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' • SPILLWAYS <br />PECOCO will have separate principal and emergency spillways (see Exhibit 7-18 for location <br />and configuration of spillways). The principal spillway will consist of a 24" diameter <br />I, CMP with a trash rack at the inlet. This pipe wi 11 maintain the water level to the <br />6774,9' elevation. Peak stage at the principal spillway during the passage of the <br />10-year, 24-hour event will be elevation 6775.10. This results in 1.9 feet of freeboard <br />it to the inlet or the emergency spillway. <br />The emergency spillway will consist of a trapezoidal channel. Assuming the principal <br />spillway was plugged, the trapezoidal channel could safely pass the 100-year, 24-hour <br />I <br />storm runoff volume. Peak stage elevation during the passage of the 100-year storm is <br />6777.4, leaving 3.6 feet of freeboard to the top of embankment. 15'i th a velocity of 2,90 <br />i fps, the grass lined emergency spillway channel and outsl ope will be stable. Please refer <br />to Addendum 2 for capacities of both spillways during passage of the 10 year, and 100-year <br />storm events. The design details for the emergency spillway are as follows. <br />• <br />Type <br />Bottom Width <br />Length <br />Side Slopes <br />Outf all Slope <br />Inlet Elevation <br />100-year, 24-hour Peak Stage <br />Trapezoidal Channel <br />10 feet <br />40 feet <br />3H:1V <br />2va <br />6777.0 <br />6777,4 <br />• <br />SUMMARY <br />Impountlment capacity below the principal spillway is completely incised. During passage <br />of [he 10-year, 24-hour, storm the emergency spillway does not di scharne >ediment <br />downstream nor is there any flow through the emergency spillway. The pond will safely <br />pass [he flow from the 100-year, 24 -hour precipitation event. <br />7-6g-17 <br />