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Don’t Go With the Flow
Around this time of year, winter’s charms start to wear thin and the mind turns to anticipating spring’s blooms. But first come those April showers. And mid-March showers. Big, fat storms that bring the worry in the region I live in that the still frozen ground will not be able to absorb the water. The stormwater runoff will overwhelm my city’s combined sewer stormwater system, causing all manner of unpleasant consequences. In the United States, nearly 860 municipalities have combined sewer systems, and combined sewer overflows are a serious contributor to water pollution, according to the U.S. Environmental Protection Agency.
Commercial facility roofs, usually large and low-sloped, serve as enormous catch basins for this rain, sending it in cascades through downspouts, washing across parking lots, which in themselves contribute to the problem of stormwater flooding and pollution. But facility roofs could instead be part of the solution, serving to detain the stormwater. One incredibly novel solution I saw in a multi-roofed high-rise deployed multiple strategies, with one roof serving as a detention pond which slowly fed water to a lower vegetated roof. In slowing the water down on the roof, the strategy also allowed some of the water to evaporate directly back to the atmosphere, once the sun was shining again.
The typical facility roof is designed to shunt water away as soon as possible, not hang on to it. Creating a “blue roof” solution at a commercial facility requires careful engineering, considerations of structural load capacity, and impeccable roofing design and maintenance. But it could be a viable way to get your roof to work double duty, adding value to the facility while also protecting your municipality's water resource. (For more ideas on how to add value with your roof, check out this article.)
While you are preparing to supercharge your next major reroofing project, there are near-term strategies more easy to deploy to help manage stormwater runoff at your facility. Where legal, rain barrels and other catchment systems are available to store water for landscape irrigation at a later time. Some systems can be shaped into benches or fit snugly against walls to save space or provide additional functionality. Downspouts can be directed towards rain gardens, which are depressions filled with water-loving plants, or bioswales that will help to detain stormwater and percolate it back into the water table. These have to be carefully constructed due to the volume and velocity of water coming from a roof. Many more strategies exist (look up “soil sponge,” for starters) to turn your roof’s torrent into a beneficial trickle.
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