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1 <br />1 <br />1 <br />1 <br />1 <br />u <br />1 <br />construct small parabolic shaped channels.) <br />Subsurface drainage, or riprap channel bottoms, may be necessary on sites that <br />are subject to prolonged wet conditions due to long duration flows or a high water <br />table. <br />. Provide outlet protection at culvert ends and at channel intersections. <br />• Grass channels, at a minimum, should carry peak runoff for temporary construction <br />drainage facilities from the 10-year, 24-hour storm without eroding. Where flood <br />hazard exists, increase the capacity according to the potential damage. <br />• Grassed channel side slopes generally are constructed 3H:1 V or flatter to aid in <br />the establishment of vegetation and for maintenance. <br />• Construct channels a minimum of 0.2 foot larger around the periphery to allow for <br />bpreparations and sod buildu soil bulking during seedbed . p <br />Maintenance Standards <br />During the establishment period, check grass -lined channels after every rainfall. <br />. After grass is established, periodically check the channel; check it after every <br />heavy rainfall event. Immediately make repairs. <br />It is particularly important to check the channel outlet and all road crossings for <br />bank stability and evidence of piping or scour holes. <br />. Remove all significant sediment accumulations to maintain the designed carrying <br />capacity. Keep the grass in a healthy, vigorous condition at all times, since it is the <br />primary erosion protection for the channel. <br />2014 Stormwater Management Manual for Western Washington <br />Volume 11 - Chapter 4 - Page 335 <br />