TRACK 1, DAY 2
Flood Damage-Based Prioritization of Retrofit Opportunities for At-Source Stormwater Retention in the Humber River Watershed
Mila Mahya and Yuestas David, Toronto and Region Conservation Authority (TRCA)
Wednesday, April 1, 2026 | 2:15 p.m. to 2:45 p.m. | Hall A
ABSTRACT
Urban flooding in the Humber River watershed is intensifying due to aging infrastructure and climate-driven increases in rainfall intensity. To support targeted, cost-effective flood mitigation, this study develops a data-driven framework that links stormwater retention modeling with flood damage assessment to prioritize retrofit opportunities across the watershed.
Using the Visual OTTHYMO model, retention scenarios were applied to impervious areas to represent at-source stormwater management practices. Reductions in downstream peak flows at Flood Vulnerable Clusters (FVCs) were then translated into avoided damages using established peak flow–damage relationships derived from the Toronto Flood Risk Ranking Study.
Results show that retrofitting highly urbanized subcatchments, such as the Black Creek area could avoid up to approximately $950,000 in annual flood damages if retention targets were achieved. The framework offers a transparent and quantitative methodology to identify where at-source retention delivers the greatest hydrologic and economic benefits, supporting data-driven stormwater investment planning and climate adaptation in urban watersheds.
ABOUT THE PRESENTERS
Mila Mahya, Toronto and Region Conservation Authority (TRCA)
Mila Mahya is a Research Analyst at Toronto and Region Conservation Authority (TRCA), where she works on watershed hydrology, water quality modeling, and climate data analysis to support regional watershed planning.
Her work includes developing and calibrating SWAT and SWMM models to assess water quality and water balance under current and future conditions, and contributing technical analysis to projects that apply hydrologic insights to watershed management actions.
Before joining TRCA, Mila worked at Deltares in the Netherlands on groundwater modeling, flood risk assessments, and freshwater management initiatives in Southeast Asia and Africa. She holds an MSc in Hydrology from Vrije Universiteit Amsterdam.
Her current research focuses on evaluating at-source stormwater retention and developing data-driven approaches to support flood damage reduction and stormwater retrofit planning.
Yuestas David, Toronto and Region Conservation Authority (TRCA)
Yuestas David is a Senior Research Scientist at Toronto and Region Conservation Authority (TRCA) for the Ecosystem and Climate Science Team.
He graduated with a Master’s of Science from the Geography program at York University with a focus on hydrological modeling. He manages research, data analysis, development of tools, frameworks, and guidance documents for climate adaptation with the goal of making the state of the knowledge more accessible to practitioners and decision makers.
Currently, he’s coordinating projects that help assess and communicate impacts of climate change for local municipalities. He’s particularly interested in understanding the hydrological impacts of climate and land use change on local watersheds.