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• -3- . <br />MCR proposes to utilize the existing access road to <br />intercept this ditch as shown on map C-la. The road will be <br />graded in its entirety in the form of a trapezoidal trough, <br />thus forming a ditch 12 feet or greater in width. The angle <br />of the side slope against the hillside would be the bank as <br />it currently exists, which varies upward from less than <br />2:1. The outside berm will be a minimum of 18 inches high <br />with a nominal slope of 3:1. Our calculations indicate that <br />in this configuration flow depth at peak discharge will be <br />0.16 feet with a velocity of 4.4 feet per second (without <br />riprap). Sections greater than 11% in grade or where <br />velocities greater than 5.0 fps may be calculated after <br />final configuration will be riprapped with appropriately- <br />sized material. <br />The proposed configuration is given as cross-section A-A' on <br />Figure 1. <br />AREA II <br />Area II consists of a short identifiable ephemeral channel, <br />approximately 1/4 mile in length, with an ill-defined area <br />of overland-flow drainage above it for another half-mile. <br />This drainage area, which totals approximately 59 acres, is <br />intersected by the quarry itself, and the topography <br />virtually prohibits diverting runoff around the quarry. <br />Including the ill-defined area, the drainage has an average <br />gradient of approximately 39.5%, with elevations varying <br />from 6,700 feet at the quarry to approximately 8,425 feet at <br />its highest point. Topographic, geologic and vegetation <br />regimes are similar to Area I as described above. <br />Calculations using the OSM Storm program indicate a peak <br />discharge for Area II of 2.86 cfs, with a total 10-year 24- <br />hour storm drainage volume of 0.84 acre feet. MCR proposes <br />to slope the main bench floor toward the highwall to <br />establish positive drainage to contain this discharge, as <br />well as upper quarry drainage. The area of the proposed <br />bench retention area, as indicated generally on map C-la, is <br />approximately 400 feet long and 55 feet in width; at a <br />gradient of 10% this will yield a storage volume of <br />approximately 1.25 acre-feet. The entire bench, except for <br />certain access roads and equipment operation areas, will be <br />sloped toward this area basin to prevent runoff over the <br />outslope. At the east end, against the highwall and the <br />