PERMFILE46723 - Laserfiche WebLink

Home Browse Search

derived from larger scale, aerial photo produced topographic maps. these input parameters were rechecked and are believed to be accurate. No application change necessary. 50. The capacity of the ditches are acceptable at the sha))ow s)opes used in the calculations, and indeed may be oversized. However, no evaluation of channel-bottom stability was performed as apart of ditch design. At 100-year, 24-hour peak flows, the velocities are erosive (e. g. Type 2 channel at 228 cfs equals 10 fps at 1.T foot f]ow depth). The stability of the ditches should 6e evaluated and channe)-bottom treatments specified for the slope conditions to be encountered along the ditch. Rip rap sizing or other treatment criteria should be shown. For temporary channels a IO-year, 24-hour peak flow would 6e appropriate, for permanent channels a 100-year, 24-hour design storm i should be used for estimating peak flow. Response: Revised ditch designs including riprap sizing is included in revised Section D.9 and Appendix G. It should be noted that riprap selection will occur using run-of-mine rock and mine equipment will be used to place the riprap. BMR will make every attempt to ensure that the channels are stable. Exhibit D, Section D.9 and Appendix H revised 2j15J89. 51. A segment face. This of upland diversion ditch does not appear to be a is shown to traverse the west pit preferred design due to stability concerns. If this segment can be redesigned, please do so. If it cannot, describe what measures wi ll be taken to ensure long-term stability. Please clarify whether this ditch will be a permanent structure. 1 Response: The ditch segment crossing the West Pit will cross on a mine bench. Figure C-3 shows the pit bench and highwall configuration. This ditch will be a permanent structure. No application change necessary. 52. No design storm runoff calculations were provided for the ditches below the waste rock disposal facilities. What method was chosen for sizing ditches, and how was the adequacy of this design evaluated? RESponse: The ditches sh designed for an because they wi I control during of security to drainage, but constructed usi 1 the ditch capac site runoff. own for the waste rock disposal areas are not y particular storm event. The ditches are shown 11 be constructed to aid in sediment and erosion normal site runoff, and add an additional level waste rock disposal area grading to ensure they are not necessary. The ditches will be ng a dozer and, using this construction aethod, ities will be more than adequate to handle normal No application change necessary.