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Warning: This page is an edit and testing page use by the wiki authors. It is not a content page for the Manual. Information on this page may not be accurate and should not be used as guidance in managing stormwater.

Operation and Maintenance of Stormwater Treatment Wetland Practices

Overview of Typical O&M Issues

Stormwater treatment wetland practices are constructed depressions and pools planted with emergent aquatic or wetland vegetation. Wetlands typically remain wet due to relatively impervious sublayers and have retention times that allow pollutants to settle out of stormwater and into the sediment. The vegetated pools can provide excellent wildlife habitat, enhance nutrient cycling, sequester carbon, and offer aesthetic improvements to urban and rural areas if properly maintained.

Wetlands can provide stormwater and other ecosystem services for many years if they are properly maintained. Typical lifespans range between 25 and 75 years, depending on local conditions and ongoing maintenance to the systems (Torres et al., 2015). The most common O&M concerns for stormwater wetland practices include:

• Erosion in the storage pools causing turbid effluent.
• Clogged inlets and outlets. Clogs may occur from accumulation of trash, debris, and sediment.
• Poor vegetative establishment.
• Overgrowth of unwanted vegetation.

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

Design Phase O&M Considerations

Designers should design stormwater treatment wetland practices in ways that prevent or minimize O&M issues. In general, wetland designs should mimic natural wetlands and introduce few complex components. Design phase O&M considerations include:

• Providing pre-treatment and trash racks to prevent clogging or trash accumulation.
• Designing for weather and climate extremes.
  • Flooding and droughts can impact the ecosystem health if not anticipated.
  • Freezing conditions should be planned for in Minnesota (see Cold Climate Suitability). Inlets should not be submerged to avoid freezing. Outlet designs should include baffle weirs or other features to avoid ice formation.
• Anticipating a multi-year establishment phase.
• Shaping the wetland using existing topography and geology, if possible.
• Introducing plants with deep roots along slopes to prevent erosion, emphasizing native species (see Plants for Stormwater Design).
• Selecting plantings suitable for the designed water depth and climate patterns.
• Considering the land use in the drainage area and selecting pollution tolerant species (e.g. salt tolerant species if heavy winter maintenance occurs in the drainage area).
• Completing a planting list with species that will enhance green infrastructure co-benefits, such as pollinator and wildlife habitat, improve infiltration and evapotranspiration, reduce urban heat island effect, provide optimized carbon sequestration, and provide climate adaptation.
• Considering whether vegetation will be established with seeds, seedlings, or transplants. The establishment period will be influenced greatly by this decision.
• Providing easy access to infrastructure that will receive routine maintenance (e.g. inlet and outlet pipes).
• Providing easy access points for all monitoring equipment. Right-of-way access should be designated when the wetland is setback from public or private roads. Right-of-way access should be at least 12 feet wide and minimal slope in order to stage larger vehicles and equipment.
• Providing educational signage to increase public awareness.
• Installing measures like low fencing to prevent damage from pedestrian foot traffic.

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, exterior plantings in the public right of way that conflict with any traffic safety considerations (e.g. sight lines) could require increased O&M, such as pruning or complete removal.

Designers should also recognize the need to perform frequent landscaping maintenance to remove trash, check for clogging, and maintain vigorous and healthy vegetation. Designers can incorporate design solutions to facilitate maintenance activities. Examples include:

• Incorporating multiple and easy site access points
• Installing observation wells
• Providing recommendations of vegetation appropriate to the location

The designer should also provide a site-specific O&M plan that includes the following:

• Construction inspection schedule and checklists
• Post-construction routine maintenance schedule and checklists
• Operating instructions for the practice (if applicable)

For more design information for stormwater wetlands practices, see the “design criteria for stormwater wetlands” page.