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Green Infrastructure – Cost Effectiveness and Technical Challenges for Flood Mitigation, Robert J. Muir, M.A.Sc., P.Eng.
Manager, Stormwater, City of Markham, January 30, 2018 - Mississauga, Ontario
The presentation presents regulations and policies regarding cost effective infrastructure, explores green infrastructure capital costs in Ontario based on recent project tender costs and other North American extensive program sources, explores lifecycle cost (LCC) impacts of widespread green infrastructure implementation in Ontario, including cost per household and impacts on the current infrastructure deficit, and presents benefit cost analysis for city-wide grey and green infrastructure strategies including benefit/cost ratios for flood damage reduction. Unit costs of no regret programs such as sanitary downspout disconnection and plumbing isolation programs, and wastewater and stormwater system upgrades, and green infrastructure retrofits are presented per hectare. Gaps in research relying on meta-analysis estimates of flood control benefits that do not consider local engineering or costs are presented. Impacts of green infrastructure on wastewater systems and infiltration stresses is presented, and correlation of wastewater infiltration stresses with local sewer back-up risks is shown for the City of Markham. Water supply risks of green infrastructure relying on infiltration including chloride stresses are explored. The unfavourable benefit-cost profile of green infrastructure and potential impacts on wastewater system flood risks and municipal water supplies suggests a strategic review of implementation targets and policies is warranted to identify financially sustainable and technically-appropriate requirements.