Measuring Urban Forest Canopy Effects on Stormwater Runoff in Guelph, Ontario

Abstract

Cities are complex and contribute to urban stream degradation due to increased stormwater runoff volumes and velocities and ineffective stormwater management infrastructure. Trees provide measurable benefits to cities including rainfall interception which can decrease stormwater runoff, demonstrating their effectiveness as a stormwater management tool. This study quantifies the effects of urban forest canopy on stormwater runoff to assess proportions of canopy cover required to effectively reduce runoff levels. i-Tree Hydro, a semi-distributed hydrological model, was used to measure hydrologic effects of the City of Guelph’s urban forest. Varying proportions of canopy cover were used to compare Guelph’s current and potential urban forest. Results show that increasing canopy cover in plantable spaces decreased overall flow within the City, however, runoff over impervious surfaces increased. The findings can inform design decisions related to urban stormwater management and improve urban forest management measures, however, impervious surfaces remain a design challenge.