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CITY OF EVERETT STORMWATER MANAGEMENT MANUAL <br /> Typical Biofiltration Swale <br /> Date <br /> Drainage <br /> System Maintenance Activities and Conditions <br /> Frequency Feature ✓ ✓ ✓ ✓ Problem Conditions to Check For That Should Exist <br /> M General Sediment Sediment depth exceeds 2 Inches or inhibits Remove sediment deposits on grass <br /> Accumulation on vegetation growth in 10 percent or more of treatment area of the bioswale.When <br /> Grass swale. finished,swale should be level from side to <br /> side and drain freely toward outlet. <br /> There should be no areas of standing water <br /> once inflow has ceased. <br /> M General Standing Water When water stands in the swale between storms Any of the following may apply:remove <br /> and does not drain freely. sediment or trash blockages,improve grade <br /> from head to foot of swale,remove clogged <br /> check dams,add underdrains or convert to a <br /> wet biofiltration swale. <br /> M General Flow spreader Flow spreader uneven or clogged so that flows Level the spreader and clean so that flows <br /> are not uniformly distributed through entire are spread evenly over entire swale width. <br /> swale width. <br /> M General Constant Baseflow When small quantities of water continually flow Add a low-flow pea-gravel drain the length of <br /> through the swale,even when the weather has the swale or by-pass the baseflow around the <br /> been dry for weeks,and an eroded,muddy swale. <br /> channel has formed in the swale bottom. <br /> M General Poor Vegetation When grass is sparse or bare or eroded patches Determine why grass growth is poor and <br /> Coverage occur in more than 10 percent of the swale correct that condition.Re-plant with plugs of <br /> bottom. grass from the upper slope:plant in the swale <br /> bottom at 8-inch intervals.Or re-seed into <br /> loosened,fertile soil. <br /> M General Vegetation When the grass becomes excessively tall Mow vegetation or remove nuisance <br /> (greater than 10 inches);when nuisance weeds vegetation so that flow not impeded. <br /> and other vegetation starts to take over. Grass should be mowed to a height of 3 to 4 <br /> inches.Remove grass clippings. <br /> M General Excessive Shading Grass growth is poor because sunlight does not If possible,trim back over-hanging limbs and <br /> reach Swale. remove brushy vegetation on adjacent <br /> slopes. <br /> Appendices <br /> F-21 <br />