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<br />resistant soils are Vn = 7 ft/sec and Yo = 5 ft., the maximum q allowed <br />is q = VnYn = (7 ft/sec)(5 ft) = 35 ft3/sec/ft. This q is also the <br />practical limit for the largest riprap specified in the revised riprap <br />section of the USDCM. <br /> <br />The design chart is also based upon a prismatic channel section <br />throughout, from the upstream channel through the drop to the downstream <br />channel. The maximum (steepest) allowable side slope for the riprap <br />lined channel within the drop structure is 4:1. Flatter side slopes are <br />allowable and encouraged when available right-of-way permits. <br />The classification of riprap chosen for the sloping portion of the <br />structure should be used throughout the structure, including the <br />upstream and downstream aprons, the channel bottom and side slopes. The <br />riprap should extend up the side slopes to a depth equal to one foot <br />above the normal depth projected upstream from the downstream channel, <br /> <br />or one foot above the critical depth, whichever is greater. The maximum <br />fall allowed at anyone drop structure is four feet from the upper <br />channel bottom to the lower channel bottom, excluding the trickle <br />channel. <br /> <br />A detailed description of the drop structure and the design <br /> <br />procedure, going from upstream to downstream is given below and shown 9n <br /> <br />Figure Z. <br /> <br />~. <br />." <br /> <br />ELEMENTS OF THE SLOPING DROP STRUCTURE <br /> <br />1. The upstream and downstream channels will normally be grass <br />lined trapazoidal channels with trickle channels to convey normal low <br />water flows. The maximum normal depth Yn is 5 feet and the maximum <br /> <br />4 <br />