Evaluation of the Storm Water Volume Control Target in Ontario

This study evaluates the “proposed stormwater volume control target in Ontario,” which is set at the 90 percentile of rainfall event volume, in terms of a) the percentage of total rainfall volume- controlled; b) the effectiveness of using low-impact-development (LID) measures for a development site to meet the proposed target. Based on the analyses of daily and hourly rainfall data from 122 hydrological stations in Ontario, the total rainfall volumes corresponding to daily and hourly 90th percentile rainfall depth were computed to be approximately 68% and 79%, respectively. Using a hydrologic model of a hypothetical catchment of 100m by 100m, it was determined that it would be difficult to retain 90% of the total rainfall volume on-site by applying a LID designed to retain 90 percentile rainfall event volume.