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I ~ The SEDIMOT II hydrology and sedimentology computer model was used to calculate <br />runoff from the 10-year, 24-hour and 25-year, 24-hour storm events. Results of <br />the SEDTMOT II modeling are presented in Appendix 7-6b. <br />Exhibit 7-11 indicates that the permanent pool elevation is 6,577.10 feet, with <br />a designed pond storage capacity of 5.13 acre-feet. Consequently, there is <br />5.13 acre-feet of sediment storage available, which equates to 104.7 10-year, <br />24-hour precipitation events. The SEDIMOT modeling indicates that runoff <br />volume and peak inflow for the 10-year, 24-hour storm event are 0.41 acre-feet <br />and 1.85 cubic feet per second (cfs), respectively, The peak stage is 6,577.4 <br />feet. This is 2.6 feet below the invert for the emergency spillway. SEDIMOT <br />indicates that the average settleable solids concentration in the pond <br />discharge during the peak 24-hour period will be 0.0 milliliters per liter <br />(ml/1). The Water Quality Control Commission (WQCC) settleable solids effluent <br />limit is 0.5 ml/1. The SEDIMOT modeling demonstrates there is sufficient <br />storage capacity available, and that the settleable solids effluent <br />concentration is less than the applicable water quality standard. Therefore, <br />Pond 003 as constructed and operated meets the intentions of Rule 4.05.6(3)(a). <br />The calculated peak discharge from the 10-year, 24-hour storm event is 0.19 cfs <br />with a peak stage of 6,577.4 feet. The invert for the emergency spillway is at <br />6,580.0 feet. This demonstrates that no flow will occur through the emergency <br />spillway during the 10-year, 24-hour event. Therefore, the pond as constructed <br />and operated meets the intentions of Rule 4.05.9(2)(b). <br />The SEDIMOT modeling indicates the 25-year, 24-hour storm event peak inflow is <br />5.73 cfs with a peak stage at 6,577.7 feet. This stage elevation is 2.3 feet <br />below the invert of the emergency spillway, consequently, no flow will occur <br />through the emergency spillway (stage elevation of 6,580.0) as a result of the <br />25-year, 24-hour storm event. The emergency spillway is a trapezoidal channel, <br />with a bottom width of 10 feet and 3H:1V side slopes. The top of the <br />embankment is at 6,582.0 feet (see Exhibit 7-11). The peak discharge is 0.42 <br />cfs with a flow depth of less than 0.2 feet (stage of 6,580.1 feet). If the <br />principal spillway was to clog, or become inoperable for some reason, the <br />rating curve demonstration in Appendix 7-6b shows that the emergency spillway <br />is of sufficient size to safely pass the peak discharge from the 25-year, 24- <br />hour storm event. Pond 003 as constructed and operated is in compliance with <br />Rule 4.05.9(2)(c)(ii). <br />TR-37 Revised 04/05 <br />