Watershed assessment and mitigation of urban impacts using continuous simulation

Jim Dumont, Consultant, Salt Spring Island, BC, Canada


Mitigation of the effects of urban development has been mandated by many jurisdictions. Many of the standards that have arisen to date involve assessment of a property to identify pre and post development hydrology using a single event methodology. These practices have arisen due, in part, to the limited availability of direct hydrologic information. This current practice has been extended to include water quality discharge standards which has led to the use of increasingly stringent infiltration targets. A limitation of this practice is in establishing the condition and hydrologic response of receiving stream and subsequently the operational characteristics and the effectiveness of proposed mitigation works.

This paper describes a process using assessment of regional streamflow gauges to validate a continuous simulation model that demonstrates both flood frequency and water balance. The model was subsequently modified to include watershed development and a system of mitigation facilities. Optimizing the size and operation of the facilities can be used to demonstrate the effectiveness of the mitigation plan in protecting the receiving stream. This approach provides a cost effective methodology for creating watershed plans with optimized and effective mitigation facilities for a minimum total cost. 

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