Laserfiche WebLink
<br />_K~~, <br /> <br />Cover <br /> <br />Slope Range <br />% <br /> <br />Permissible <br />Veloci ty~f.p.-s. <br /> <br />I~ <br />,.., <br />.;.d <br />" <br />~ <br />I <br /> <br />, <br /> <br />II <br /> <br />---~---~ <br />~--- ... <br /> <br />~. <br /> <br />* For these materials, permissable velocities are equal to or <br />less than desired minimum velocities. Therefore, if minimum <br />velocities are maintained, erosion will occur and erosion <br />resistant lining material will be necessary. <br /> <br />TABLE IV-3 <br /> <br />PERMISSIBLE VELOCITIES - GRASS LINED CHANNELS <br /> <br />Bermuda Grass <br />Buffalo Grass <br />Grass mixture <br /> <br />0-10 <br />0-10 <br />0-5 <br />5-10 <br />0-5 <br />0-5 <br />0-5 <br />0-5 <br />0-5 <br />0-5 <br /> <br />5.0 <br />5.0 <br />5.0 <br />4.0 <br />3.5 <br />3.5 <br />3.5 <br />3.5 <br />3.5 <br />3.5 <br /> <br />Lespedeza sericea <br />Weeping love grass <br />Yellow blue stem <br />Kudzu, alfalfa <br />Crabgrass <br />Annuals <br /> <br />2. Freeboard <br /> <br />The minimum required freeboard above the maximum water <br />surface may be determined with values given in Figure <br />IV-I. For renovation of older channels with super- <br />critical flows and channels designed to flow at super- <br />critical flow due to adjacent structural restraints, ._____ <br />the freeboard should be calculated above the alternate <br />depth or depth of subcritical flow to ensure freeboard <br />should debris cause a hydraulic jump. This depth in <br />rectangular channels can be computed with the equation: <br /> <br />Y2 <br /> <br />Yl <br />="2 <br /> <br />(11 + 8Fl2 <br /> <br />- 0 <br /> <br /> <br />where: <br /> <br />Y2 = alternate depth, feet <br /> <br />YI = supercritical depth, feet <br />Fl = Froude number at supercritical depth <br /> <br />Where channels with nonrectangular cross-sections are <br />encountered, refer to Open Channel Hydraulics by V.T. Chow or <br />Handbook of Hydraulics by King and Brater. <br /> <br />36 <br /> <br />