About Infiltration Basins

Infiltration basins are low areas in the ground that temporarily collect runoff where it has time to soak gradually into the ground. These basins are usually dry except after a heavy rainfall. They are useful in residential and other urban settings to hold extra runoff and reduce the flow of runoff into streams. They require the right kind of soils which allow water to soak in. Soil texture and plant roots create spaces in the soil for water to flow into. Different soils absorb runoff at different rates; it depends on how wet the soil already is, and the amount of rainfall at the time. Sandy soils have spaces between each grain which allow water to soak in more quickly. Once water soaks into the basin area, it stays there until it’s taken up by plant roots or filters down and recharges the groundwater. Some of the water evaporates during warm summer months.

Water Quality Benefit: They improve water quality by settling and filtering out pollutants which prevents pollutants from being carried into streams. They also recharge groundwater. However, fast flowing water may not be in contact with the soil long enough for any treatment. When trees are planted in or left around infiltration basins, they can shade buildings and parking lots or other paved areas which reduces runoff temperatures. Preventing warmer runoff from entering streams is good for the creatures that live there.

Water Quantity Benefit: Infiltration basins are commonly used when there is an opportunity to reduce surface runoff. They are designed to imitate the natural movement of water and evaporation. By infiltrating some of the runoff, this reduces flows downstream. Anything you can do to hold water upstream reduces the size of piping needed downhill. Infiltration is the quickest way to address stormwater flows.