1001 14TH ST 2024-03-01 - Laserfiche WebLink

Table V-A.8: Maintenance Standards - Typical Biofiltration Swale Maintenance Defect or Prob- Condition When Maintenance is Needed Recommended Maintenance to Correct Problem Component lem Sediment Accu- Remove sediment deposits on grass treatment area of the bio-swale. When finished, swale should be level from side to side and drain freely mulation on Sediment depth exceeds 2 inches. toward outlet. There should be no areas of standing water once inflow has ceased. Grass General Standing Water When water stands in the swale between storms and does not Any of the following may apply: remove sediment ortrash blockages, improve grade from head to foot of swale, remove clogged check dams, drain freely. add underdrains or convert to a wet biofiltration swale. Flow spreader Flow spreader uneven or clogged so that flows are not uniformly Level the spreader and clean so that flows are spread evenly over entire swale width. distributed through entire swale width. Table V-A.8: Maintenance Standards - Typical Biofiltration Swale (continued) Maintenance Defect or Prob- Condition When Maintenance is Needed Recommended Maintenance to Correct Problem Component lem Constant Base- When small quantities of water continually flow through the swale, flow even when it has been dry for weeks, and an eroded, muddy chan- Add a low -flow pea -gravel drain the length of the swale or by-pass the baseflow around the swale. nel has formed in the swale bottom. Poor Vegetation When grass is sparse or bare or eroded patches occur in more Determine why grass growth is poor and correct that condition. Re -plant with plugs of grass from the upper slope: plant in the swale bottom at 8- Coverage than 10% of the swale bottom. inch intervals. Or re -seed into loosened, fertile soil. When the grass becomes excessively tall (greater than 10- Mow vegetation or remove nuisance vegetation so that flow not impeded. Grass should be mowed to a height of 3 to 4 inches. Remove grass clip - Vegetation inches); when nuisance weeds and other vegetation starts to take over. pings. Excessive Shad- Grass growth is poor because sunlight does not reach swale. If possible, trim back over -hanging limbs and remove brushy vegetation on adjacent slopes. ing Inlet/Outlet Inlet/outlet areas clogged with sediment and/or debris. Remove material so that there is no clogging or blockage in the inlet and outlet area. Trash and Debris Trash and debris accumulated in the bio-swale. Remove trash and debris from bioswale. Accumulation Eroded or scoured swale bottom due to flow channelization, or For ruts or bare areas less than 12 inches wide, repair the damaged area by filling with crushed gravel. If bare areas are large, generally greater Erosion/Scouring higher flows. than 12 inches wide, the swale should be re -graded and re -seeded. For smaller bare areas, overseed when bare spots are evident, or take plugs of grass from the upper slope and plant in the swale bottom at 8-inch intervals. 2019 Stormwater Management Manual for Western Washington Volume V - Appendix - Page 1010