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Slope Shape <br />The size, shape, and slope of a <br />reclaimed site will influence the runoff <br />characteristics. Slope angle and slope length <br />can be modified to reduce the water velocity <br />or runoff period. Complex or concave slope <br />shapes should be used on any slopes steeper <br />than 5h:1 v and/or with a length of greater than <br />15 feet. Erosivity of the soil will play a major <br />factor in design. <br />Basic Design and <br />Construction Criteria <br />Selection of Shape <br />To determine which landforms are most suitable for a reclaimed site, observe the <br />landforms of undisturbed watershed areas that have similar soils and characteristics as <br />the site. Long term mass stability requirements must be considered. Slope stability <br />must be evaluated by a Geotechnical <br />Engineer when large fills, tailings, or <br />waste embankments are involved. <br />Convex slope shape is more <br />erodible than a uniform slope because <br />it is steepest near the toe. Concave <br />slopes produce less sediment than <br />either the convex or uniform slope <br />because the concave slope is steepest <br />where the flow is least and has a <br />deposition zone near the bottom of the <br />slope. Long slopes should be broken <br />up with a series of varying lengths that <br />create complex slopes. Concave or <br />complex slopes provide a series of flat <br />toe areas that serve as sediment <br />deposition zones. <br />Flatter slopes will increase <br />rainfall infiltration and decrease <br />sedimentation. However, long <br />moderate slopes are not always better. <br />Reduce slope length by quickly <br />increasing slope angle on sites with low <br />vegetative cover, low soil permeability, <br />Uniform <br />Engineered Fill <br />or Stockpile <br />Stockpile or Fill <br />with Complex <br />Slopes <br />Plan View <br />Cross Section <br />nplex <br />Figure 5.2: Slope shapes, complex slopes maximize <br />sediment deposition zones. Adapted from Norman et. al <br />1996. <br />119 <br />Figure 5.1: Concave slopes reduce amount of fill <br />material required to backfill the distrubance. Gordon <br />Creek 2, 7, & 8 Mines.