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_ requirement provides for the stability of the material under loads transferred by flowing water <br />~• and for mass stability of the riprap itself. If it is found that placing riprap this size in not <br />practical, it is suggested that the D60 (diameter that passes 50 percent of the material in a <br />gradation analysis) material size, 19-inches, be placed and secured using grout. Grouted rip- <br />rap would then have to be checked periodically, and maintained as required. <br />Ditches also route runoff around from the back of the waste bank crest and into the side <br />ditches. This crest ditch should be constructed at a 2 percent minimum grade, a 1.5-foot <br />minimum depth, and 2:1 side slopes. Flow rates of approximately 3.9 cubic feet per second <br />(cfs) produced in these ditches may require slope protection, but since their position changes <br />with the development of the waste bank, it is suggested that slope 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 will 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 flow direction to the west, and discharge <br />• in a western drainage as shown on Drawing 95255-01. The minimum depth should be 1.5 <br />feet, with 2:1 side slopes. Riprap slope protection will 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 D~ rock size if it is grouted in place and maintained. <br />-~ <br />The upland diversion ditch discharges into another draw adjacent to the west. A CMP culvert <br />exists below the railroad tracks at the mouth of this draw to transport runoff. To augment the <br />existing CMP culvert at this location, it is suggested that an additional CMP culvert be installed <br />with the capacity to handle the additional flows contributed by the upland diversion ditch. A <br />24-inch diameter CMP culvert was calculated to adequately transport the additional flows on <br />an 8 percent slope. <br />96256/1424.RPT Cael Mine Weate Bank Design for the senborn Creek Mins <br />October 1898 WESTEC, Inc. ~ t <br />