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Jared Ebert <br />Page 2 of 2 <br />July 16, 2014 <br />check dams including calculations of flow velocity to demonstrat <br />reduce the flow velocity such that the channel is stable. <br />The required information for the Oak drainage, for instance, wou <br />discharge resulting from the drainage area (310.7 acres) as a re-24hr storm <br />(23.2 cfs), taken from Appendix Q. Using the currently available maps for t <br />the channel slope can be estimated at 14%. Using the SEDCAD chawith the <br />proposed channel dimensions, the flow depth in the channel would be 0.11 feet, so a minimum <br />depth of 0.41 would be required; the design information would need to indicate that the Oak <br />drainage channel will be at least 0.41 deep to provide adequate capacity to convey the design <br />event. <br /> <br />In addition, in the case of Oak drainage, the SEDCAD utility calculation also shows that a rip rap <br />lining with a D50 of 6.0 would be necessary to ensure that the <br />Trapper elects to substitute check dams for rip rap lining, supp <br />dams would need tobe included, demonstrating that the proposed generic check dam sizing <br />and spacing would be sufficient to keep velocities between check <br />Trapper must submit detailed design information (discharge, flow depth, velocity, and <br />channel lining) for all of the postmining drainage channels to be constructed, completed, or <br />reconstructed during the current permit term. <br /> <br />Should you or the operator have any questions, please let me kno <br />