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BOARD01971
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Last modified
8/16/2009 3:09:30 PM
Creation date
10/4/2006 7:05:55 AM
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Board Meetings
Board Meeting Date
3/22/2005
Description
WSP Section and CF Section - Feasibility Study Status Report - La Plata Water Conservancy District - Long Hollow and Red Mesa Ward Reservoirs
Board Meetings - Doc Type
Memo
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<br />., <br /> <br />Long Hollow Reservoir <br />Feasibility Study <br /> <br />The crest elevation of the dam will be 6,330 feet, with a camber for settlement making the <br />maximum elevation at the center of the dam approximately 6,336 feet. The upstream slope of the <br />dam will be constructed on 3 horizontal to 1 vertical slopes and will be covered with sandstone <br />riprap. Sandstone will be obtained from a quarry site in the Cliff House Sandstone that underlies <br />the Lewis shale, This quarry site will have to be identified in the final design stage, and WWE <br />anticipates that it will be necessary to blast to obtain sandstone for the riprap. The dam's crest <br />will be 25 feet wide, as required by SEO regulations (Department of Natural Resources 1988). <br />The downstream slope will be constructed in an overall 2'1>-to-1 slope, A 10-foot-wide <br />maintenance and instrumentation barrier may be appropriate at mid-height on the downstream <br />slope, <br /> <br />The outlet works for the embankment is a 48-inch-diameter welded steel pipe encased in <br />concrete. This conduit of steel-lined concrete will require firm, unyielding foundation support to <br />prevent cracking of the concrete and displacement of the pipe. The alignment of the new outlet <br />pipe is shown on Exhibit 3,1-3. The fmal alignment will depend upon subsurface conditions. e <br /> <br />''''', <br /> <br />A 24-inch-diameter Howell Bunger (fixed-cone) valve will control the outlet pipe. This valve <br />will be located at the downstream end of the outlet pipe. A 12-inch-diameter Jet valve will be <br />placed on a Y pipe section near the fixed-cone valve. The Jet valve can be used for routine low- <br />level releases. <br /> <br />A vertical shaft will be constructed through the upstream'slope of the dam. The shaft will' be <br />gated with two 48-inch-by-48-inch valves and a 30-inch-by-30-inch gate valve near the mid- <br />height of the reservoir. This configuration of gates will allow water to be released from either the <br />bottom or the mid-height of the reservoir. The vertical shaft for the operating gates will be <br />accessed by a single-span prefabricated weathered-steel truss bridge. The bridge will have an 8- <br />foot-wide wood deck and will be capable of supporting a vehicle with a 10,000-pound axle load. <br /> <br />The geotechnical investigation indicated that the rock in the foundation' beneath the dam <br />embankment is relatively permeable, In addition, high concentrations of sulfate were identified <br />, in sections of the rock core on both abutments, These conditions will require design features in <br /> <br />e <br /> <br />991-077.120 <br />March 2005 <br /> <br />Wright Waler Engineers, Inc. <br /> <br />Page 4 <br />
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