Operation and maintenance of wet swale (wetland channel)

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The most frequently cited maintenance concern for wet swales is that they provide a breeding ground for mosquitoes. Common operational problems include:

• blockage by debris and vegetation;
• sediment accumulates in the swale, reducing the storage volume;
• slope stabilizing vegetation is lost; and
• invasive plants out-compete native vegetation

Design phase maintenance

Implicit in the design guidance is the fact that many design elements of filtering systems can minimize the maintenance burden and maintain pollutant removal efficiency. Key examples include:

• limiting drainage area;
• providing easy site access (REQUIRED);
• providing pretreatment (RECOMMENDED); and
• utilizing native plantings (see Plants for Stormwater Design).

Wet swales can be designed, constructed and maintained to minimize the likelihood of being desirable habitat for mosquito populations. Designs that incorporate constant inflows and outflows, habitat for natural predators, and constant permanent pool elevations limit the conditions typical of mosquito breeding habitat (see section on mosquito control). For more information on design information for wet swales, link here.

Construction phase maintenance

Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). Inspections during construction are needed to ensure that the wet swale practice is built in accordance with the approved design standards and specifications. Detailed inspection checklists should be used that include sign-offs by qualified individuals at critical stages of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided below.

Wet swale construction inspection checklist.
Link to this table
To access an Excel version of form (for field use), click here.

Project:
Location:
Site Status:
Date:
Time:
Inspector:
Construction Sequence	Satisfactory / Unsatisfactory	Comments
1. Pre-Construction
Pre-construction meeting
Runoff diverted (Note type of bypass)
Facility area cleared
Project benchmark near site
Facility location staked out
Temporary erosion and sediment protection properly installed
2. Excavation
Size, location, and inverts per plans
Side slopes stable
Lateral slopes completely level
Longitudinal slopes within design range
Groundwater/bedrock verified
Stockpile location not adjacent to excavation area and stabilized with vegetation and/ or silt fence
Verify stockpile is not eroding
3. Structural Components
Outlets installed pre plans
Pretreatment devices installed per plans
Soil bed composition and texture conforms to specifications
Inlets installed per plans
4. Vegetation
For native wet swales, plants and materials ordered 6 months prior to construction
For native wet swales, construction planned to allow for adequate planting and establishment of plant community
Complies with planting specs
Topsoil complies with specs in composition and placement
Soil properly stabilized for permanent erosion control
5. Final Inspection
Project:
Dimensions per plans
Check dams operational
Pre-treatment operational
Inlet/outlet operational
Effective stand of vegetation stabilized per specifications
Construction generated sediments removed
Contributing watershed stabilized before flow is diverted to the practice
Comments:
Actions to be taken:

Post-construction operation and maintenance

Proper maintenance is critical to the successful operation of a wet swale. Without regular maintenance, wet swales can fill in with sediment and lose important vegetation. This can lead to a reduction or elimination of pollutant removal capacity. Warning: A maintenance plan clarifying maintenance responsibility is REQUIRED. Effective long-term operation of filtration practices necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value.

Inspection and maintenance planning

A maintenance plan clarifying maintenance responsibilities is REQUIRED. Effective long-term operation of wet swales necessitates a dedicated and routine maintenance schedule with clear guidelines and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value. Some important post-construction considerations are provided below along with RECOMMENDED maintenance standards.

• A site-specific O&M plan that includes the following considerations should be prepared by the designer prior to putting the stormwater practice into operation:
  • Inspection and routine maintenance checklist (see below)
  • Vegetation maintenance schedule

Related pages

• Terminology for swales (grass channels)
• Overview for wet swale (wetland channel)
• Types of filtration
• Design criteria for wet swale (wetland channel)
• Construction specifications for wet swale (wetland channel)
• Operation and maintenance of wet swale (wetland channel)
• Assessing the performance of wet swale (wetland channel)
• Calculating credits for wet swale (wetland channel)
• Cost-benefit considerations for wet swale (wetland channel)
• Case studies for wet swale (wetland channel)
• External resources for wet swale (wetland channel)
• References for wet swale (wetland channel)
• Requirements, recommendations and information for using wet swale in the MIDS calculator
• Requirements, recommendations and information for using swale side slope as a BMP in the MIDS calculator
• Wet swale (wetland channel) and interesting websites