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~ • <br />' bedding material under{ayments will be used for riprap linings as needed to ensure structure <br />stability (Figure B-3). <br />' Check dams az critical locations along a diversion or channel may be used to promote channel <br />stability (Figure B-4). Check dams are oriented perpendicular to the flow of water and may be <br />constnrcted using hay bales, loose rock fills or a combination of compacted earthen dams or <br />embankrnents with a loose rock outlet structure that retards surface flow without permanently <br />impounding water (Figure B-5 and Figure B-6). Their primary use is to reduce flow velocrties <br />and to a lesser extent the trapping of sediment. In lower gradient drainages multiple check <br />dams may be used as an intermittent channel liner, replacing riprap or other hard continuous <br />lining materials. A check dam may be a temporary or permanent fixture. Check dams are less <br />effective in continuous flow channels or in drainages that are more than 10 acres in size. Areas <br />prone to flash flooding may further reduce their effectiveness. They can be extremely effective <br />m repairing erosion in large ephemeral gullies. <br />Straw bale filters and check dams may be used for temporary erosion and sediment control <br />' during establishment of vegetation th a concentrated flow structure. Straw bale check dams are <br />usually effective for one growing season or less. Maximum channel slopes for effective use of <br />straw bale filters is less than 20`90. Straw bales will be placed end to end and keyed into the <br />' channel to avoid undercutting. Excessively rocky soils will be avoided when placing straw <br />bale check dams. Properly installed bales will reduce runoff velocities and trap sedrment <br />during the vegetation establishment period. Straw bale check dams will be used where runoff <br />volumes are low. They will be placed on the contour. When used in series the maximum <br />' spacing between bales will vary based on percentage slope between dams (Table B-1). Straw <br />bale dams will be inspected after significant runoff events and maintained as necessary. <br /> <br /> <br />i <br />1 <br /> <br /> <br /> <br /> <br /> <br />Table B-1 Straw Bale Check Dam Maximum Spacing <br />o ( Maxrmum traw B e ec Dam terval <br /> <br />> < l <br />>5<l0 50 <br />>1 < <br />> <_ <br />Rock check dams will be used when channel erosion control is required for more than one <br />growing season or the flow velocities and volumes are larger. Rock check dams may be placed <br />and constructed using typical designs provided that rock is sized for the anticipated flow <br />volumes and permissible velocities. A combination of earthen embanlanent and loose rock <br />check dam (the rock portion functions as aflow-through, non-impounding outlet) may be used <br />to improve construction economics. Use of earthen materials with loose rock will be <br />detertnmed az American Soda's discretion. Gabions may be used to secure rock in check dams <br />in high velocity flow areas (Figure B-7), particularly in narrow restricted channels. The <br />spacing of loose rock check dams may be calculated using the formula: <br />Where: <br /> <br />D =Distance Between Loose Rock Check Dams <br />H =Height of Dam in Feet <br />B-3 <br />