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r <br />2.1.1.5 Straw Bale Filters <br /> <br />Straw bale filters and check dams may be used for temporary erosion and sediment <br />control during establishment of vegetation in a concentrated flow structure. Straw bale <br />check dams are usually effective for one growing season or less. Maximum channel <br />slopes for effective use of straw bale filters is less than 20 percent. Straw bales will be <br />placed end to end and keyed into the channel to avoid undercutting. Excessively rocky <br />soils will be avoided when placing straw bale check dams. Properly installed bales will <br />reduce runoff velocities and trap sediment during the vegetation establishment period. <br />Straw bale check dams will be used where runoff volumes are low. They will be placed <br />on the contour. When used in series the maximum spacing between bales will vary <br />based on percentage slope between dams (Table 2-1). Straw bale dams will be <br />inspected after significant runoff events and maintained as necessary. <br />Table 2-1 Straw Bale Check Dam Maximum Spacing <br />Slo e (%) Maximum Straw Bale Check Dam interval (ft) <br />< 2 250 <br />>2 < 5 100 <br />>5<10 50 <br />>10 < 15 35 <br />> 15 < 20 25 <br />2.1.1.6 Rock Check Dams <br />Rock check dams will be used when channel erosion control is required for more than <br />one growing season or the flow velocities and volumes are larger. Rock check dams <br />may be placed and constructed using typical designs provided that rock is sized for the <br />anticipated flow volumes and permissible velocities. A combination of earthen <br />embankment and loose rock check dam (the rock portion functions as aflow-through, <br />non-impounding outlet) may be used to improve construction economics. Use of <br />earthen materials with loose rock will be determined at American Soda's discretion. <br />Gabions may be used to secure rock in check dams in high velocity flow areas (Figure <br />B-7), particularly in narrow restricted channels. The spacing of loose rock check dams <br />may be calculated using the formula: <br />D = H/(0.55) <br />Where: <br />D =Distance between loose rock check dams <br />H =Height of dam in feet <br />Preliminary Response Plan A_8 <br />Yankee Gulch Sodium Minerals Protect <br />American Soda, L.L.P. <br />