ClimateChange Assessment Guide.pdf - University of Waterloo

Appendix E E-7Subwatershed 19 Case StudyThe Ministry of Environment (MOE, 2009) has published the technical rules which provide instructions on completinga Tier Two Subwatershed Stress Assessment and a Tier Three Local Area Risk Assessment. In addition, theProvince (MOE, 2007) developed the Provincial Guidance Module 7 Water Budget and Water Quantity RiskAssessment which provides further instruction on how to complete a Subwatershed Stress Assessment. As outlinedin Guidance Module 7, the stress assessment determines the level of potential stress in each assessment area orsubwatershed by using the percent water demand calculations and the potential stress thresholds for both surfacewater and groundwater.At present, the Technical Rules do not require that Tier Two and Tier Three Assessments include climate changeimpact evaluations; however, the assessments should identify and document any observed climate trends in awatershed or subwatershed and also document any past climate change assessments completed in the area.Credit Valley Conservation (CVC) completed a Tier Two Water Budget and Subwatershed Stress Assessment(AquaResource, 2008) following the methodologies outlined in the Technical Rules and Guidance Module 7. TheTier Two Assessment estimated the groundwater percent water demand for Subwatershed 19 to be 14%. As thispercent water demand is above the Provincial threshold of 10%, Subwatershed 19 is classified as having a“Moderate” potential for stress (see Section 7.1). Municipal water supplies for the Towns of Orangeville, Mono, andAmaranth are located within Subwatershed 19, and the majority of the Town of Orangeville’s groundwater suppliesare located within this subwatershed. As a result, the Town was required to complete a Tier Three Assessment underthe Water Budget Framework. As of spring 2010, this study has not yet been completed. However, detailedcontinuous streamflow and groundwater flow models have been developed as part of this study and those models areused as part of this assessment. The primary purpose of this Case Study is to determine how climate change affects the hydrologic system and waterbalance of Subwatershed 19 in the Credit River Watershed. More specifically, from a Drinking Water SourceProtection perspective and in response to Ontario’s Clean Water Act, this study aims to evaluate the risks of municipalwater supply shortages in the future, in the communities partly or wholly within Subwatershed 19 (i.e., the Towns ofOrangeville, Mono and Caledon and the Townships of East Garafraxa and Amaranth) and the sensitivities in thesystem that lead to change.Secondary purposes of the study are to support public education and inform other types of studies routinelyconducted by the CVC (i.e., fisheries management, terrestrial management, water quality, etc.). The water resource quantity issues in Subwatershed 19 include the following:• Availability and reliability of groundwater based municipal water supplies in the future;• Baseflow-low flow concerns from a fisheries and wastewater assimilation perspective; and• High flow and peak flow concerns from a flood risk and instream erosion perspective.The Town of Orangeville currently maintains nine municipal wells, most of which are located within Subwatershed 19.The Town of Mono operates four municipal supply wells. Average annual water demand for the Towns of Orangevilleand Mono is approximately 9,500 m 3 /d. The Province has included the Towns within area affected by the ‘Places toGrow’ legislation, and therefore, has encouraged the municipalities to plan for high populations and populationdensities. An increase in the population in the area would require drawing on additional groundwater supplies as wellas ensuring that existing groundwater supplies would be available in the future.Fisheries habitat exists throughout the subwatershed; they are found mostly in the northeast portion of thesubwatershed, except in the ephemeral streams. Local water quality and hydrology generally support a healthy