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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.