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o Slurry wall cutoff walls are identified in the Bureau of Reclamation's Design of Small Dams manual as <br /> an effective method to protect against piping. <br /> - Potential for Overtopping Failure <br /> o Overtopping failure during a flood event on the South Platte River is unlikely because the embankment <br /> will be nearly submerged in the backwater area of Baseline Road where shallow flooding and relatively <br /> low velocities are documented in a detailed study approved by FEMA <br /> Civil Resources recommends the following minor improvements to add additional protections and to improve the Site for <br /> future operations: <br /> - Grade/Fill:Hall-Irwin has large stockpiles of material on-site that should be used to fill-in low areas on the <br /> downstream side of the subject fill areas(see picture below). This will provide protection against erosion of the <br /> downstream embankment and create a larger crest width to further reduce the potential for piping or <br /> overtopping failure and associated peak release rates. <br /> Overfill/Emergency Spillway. Civil Resources recommends that Hall-Irwin construct a 100-foot long grade <br /> control spillway on the east side of the reservoir site, this will alleviate operational issues in the event the inflow <br /> ditch or pipe malfunctions and help control flood water inflows and outflows. <br /> Based on the information above and the proposed improvements, Civil Resources recommends the facility receive a No <br /> Public Hazard determination by the Office of the State Engineer, Dam Safety Division. <br />