Stormwater Management and Significant Channel Flows below the Two-year Return
Historically, hydrology and hydraulic targets and considerations associated with urban stormwater management have focused on flows equal to, or larger than, the two-year return. More recently, targets linked to concepts of effective and bankfull discharge have been defined to limit geomorphic impacts to receiving watercourses. These are generally tied to flows equal to, or of somewhat higher frequency than, the two-year return. Unfortunately, in many cases flows that have a significant impact on aquatic habitat, stream geomorphology and water quality are well below the two-year return event. A series of simple conceptual models are outlined to examine these flows. These flows are also examined in the context of the watersheds of the Greater Toronto Area, by combining simple conceptual models of these flows with geomorphic data from the Toronto and Region Conservation Authority’s Regional Monitoring Network.
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