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<br />desired length and installed similarly to wattles made of wood. The roll will be <br />partially buried in a shallow trench cut on the contour. It is expected that the trench <br />and partially buried roll will act as asemi-permeable water and sediment trap, serving <br />to provide an improved growth zone on steep dry slopes. Once rows of vegetation are <br />established they may be expected to create their own habitat and continue to invade the <br />slope. As the rolled blanket deteriorates over time, the vegetation will effectively <br />replace it. <br />2.1.2.6 Level Spreader <br />A level spreader is a level section of ditch that is used to pool water at the end of a <br />ditch, diversion, or channel. The pool formed by the spreader transforms small <br />concentrated flows into sheet flows when it overFlows (Figure C-4). Sheet t7ow is less <br />erosive than a concentrated flow and it may be used to irrigate vegetation. The gradient <br />of the level spreader ditch must be 0 percent. The ditch should be at least 6 inches deep <br />and 6 inches wide at the containment level. The lip of the spreader should be of non- <br />erodible material or be protected with erosion control blanket or gravel mulch (Figure <br />C-5). The structure should be inspected and maintained after significant runoff events. <br />Spreaders help to prevent erosion and improve soil moisture content, which in turn <br />improves plant growth. <br />2.1.2.7 Terracing <br />The slope and length of a hillside combined with soil physical characteristics affect its <br />stability. The longer a slope becomes the more susceptible it is to water erosion. <br />Hillsides of equal slopes and lengths but with different soil physical characteristics will <br />erode at different slope distances. Terraces may be used to limit slope length and <br />effectively control erosion and sedimentation (Figure C-6). Terraces can be built on the <br />level and adequately sized to provide total containment for the slope that drains to <br />them, They can also be placed on low gradient slopes and drain to reconstructed <br />channels. Terrace spacing will be adjusted for slope and soil characteristics. Factors <br />taken into consideration include rainfall, soil erodibility, and steepness of slope. On <br />very steep slopes (i.e., greater than 2h:ly) terracing may be impracticable because of the <br />amount of material that must be moved and the relatively short distance between <br />structures. Terraces make good permanent secondary drainage features for reclaimed <br />areas. <br />2.1.3 Water Treatment <br />A variety of water treatment structures may be used to finish water before it is <br />discharged offsite. Vegetative filters and silt fences will be used to treat overland and <br />concentrated surface flows from small watersheds. For watersheds that are moderate in <br />size or smaller, flows can be treated using a variety of sediment traps either singly or in <br />series. For large watersheds or areas that require special water treatment, <br />Preliminarv Response Plan A-11 <br />Yankee Gulch Sodium Minerels Project <br />American Soda, L.L.P. <br />