Municipalities across Canada face a familiar list of stormwater management challenges: aging and inadequate stormwater infrastructure, the threat of increasing flood damages, climate change, and the unintended consequences of past urban development.

A business-as-usual approach to stormwater management planning will result in continuing degradation of our waterways, increasing flood risk due to climate change, and a mounting infrastructure deficit. A fresh approach is needed to meet these challenges.

STEP Water advocates for a strategic, watershed-based planning approach that augments or replaces existing grey, end-of-pipe stormwater infrastructure with green infrastructure, including low impact development (LID) practices and natural assets such as forests and wetlands. Lately, STEP has turned its attention to tackling the barriers preventing this wider-scale 
LID implementation.

Technical feasibility and performance are not the main obstacles preventing the needed change in stormwater management planning. Rather, the costs required to make this transformation form the greatest obstacle. Significant investment is needed to transform our stormwater systems, and risk-averse municipalities unfamiliar with LID are hesitant to make these investments without knowing that they are worthwhile.

STEP’s partners have begun tackling these obstacles. The first step in any cost-benefit analysis is, of course, ensuring that cost projections are reasonable 
and comprehensive.

Life-cycling costing made (relatively) easy

Developed in 2013, the STEP Life-Cycle Costing Tool (LCCT) needed a refresh. In addition to updating line item costs and costing algorithms, the updated version’s back end is open for users to modify, from financial assumptions to design specifications. It only takes a few basic inputs to generate realistic life-cycle costs for several BMP practices. The intent of the tool is to help users understand and calculate the cost of potential LID practices in the early planning and design phases. The LCCT is available for free at sustainabletechnologies.ca.

“As municipalities across Canada turn to LID practices for stormwater management, accurate life-cycle cost estimation will become critical for gaining buy-in from municipal councils and other funding agencies,” said Phil James, senior manager at Credit 
Valley Conservation. “Municipalities new to LID can capitalize on STEP’s experience with the financial side of LID implementation by adapting the LCCT to suit their needs.”

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Initial sensitivity analyses considering several LID municipal projects implemented in the Greater Toronto Area show that the tool gives results, to within ±14 per cent of contractor bids on several STEP-led projects. STEP hopes to conduct more sensitivity analyses and make regular updates to the tool based on user input. “We’re taking a new approach to updating our guidance and tools. Rather than releasing an update every five or 10 years, we’re making efforts to provide more frequent updates based on user input, industry trends, and new research,” said James.

An essential part of this strategy is sharing the tool with consultants. This collaboration has already produced results for both parties. STEP gets comments and feedback from industry professionals, and the consultants get a useful tool. “When it comes to providing my clients with preliminary cost estimates for green stormwater infrastructure design projects, the STEP team’s Lifecycle Costing Tool is tough to beat,” said Bill Trenouth, water resources engineer and project manager at AECOM.

This update to the LCCT was driven by the need to provide current, realistic costing for two economics-focused STEP projects: CVC-led Making Green Infrastructure Mainstream and LSRCA-led Achieving Sustainable 
Stormwater Management.

Making green infrastructure mainstream

Most cities have limited space for stormwater management, especially in areas developed before stormwater management controls became common. This leaves municipalities with few options. They can wait for scheduled road reconstruction projects and package them together with LID retrofits, create redevelopment policies which require source controls, or purchase land for stormwater ponds.

The first two options could take decades to produce results and purchasing land for stormwater ponds is an expensive proposition.

“Our research indicates that municipalities could save significantly by incentivizing private property owners to retrofit their properties for improved stormwater management, rather than working on public property only” said Kyle Vander Linden, program manager at CVC.

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“Not only are there potential cost savings available, but these retrofits could take place relatively quickly, allowing us to realize significant gains—including reduced overland flood risk when designed properly—in a timely fashion,” added Linden. “As the predicted effects of climate change take hold, preparing for predicted increases in rainfall and extreme weather should happen sooner rather than later.”

This technical and financial feasibility study looks at retrofitting 13 industrial and commercial properties in south Mississauga, Ont. with communal LID infrastructure. Many properties in the study area suffer from regular nuisance ponding and the resulting eyesores and maintenance burdens. Some have even incurred significant flood damages in the recent past.

“The updated LCCT allows us to make accurate comparisons between the public and private property scenarios, because the tool uses the same unit costs and methods to evaluate all options” said Vander Linden. “We hope to begin releasing our findings early in 2021. 
Stay tuned!”

Achieving sustainable stormwater management

This comparative study examines the use of scale (municipal versus watershed) and integration (municipal public property only versus public and private property) to achieve optimal SWM performance at the greatest cost-efficiency.  The study is testing the hypothesis that improved environmental outcomes can be realized at lower capital and operating costs via a watershed-based approach to SWM that includes siting centralized and distributed green and grey infrastructure on both publicly-owned and privately-owned properties.

LSRCA selected the East Holland River watershed as the study area for the project. This watershed includes a mix of urban and rural land use, is undergoing growth and intensification, and falls within multiple municipal boundaries, making it an ideal test case.

The project team first developed a continuous simulation model called LSPC and calibrated it to represent current hydrology and water quality conditions within the East Holland River watershed. This current state model was then linked to SUSTAIN (System for Urban Stormwater Treatment and Analysis), a future state model developed by the U.S. EPA.

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SUSTAIN is a process-based decision model that continuously simulates thousands of stormwater management scenarios to generate cost-benefit curves, with benefits including reduction in phosphorus loads and water quantity. Ensuring accurate life-cycle costs for the SWM features is a critical aspect of the project, necessitating the update to the LCCT described above.

“We’re developing a pilot LSPC-SUSTAIN model that will help municipalities within the East Holland River sub-watershed adopt a cross-jurisdictional approach to stormwater management,” said Ben Longstaff, general manager at LSRCA.

“LSPC-SUSTAIN looks for spatial configurations of LID practices and other stormwater measures which provide the most stormwater quantity control and quality treatment per dollar,” added Longstaff. “We are fostering next steps for municipalities to use this tool for developing equitable cost-sharing and payment for ecological service arrangements agreements to rehabilitate their shared watersheds.”

Existing SWM practices will serve as the Baseline Condition.  Potential new, retrofit, and re-purposing SWM approaches will provide Optimization Options under multiple scenarios (e.g., growth, climate change, uptake rates, etc.). Optimization options include LID, natural assets (wetlands, forests, open fields, etc.), and conventional grey infrastructure on both public and private lands.

The project also calibrates the SUSTAIN models with previously established risk management flood models (developed in HYMO and HEC RAS) to provide reasonable flood-damage curve estimations.  The results can be used to calculate the cost-benefit for flood risk reduction. The project team is also working toward methods for gauging the co-benefits of LID implementation, for example air quality improvements and urban heat 
island reduction.

Stormwater management planning needs a shakeup to avoid the outcomes we can expect with a business-as-usual approach: increasing vulnerability to flooding and continued degradation of our waterways. These two STEP projects have the potential to be transformative.

This article was written by Credit Valley Conservation’s Kyle Menken for the September/October 2020 issue of Water Canada.

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