Proactive Responses and Concerns in Stormwater Management to Climate Change Evidence in Urban Regions of Canada

Major initiatives are being pursued in Canada with foci on characterizing the degree to which evidence of climate change is occurring, and proactive efforts implemented to reduce the impacts to urban areas. Specifically, informative results that will demonstrate concerns being experienced, include:

(i) Characterizing the rate of change of heavy storm intensities - Heavey storms, ranging from those occurring several times a year up to storms that have recurrence intervals of ive years, are being proactively investigated. The heavy storms are of key interest since they stipulate how municipal infrastructure systems must be designed. While precipitation rates are increasing, there is no apparent change in the number of dry days between storms but instead, increasing precipitation rates associated with the heavy storms. This results in challenge swhenthe design life of municipal infrastructure is ~60 years, but storms for which there is an expectation for control are increasing rates of precipitation at approximately 2 percent per year, implying there are very real challenges to establish design storms for which storm sewers must be designed;

(ii) Utilization of Low Impact Development (LIDs) scenarios to Decrease Urban Flooding Have the Potential to Increase Basement Flooding - With increasing heavy storms intensities, there are substnatial efforts beign introduced to decrease runoff at `lot level` through implementation of LIDs. While this is helpful at the district level, serious questions are being raised at enhanced levels of infiltration at lot level which, while accomplishing both increasing groundwater recharge which improves potential to recover the groundwater as a resource and decreasing the runoff per hectare which helps the district- but the challenge is that elevated infiltration is causing increased basement flooding;

(iii) Implications of Disconnecting Downspouts from Rooftops and Weeping Tiles from Sanitary Sewers has real value on decreasing surchage levels in santiary sewers are proving substantial - Reduced sanitary flows during rainfall events have been been observed at 78% and the peak flow reduced by 32%, showing there are substantial opportunities to reduce sanitary sewer flows and hence, decreasing basement flooding.

Various examples of issues and findings are described which illustrate the trade-offs that are being identified in urban regions in Canada.