Baseflow and Water Use Assessment – Report on Current Conditions

Baseflow and Water Use Assessment – Report on Current Conditions

Don River Watershed Plan Baseflow and Water Use Assessment – Report on Current Conditions 2009 Prepared by: Toronto and Region Conservation Don River Watershed Plan: Baseflow and Water Use Assessment – Report on Current Conditions Table of Contents Table of Contents............................................................................................................................ 2 List of Tables................................................................................................................................... 3 List of Figures.................................................................................................................................. 3 1.0 Introduction............................................................................................................................... 4 2.0 Understanding Groundwater Recharge and Discharge .......................................................... 4 2.1 Don River Watershed Water Budget Modeling .................................................................... 5 2.2 Regional Groundwater Modeling.......................................................................................... 5 2.3 TRCA Role/Interest in Low Flow ........................................................................................... 5 3.0 Data Sources and Methods...................................................................................................... 6 3.1 Baseflow Data Collection ...................................................................................................... 7 3.1.1 Baseflow Spatial Analysis............................................................................................. 10 3.2 Water Use Data Collection.................................................................................................. 10 3.2.1 York Region Water Use Assessment ........................................................................... 11 3.2.2 Surface Water Vulnerability Assessment ..................................................................... 11 3.2.3 Study Limitations.......................................................................................................... 12 3.2.4 Groundwater Data Sources.......................................................................................... 12 4.0 Existing Conditions in the Don River Watershed ................................................................... 13 4.1 Baseflow Conditions ........................................................................................................... 13 4.1.1 Baseflow Findings ........................................................................................................ 16 4.1.2 Baseflow Issues in the Don.......................................................................................... 29 4.2 Water Use and Allocation Conditions................................................................................. 30 4.2.1 Surface Water Use Assessment................................................................................... 33 4.2.2 Vulnerability Assessment ............................................................................................. 35 4.2.3 Water Use and Allocation Issues in the Don ............................................................... 37 4.3 Ratings for the Baseflow and Water Demand Indicators ................................................... 37 4.3.1 Rating for the Baseflow Indicator ................................................................................. 38 4.3.2 Rating for Water Demand Indicator ............................................................................. 40 5.0 Low Flow Management Strategies......................................................................................... 42 5.1 Climate Change .................................................................................................................. 42 5.2 Drought Management......................................................................................................... 43 5.3 Integrated Water Management ........................................................................................... 43 6.0 Conclusions and Management Considerations..................................................................... 44 6.1 Surface Water Use .............................................................................................................. 44 6.2 Baseflow .............................................................................................................................. 45 7.0 References .............................................................................................................................. 47 Appendix A – TRCA Low Flow Monitoring Protocol..................................................................... 49 Appendix B – TRCA Water Use Assessment User Surveys......................................................... 53 Appendix C – Methodology for the Merging of Three Water Use Databases ............................. 58 Toronto and Region Conservation CFN: 37590 2 2009 Don River Watershed Plan: Baseflow and Water Use Assessment – Report on Current Conditions List of Tables Table 1: Ratings for the potential impact of water users on baseflow......................................... 12 Table 2: Flow characteristics for Don River stream gauges. ....................................................... 14 Table 3: Percentage of baseflow to total flow. ............................................................................. 14 Table 4: Measured and recommended flow for Don River gauges (cubic meters per second). 15 Table 5: Measured baseflow discharge as compared to preliminary environmental flows........ 16 Table 6: Percent contribution to baseflow/groundwater discharge by subwatershed. .............. 18 Table 7: Water Withdrawals by Subwatershed – Don River Watershed, 2003............................ 31 Table 8: Percent change in median daily baseflow discharges (May - August) from 1995 - 2005 in the Lower West Don River and Lower Don River..................................................................... 38 Table 9: Surface water users, high impact water users, and baseflow allocated in Don River watershed subwatersheds............................................................................................................ 41 List of Figures Figure 1: Baseflow monitoring sites in the Don River watershed.................................................. 8 Figure 2: Typical sampling stream cross-section. ......................................................................... 9 Figure 3: Physiographic regions in the Don River watershed. .................................................... 17 Figure 4: Don River subwatersheds – 2005 subwatershed percent contribution to baseflow. .. 19 Figure 5: Don River subwatersheds – 2006 subwatershed percent contribution to baseflow. .. 20 Figure 6: Normalized baseflow as calculated from 2003 and 2006 summer measurements. ... 21 Figure 7: Upper Don River subwatersheds – 2003 percent change to baseflow discharge. ..... 25 Figure 8: Percent of water users by sector. ................................................................................. 32 Figure 9: Percent of total withdrawal by sector............................................................................ 33 Figure 10: Don River surface water use reach vulnerability assessment.................................... 36 Figure 11: Percent change in median daily baseflow discharges (May – August) from 1995 – 2005 in the Lower West Don River and the Lower Don River...................................................... 39 Figure 12: Total numbers of surface water users and high impact surface water users in Don River watershed subwatersheds. ................................................................................................. 41 Toronto and Region Conservation CFN: 37590 3 2009 Don River Watershed Plan: Baseflow and Water Use Assessment – Report on Current Conditions 1.0 Introduction The Toronto and Region Conservation Authority (TRCA), in consultation with the multi- stakeholder Don Watershed Regeneration Council and watershed municipalities, is developing a watershed plan for the Don River. This watershed planning process has been initiated in response to a number of recent policy and planning developments, including the need to fulfill York Region’s watershed planning requirements under the Oak Ridges Moraine Conservation Plan (ORMCP, Ontario Regulation 140/02) and to update the original management strategy outlined in Forty Steps to a New Don (Metropolitan Toronto and Region Conservation Authority [MTRCA], 1994). The goal of the watershed planning study is to recommend updated management strategies that will guide land and water use decisions, such that the overall ecological health of the Don River watershed is protected and improved. The aim is to build on the Forty Steps’ principles to protect what is healthy, regenerate what is degraded, and take responsibility for the Don. Recognizing the significant watershed planning work that has already been completed, and given that there are limited undeveloped lands remaining on the Oak Ridges Moraine within the watershed boundary, this study will focus mainly on filling information gaps, guiding land use planning and approval decisions and providing direction to advance implementation of regeneration priorities. This report has been prepared as part of the scoping and characterization

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