Detention water is detained and released to receiving stream or storm sewer through a controlled outlet over a specified time period. Removal of the pollutants is by sedimentation. Filter strips achieve pollutant removal through velocity reduction, filtration by vegetation and infiltration. Grassed Swales vegetated channels that convey stormwater and remove pollutants by filtration through grass and infiltration into site soils. Sand Filters use sand to remove sediment and pollutants from first flush runoff.
Sand filters are well suited for space-limited areas.
These facilities do not have a permanent water pool. Wet ponds hold a permanent pool of water between storm events. These are not generally considered appropriate for TxDOT applications because of liability issues associated with standing water. Constructed Wetlands similar to wet ponds but a major portion of the surface area contains wetland vegetation. Wetlands perform best when linked with upstream sediment control structures.