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existing conduit. Minor over-excavation of the foundation may be required to achieve <br /> satisfactory subgrade prior to placing the new outlet works conduit. The embankment <br /> would be replaced using the excavated material placed at 95 percent of a Standard <br /> Proctor and 1 percent below to 2 percent above the optimum water content. A sand filter <br /> with a drain outfall pipe would be constructed on the downstream side of the <br /> embankment to collect seepage that may flow along the new conduit. <br /> Riprap slope protection would be placed on the existing embankment(including the <br /> backfill placed after outlet works replacement) upstream slope. The riprap is expected to <br /> be screened from rock available on site. <br /> 2.2 Intake Structure <br /> The intake structure would be constructed at the upstream toe of the dam and would <br /> support a 14-inch slide gate enclosed in trash racks. The slide gate would be used for <br /> reservoir releases and would allow access to the pipe for inspection and maintenance. A <br /> stainless steel gate stem, encased in oil to prevent freezing, would be located on the face <br /> of the dam to the dam crest, where it would be manually operated. The existing slide gate <br /> appears to have been installed during the original construction and has been deemed to be <br /> in poor condition in the SEO June 2013 inspection report. Based on the age, condition, <br /> and size of the existing gate, it is recommended a new gate be installed. <br /> -4- February 18, 2014 <br /> An air vent will be required immediately downstream of the slide gate to prevent vacuum <br /> pressures in the outlet pipe when closing the gate. It is envisioned that the gate stem and <br /> the air vent would share a concrete encasement or concrete pier supports along the face of <br /> the dam to the dam crest. In accordance with SEO criteria,the trash racks will be sized to <br /> prevent large debris from entering the outlet conduit. <br /> 2.3 Conduit <br /> SEO criteria requires that the low-level outlet be capable of releasing the top 5 feet of the <br /> reservoir in five days starting at the normal high-water line (spillway crest elevation). A <br /> preliminary elevation capacity curve for the reservoir was calculated by digitizing the <br /> reservoir contours on the available 1950s drawings. The total volume of water in the top <br /> 5 feet of the reservoir between Elevation(El.) 8774 and El. 8769 is approximately 145 <br /> ac-ft. <br /> The average drawdown rate of this volume over 5 days is approximately 15 cfs. <br /> The Company has historically made reservoir withdrawals through a 10-inch-diameter <br /> conduit; however, a preliminary analysis of the conduit diameter needed to meet SEO <br /> evacuation criteria shows that a 14-inch-diameter conduit is required. The velocities in a <br /> 14- inch conduit are approximately 19 feet per second(fps); therefore, we selected a steel <br /> pipe with epoxy or polyurethane lining encased in concrete. <br /> 2.4 Outlet Structure <br /> A stilling basin is recommended to dissipate energy at the toe of the dam to prevent scour <br /> and potential subsequent undermining of the dam. RJH selected a U.S. Bureau of <br /> Reclamation(USBR) Type VI impact type stilling basin for conceptual design because <br /> these basins have a long history of good performance for similar applications. A USBR <br />