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„~, ESPEY, nUSTOr+ d ASSOCIATES, InC. <br />eh <br />i <br />nomographs developed by the Soil Conservation Service contained in a document <br />entitled 'Procedures for Determining Peak Flows in Colorado". The procedure <br />involved determination of (a) a curve number based on soils and vegetation data, <br />(bl the size of the contributing watershed azea, (c) the time of concentration of the <br />watershed area, and (d) the amount of total rainfall. These nomography aze based oa <br />gaging records developed by the Soil Conservation Services. The stretch of <br />watershed diversion ditch that drains most of the watershed (Stn 0 + 00 to 18 + 50) <br />has been designed Eor the 100-year 24-hour discharge. The flow to be expected is <br />the upper part of the watershed diversion ditch (18 + 50 to end) has been calculated <br />in similar fashion and was found Lo be 90 CFS. Therefore, this uppes pazt of the <br />ditch was designed to carry that Row (see Fi¢s, 13.1.4. 13.1.5 and 13.3.4). <br />Post-reclamation design calculations are given in the clear <br />pocket beginning on page 13-52. <br />13.3.4.2 Sedimentation Control Features <br />The refuse disposal azea and the stockpile area aze to be drained by <br />sedimentation pond collector ditches feeding into the sediment pond as required by <br />30 CFR 817.46. These ditches are sized to carry the 100 year 24-hour flow of 32 cfs <br />at a minimum grade of one percent. The pond itself has been sized to contain the <br />ZO-year 24-hour storm event from the entire disturbed area as well as sediment <br />storage volume of 0.1 acre-feet per acre of disturbed area (30 CFR 817.46). An <br />emergency spillway has been designed to safely pass the 25-year, 24-hour storm <br />event. Location and general configuration of the collector ditches and ponds can be <br />seen on Fig. 13.1.4. Details aze shown on Figs. 13.1.5 and 13.3.5. <br />13.3.5 Roadway <br />Figures 13.1.4 and 13.3.6 show the location and profile of the proposed <br />haul road. Figure 13.3.7 details the cross section. Thi9 roadway has been designed <br />as a Class Z haul road (30 CFR 817.160-8]7.!66). It has been designed to accommo- <br />date end dump [rucks expected to be used by Northern [o transport refuse to [he <br />;~ disposal facility. <br />• <br />I/17/~l O <br />13-lla <br />