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Ditch #8 Design <br /> As previously described , this ditch will employ the C- 125 liner due <br /> to the steep slope ( 19 . 2%) of this drainage. The channel will <br /> vegetate itself with the liner and will be shown to provide long- <br /> term stability . The peak flow obtained at the bottom of the <br /> drainage (Structure 5 ) will be used to design the channel . This <br /> peak flow is 10 . 62 cfs . <br /> Long Term Case - Vegetated Channel <br /> The methods used to design the revegetated channel are those <br /> described on pages 166- 184 of "Applied Hydrology and Sedimentology <br /> of Disturbed Areas" , by Barfield , Warner and Haan . Using a <br /> revegetation mix of smooth brome , timothy and orchardgrass , this <br /> will result in a Retardance Class B revegetation . As seen in the <br /> enclosed Table 1 of permissible velocities , at a channel slope o- <br /> 19 . 2%, the permissible velocity for this grass is 5 feet per <br /> second . <br /> Using Q = A x V , 10 . 6 = A x 5 , therefore A = 2 . 12 ft2 <br /> The enclosed Figure 1 for Retardance Class B Grass shows that at a <br /> velocity of 5 feet per second and a grade of 19 . 2%, the hydraulic <br /> radius is 0 . 53 . The chart also shows that the Manning ' s n for this <br /> condition is 0 . 082 . <br /> Using the equation for the area of a trapezoidal channel and a <br /> bottom width of 5 . 0 feet and 2 : 1 sideslopes : <br /> A = bd + Zd2 2 . 12 = 5xd + 2xd2 d = 0 . 37 <br /> Check R using d = 0 . 37 , b = 5 . 0 , z = 2 <br /> bd + Zd2 <br /> R = ------------- R = 0 . 319 , lower than 0 . 53 so <br /> 2xd4 ( z2+ 1 ) design is O. K . <br /> Using Manning ' s equation to check design with inputs of : <br /> 33 g f�61Q3 <br />