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<br />PROJECT SUMMARY
<br />
<br />Hourglass Dam Is located on a small Beaver Creek tributary just east of Comanche Dam, about nine
<br />miles south of Rustic, Colorado. It Is a 45 foot high, 2,400 foot long earth embankment dam, It
<br />Impounds 1,693 acre-feet of storage at water surface elevation of 9,366,5 feet (34,5 gage), The dam's
<br />crest is at elevation 9,372 feet (40 gage),
<br />
<br />Hourglass Dam was built around 1898, Since then ~ has been enlarged, abandoned, and rehabilitated,
<br />The last rehabil~ation work was done in 1967, The reservoir is currently under a State Engineer's 9,363
<br />foot (31 gagEl) maximum water level restriction. The restriction was Imposed because excessive seepage
<br />occurs at that reservoir level. The excessive seepage saturates the downstream toe of the dam
<br />embankment thereby reducing the strength of the earth materials and reducing the dam's stability. The
<br />ma'<imum water level restriction reduces the useable r'Ose"Vcir capaci\y, from 1,593 to 1,434 acre feet,
<br />a loss of 259 acre-feet of storage.
<br />
<br />TrlConsultants (formerly McCall-Ellingson & Morrill, Inc,) initiated field investigations to determine existing
<br />cond~lons at the dam and reservoir s~e under a contlact with Greeley dated October 19, 1983,
<br />Woodward-Oyde Consultants were used as geotechnical sub-consultants. S~e Investigations W'lre
<br />carried out at the s~e during several days beginning on October 23, 1989, A second contract dated
<br />July 16, 1990, received August 13, 1990, was received from Greeley to prepare this feasibility study for
<br />Hourglass Dam and Reservoir.
<br />
<br />The feasibility study included two add~ional site vls~s, a simplified seepage loss determination,
<br />consideration of seven alternatives, two Informal progress meetings and further consideration of two
<br />proposed rehabDitation plans. Plans ranged from providing an essentially water tight liner for the entire
<br />reservoir and dam face, to a relatively simple plan for enhancing dam stabUity. Feasibility level cost
<br />estimates range from 40 mUllon dollars to' 500 thousand dollars.
<br />
<br />It Is not cost effective to provide a high degree of seepage reduction in Hourglass Reservoir at this time,
<br />Other Greeley dam projects can probably provide reservoir storage at lower cost. The two final plans
<br />proposed are: Option 1 - Downstream Drainage Construction to simply enhance dam safety; and Option
<br />2 - Partial Slurry Wall, a cut off at the dam to partially reduce seepage and to further enhance dam
<br />safety. The feasibility level construction cost estirnates of these two plans are 328,075 dollars for Option
<br />1, and 1,346,975 million dollars for Option 2, The options are designed so that Option 1, the
<br />downstream drainage construction, can be completed as soon as possible to bring the dam up to State
<br />standards and to have the storage restrictions lifted, Option 2 could be implemented late, with minimum
<br />
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