seepage was observed entering the gully from the left abutment. The erosion was <br />promptly backfilled, The dam performed satisfactorily at the post reconstruction reservoir limit elevation <br />