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<br />concentrated flow structures. Where such gradients are exceeded, appropriate lining <br />materials will be used. <br />2.1.1.2 Vegetation Linings <br />Vegetation linings provide the next level of stability over unlined channels. Vegetation <br />linings are relatively inexpensive to establish providing site moisture conditions allow <br />adequate growth. Vegetation species selection is very important in the establishment of <br />an adequate vegetation lining. Species used may include grasses, sedges, rushes, <br />bulrushes, cattails, or other hydrophilic, mat forming plant species. Higher velocity <br />flows may use mat or matrix reinforced vegetation linings to improve root anchoring. <br />Such subsurface reinforcing materials will be applied per manufacturers' specifications. <br />Erosion control blankets may be used to improve surface stability of a concentrated <br />flow structure during the establishment of vegetation linings. Various erosion control <br />blankets are manufactured for different types and lengths of application. When erosion <br />control blankets are required to establish vegetation in flow structures, the type used <br />will be selected for the site according to anticipated plant establishment periods and <br />associated erosion protection needs. <br />2.1.1.3 Riprap <br />Riprap may be used to line concentrated flow structures where steeper channel <br />gradients are necessary. Riprap sizing is critical to the success of this lining method. <br />Materials used for riprap linings will meet or exceed the specifications for rock sizing. <br />Riprap sizing will be determined using generally accepted hydrologic engineering <br />methods. Sizing requirements for riprap will be specified in purchase orders and <br />materials supplied subject to sizing verification. Angular rock will be preferred over <br />smoother materials. Geotextile fabric and bedding material underlayments will be used <br />for riprap linings as needed to ensure structure stability (Figure B-3}. <br />2.1.1.4 Check Dams <br />Check dams at critical locations along a diversion or channel may be used to promote <br />channel stability (Figure B-4). Check dams are oriented perpendicular to the flow of <br />water and may be constructed using hay bales, loose rock fills, or a combination of <br />compacted earthen dams or embankments with a loose rock outlet structure that retards <br />surface Flow without permanently impounding water (Figure B-5 and Figure B-6). <br />Their primary use is to reduce flow velocities and to a lesser extent the trapping of <br />sediment. In lower gradient drainages multiple check dams may be used as an <br />intermittent channel liner, replacing riprap or other hard continuous lining materials. A <br />check dam may be a temporary or permanent fixture. Check dams are less effective in <br />continuous flow channels or drainages that are more than 10 acres in size, Areas prone <br />to flash flooding may further reduce their effectiveness. They can be extremely effective <br />in repairing erosion in large ephemeral gullies. <br />Prehminarv Response Plan A_7 <br />Yankee Gulch $udmm Minerals Project <br />American Soda, L.L.P. <br />