Infiltration basin

Component: Infiltration basins

Description

Infiltration basins are vegetated depressions designed to store runoff on the surface and infiltrate it gradually into the ground. They are dry except in periods of heavy rainfall.

Advantages & disadvantages

Advantages	Disadvantages
Reduces the volume of runoff from a drainage area Can be very effective at pollutant removal via filtering through the soils Contributes to groundwater recharge and baseflow augmentation Simple and cost-effective to construct Changes in performance easy to observe.	Potentially high failure rates due to improper siting, poor design and lack of maintenance, especially if appropriate pre-treatment is not incorporated Comprehensive geotechnical investigations required to confirm suitability for infiltration Not appropriate for draining pollution hotspots where high pollution concentrations are possible Requires a large, flat area.

Where component can be used

Residential: Yes

Commercial/industrial: Yes

High density: No

Retrofit: No

Contaminated sites: No

Sites above vulnerable groundwater: No

Performance

Peak flow reduction: Average

Volume reduction: Good

Water quality treatment: Good

Amenity potential: Good

Ecology potential: Good

Quantity

Infiltration techniques:

store runoff by allowing temporary and shallow ponding on the surface;
enhance the natural ability of the soil to drain the water. They do this by providing a large surface area in contact with the surrounding soil, through which the water can pass.

The amount of water that can be disposed of by an infiltration basin within a specified time depends mainly on the infiltration potential of the surrounding soil. The size of the device and the bulk density of any fill material will govern storage capacity.

Quality

Runoff is treated in different ways in an infiltration basin. These include:

physical filtration to remove solids
adsorption onto the material in the surrounding soil
biochemical reactions involving micro-organisms growing on the fill or in the soil.

The level of treatment depends on the size of the media and the length of the flow path through the system, which controls the time it takes the runoff to pass into the surrounding soil. Pre-treatment may be required before polluted runoff is allowed into an infiltration basin.

Amenity

Infiltration basins are easy to integrate into a site. They are ideal for use as playing fields, recreational areas or public open space. Infiltration basins can be planted with trees, shrubs and other plants, improving their visual appearance and providing habitats for wildlife. They increase soil moisture content and help to recharge groundwater, thereby mitigating problems of low river flows.

Maintenance

Regular inspections for signs of deterioration in performance, clogging and other blockages
Litter/trash removal
Inlet/outlet cleaning
Vegetation management
Regular removal of sediment from pre-treatment.