2018-08-08_PERMIT FILE - C1982056 (17)

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REVISED 7/30/85 Runoff parameters and watershed characteristics were utilized in deriving total runoff and peak flow rates for each sub -watershed, using the methods outlined in Procedures for Determining Peak Flows in Colorado (SCS, 1977). Total runoff was used to design impoundment structures; peak flow rates were used to design diversion ditches, culverts and outlet works. Sedimentation Parameters The established design criteria for drainage and sediment control facilities is the amount of runoff resulting from 10 -year, 24-hour precipitation event. Therefore, the sediment storage capacity of a sedimentation pond should be adequate to store the volume of sediment generated by a 10 -year, 24-hour precipitation event at all times. The method of determining this volume is to calculate the total runoff and peak flow for the desion event and insert these values in the Modified Universal Soil Loss Equation (MUSLE). This method is described in Applied Hydrology And Sedimentology For Disturbed Areas (Barfield, Warner and Haan, 1981, pp. 365-380). The sediment yield thus derived is the minimum allowable storage volume of the pond. Since the permanent pool area must be cleaned out when it is 60 percent full of sediment, the storage capacity is calculated by multiplying the 10 -year, 24-hour sediment yield times 100/40. Thus, even when the perr.anent pool is 60 percent full of sediment, there is adequate capacity to contain and treat the 10 -year, 24-hour event. This method was applied to Pond E and the detention basin at the Fish Creek Tipple. SEDIMENT CONTROL FACILITIES Sedimentation Pond E The design of Pond E and associated ditches and culverts was approved by the CMLRD under a Technical Revision to Permit 76-16 on March 18, 1983. The pond is located in the southwest quarter of Section 2, Township 5 North, Range 86 West, and receives drainage from the Tipple No. 3 facilities. Tributary disturbed area is 24 acres; tributary undisturbed -3-