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Best Management Practices:Diversion Ditches <br /> not flow so fast that water erodes and scours Considerations <br /> the ditch walls. In order to accommodate this, Although in most cases, water that flows <br /> a minimum slope of IOO:I 400 feet horizon- through a mine waste pile will degrade in <br /> tal to one foot vertical)and maximum slope of quality, in a few cases water quality will <br /> 33:I(33 feet horizontal to one foot vertical)is remain the same or even improve. There- <br /> recommended. The bottom of the ditch fore, it is important to sample the water <br /> should be smooth with no pits or holes. above and below the pile to determine the <br /> changes in water quality before doing any <br /> The ditch should be vegetated to slow the ditch construction. <br /> water flow and decrease the opportunity for <br /> erosion of the ditch by moving water. Seeding <br /> of the ditch walls and bottom is easiest during Initial costs <br /> low flow times of the year such as late summer Cost of diversion ditches will vary depending <br /> or fall. Recommendations for vegetation are on their length and the equipment used to <br /> discussed in BMP#6 of this brochure. construct them. <br /> If the slope of the ditch must be greater than <br /> 33:I, then the ditch should be lined with Maintenance <br /> riprap (medium to large rocks) to slow the Periodic inspection and maintenance is <br /> flow of water and decrease the erosion and required for continued effectiveness of diver- <br /> scouring along the ditch walls. If riprap is sion ditches. Water should flow smoothly <br /> used, it is important to select rocks that are along the base of the ditches and should not <br /> not contaminated by mining and will not overflow the ditch walls. Ditch maintenance <br /> degrade the water in the ditch. Often in high- should include cleaning debris out of the <br /> altitude areas, suitable rocks can be found at ditches, checking that there is a constant drop <br /> the base of steep talus slopes. in slope of the ditch bottom, and repairing <br /> erosion along ditch walls. Generally, inspec- <br /> tions should be conducted before and after <br /> When to do it spring runoff and after major storm events. <br /> Construction is generally easiest when per- <br /> formed during low flow times of the year,such <br /> as late summer or fall. <br /> ow <br /> DIVERSION DITCH IN ROCKY AREA DIVERSION DITCH LINED WITH RIPRAP <br /> 15 <br />