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Mineral Joe Mine — Drainage Design Plan 3 <br />S _ 1000 _ 10 <br />CN <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 (NRCS, 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 j 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 (T,h) plus the travel time for shallow concentrated overland flow (TSB) plus <br />the travel time for channel flow (T,h). <br />..S/xe/ flsa) <br />.shA / /ei <br />GontlnHct/ts <br />ChannL� <br />e/ / /..i <br />tw�!•ar <br />nttn.ra/ed <br />f /�a) <br />Sheet flow occurs over plane surfaces in the "headwaters" or uppermost reaches of the watershed, as shown <br />above. For the Mineral Joe Mine drainage design, sheet flow is assumed to occur in the upper 80 feet of <br />the sub - basin. Sheet flow travel time is calculated using the simplified form of Manning's kinematic <br />solution from Overtop and Meadows (1986) which is Equation 3.3 of TR55 (NRCS, 1986): <br />where: <br />0.007 (nL)0.8 <br />T,h = pOSSOA <br />T,h = sheet flow travel time (hr) <br />n = Manning's roughness coefficient for surface flow <br />L = flow length (ft) <br />4148B.131029 Whetstone Associates <br />