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<br />I <br />I <br />II <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 />5.0 <br /> <br />5.1 <br /> <br />PLAN OF DEVELOPMENT <br /> <br />HISTORY AND BACKGROUND <br /> <br />Hourglass Reservoir, also known as Big Beaver Reservoir, Is an off-channel reservoir of Big <br />Beaver Creek. The reservoir is located about nine miles south of Rustic, Colorado, in the <br />Roosevelt National Forest. The reselVoir was originally a natural lake formed by glacial moraine. <br />To provide an outlet to the reservoir. a channel was cut part way through the morainal ridge <br />by placer mining techniques about the turn of the century. An outlet pipe was installed in the <br />channel and an embankment placed above it. At that time, the capacity of the natural reservoir <br />was also increased by placing a five to ten foot-high dike on the moraine, It Is believed that <br />little or no effort was made to compact the dike material, and that the material was glacial In <br />origin, Problems with the outlet works and the dam in the late 1940's resulted in the reduced <br />use of the reservoir and the eventual elimination of storage in the reservoir. Storage in <br />Hourglass Reservoir is augmented by a feeder ditch and outlet works from Comanche Reservoir, <br />approximately one mile upstream. In 1966, the structure was rehabilitated including: <br /> <br />1) Removal of the original oudel and the installation of a 33-inch diameter reinforced <br />concrete outlet conduit controlled by two parallel upstream slope control gates, A <br />stilling basin was also provided on the downstream end of the outlet. <br /> <br />2) Reshaping portions of the dam and raising the crest elevation of the dam in those areas <br />necessary to establish a uniform crest elevation. <br /> <br />3) Providing riprap on a portion of the upstream face of the dam at the maximum section. <br /> <br />4) Constructing a primary spillway on the feeder ditch to the reservoir at the decreed gage <br />height of 34.5 feet. <br /> <br />5) Construction of a secondary spillway at the right abutment of the dam. <br /> <br />Following these rehabilitation measures to the embankment and the filling of the reservoir to the <br />decreed gage height, adverse seepage developed at the downstream toe of the dam adjacent <br />to the stilling basin, At this time, the downstream toe was found to be soft and saturated, and <br /> <br />5-1 <br />