Low Impact Development –  Webinar offers insights into managing stormwater run off challenges

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Ontario Construction Report staff writer

Developers can capture savings on their development charges and fees and ongoing operating costs by effectively introducing stormwater runoff management systems in their plans, says Jen Hill, a research scientist with the Toronto Region Conservation Authority (TRCA).

Speaking at webinar in late October co-ordinated by the Enbridge Savings by Design program with Sustainable Buildings Canada, Hill outlined the measures available to alleviate flooding and waste caused when development interferes with the natural water cycle.

The Low Impact Development (LID) concept need not be expensive or difficult to implement – but it is important to set things up at the early planning stages for new projects, she said.

“Integrating any of these tools into your site plan or into your development is going to get increasingly costly, if they’re bolted on towards the end.”

She started by explaining the distinction between retention and detention in stormwater management.

If natural trees, plants and soil are removed from a development site, when it rains, the water rushes into storm sewers and can quickly cause flooding, she said. The traditional engineering solution is to build in “detention” systems, which allow excess stormwater to be temporarily stored in underground cisterns until the peak runoff ends.

This runoff control approach continues to be useful.

However, a more environmentally responsible approach is to slow or stop the water from running off in the first place, ideally through natural processes. Designing sites and subdivisions so that trees, shrubs and natural run-off channels can be retained, will allow the water to be absorbed by the plants and ground, while preserving the natural habitat.

These planning approaches of course work best on larger sites and subdivisions, and are less useful in densely populated urban areas, where land is scarce – especially where there are high-rise developments.

Still, systems can be developed, incorporating diversions tied in with trees and natural foliage, which can absorb much of the water while enhancing the environment.

Alternatively, developers can can consider green roofs, walls, and facades, while designing the building structures themselves to manage and possibly reuse storm water, for example for toilets and site irrigation.

Green roofs are an obvious example – where the foliage on the roof absorbs the water when it rains, and allows for evaporation.  Full-scale “green walls” are more problematic – they are structurally heavy, difficult to maintain, and perhaps any of their water and energy advantages is more than offset by the maintenance and (in one Asian case) unwelcome insect infestations. However, green facades, with lesser demands on the building infrastructure, may work in some cases.

Why go to the trouble of introducing LID stormwater management into development plans? Beyond the environmental advantages, Hill suggests that thoughtful implementation will help reduce ongoing costs and these savings, coupled with various environmental credits and savings, would make the initiatives worthy of implementation.

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