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• 58 <br />material. The recommended velocity is 3.75 feet per second. For the existing <br />minor diversions, the maximum slope allowable for the permissible velocity is <br />also calculated. lihen the final designs of existing and proposed minor diversions <br />are determined by G.E.C. Hinerals, Inc., the local slopes should be considered. <br />If the slopes are significantly milder through individaul sections, the di- <br />version should be given additional depth. If the slopes are much steeper and the _ <br />resulting velocities too high, measures should be taken to reduce the slope or <br />dissipate the energy. Locations of all existing and proposed minor diversions <br />are shown on Hydrology Map 2, Appendix A. <br />The increased depth in the minor diversions due to aggradation will be small <br />since the diversions have higher transport capacity than the overland flow areas <br />~. from which they receive sediment. An aggradation value of 0.50 feet vas added <br />to all the triangular channels since the bottom portion of the channel is small <br />(' and can be quickly filled with debris or loose dirt which blows into the <br />diversions.. No aggradation was added to the trapezoidal channels. <br />The increase in depth of flow due to sand-wave movement is the result of <br />antidune formation. Antidunes consist of sand waves which are in phase with the <br />water surface. in other words, the water waves on the water surface correspond <br />to similar sand waves on the channel bed. Antidunes will form in sand beds when <br />the combination of velocity, shear stress on the bed, and sediment diameter <br />reach specified limits. The median sediment size in the channels is 24 mm. <br />From Simons and Senturk (1977) for sediment of this size, the flow will be in <br />the antidune range rhen the product of velocity and shear stress (referred to as <br />"stream power") is in excess of five pounds per second per foot. The shear stress <br />on the bed is the product of energy slope, depth of flow and specific weight of <br />water. Table 16 presents the estimated stream power for each :.:inor di~ersicn. <br />For the diversions which antidunes are expected to form, their height can <br />be predicted by the equation <br />2 <br />Ah ~ (0.14) (2n) 9 (1) <br />in which Ch is the antidune wave height, V is the average 'low velocity, and <br />g is the acceleration due to gravity. The waves will break i. their heicht is <br />. larger than the depth of flow. Therefore, if the calculated antidune wave height <br />is larger then the depth of flow, the flow depth is the actual wave height. <br />The antidune wave height is given in Table 16 for those minor diversions where <br />