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<br />Ditches <br />Diversion ditches, except as previously noted, were <br />correctly placed and sized. The Manning 's equation for flow in <br />open channels, <br />Q = 1.486 AR 2/3 g 1/2 <br />n <br />was applied to a standard channel to determine if the carrying <br />capacity was more than the calculated peak flow for the 10 year <br />event, except for the in-mine ditches and ditch E which was <br />designed to carry the 25 year peak flow from the temporary <br />impoundment. The value of n in all cases was 0.030 which is <br />correct for a smoo th earthen channel. Freeboard was adequate in <br />all cases. <br />Velocities and Froude numbers were calculated for all <br />ditches and indicated potential supercritical flow conditions in <br />several instances as shown in Table 1. <br />Table 1 <br />Ditch V fps Fr <br />A-east \~\ X30 <br />B-east _ 1:2"3 <br />D ~, \ 1 .18 <br />E 9.6 6 ~'\oy Pc~~ 1 .8 7 <br />In-mine ditches 10.7 ~ J 2.95 <br />Ditch east of spoil pile, <br />Pit 1 8.5 2.15 <br />-14- <br />