Just a few GIS maps illustrating urban flooding risks in Toronto and Missisauga, showing lost rivers and historical flooding locations (Toronto May 2000 [orange symbol] and Toronto August 2005 [red symbol] storms and Mississauga July 2013 [yellow symbols]). The lost river major overland flow paths for small catchments (less than 1000 hectare drainage area) are estimated using the rationale method with the SOLRIS Version 2 land use-derived runoff coefficients, times of concentration derived from the MNRF WRIP enhanced DEM to estimate peak rainfall intensity, and approximate uniform flow depth and spread approximations along the centreline flow path. The land use shown is the province of Ontario's SOLRIS Version 3 data, which helps show where overland flow paths are in channels, open spaces, parks and easements vs. through developed areas where original drainage features have been enclosed over time.
Toronto - East End: good slopes toward Lake Ontario, the Don River valley and Taylor Creek. Little flooding in May 2000 and August 2005 (those storms did not affect this area greatly however).
Toronto - West End: a few flood clusters along the lost river flow paths.
Toronto - North End (Newtonbrook area): significant flooding in low relief areas, clusters of flooding along other lost river flow paths. Highest concentration of flooding area in 'partially separated' sewer servicing areas where foundation drains contribute wet weather flow to the wastewater collection system and overland flow paths were not explicitly designed.
Mississauga - Malton Area: Older development, less resilient servicing standards. Flooding locations are approximate but appear to show concentration along the downstream end of the large central 'lost river', north of the 401.
Mississauga - Cooksville Creek: A large 2000 mm diam. trunk sewer runs along the 'lost river' flow path in the centre of the map, south the the QEW. This branches to two large trunk under the QEW and upstream. Flooding locations are approximate.
