Laserfiche WebLink
<br />Long Hollow ReselVoir <br />Feasibility Study <br /> <br />nprap. Sandstone will be obtained from a quarry site in the Cliff House Sandstone that underlies <br /> <br />the Lewis Shale. This quarry site will have to be identified in the final design stage, and Wright <br /> <br /> <br />Water Engineers, Inc. (WWE) anticipates that it will be necessary to blast to obtain sandstone for <br /> <br />the riprap. The dam's crest will be 25 feet wide, as required by SEO regulations (Department of <br /> <br />Natural Resources 1988). The downstream slope will be constructed in an overall 2 Yz-to-l slope. <br /> <br />A 10-foot-wide maintenance and instrumentation barrier may be appropriate at mid-height on the <br /> <br />downstream slope. <br /> <br />The outlet works for the embankment is a 48-inch-diameter welded steel pIpe encased in <br /> <br />concrete. This conduit of steel-lined concrete will require firm, unyielding foundation support to <br /> <br /> <br />prevent cracking of the concrete and displacement of the pipe. The alignment of the new outlet <br /> <br />pipe is shown on Exhibit 3.1-3. The final alignment will depend upon subsurface conditions. <br /> <br />A 24-inch-diameter Howell Bunger (fixed-cone) valve will control the outlet pipe. This valve <br /> <br />will be located at the downstream end of the outlet pipe. A l2-inch-diameter Jet valve will be <br /> <br />placed on a Y pipe section near the fixed-cone valve. The Jet valve can be used for routine low- <br /> <br />level releases. <br /> <br />A vertical water-intake shaft will be constructed through the upstream slope of the dam. The <br /> <br />shaft will be gated with two 48-inch-by-48-inch valves and a 30-inch-by-30-inch gate valve near <br /> <br /> <br />the mid-height of the reservoir. This configuration of gates will allow water to be released from <br /> <br />either the bottom or the mid-height of the reservoir. The vertical shaft for the operating gates <br /> <br />will be accessed by a single-span prefabricated weathered-steel truss bridge. The bridge will <br /> <br />have an 8-foot-wide wood deck and will be capable of supporting a vehicle with a 10,000-pound <br /> <br /> <br />axle load. <br /> <br />The geotechnical investigation indicated that the rock in the foundation beneath the dam <br /> <br />embankment is relatively permeable. In addition, high concentrations of sulfate were identified <br /> <br />in sections of the rock core on both abutments. These conditions will require design features in <br /> <br />the final design, which will reduce seepage through the abutments and the dam foundation. <br /> <br />WWE has included in this feasibility-level design three features to reduce seepage. The first is a <br /> <br />991-077.120 <br />March 2005 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 4 <br />