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<br />DRAINAGE CRITERIA MANUAL <br /> <br />MAJOR DRAINAGE <br /> <br />Typical cross-sections suitable for grass lined channels are given in Figure <br />2-4. <br /> <br />2.3.4 Roughness Coefficients, The hydraulic roughness of man-made grass lined <br />channels depends on the length of cutting, if any, the type of grass, as well as <br />the depth of flow (11). Typical roughness coefficients are as follows: <br /> <br />TABLE 2-4 <br /> <br />MANNING ROUGHNESS COEFFICIENTS, n* 1 <br /> <br />Depth of <br />Flow of <br />0.7 -1. 5 ft. <br />Bermuda grass, Buffalo grass, Kentucky Bluegrass <br /> <br />Depth of <br />Flow Greater <br />Than 3.0 ft, <br /> <br />a. Mowed to 2 inches <br />b. Length 4-6 inches <br /> <br />0.035 <br />10.0401 <br /> <br />0.030 <br />0.030 <br /> <br />Good stand any grass <br /> a, Length of 12 inches <br /> b. Length of 24 inches <br />Fair s ta nd any grass <br /> a, Length of 12 inches <br /> b. Length of 24 inches <br /> <br />0.070 <br />0,100 <br /> <br />0.035 <br />0.035 <br /> <br />0.060 <br />0,070 <br /> <br />0.035 <br />0.035 <br /> <br />*For straight channels without shrubberY or trees <br /> <br />The 0,7 to 1.5 foot depth in Table 2-4 is generally suitable for computing the <br />wetted channel portion for the initial storm runoff, while the greater than 3 <br />foot depth is suitable for the major runoff computations. A depth of flow of <br />2.0 feet or more will begin to lay the grass down to form a smoother bottom <br />surface. <br /> <br />UDFCD, 1990 <br />