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The design will be done for two cases . First , the initial case <br /> where the fabric is stapled to the ground but no vegetation is yet <br /> present . In this case , the Manning ' s n of the fabric is low and the <br /> stream must be shown to be stable from the standpoint of <br /> permissible shear . Second , once the streambed is revegetated , the <br /> Manning ' s n is greatly increased and the streambed must be shown to <br /> handle this condition without erosion . This is the long term <br /> condition for the permanent diversion . <br /> Case 1 Design - Unvegetated Lined Channel <br /> In this case , the Manning ' s n of the fabric is 0 . 014 . A trapezoidal <br /> channel of 7 feet width is chosen for worst case shear . The North <br /> American Green Company provides a short computer program which <br /> compares the permissible shear for the particular fabric <br /> installation to the calculated shear for the channel with the known <br /> dimensions , grade and peak flow. As can be seen from the enclosed <br /> printout , the lining is stable from the calculated shear even <br /> though the velocity is high . This case only exists for the short <br /> term where no vegetation exists in the diversion channel . <br /> Case 2 Design - 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 of <br /> 4 . 68%, the permissible velocity for this grass is 7 feet per <br /> second . <br /> Using Q = A x V, 105 . 3 = A x 7 , therefore A = 15 . 04 ft2 <br /> The enclosed Figure 1 for Retardance Class 6 Grass shows that at a <br /> velocity of 7 feet per second and a grade of 4 . 68%, the hydraulic <br /> radius is 1 . 27 . The chart also shows that the Manning ' s n for this <br /> condition is 0 . 049 . <br /> Using the equation for the area of a trapezoidal channel and a <br /> bottom width of 7 . 0 feet and 2 : 1 sideslopes : <br /> A = bd + Zd2 15 . 04 = 7xd + 2xd2 d = 1 . 50 <br /> g� <br />