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JD -7 Mine — Drainage Design Plan 7 <br />Site soils consist predominantly of Bodot and Ustic Torriorthents, which are listed as hydrologic soil group <br />C in the NRCS Web Soil Survey (MRCS, 2012a, 2012b). Site - specific curve numbers are discussed in <br />Section 3. <br />Runoff volume (Q) is obtained from: Q = qd / 12 • A • 43,560 <br />where: Q = Runoff volume, cubic feet <br />qd = Runoff depth, inches <br />A = Catchment area, acres <br />2.2.2 Peak Discharge <br />Peak discharge is calculated using Time of Concentration (T�) which is the time it takes for runoff to travel <br />from the most hydraulically distant point in the watershed (or sub - basin) to a point of interest. T. is the <br />sum of travel time for sheet flow (Tsh) plus the travel time for shallow concentrated overland flow (Ts,) plus <br />the travel time for channel flow (T,h). <br />3Jxe1 �e�J <br />,Sha/�a4J <br />CenCtntra.� <br />�ar�nel <br />�i �ieal <br />nctnlro%f <br />Figure 4. Location of Sheet Flow, Shallow Concentrated Flow, and Channel Flow within a <br />Basin <br />Sheet flow occurs over plane surfaces in the "headwaters" or uppermost reaches of the watershed, as shown <br />in Figure 4 above. For the JD -7 Mine drainage design, sheet flow is assumed to occur in the upper 80 feet <br />of the sub - basin. Sheet flow travel time is calculated using the simplified form of Manning's kinematic <br />solution from Overton and Meadows (1976) which is Equation 3.3 of TR -55 (MRCS, 1986): <br />where: <br />Tsh = sheet flow travel time (hr) <br />0.007 (nL) 0•8 <br />_ <br />Tsh P0.5sO.4 <br />4149A.130926 Whetstone Associates <br />