ECONOMIC ASSESSMENT OF CLIMATE CHANGE SCENARIOS ON DRAINAGE INFRASTRUCTURE DESIGN

The potential impacts of climate change on the ability of existing and planned drainage infrastructure to safely convey flood flows and prevent off-site erosion, is causing municipalities to examine the recent shifts in storm patterns (rainfall volume, intensity and frequency) and the associated implication to design approaches. This paper examines, by way of two case studies, the approaches taken by different southern Ontario centres, specifically the communities of Cambridge and Milton. Major flooding problems were caused by severe storms in excess of a 50 year return period in 2005 and again in 2006 in the City of Cambridge. In response, a plan was prepared to alleviate the existing flood risk by way of increasing conveyance infrastructure capacity and providing designated flood storage. The uncertainty related to potential climate change impacts was examined by developing various configurations of drainage infrastructure designed to events of decreasing frequency including 100, 200, and 500 year storms, based on current intensity duration frequency relationships. Each scenario was costed and the economic implications provided to City of Cambridge administrators to review in terms of risk versus costs, in order that more informed decisions could be made when planning the City’s Capital Program. The City adopted the more conservative design standards due to concerns associated with Public safety. The key project components were constructed accordingly in 2008 and 2009 (on-going). In the Town of Milton case study, an on-going subwatershed study supporting future planned development of a Major Business Park provided the opportunity to apply meteorologic time series related to climate change scenarios, originally developed by Environment Canada and subsequently modified by Credit Valley Conservation for use in a neighbouring watershed scale assessment. A calibrated hydrologic model was used to assess the impact of modified meteorologic conditions (reflecting potential climate change scenarios) on off-site flood and erosion susceptibility, as well as the design of stormwater management infrastructure. The economic impacts, in terms of land consumption and capital costs for construction, were assessed and compared for stormwater management systems designed under current (standard) and future climate change scenarios