Watershed-scale stormwater management yields better results

Lake Simcoe study backs collaboration among Canadian municipalities, instead of the prevailing practice for municipalities to deploy stormwater infrastructure on public lands exclusively within their own municipal boundaries.

Findings from a two-year stormwater management and economic study, led by the Lake Simcoe Region Conservation Authority (LSRCA), underscore the pivot toward a more effective, collaborative approach to reduce stormwater runoff and improve water quality in a shared watershed – away from the current, more costly municipal approach.

The prevailing practice is for municipalities to deploy stormwater infrastructure on available public lands exclusively within their own municipal boundaries.

If municipalities in a watershed collaborate across boundaries and consider both public and private lands to achieve ‘optimal’ implementation of stormwater infrastructure, they can manage stormwater and build more resilient, water secure communities at 28% lower cost based on comparative analysis of the current municipal approach.

Dr. Ben Longstaff, Integrated Watershed General Manager at LSRCA and study lead, said that “finding a more cost-effective way to adapt our stormwater infrastructure was a major objective of the study.”

Watershed modeling

Located in one of the fastest urbanizing areas in Canada and Ontario in particular, the East Holland River watershed drains into Lake Simcoe. The freshwater lake is threatened by excessive nutrients in runoff. To achieve pollution control and provincial water quality goals, the project team set a target of 40% phosphorus reduction to the water body.

A computer model and decision-support system were developed for this watershed to evaluate stormwater management strategies based on their impact on watershed processes and cost-effectiveness. Detailed lifecycle costs for infrastructure were included in the model. Future conditions were also taken into account, in terms of projected climate change pathways and planned growth and development scenarios.

Developed by the US Environmental Protection Agency (EPA), the SUSTAIN computer model processes thousands of stormwater best management practices (BMP) options under current and future state conditions to generate cost curves.

image source: Lake Simcoe Conservation Authority

Each dot in the cost curve represents an entire stormwater management strategy — a combination of ‘representative’ measures from hybrid wetlands and rain gardens to infiltration trenches and green streets.

Red dots along the top of the cost curve represent more cost-effective strategies. The red dot within the green circle represents the most cost-effective strategy based on the LSRCA study objectives and targets.

Building resiliency through collaboration

As municipalities remain constrained by limited resources, they are facing new challenges and critically need efficient solutions. Anca Mihail, manager of engineering and capital delivery at the Town of Aurora, a Lake Simcoe partner, summed up the results, “The study clearly showed that by working collaboratively and sharing expertise and resources, municipalities can better plan and manage stormwater, lower costs and build resilient, future-ready systems.”

In addition to partners with public lands, Dr. Longstaff explained that private partnerships are essential. “In fact, the model selected multiple private lands as preferred or optimal sites for stormwater infrastructure over some public land locations and readily met the study target of 40 percent phosphorous reduction.” Using solely available public lands – the current practice — reached a maximum achievable phosphorous reduction of only 15%.

Rachel Prudhomme, director of engineering services at the Town of Newmarket, another LSRCA study partner, emphasized that “findings clearly point to the benefit of working together with property owners to find collective solutions. We all want to live in greener, healthier communities and we all benefit from better air quality, cleaner streams and lakes, and reduced risk of flooding and property damage.”

Costs associated with flood damage across Canada exceeded $2.4 billion in 2020 alone, according to the Insurance Bureau of Canada. More frequent and more extreme storms are expected in the future.

To support freshwater monitoring efforts, KISTERS provides comprehensive environmental data management software to Lake Simcoe Region Conservation Authority and the overwhelming majority of Conservation Ontario members. WISKI software enables the authority to maintain its own datasets in addition to receiving information from partners, in order to establish a watershed or even regional understanding of environmental health or stressors.