AbstractFor many jurisdictions, the current design criteria for low-impact development practices (LIDs) including infiltration trenches require LIDs to provide enough storage capacity to store catchment runoff from the location’s 90th-percentile storm. The 90th-percentile storm used in Ontario, Canada, has a depth of approximately 25 mm. This study examines the performances and costs of infiltration trenches built in Ontario but sized to accommodate alternative storm depths ranging from 5 to 50 mm. Analytical equations are used to determine the runoff reduction ratios of infiltration trenches, and a cost estimation tool specifically developed for LIDs is used to estimate their overall costs. Results indicate that the current 90th-percentile storm criterion is probably too high and not cost efficient. An evidence-based methodology for selecting more appropriate design criteria is proposed. Using this methodology, it was found that the economically more efficient design criterion for Ontario averages about 20–22  mm for different design cases. Significant savings can be realized if a lower design criterion is implemented. The proposed methodology is therefore recommended for jurisdictions seeking more cost-efficient design criteria.

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