ClimateChange Assessment Guide.pdf - University of Waterloo

Appendix E E-53Subwatershed 19 Case Studypermitted surface water takings in subwatershed 19 and as a result a stress assessment cannot be completed for thesubwatershed. However, the assessment of climate change impacts on a surface water stress assessment would becompleted very similar to the groundwater case, with the surface water supply terms being recalculated for eachclimate change scenario. A Tier Three Water Budget and Local Area Risk Assessment is completed to estimate the likelihood that amunicipality will be able to sustain its planned pumping rates and to identify drinking water threats that may influencethe municipality’s ability to meet its planned pumping rates. A local area water budget must be developed using aLocal Area (Tier Three) Water Budget Model for all Type I, II and III drinking water systems where:1. There have been historical source water issues meeting demand, or2. The Tier Two subwatershed stress level is moderate or significant.A Tier Three water budget uses detailed groundwater and/or surface water numerical models, refined from the TierTwo models whenever possible. These models should be developed with the accuracy and refinement needed toevaluate hydrologic or hydrogeologic conditions directly at a water supply well or intake; be of sufficient spatial scaleto evaluate the potential impacts of increased future water demands on external water quantity receptors such asother water users and the environment; represent a refined conceptual hydrologic or hydrogeologic model; and becalibrated to the best extent possible to represent average typical conditions as well as longer term climatic trends.In a Tier Three Local Area Risk Assessment, the water budget models are used to estimate the likelihood that a wellor surface water intake will be able to pump an allocated pumping rate in response to a series of water demand,climate and land use scenarios. The risk associated with operating a well or intake is ‘significant’ if there are potentialproblems meeting demand under a specific scenario or, by operating the well, there are significant impacts to otherwater uses. The risk of operating a well or intake is moderate if allocated demands can be met but there are potentialimpacts to other users. The risk of operating a well or intake is ‘low’ if planned demands can be met during eachscenario and there are no impacts to other users.In 2006 MNR initiated a Pilot Project for the Tier Three process in Subwatershed 19. This pilot project included thedevelopment of the detailed surface water and groundwater flow models used for this case study.Vulnerable areas, referred to as the WHPA Q1 and WHPA Q2 for groundwater and the IPZ Q for surface water aredelineated as part of the Tier Three process. Examples of these areas for groundwater are shown on Figure 7-3 forthe municipal water supplies in Subwatershed 19. If municipal wells located within this area are found to have asignificant risk, all consumptive water demands within the vulnerable area are classified as significant threats. Theseclassified threats are key deliverables from the Tier Three process.