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JD -7 Mine — Drainage Design Plan 8 <br />n = Manning's roughness coefficient for surface flow <br />L = flow length (ft) <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 a diversion or drainage ditch at the JD -7 Mine. The travel time for shallow concentrated flow is <br />calculated as: <br />where: <br />L <br />_ <br />TS` 3600 • V <br />T,, = 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 />IYE <br />where: <br />1.49 7_2/3S1/2 <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 sl /Z <br />Channelized flow occurs in defined channels or intermittent drainages. The travel time for channelized <br />flow is calculated using Manning's equation for channelized flow and the channel - specific geometry and <br />hydraulic characteristics (rather than the simplifying assumptions used for shallow concentrated flow). <br />Shallow concentrated flow has been assumed to occur from the end of sheet flow until the flow path <br />reaches a channel mapped as intermittent or a channel with a known or required cross section, such as <br />diversion or drainage ditch at the JD -7 Mine. The travel time for shallow concentrated flow is calculated <br />as: <br />where: <br />L <br />T`h 3600 • V <br />Tch = channel flow travel time (hr) <br />L = flow length (ft) <br />3600= conversion factor for seconds to hours <br />V = velocity (ft/sec) calculated using Manning's equation for channelized flow: <br />1.49 r2/3S1/2 <br />V= <br />n <br />4149A.140207 Whetstone Associates <br />