Swales

Component: Swales

Description

Swales are shallow, broad and vegetated channels designed to store and/or convey runoff and remove pollutants. They may be used as conveyance structures to pass the runoff to the next stage of the treatment train and can be designed to promote infiltration where soil and groundwater conditions allow.

Check dams and berms also can be installed across the flow path of a swale in order to promote settling and infiltration.

Advantages and disadvantages

Advantages

Disadvantages

Easy to incorporate into landscaping
Good removal of urban pollutants
Reduces runoff rates and volumes
Low capital cost
Maintenance can be incorporated into general landscape management
Pollution and blockages are visible and easily dealt with.

Not suitable for steep areas or areas with roadside parking
Limits opportunities to use trees for landscaping
Risks of blockages in connecting pipe work

Where component can be used

Residential: Yes

Commercial/industrial: Yes

High density: Limited (depends on design)

Retrofit: Limited (depends on design)

Contaminated sites: Yes (with liner)

Sites above vulnerable groundwater: Yes (with liner)

Performance

Peak flow reduction: Medium

Volume reduction: Medium

Water quality treatment: Good

Amenity potential: Medium/Good

Ecology potential: Medium

Quantity

Swales are usually designed as conveyance systems, but can also be designed with check dams to increase attenuation and, where applicable, infiltration.

Quality

Swales are effective at removing polluting suspended solids through filtration and sedimentation. The vegetation traps organic and mineral particles that are then incorporated into the soil, while the vegetation takes up any nutrients.

Amenity

Swales are often integrated into the surrounding land use, for example public open space or road verges. Local wild grass and flower species can be introduced for visual interest and to provide a wildlife habitat.

Maintenance

Litter/debris removal
Grass cutting and removal of cuttings
Clearing of inlets, culverts and outlets from debris and sediment
Repair of eroded or damaged areas.