Abstract Manager

The Highway 401 Expansion Project involves widening and reconstructing approximately 18 km of Highway 401 in the western Greater Toronto Area (GTA), from east of the Credit River in Mississauga to west of Regional Road 25 in Milton. The project involves expanding the existing six-lane configuration to 10-lane or 12-lane sections and making changes to existing infrastructure to accommodate the proposed widening. This includes constructing nine new, replaced, or widened bridges, rehabilitating five existing bridges, rehabilitating retaining walls, and replacing, extending, or rehabilitating seven culverts.

In addition to the required drainage modifications, the proposed highway widening provides an opportunity to implement stormwater management (SWM) measures, where presently no SWM strategy is in place for over 90% of the Project limit. Within the Project limit, primarily within the East Segment, the majority of Highway 401 is severely encroached upon by existing industrial and commercial developments. As such, there was limited opportunity to construct traditional SWM facilities (e.g., wet ponds, wetlands, etc.). Linear retention/detention options within the MTO right-of-way were considered in the SWM strategy and the SWM design was supported by a hydrodynamic modelling approach.

Highway 401 within the Project limit crosses numerous watercourses and controlling the drainage, reducing erosion, and managing sediment-laden runoff generated during construction was vital. The Project limit was divided into seventeen (17) zones and a site-specific erosion and sediment control plan (ESCP) and drainage and sediment management plan (DSMP) for each zone were developed to present strategies and measures for erosion control, management of sediment-laden runoff and temporary drainage during construction. The site-specific ESCPs/DSMPs were updated every 80 business days to adapt erosion and sediment control (ESC) measures through each stage of construction and to provide interim drainage and sediment management guidance to active construction activities.

This presentation outlines the strategies implemented to address SWM and ESC challenges within the context of the Highway 401 Expansion Project, a large-scale infrastructure development in a densely populated urban area and severely restricted right-of-way.

Keywords: Drainage, Stormwater Management, erosion, sediment, temporary drainage