Parking Lot Detention

Perhaps the most important storm water management feature that can be included within community landscape codes is the parking lot detention.

Parking lot detentions are generally dry retention areas that set aside to capture run off from large surface parking lots and roof tops during storm water events.. The detentions are sized to store the required volume of water, the design storm assumed to be one (1) inch of rainfall that is generated over the extent of the impermeable area of the VUA. A well designed dry detention may be constructed to capture as much as ninety (90) percent of all rain that falls on a vehicular use areas that are larger than five (5) acres.  They are also engineered to make sure they do not flood and can trickle out a specified amount of rain water over a proscribed period of time.

Parking lot detentions may be grassed, may serve as over flow parking with porous paving or be designed to be of contrived plantings that can feature planted buffers, streams or rain gardens.  Some dry detentions are designed to be patterns of porous stone and gravel.

Detentions feature several facilities that make them operate effectively. The include a porous surface base that will infiltrate rain water quickly, inflow ramps usually constructed of concrete or other hard surface material, underground inflow pipes with headwalls and overflow structures and out flows.  The latter insure that the detentions will not flood during extra exceptional rainfall events.

These detentions are best used along roadway frontages where they can add to the open space percentage of development site and the visual appearance of the project.  And of course, well designed detentions can add to any development site. They can add beauty and add significant open space to any site if properly sited and designed.  Plantings of trees, shrubs and ground covers upon the lip of the detention, on its side slopes or within its bottom can create color, texture and form that will give striking visual character to what would other wise be an engineered wasted space that is normally seen surrounded unsightly and weed covered chain link fencing.