A Stormwater Management Report (SWM Report) demonstrates how a development site will manage stormwater runoff — addressing quantity, quality, and water balance to the satisfaction of the municipality and, where applicable, the local conservation authority. Ontario’s SWM guidelines require that post-development peak flow rates do not exceed pre-development rates for design storm events, typically the 2-year, 5-year, and 100-year return periods.
Quality control requirements specify minimum Total Suspended Solids (TSS) removal rates that vary depending on the receiving water body classification. Water balance requirements address groundwater recharge, particularly in areas identified as sensitive recharge zones. For sites in or near regulated areas, the report must also satisfy the relevant conservation authority’s requirements, which may be more stringent than the municipality’s.
The SWM Report is typically submitted alongside the FSR as part of the servicing component of a development application. A licensed P.Eng. prepares and seals the report. Depending on site complexity, the SWM Report may include detailed hydrologic modelling, pond sizing calculations, and Low Impact Development (LID) documentation.