Towards Establishing Targets for the Water Needs of Streams and Wetlands in Ontario, Canada

Ontario has joined other jurisdictions around the world in assessing ecological flow assessment methodologies. The need to better manage water takings in the Province was the impetus for the work. It has been necessary to raise awareness of the need to move from consideration of single, minimum threshold flows to consideration of a flow regime that can maintain the ecological integrity of aquatic ecosystems. Pilot projects have been undertaken in several watersheds in southern Ontario to evaluate the applicability of various ecological flow assessment tools to assign instream flow requirements. Using a bottom up approach, a variety of methods are needed to identify the flow required to satisfy various ecological needs including those required to sustain communities of aquatic organisms; prevent disruption of geomorphic processes; achieve water quality objectives; and maintain connectivity. Historic flow, hydraulic and geomorphic methods were applied in the pilot studies. The Range of Variability Approach in combination with detailed hydrologic modeling was also applied to assess the acceptable departure from natural conditions within a top-down approach. Further work is required to evaluate the potential for various techniques to be transferred to areas of the Province with different climate, physiography, and development intensity. Regardless of the methods used to assign flow requirements, a framework is needed that allows for adaptive environmental management and refinement of techniques and targets as knowledge of ecosystem responses is gained.