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Knight Resold <br />p ONSU LTINp <br />3.0 Construction Details <br />3.1 Sediment Dam <br />' The sediment dam is to be constructed to a minimum height of 12 feet above the embankment <br />foundation with a dam crest of 15 feet. The existing streambed will be leveled and sloped <br />downstream at 8 percent and compacted to provide a 6-inch soil embankment foundation. The <br />upstream embankment of the dam will be composed of soil and have a slope of 2.5:1; the <br />downstream embankment may be composed of either soil or rock with a slope of 2.5:1. A key <br />trench will be excavated below the centerline of the dam. The key trench hinders flow of <br />effluent through the ground by lengthening the seepage path, prevents erosion, and offers <br />structural stability to the embankment. <br />Sediment dam layout and section details can be found on Figures 3 and 4, Plan and Profile of the <br />Relocated Sediment Dam PS and Typical Sediment Dam Sections and Details. <br />3.1.1 Spillway <br />A spillway will be constructed at the 100-year/24-hour storm event elevation, approximately <br />10 feet above the embankment foundation. The spillway inlet will be located on the east, <br />upstream side of the dam and will encircle the dam at least 3 feet away from the base. The <br />' bottom width of the spillway will be 10 feet and have a channel depth of 2.0 feet. The spillway <br />channel will have a side slope of 2 (H):1(V); it will then have a longitudinal slope of 0.5(H):1(V) <br />until the slope daylights to existing ground. The spillway will be riprapped along the entirety of <br />its length if possible. Very steep slopes may make riprap placement impossible. The spillway <br />1 will gradually slope down along the side of the dam embankment into the stilling basin. <br />' 3.1.2 Perforated Riser <br />The perforated riser is located upstream of the dam embankment toe. The perforated riser will <br />be constructed out of 18-inch-diameter CSP and will rise to 5 feet above the embankment <br />t foundation approximately 2 feet above the maximum allowable sediment height. A cone of <br />gravel with a DSo of 1.5 inches will be placed azound the riser, and the gravel will be sloped to <br />' 1.7(H): 1(V) up to the height of the riser. An 18-inch-diameter CSP elbow will connect the riser <br />to an 18-inch CSP outlet pipe. A 3-foot by 3-foot by 8-inch thick reinforced concrete pad will be <br />placed under the elbow, flush to the embankment foundation. The CSP outlet will be placed on <br />- the embankment foundation and will extend the length of the embankment dam flowing into the <br />Ga01\00100.02'N\Reports\KP\Design Report.tloc 4 January 30, 20C5 <br />