Planners have come up with many innovative ways to prevent flooding caused by heavy downpours — from planting rain gardens to installing green roofs.
But in many cases, nothing works quite as well as a simple hole in the ground — a detention basin.
That’s the finding of an analysis by University of Cincinnati geography students in a research collaboration with the Hamilton County Conservation District.
Lead author and UC College of Arts and Sciences doctoral student Man Qi said cities are developing new ways to trap rainwater and direct it where it’s most wanted, especially during droughts. They call these low-impact development practices, which include innovations such as permeable pavement that allows rainwater to seep into the ground instead of diverting it elsewhere.
Another innovation is a bioretention cell composed of ornamental or landscaping plants atop soil specially designed to drain quickly spread over a thick bed of gravel that does likewise. This soaks up large volumes of rain without creating standing pools of open water.
New commercial or housing developments typically must prevent rainwater from spilling out to other neighboring properties or roads. Hard surfaces like buildings and parking lots can’t absorb heavy rains so planners must collect or divert the water to prevent property damage.
“A detention pond is a common practice,” Qi said. “It temporarily stores the water and releases it into the air or the groundwater or nearby streams at a low rate to reduce the risk of flooding. It also provides some ecological benefits.”
Qi worked with the Hamilton County conservation district to measure the effectiveness of flood-prevention techniques such as detention basins and bioretention cells under five scenarios.
Qi presented their results at the annual American Association of Geographers’ conference in Denver.
“In residential areas where the impervious area is less than 40%, low-impact development practices are better. But if 70% or more of the ground surface is impervious, it’s best to put in detention basins,” Qi said. “The flood risk can be greatly reduced.”
Climate change is expected to increase both the frequency and severity of rainstorms, which means making deliberate plans for drainage will become even more important in …
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