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Integrated Modelling as a Tool for Assessing Groundwater Sustainability under Future Development and Drought


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Integrated Modelling as a Tool for Assessing Groundwater Sustainability under Future Development and Drought

  1. 1. 1 Integrated Modelling as a Tool for Assessing Groundwater Sustainability under Future Development and Drought in York Region, Ontario, Canada CWRA 2014 Earthfx Incorporated Toronto, Ontario, Canada
  2. 2. 2 Presentation Objectives ► Overview of Presentation:  Overview of Study Area  Technical background, goals and challenges  Modelling Approach  Modelling Result Highlights ► Emphasis on the unique technical aspects of this project ► Special thanks to all the staff at Earthfx and our study team partners for their efforts on this project.
  3. 3. 3 Region of York Study Area ► Region of York  Population 1.03 million (2011)  840,000 urban residents ► West Holland Marsh Ag. Area  40% Marsh  60% Agriculture (3x more productive/acre than Ontario average) ► Study area ranges from highly urban to highly productive farmland ► York Municipal Water Supply  41 York Municipal Wells  19 Other Municipal Wells ► Key geologic features:  Oak Ridges Moraine  Subglacial tunnel valley systems
  4. 4. 4 Tier 3 Water Quantity Risk Assessment Objectives ► Evaluation of 4 sub-watersheds identified at the Tier 2 stress level ► Delineation of Vulnerable Areas  WHPA-Q1/Q2 ► Risk Assessment/Wellfield Sustainability Scenarios  Existing Land Use and Takings  Allocated Demand and Future Land Use  Drought Conditions – Existing/Future ► Impacts on Other Uses  Cold Water Streams and Wetlands ► Significant GW Recharge Areas Municipal Wells and Stressed Catchments
  5. 5. 5 York Region: Water Use ► Municipal Water Supply: 41% of total GW taking  41 York Municipal Wells  19 Other Municipal Wells ► Other Water Takings  248 permitted non-municipal GW combined GW/SW takings  286 non-permitted known takings  432 permitted SW takings ► All SW and GW sources simulated using actual daily values, including peaking rates, so as to fully assess drought sustainability
  6. 6. 6 York Region Study Area Challenges ► Geologic Issues  Complex conceptual model, with erosional tunnel valley features ► Hydrogeologic Issues  Multiple aquifers with variable aquifer confinement  Over 1000 SW and GW takings ► Significant agricultural and golf course water use ► Fluctuations in municipal water use ► Surface Water and Hydrology Issues  Hummocky topography – focused recharge  Urbanization  Lowland areas with significant Dunnian GW feedback ► Integrated SW/GW issues  Significant GW/SW interaction including springs, wetlands, intermittent reaches, and stream leakage in the welllfield areas
  7. 7. 7 York Region Model: Technical Foundation ► 2002 MOE GW Protection Fund Work produced:  ORM Database/York Region Sitefx Database  Oak Ridges Moraine Regional Model (GSC Surfaces)  YPDT “Core Model” (Earthfx Surfaces) ► 8 Layer Conceptual Model ► Steady State MODFLOW Model  Many technical insights and applications ► Since 2004  Many applications of the database, model and understanding (sewer construction, etc.)  Additional transient data compilation (York Region and PGMN network)  Evolving conceptual understanding of the till stratigraphy  Improvements in integrated modelling  2002 Models used extensively for Tier 1 and 2 SWP assessments ► 2010: Start of the Tier 3 Study  Some resistance to doing a major model update: was it necessary? Legend: Halton Till Oak Ridges Complex Northern/Newmarket Till Thorncliff Fm. Sunnybrook Fm Scarborough Fm (Note: Formation name or equivalent) Scale: (metres) 0 5000 10000 15000 ORM Laurentian River Valley Newmarket Till Tunnel Channel Thorncliff Fm North South Lake Ontario North South Section: Yonge Street 0 20000 40000 Sec tionD is tance 0100200300 Elevation
