Operation and maintenance of dry swale (grass swale)

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Green Infrastructure: Dry swales can be an important tool for retention and detention of stormwater runoff. Depending on design and construction, swales may provide additional benefits, including cleaner air, carbon sequestration, improved biological habitat, and aesthetic value.

The most frequently cited maintenance concern for dry swales is surface soil/media and underdrain clogging caused by organic matter, fine silts, hydrocarbons, and algal matter. Common operational problems include:

• standing water;
• clogged soil/media surface;
• clogged inlet, outlet or underdrains; and
• invasive plants out-compete native vegetation.

Design phase maintenance

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

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

For more information on design information for dry swales, link here.

Construction phase maintenance

Proper construction methods and sequencing play a significant role in reducing problems with operation and maintenance (O&M). In particular, with construction of filter and infiltration practices the most important action for preventing operation and maintenance difficulties is to ensure that the contributing drainage area has been fully stabilized prior to bringing the practice on line (this is a REQUIRED practice).

Warning: It is required that the contributing drainage area has been fully stabilized prior to bringing the practice on line

Inspections during construction are needed to ensure that the filter/infiltration 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.

Dry swale construction inspection checklist