1001 N BROADWAY LEARNING RESOURCE CENTER 2026-01-15

Table V-A.21: Maintenance Standards - Bioretention Facilities Recommended Frequency a Maintenance Com- Condition when Maintenance is Needed (Stand- Action Needed (Procedures) ponent Inspection Routine Main- ards) tenance Facility Footprint • Eliminate cause of erosion and stabilize damaged area(regrade, rock, vegetation, erosion control matting) • For deep channels or cuts (over 3 inches in ponding depth), temporary erosion control measures should be put in place Erosion(gullies/rills)greater than 2 inches deep until permanent repairs can be made. B, S Properly designed, constructed and established facilities with appropriate flow velocities should not have erosion rob- around inlets, outlet, and alongside slopes P Y 9prob- lems except perhaps in extreme events. If erosion problems persist, the following should be reassessed: (1)flow volumes from contributing areas and bioretention facility sizing; (2)flow velocities and gradients within the facility; and (3)flow dissipation and erosion protection strategies at the facility inlet. Earthen side slopes and berms A Erosion of sides causes slope to become a hazard Take actions to eliminate the hazard and stabilize slopes A, S Settlement greater than 3 inches (relative to undis- Restore to design height turbed sections of berm) A, S Downstream face of berm wet, seeps or leaks evid- Plugan holes and compact berm ma require consultation with engineer, particularly for larger berms Y P (may q 9 P Y 9 ) • Eradicate rodents (see"Pest control") A Any evidence of rodent holes or water piping in berm • Fill holes and compact(may require consultation with engineer, particularly for larger berms) • Repair/seal cracks Concrete sidewalls A Cracks or failure of concrete sidewalls • Replace if repair is insufficient Rockery sidewalls A Rockery side walls are insecure Stabilize rockery sidewalls(may require consultation with engineer, particularly for walls 4 feet or greater in height) All maintenance vis- Facility area its (at least bian- Trash and debris present Clean out trash and debris nually) Remove excess sediment Accumulated sediment to extent that infiltration rate • Replace any vegetation damaged or destroyed by sediment accumulation and removal A, S is reduced(see"Ponded water")or surface storage • Mulch newly planted vegetation Facility bottom area capacity significantly impacted . Identify and control the sediment source(if feasible) • If accumulated sediment is recurrent, consider adding presettlement or installing berms to create a forebay at the inlet During/after fal I leaf drop Accumulated leaves in facility Remove leaves if there is a risk to clogging outlet structure orwaterflow is impeded Sediment,vegetation, or debris accumulated at or A, S blocking(or having the potential to block)check dam, Clear the blockage Low permeability flow control weir or orifice check dams and weirs A, S Erosion and/or undercutting present Repair and take preventative measures to prevent future erosion and/or undercutting A Grade board or top of weir damaged or not level Restore to level position 2019 Stormwater Management Manual for Western Washington Volume V-Appendix A -Page 1019