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• Exhibit DD shows cross-sections for Engleville Gulch. Cross <br />sections A-A' through H-H' were developed during the initial <br />environmental inventory. The locations of these cross sections on <br />a plan view map are shown on Exhibit AA. <br />Three additional cross sections are added (I-I' through R-R') to <br />provide better information in the permit area. These cross <br />sections are shown on Exhibit MM because their vertical scale has <br />not been exaggerated. The locations of these cross sections are <br />given oa Exhibit 1(K. <br />Cross sections I-I' through <br />for Engleville Gulch during <br />cross sections are critical <br />facilities ouch as the haul <br />plains were calculated by d~ <br />sectional area is needed to <br />R-R' are used to develop flood plains <br />the 100 year - 24 hour event. These <br />because they are closest to <br />road and the sediment pond. The flood <br />:termininq what channel cross <br />pass the design flow of 1559 cfs. <br />Using Manning's Equation: <br />Q = 1559 cfs <br />Manning's n = .OS (stony sections of natuzal channels) <br />Channel grade s = 3.9+! <br />• By assuming a certain channel level, the wetted perimetez, <br />hydraulic radius and area are calculated. Sy trial and error, the <br />level of flow for each cross section is determined. These flow <br />levels are also shown on the cross sections of Exhibit DD. <br />As is seen from the flow levels on the cross sections, the peak <br />of 1559 cfs is adequately contained although Lhe flood plain doss <br />extend slightly east of the channel in cross section J-J'. This <br />should not present a problem because no facilities are planned in <br />the vicinity. The embankment between Engleville Gulch and the ~1 <br />Collection Ditch in the same area contains a freeboard of 2 feet. <br />This freeboard will be maintained in this area to ensure against <br />overtopping. If overtopping or washout of the embankment would <br />occur, the Engleville Gulch flow could enter the sediment pond <br />and possibly erode the dam. In addition to maintaining this <br />freeboard, large erosion protection rip-rap will be installed on <br />the embankment, if it is determined that .the existing bank <br />material may not be adequate. <br />Exhibit KR shows the mine facilities in relation to Engleville <br />Gulch. No facility is within reasonable threat of being affected <br />by the 100 year flow. <br /> <br />16 <br />Rev. 04/30/90 <br />