Bio-retention Basins

An alternative to the development of detention basins is the implementation of bio-retention basins.  A bio-retention basin is a shallow runoff catchment area that can be filled with organic mulch and planted with trees, shrubs, and wildflowers tolerant of polluted runoff and occasional inundation.  A few benefits of bio-retention basins include:

  • Reduced runoff and greater groundwater recharge
  • Improved shading and lower energy use for cooling devices
  • Diffused pollutant runoff through absorption and filtration processes
  • Enhanced wildlife habitat and aesthetics

While the implementation of bio-retention basins on a small scale won’t mitigate large scale flooding, basins can help diminish localized runoff and reduce pressures on water use through passive irrigation.  When implementing bio-retention basins, care should be taken to use dimensions that maximize catchment of runoff and supports vegetation through passive irrigation, but does not produce mosquito breeding habitat or a drowning concern.

Design Variations

A cross-section of a basic basin with important design considerations.

Various approaches can be taken with respect to basin priorities.  In some cases there are constrictions on right-of-way space or urban flooding is a greater concern than treatment of stormwater pollutants.  In these instances, a higher density of of deep basins along streets or parking lots could help remove water from gutters and take pressure off of stormwater drains.  A greater emphasis on basin volume might restrict the type of vegetation species that can be used due to prolonged inundation during precipitation events.  In other instances, more organic aesthetics or stormwater treatment is a priority.  Addressing these objectives may be more easily met with less linearly engineered basins with greater berm surface area for infiltration and colonization by vegetation. Whatever the case may be, basin design can be altered to address the most pressing concerns at the site to be landscaped.  An example of a basic cross-section of a basin with some important design considerations can be found above.  Additional examples of different basin design characteristics can be found below.

 

A higher density of basins such these in Columbus, Ohio can help alleviate local street flooding and provide substantial passive irrigation to shade producing trees. One limiting factor of the concrete berm design is that there is less lateral infiltration and bio-remediation of stormwater pollutants.

Deeply engineered basins capture large volumes of water, but preclude the use of vegetation that won't tolerate prolonged inundation.

 

 

More organically designed basins may be impractical in narrow right-of-ways, but could offer better treatment of stormwater pollutants.

 

 

 

 

 

 

 

 

 

 

 

Organic berms require more space, but can yield more plant cover and infiltration surface area.