AquaResource Develops Refinement for Ontario's Permit to Take Water (PTTW) Evaluation Process

AquaResource has worked closely Ontarioís Ministry of the Environment (MOE) to develop a protocol to evaluate highly consumptive permits to take water. Ontarioís Ministry of the Environment (MOE) allocates permits for major water taking within Ontario to municipalities and industries.  The traditional approach to issuing permits is to characterize local conditions and assess potential local impacts, however no assessment of existing regional allocations or regional impacts was undertaken.  To improve the ability of permit issuers to evaluate the availability of water and the potential for regional impacts, AquaResource worked closely with MOE to develop a screening tool to quantify the percentage of water available that is currently being used within all watersheds in Ontario.

Water budgeting approaches vary from simplified one-dimensional flow calculations to spatial analysis and detailed numerical modeling.  As the methodology for PTTWís was required to be uniformly applied across Ontario, detailed methods were not appropriate.  GIS spatial analysis techniques were applied to evaluate both the amount of water flowing through a watershed and the volume of water used within the same area.  Recognizing the interconnections of groundwater and surface water resources, they were not differentiated in this assessment.  A volume of streamflow was also ìreserved from allocationî to ensure that water resources are not over-allocated.

The percent water use for every watershed across Ontario was calculated as consumptive water demand over the available flow (less reserve amount).  Threshold values were used to limit allocation to rates well below reserve values.  Water consumption was evaluated utilizing permitted water takings and estimates of the amount of water consumed by each type of water use (consumption << pumping).  The components of this calculation were evaluated across the province and then spatial analysis tools were used to compute and map results.  Percent water consumption calculations are developed for both average annual and summer low flow conditions, to evaluate the water availability under both flow regimes.