Stormwater discussion explores green infrastructure design

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Carleton Place resident Mark Smith holds water samples he took in the Highgate storm pond as well as 140 metres down a swale following an Aug. 14, 2016 rainstorm. He brought the samples to Carleton Place Town Council to illustrate significant differences in the water quality from the two locations as part of a discussion on low impact development approaches to rainwater runoff.
Posted on: February 22, 2017

Matthew Behrens
editorial@pdgmedia.ca

Carleton Place council held an extensive discussion on Feb. 21 on low impact design (LID) as an improved stormwater management tool. LID will often include rain gardens, low slope swales, and other designs that contain, cleanse, and redirect rainwater runoff into the ground rather than through pipes and channels to a surface outlet.

Chief Administrative Officer Paul Knowles explained that while he believed the concept was a good one, LID’s application was very much circumstance-dependent, from the nature of soil conditions to connections with municipal sewer systems.  Knowles pointed to examples where redirected water has raised the levels of the underground water table, resulting in erosion and other unintended consequences. He also cited the University of British Columbia, where redirected water enveloped asbestos-covered underground pipes.

Councillor Doug Black discussed the need to reduce reliance on storm ponds to handle rain runoff, and noted that with revised LID guidelines coming into play this June, it’s a good opportunity for the town to consider how new projects can incorporate a development approach with potential long-term benefits for the Mississippi River watershed.

Town resident Mark Smith, a member of the Carleton Place Urban Forest/River Corridor Advisory Committee, addressed his support of LID to council, citing examples from Kitchener as well as Markham, where the Honda campus has used LID features such as biofilters, permeable pavements, swales, and rainwater reuse for landscape irrigation to reduce storm water discharge by 35%.

“Any new developments, especially commercial and industrial, should be required to complete an environmental and hydrological survey of the property in respect to incorporating possible LID in the design prior to the draft engineering plans,” Smith said. He noted that trees can play a valuable role in absorbing runoff with mature oaks and weeping willows capable of absorbing up to 100 gallons a day.

While Council passed a motion that “LID storm systems be considered only in appropriate circumstances,” Smith expressed disappointment. “Without studies to determine if LID is appropriate for a site, who and how will we determine what site is appropriate?”