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• <br />~1 <br /> <br />requirernant provides for the stability of the material under loads transferred by flowing water <br />and for mass stabiliry of the riprap itself. If it is found that plactng riprap this size in not <br />practical, k is suggested that the D„ (diameter that passes 50 percent of the material in a <br />gradation analysis) material size, 19-inches, ba placed and secured using grout. Grouted rip- <br />rap would then have to be checked periodically, and maintained as required. <br />Ouches also route runoff around from the back of the waste bank crest and into the side <br />ditches. This crest ditch should be constnuted at a 2 percent minimum grade, a 1.5-foot <br />minimum depth, and 2:1 side slopes. Flow rates o! approximately 3.9 cubic feet par second <br />(cfsl produced n these dkches may require slope protection, but sines their position changes <br />with the development of the waste bank, h is suggested that sops protection be placed only <br />if the waste bank crest is not expected to advance for an extended period and monitored <br />closely for excess erosion. <br />An upland diversion ditch wiY be constructed above the site to manage flows from the upland <br />watershed of approximately 150 acres. This upland ditch can be constructed partly along an <br />existing road, and partly below the road to induce fbw direction to the west, and disdwrge <br />in a western drainage as shown on Orawing 95255-01. The minimum depth shook( be 1.5 <br />feet, with 2:1 side slopes. Riprap slope protection wip be required to prevent scour. The <br />slope protection requirements are provided on Drawing 95255-03. The maximum rock size <br />may be replaced with the aia rock size if it is grouted in place and maintained. <br />The upland diversion ditch dsdtarges into another drew adjacent to the west. A CMP culvert <br />exists bebw the rairoad trades at the mouth of mu draw to transport runoff. To augment the <br />existing CMP culvert at this loeadon, h is suggested that an additional CMP culvert be installed <br />with the capacity to handle the additional flows contributed by the upland d'rversan ditch. A <br />24inch diameter CMP covert was calculated to adequately transport the additional flows on <br />an 8 percent sbpa. ' <br />96266/t424.HPT Col Mi[N W~sn B~Mi Dwgi far tfu sa~florr[ tSwk Mlrw <br />Oe[otw 1990 WESTEC, Iro. <br />11 <br />