Tuesday, 20 December 2011

Stormwater Basins

A common method to manage stormwater runoff is through stormwater basins or ponds, which collect and release runoff at a controlled rate to avoid flooding or erosion of downstream areas. Stormwater basins can either be detention basins, which are dry between storms, or retention basins, which have a permanent pool of water. Detention basins only contain water after a rain event, while retention basins always hold water.

The Canada Games Centre on Lacewood Drive in Halifax has an underground detention basin on-site that collects stormwater runoff from the building’s roof, parking lot and lawn area. Underneath a field beside the Centre lies a 10m deep hole that is filled with rock. Large, boulder size rocks were used to increase infiltration. Two metres beneath the surface lies a perforated pipe that runs across the length of the field and catches any overflow. During a heavy precipitation event, water enters the dry detention pond and infiltrates the rock layer. Water only enters the perforated pipe if the water level rises to 2 metres below the surface, and Jeff Pinhey, the site engineer has never witnessed an overflow event. The detention pond was built during the construction of the building. 

Underground detention pond at the Canada Games Centre
Underground detention ponds are safe, do not need to be fenced and provide additional space for on-site recreation. Detention ponds can also be above ground, such as this example in Dartmouth Crossing. We’ll explore wet retention ponds in more detail in future posts.
Above-ground dry detention pond in Dartmouth Crossing

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