A Methodology for Environmental Protection of Ontario Watercourses With Respect to the Permit to Take Water Program

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Watt, Sean Patrick
PTTW , Instream Flow Requirements
The Ontario Water Resources Act requires a Permit To Take Water (PTTW) for withdrawals greater than 50,000 L/day. The permitting process includes a requirement to minimize the environmental effects of the withdrawal, but does not include a specific framework to do so. A methodology is proposed for estimating the water supply, the water demand, both anthropogenic and ecological, and the amount available for withdrawal. Water supply is estimated using statistical analysis of recorded daily flows in the watershed of interest, in adjacent watersheds, and in the region. Anthropogenic demand is given by the Ontario Ministry of the Environment’s PTTW database. Ecological demand is also estimated using statistical analysis of recorded daily flows, and through field measurement methods such as the Wetted Perimeter method. A case study of Millhaven Creek in eastern Ontario shows that the methodology is appropriate for this area and, with minor modifications, would apply to the rest of Ontario. Evaluation of the existing methods for water supply estimation showed that using long-term data for analysis is the best method, and that the regional analysis work completed for Ontario is out of data and needs revising. Estimation methods for ecological demand are not necessarily appropriate for all areas. A single instream flow requirement based on the Mean Annual Flow is not appropriate for Millhaven Creek, and even a set of flows based on Mean Monthly Flows needs modification to be acceptable for Millhaven Creek. Supply minus demand varies from month to month, and therefore the decision on whether to issue a permit depends on the season as well as the duration of the withdrawal (e.g. seasonal vs. continuous) and type of use proposed (e.g. golf course irrigation vs. municipal drinking water).
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