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Operation and Maintenance of Vegetated Filter Strips

Overview of Typical O&M Issues

Vegetated filter strips, also known as buffer strips or buffers, are vegetated land areas between a pollutant source and a surface water body. They can be stand-alone practices or used as a pre-treatment practice to other practices like bioretention or ponds. They reduce the flow velocity of water and filter and infiltrate pollutants such as sediment from stormwater. Vegetated filter strips may be subject to high public visibility, trash loads, sedimentation, pedestrian traffic, and even vehicular traffic or loads.

Vegetated filter strips require dedicated and regular maintenance to ensure proper and long-lasting operation, and in most cases a vegetated filter strip should be designed to be effective for at least 10 years (NRCS, 2010). The most frequently cited O&M concerns for vegetated filter strips include:

  • Flow channelization and erosion.
  • Insufficient/inadequate vegetative cover.
  • Sediment and debris accumulation leading to practice clogging.

The sections below describe best practices to prevent or minimize these common problems.

Design Phase O&M Considerations

Designers should design these practices in ways that prevent or minimize O&M issues. Examples include:

  • Using a maximum drainage area to filter strip area ratio of 6:1
  • Limiting the lateral slope to less than or equal to 1%
  • Checking that the maximum groundwater level is 2 to 4 ft below the filter strip
  • Providing a vegetation design plan, emphasizing erosion resistant and native plantings (see Plants for Stormwater Design) to enhance pollinator and wildlife habitat, improve infiltration and evapotranspiration, reduce urban heat island effect, provide optimized carbon sequestration, and provide climate adaptation. Site-specific plant selections should take into account sun exposure, shade, proximity to traffic corners (visibility issues), interior vs exterior plantings, salt-tolerant plants, etc. The selection of plantings suitable to their immediate surroundings will minimize long-term care and replacement frequency.
  • Designing the filter strip length based on the hydrologic soil group, slope, and vegetation (PADEP 2006).
  • Providing pretreatment (e.g. gravel trench spreader) if necessary. Pretreatment can be used to dampen the effects of high or rapid inflow, dissipate energy, provide additional storage, and prevent the BMP from becoming overloaded by sediment. Pretreatment is a required part of infiltration and filtration practices covered under the Minnesota Construction Stormwater General Permit. Vegetated filter strips are often used as a pretreatment practice to meet the intent of the stormwater permit, as identified in sections 16 and 17, but are designed with a different set of standards when they are a standalone structural practice.
  • Installing berms where necessary to direct the flow and prevent bypassing.
  • Prohibiting any kind of traffic through the installation of a visible barrier or signage.
  • Providing educational signage to increase public awareness.

Designers should consult and include any local requirements regarding green infrastructure. O&M considerations often depend on whether the practice is located on public land, private land, or in the public right of way. For example, plantings in the public right of way that conflict with any traffic safety considerations could require increased O&M, such as pruning or complete removal.