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• 62 <br /> From the results of the hydraulic calculations, none of the existing minor <br /> diversions have excessive velocities. Minor diversion T2 has an estimated ve- <br /> locity of (3.86) just greater than the permissible velocity (3.75) assumed for <br /> design of proposed minor diversions. This difference is small and should not <br /> have a significant effect. <br />• The Fronde number for each channel vas also calculated and is given in <br /> Table 15. All minor diversions are flowing subcritical except the road <br /> diversions. The road diversions have a calculated Fronde number of 1.04 and <br /> represent flow right at critical. Thus, the flow in these two channels will <br /> be near critical depth flow conditions. The flows in these channels were re- <br /> latively low and high Fronde numbers should not cause problems. <br />1 r The existing minor diversions Bl and 82 are stable based on the averago <br />. <br />1 slope. However, the last few feet of these diversions have very sharp drops <br />~' as they flow into sediment pond "H". Because of the steep slopes, these short <br /> sections become unstable in terms of erosion. This condition can result in <br /> headcutting up the entire length of the diversion. These areas should be checked <br />• in the field and adequately protected by riprap. The design depths were given <br /> in Table 17 for both existing and proposed minor diversions. The recommended <br /> design depths for the existing diversions should be checked in the field and <br /> any modifications needed to increase the depth made, if required. <br /> 6.4.2 Major Diversion Channels <br /> Within the G.E.C. permit area on the Magpie Creek drainage, there are tvo <br /> existing major diversion channels which divert runoff from large undisturbed <br /> areas through the mine pit area. One of these major diversion channels (CH-15) <br /> diverts runo_'f along the east side of the existing mine pit. This dive=~io~ <br /> channel joins the Magpie Creek diversion channel with Dorchester's permit <br /> boundary. The channel invert of CH-15 is approximately 6.5 feet above the <br /> invert of the Magpie Creek diversion channel. The existing slope of this chan- <br /> nel is 0.037 except where it flows down the bank of the Magpie Creek diversion <br /> channel at a slope of 0.212. The second major diversion channel (CH-17) diverts <br /> water through the G.E.C. permit area and is the downstream end of the N.agpie <br /> Creek diversion channel. The runoff then flows into a depression storage area <br />• and then through a nine-foot culvert under the haul road. The existing slope <br />