Building Climate Change Resiliency in Intensifying Neighbourhoods

Presentation Overview:

The Town of Oakville’s older neighbourhoods south of the QEW were largely built out through the 1950s to 1970s. Characterized by comparatively large lots with small building footprints, these locations are under increasing pressure to intensify with larger homes and amenity areas. The result is an insidious increase in imperviousness and thus runoff peaks and volumes, which is further exacerbated by climate change.

Because the area was planned and designed long before modern stormwater management, there is a lack of quantity and quality control, deficient overland flow routes (sags and low points), and numerous locations with ditches or semi-urban servicing.  In developing its Master Plan for this part of the community, the Town focused on pluvial flood risks, and in doing so, commissioned the preparation of a dual-drainage all pipes (and ditches) model for the community. This modelling effort involved over 50 discrete neighbourhoods (networks), more than 3000 catchments, over 260 km of storm sewers, and 168 km of ditches with a drainage area of nearly 40 square km.

The prevailing system performance was evaluated using existing rainfall IDF relationships and considered level-of-service objectives for the minor system (storm sewers/ditches) and major system (overland routes/roadways/remnant channels).  Flood risk was assessed based on those locations in the community with directly connected foundation drains to storm sewers, versus those with sump pumps. The system was then assessed with future intensified land use and future climate-adjusted IDF relationships.

Green infrastructure and low impact development solutions were considered for redeveloping private land and reconstructed roadways. Strategic application of 20-25 mm of runoff control would mitigate impacts due to land use and climate change for the minor system. Grey infrastructure solutions (pipe upgrades, storage, diversions, roadway retrofitting, ICDs, etc.) were then able to be confidently planned for a stable future condition.

Learning Objectives:

  • Understand how older, more mature locations, planned and designed before contemporary SWM, are often under pressure to intensify and therefore are most vulnerable to flood risks, particularly with climate change impacts to runoff potential.
  • Learn how detailed dual-drainage (major-minor) network modelling (all pipes/all ditches) can inform municipalities on current system performance and overall level-of-service, and how varying service conditions (ditched vs. sewer) and risk conditions (basement connections or not) need to be considered in prioritizing works.
  • Recognize that strategic use of green infrastructure and low impact development practices (public and private realm), along with conventional grey infrastructure, can optimize the performance of drainage systems, based on future intensified land use and climate conditions.

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