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Mineral Joe Mine — Drainage Design Plan 4 <br />P = 24 -hour rainfall (in) <br />s = land slope (ft/ft) <br />Shallow concentrated flow has been assumed to occur from the end of sheet flow until the flow path <br />reaches a stream channel mapped as intermittent or a channel with a known or required cross section, such <br />as the diversion or drainage ditch at the Mineral Joe Mine. The travel time for shallow concentrated flow is <br />calculated as: <br />where: <br />_ L <br />TS` 3600 • V <br />TSB = shallow concentrated flow travel time (hr) <br />L = flow length (ft) <br />3600= conversion factor for seconds to hours <br />V = velocity on unpaved surface, interpolated from Figure 3 -1 of TR -55 for land slope (ft/s) or <br />calculated using Manning's equation: <br />where: <br />1.49 r2 /3S1 /2 <br />V= <br />n <br />r = hydraulic radius = depth of flow = 0.4 ft <br />s = slope of the hydraulic grade line (land surface) (ft /ft) <br />n = Manning's n (roughness coefficient) for open channel flow = 0.05 <br />Simplifying for unpaved conditions: <br />V= 16.13 s' /Z <br />Channelized flow occurs in defined channels or intermittent stream drainages. The travel time for <br />channelized flow is calculated using Manning's equation for channelized flow and the channel - specific <br />geometry and hydraulic characteristics (rather than the simplifying assumptions used for shallow <br />concentrated flow). The travel time for channelized flow is calculated as: <br />L <br />T`h _ 3600 V <br />where: <br />Tch = channel flow travel time (hr) <br />L = flow length (ft) <br />3600= conversion factor for seconds to hours <br />V = velocity calculated using Manning's equation for channelized flow: <br />where: <br />1.49 r2 /3S1 /2 <br />V= <br />n <br />r = hydraulic radius = cross sectional area / wetted perimeter (A/Pw) <br />s = slope of the hydraulic grade line (channel bottom) (ft/ft) <br />n = Manning's n (roughness coefficient) for open channel flow (as discussed <br />in Section 2.3.1 and Table 3) <br />414813.131029 Whetstone Associates 6 <br />