Retention Pond

Retention ponds capture the diverted storm water runoff from streets and gutters.  Many times this is why you will see a pond in a neighborhood.  Common classifications for retention ponds are either “wet” or “dry.”    Wet ponds, known as retention ponds, continually have a pool of water in them called dead storage.  Dry ponds, detention ponds, do not have dead storage and dry out between storms.

Retention ponds provide two primary services.  First, they retain the runoff before releasing it into streams.  Retention ponds release the water at flow rates similar to those that are under natural conditions. The flood volume held in a retention pond reduces the impact on downstream storm water systems. The second benefit of a retention pond is that they provide pollution removal through settling and biological uptake. Ponds remove 30-80% of certain pollutants from water before it enters nearby streams.  Common pollutants reduced are sediments, bacteria, greases, oils, metals, total suspended solids, phosphorous, nitrogen, and trash.

The flow and the collection of pollutants is also what makes retention ponds very difficult to treat.  If the flow is excessive it is a waste to use pond dye because the dye will cycle through so rapidly.  The excess nitrogen and phosphorous will feed algae blooms making it very difficult to treat with even the best algaecides.  

However, retention ponds aren’t made to be aesthetically pleasing and a relaxing retreat.  Retention ponds are one of the most effective tools at providing channel protection and pollutant removal in urban streams.    Essentially, retention ponds provide water quality and quantity control.

For more information on retention ponds Contact Sanco.