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~ICZ <br />Mr. Brent Anderson <br />Page Four <br />February 6, 1991 <br />water velocities resulting from steep ditch gradients rather than significant flow <br />quantities. Effective control of flow velocities can best be accomplished by constructing <br />rock check dams at approximately 25 foot intervals along the length of the west ditch. <br />The check dams have been designed to allow flow over the top of the dams without <br />overtopping the ditch. Prior to installation of the check dams, the regraded ditch will <br />be revegetated by broadcast seeding. <br />FEATURE 6. 7 ~ 8 <br />Presently, disturbed area drainage from the north collection dtch and west access road <br />collection ditch flow through an undesignated culvert and then through Culvert 5-4 to <br />Pond 5/6. The inlet of Culvert 5-4, which is a 27 inch culvert approximately 85 feet <br />long, is approximately 8-10 feet below grade. The culvert outlet is approximately 6 feet <br />below grade. Erosion at the outlet of Culvert 5-4 is minimal while significant erosion <br />exists at the inset where the west access road ditch flows into the culvert. <br />In order to simplify the drainage configuration, repair existing erosion, and insure long- <br />term geomorphic stability, lt is proposed that the undesignated culvert be removed, the <br />short connecting channel and eroded areas be backfilled, regraded and revegetated, <br />Culvert 5-4 be removed or backfilled, and that an engineered, armoured channel <br />approximately 220 feet long be constructed to replace the culvert. The proposed <br />channel location is shown on Figure 2, Lower Pit 5 & Access Road -Proposed <br />Drainage Configuration and related design calculations are presented in Attachment 2 <br />to the Bond Release Request Responses. Similar to the proposed North Channel, the <br />South Channel will incorporate a vehicular crossing to provide continued access to the <br />Pit 5 area. <br />Design flow requirements for the disturbed area collection ditch connecting Culvert 5-4 <br />with Pond 5/6 have been compared with the existing ditch configuration. This <br />comparison indicates that the existing ditch is adequate to carry design flows as <br />documented by Attachment 2 to the Bond Release Request Responses. <br />~~,~~ <br />~~ ~ r~~ <br />~~`~`~ z' <br />Vii( 5 <br />