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ACS Mr. Brent Anderson Page Two February 6, 1991 Primary concerns as expressed by the CMLRD and observed in the field include varying levels of erosion in areas 4, 5, 7, 10 and 11 as designated above. Proposed remediation measures include elimination of culverts where feasible, consolidation of drainages, repair of erosion, and stabilization of critical channel sections through construction of engineered armoured channels, placement of rock check dams, and revegetation as appropriate. The proposed revised drainage configuration is illustrated by Figure 2, Lower Pit 5 & Access Road -Proposed Drainage Configuration, with specific modfications described in the following discussions. FEATURES 1 & 10 Presently the undisturbed area drainage diversion for Pit 5 parallels the existing natural ,~h ~ drainage at a separation of approximately 20-50 feet for a distance of approximately Q`,~, ~p~~1,100 feet. Since both channels carry undisturbed area flows, there is no need to retain ~~'' r th~n,,o separate channels in such close proximity. Elimination of one channel will provide j~ a,~'`'y~,, for the most effective conveyance of flows. ,,,~ ~~ ~ '~ c~ It is proposed that the diversion be connected to the natural channel in the area where c~,r ~ j- ~~ yet ~ ~f"~ v~, ~ ' ~~~ the two channels turn to the east and slope gradients decline. The connecting channel u~ ~~ ~,~°'~(~;~ `~ti segment will be constructed with the same dimensions and approximately the same ~~,~`~ ~~'~"~"~ gradient as the diversion channel and will be revegetated upon completion. Dependent ~ ~.~ upon channel characteristics at this location, lt may be appropriate to armor the natural ~ ii ~ o~ V~ channel at the junction. The existing diversion channel is relatively small and significant ~s~" we ~ 5~ vegetative cover has developed on ditch areas. Rather than redisturb the entire length ~ ~ n~~~•,~ of the diversion below the proposed junction with resultant potential for increased D ~~ ~~I erosion, placemern of water bars just below the junction and every 100 feet ~,n ,' r ' downgradient is proposed to promote sediment deposition and natural filling of the `d D o~`~ ditch. 0~ ~/~9/~j FEATURE 11 3/i~4 i~'~~Icv ~1O lv o,C O~ Flows from the Pit 5 north diversion, the existing natural drainage, and the Pit 6 west diversion presently flow through Cubert 5-3. The inlet of culvert 5-3, which is a 27 inch culvert approximately 70 feet long, is approximately 3 feet below grade. The culvert outlet is approximately 10 feet below grade. Relatively steep culvert gradient, combined with outlet flows and lack of outlet protection, have resulted in progression erosion at the outlet extending approximately 30-70 feet downgradient in the diversion ditch. In order to remediate existing erosion and provide for long term geomorphic stability, it is proposed that Culvert 5-3 be either removed or backfilled, eroded areas be backfilled, graded and revegetated, and an engineered, armoured channel segment