Vegetated Swales

Vegetated swale at Waitakere City Council carpark.

Swales are vegetated areas used in place of curbs or paved gutters to transport stormwater runoff. They also can temporarily hold small quantities of runoff and allow it to infiltrate into the soil.

A vegetated swale may also be known as a grassed channel, dry swale, wet swale or biofilter.

Vegetated swales can serve as part of a stormwater drainage system and can replace kerbs, gutters and storm sewer systems. Swales are best suited for residential, industrial, and commercial areas with low flow and smaller populations.

Swales can have significant environmental benefits but they do have limitations. Swales can reduce peak flows, remove pollutants, and promote runoff infiltration, and they tend to have lower capital costs. However, vegetated swales are typically ineffective in, and vulnerable to, large storms, because high-velocity flows can erode the vegetated cover.

While swales are generally used as a stand-alone stormwater Best Management Practice (BMP), they are most effective when used in conjunction with other BMPs, such as wet ponds, infiltration strips, and wetlands.