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Chapter II <br />installed (under the supervision of qualified personnel). To minimize erosion, <br />disturbed areas adjacent to the culverts have been kept to the smallest practical <br />size. When necessary, rip rap has been used for stabilization. <br />Almost all hairpin curves have diversion ditches to divert storm runoff onto natural <br />slopes or into streams, and ditches have been placed at the toe of all cut slopes. <br />Spacing of the ditch relief drains was approved by the Mined Land Reclamation <br />Division. <br />d. Culverts. <br /> <br />The drainage control system was originally designed by Fleming & Associates, Inc. <br />and the engineering staff of Mid-Continent, and 57 culverts were installed along the <br />haulage roads. Further study and evaluation of the system was done by the <br />Morrison-Knudsen Co, who recommended installation of 17 additional culverts. <br />In their evaluation of the system, Morrison-Knudsen used design criteria based on <br />MLRD/OSM regulations for haul roads. Additional engineering design criteria for <br />culvert location and size included consideration of: <br />- Significant tributary drainage areas; <br />- Presence of steep barren slopes on road fill; <br />- Presence of competent bedrock for ditch lining; <br />- Coinciding culvert locations with existing gully and ravine locations; <br />- Coinciding culvert locations with existing vegetated, flatter slopes <br />downstream from culvert outfall points. <br />Culverts (except Dutch Creek) were designed and constructed to convey at least <br />the runoff from a peak storm of the 10-year/24-hour storm event. The Dutch Creek <br />culvert was designed to convey the peak flow from a 100-year/24-hour storm. <br />The culverts were located so as to convey excess water from the haul and access <br />roads, and have a minimum diameter of 18 inches. Energy dissipators, such as rip <br />rap and detention basins, have been placed at the exits of culverts where excessive <br />erosion could occur. Other culverts divert runoff so as to prevent erosion in <br />disturbed areas. <br />Location, installation and periodic inspections of the culverts was/is supervised by a <br />registered engineer. See App. II-B-7 for designs and calculations. <br />e. Maintenance. <br />:: <br />Sediment ponds are examined periodically for: <br />- Seepage from the downside of the embankment, especially <br />around the discharge pipe; <br />- Erosion of embankment slopes; <br />32 <br />