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HomeMy Public PortalAboutFinal Draft Detention Basin BrochureRoutine Maintenance Mow at least two or three times a year, more frequently if desired. Do not fertilize the grass in the basin. Consider growing native prairie plants as a low maintenance alternative to turfgrass. Remove debris from all conveyances including the pilot channel, low flow orifice, and on and inside the outlet structure. Debris may include sediment, dead vegetation, trash, etc. These materials tend to accumulate in the pilot chan- nel and at the trash rack or low flow orifice. Repair areas with erosion and replant or sod patches of bare soil. Remove problem vegetation such as dense stands of cattails and trees. Shrubs and trees growing along berms and embankments must be removed. Replace missing or damaged steel grates and manhole lids on the outlet structure. Non-Routine Maintenance Repairing crumbling or cracked pipes and con- veyances such as the pilot channel and outlet control structure. Reconstruction of failed berms, collapsed re- taining walls, and washed out spillways. Dredging accumulated sediment that has col- lected within wet detention basins. Repairing or replacing safety fences along the perimeter of steep embankments. Removing nuisance wildlife such as beavers and groundhogs. Grading to restore positive drainage along the Detention Basins Post-Construction Best Management Practices (BMPs) Ownership & Maintenance MSD Project Clear Division of Environmental Compliance 10 East Grand Avenue St. Louis, MO 63147-2913 Phone: 314.436.8710 MSDProjectClear.org Find us @MSDProjectClear The Takeaway A detention basins is a private stormwater management facility and it is the property owner’s responsibility to maintain it in good working condition. Maintenance related activities should never result in a modification to a basin that could change its approved design or cause it to perform differently from its approved design. Modifications to a basin that could result in changes to its approved design must be approved by MSD Project Clear’s Development Review Program. For more information, scan to visit our Stormwater Best Management Practices (BMP) Toolbox. MSD Customer Service: 314.768.6260 Metropolitan St. Louis Sewer District Project Clear MSDProjectClear.org What is a Detention Basin? A detention basin is a stormwater management structure that collects runoff during a rain event and then releases that water through a control structure at a reduced flow rate to decrease the risk of flooding. Detention basins are required on sites with new development or redevelopment. Historically, detention basins served as flood control devices, but modern basins can also be designed to protect stream channels from excess erosion and in some cases improve water quality, which benefits local waterways and adjacent property. Detention basins may be designed to be dry between rain events, or remain wet retaining some water throughout the year. Who is responsible for maintenance? Detention basins are private stormwater management facilities and belong to the property owner. Therefore, the property owner is responsible for maintaining the detention basin and ensuring it is operated in good working condition as agreed upon. Ordinance No. 15048 provides MSD Project Clear with the authority to require the property owner to make repairs when a basin is found to be in poor condition and not functioning properly. MSD periodically inspects each basin in its service area and responds to all related complaints and concerns. Inspection & Maintenance Detention basins require regular inspection and routine maintenance to insure they work properly when it rains. If maintenance is ignored, over time the basin will stop working, which could create a public hazard and/or cause or contribute to downstream flooding and property damage. Failing basins could adversely impact aquatic habitat and create nuisances related to overgrown plants, unsightly algae, problem wildlife and insects, and even odors. Basins that are allowed to decline into a failed state can be expensive to repair! Inspections Inspections are integral to maintaining the performance of a basin and should be performed regularly or following a major storm event. An inspection generally includes examining the inlet pipe (s), forebay (if applicable), interior of the basin including the pilot channel, the embankments and berms, the outlet control structure and the outfall. The purpose of the inspection is to make sure all of these components are in good working condition and determine any maintenance activities that may be necessary to keep the basin working properly. Inspection findings such as overgrown/invasive vegetation, accumulated sediment and other debris, a blocked low flow orifice, and areas with erosion should be noted and scheduled for maintenance. Corrective actions should be taken immediately if a serious condition is discovered. Maintenance Basins should be maintained on a regularly basis or as needed in order to ensure they will operate effectively during a storm. Regular maintenance will also help to prevent minor conditions from evolving into major problems. In general, maintenance should be performed at a minimum twice each year, in late winter/early spring and in the fall. Types of Detention Basins Wet Detention Basins are basins that contain a permanent pool of standing water at a designed elevation. Wet basins function to provide both stormwater detention for flood control purposes and improve water quality. Wet basins remove stormwater pollutants through physical, biological, and chemical processes within. Dry Detention Basins are basins that detain water during and shortly after a rain event, but otherwise remain dry. Dry basins may be installed above or below ground. Above ground basins are usually planted with turfgrass for easy maintenance. Underground basins contain one or more interconnected chambers constructed of reinforced concrete, corrugated metal, high strength plastics. Dry detention basins are intended for flood control, but may capture sediment and other debris such as plant and trash material in the process.