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JD -6 Mine — Drainage Design Plan 4 <br />where: <br />TS` 3600 • V <br />Ts� = 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 "' <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 />where: <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 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 />Runoff peak discharge is calculated from the TR -55 graphical peak discharge method. This approach <br />graphically generates a unit peak discharge rate (Q„) based upon the general catchment parameters of curve <br />number (CN), initial abstraction (Ia), precipitation (P) and rainfall distribution type (type lI for Colorado) <br />4148A.131028 Whetstone Associates <br />