In recent years, the City of Hamilton, Ontario has seen an increase in re-development occurring in high-value “desirable” residential neighbourhoods in the City. Re-development such as “tear-down and rebuild” typically occur in older, existing detached residential areas of the City and typically involves lot severances and intensification. This re-development trend has been observed within rurally serviced (i.e. roadside ditches) areas in the Community of Ancaster, within the City of Hamilton. The City of Hamilton has noted concerns with the potential impact of such intensification to the receiving rurally serviced drainage systems, both in terms of conveyance capacity, as well as the potential impacts to downstream receivers.
An assessment was undertaken using a calibrated high-resolution PCSWMM model to characterize drainage system performance and downstream impacts under both baseline (existing) and potential intensification (future) conditions. To accomplish this, the PCSWMM model developed for this assessment consisted of delineating twelve (12) rurally serviced drainage system networks with a combined drainage area of 326 ha. Survey data, field reconnaissance, and as-built drawings were used to identify culverts and hybrid storm sewer drainage systems, in addition to classifying the 60 km of ditches within the networks as having one (1) of five (5) typical cross sections.
Following the simulation of the baseline and intensified conditions using the 2, 5, and 100 year design storm events, a source control strategy was ultimately advanced to mitigate the impacts of expected intensification, with a focus on private side source controls (Low Impact Development Best Management Practices, or LID BMPs). The source controls were incorporated in the future conditions PCSWMM model by increasing the pervious depression storage and altering the directly connected fraction to offset the impacts of the increased imperviousness. Similarly, potential mitigation measures to address climate change impacts were also assessed and quantified.
The baseline and intensified land use scenarios with and without source controls were also assessed under a 55-year continuous simulation to evaluate the potential impacts to downstream locations for erosion threshold exceedances as well as a water budget assessment.
It is expected that the work completed through this study will support the City of Hamilton in implementing defensible SWM targets for future developments to ensure that drainage system impacts are suitably mitigated.