  8. 8. 8 York Tier 3: Technical Goals and Improvements ► Database Driven Integrated Modelling  Conversion of York Region GW group to a comprehensive SQLServer database  Extensive review and “mining” of reports compiled since development of the Core Model  Compilation and assessment of over 1000 surface water and groundwater takings  Compilation and calibration to over 100 million water levels, stream flow and climate measurements ► Conceptual geologic model review and refinement:  Complete re-assessment of the shallow subsurface layering: where SW and GW interact  Subdivision of the Oak Ridges Aquifer into three layers to represent ORM silts and perched WT  Subdivision of the Newmarket Till into 3 layers ► Development of a fully integrated, fully distributed model  Hydrology: Fully distributed, dynamic simulation of 3D hydrology (precip., runoff and interflow) ► Complete simulation of focused recharge on hummocky topography of the moraine ► Snowpack simulation to evaluate spring freshet recharge processes ► Full simulation of urban development and changes in imperviousness  Hydraulics: Continuous simulation of stream network routing and GW/SW interaction throughout the entire 4,450 km stream network  Groundwater: Actual daily SW and GW water takings, including York Region peak pumping ► In short: a significant technical leap from a steady state GW platform
  9. 9. 9 Why choose an Integrated Approach? ► Simulation of the complete water budget:  Guaranteed Accountability: All water inputs and outputs (precipitation, SW and GW takings, streamflow and GW discharge)  Dynamics: An integrated approach is necessary because of the significant fluctuations in the water budget elements ► Seasonal changes ► Summer daily peaking rates (pumping fluctuations) ► Growth in some areas, reductions due to new pipeline supply in other areas. ► Other water use: Complex combined SW/GW takings ► Tier 3 Applications:  Well sustainability under long term drought conditions  Full simulation of reductions in recharge, runoff and streamflow leakage (both due to drought and urbanization)  Ecological issues – stream leakage near wellfields, wetland impacts
  11. 11. 11 Integrated GW/SW Modelling ► Water simply does not care what we call it (SW or GW) and it moves seamlessly between domains ► Our experience is that integrated modelling provides insights that simply cannot be obtainable from uncoupled models  Integrated models are 10x tougher to build, but 100x more insightful! ► Integrated modelling forces you to look at your “blind spots”
  12. 12. 12 USGS-GSFLOW Soil water Unsaturated zone Precipitation Evapotranspiration StreamStream Evaporation Precipitation Infiltration Gravity drainage Recharge Ground-water flow Zone 1: Hydrology (PRMS) Zone 3: Hydraulics (MODFLOW SFR2 and Lake7) Zone 3: Groundwater (MODFLOW-NWT) 1 2 3 ► GSFLOW is a significant USGS development effort  Hydrology: USGS PRMS (Precipitation-Runoff Modelling System)  GW Flow: MODFLOW-NWT: (A new version of MODFLOW optimized for shallow variably saturated (wet/dry) layers  Hydraulics: Lake and SFR2 River Routing Package ► GSFLOW is a free and open source model
  13. 13. 13 GSFLOW SW/GW/SW Components ► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)
  14. 14. 14 GSFLOW Stream Interaction ► Streams are represented as a network of segments or channels  Streams can pick up precipitation, runoff, interflow, groundwater and pipe discharges  Stream losses to GW, ET, channel diversions and pipelines ► GW leakage/discharge is based on the dynamic head difference between aquifer and river stage elevation  Similar to MODFLOW rivers, but the stage difference is based on total flow river level River Loss River Pickup
  15. 15. 15 Full Stream Network Simulation ► All streams are represented as the smallest Strahler Class 1 streams represent the greatest total stream length and have the greatest baseflow pickup (i.e. from springs and seeps) Strahler Class No. of Segments Total Length (km) % of Total Length Total Discharge (m3/s) % of Total Discharge 1 4213 2185 43% 3.65 26% 2 2118 1186 23% 2.75 19% 3 1083 832 16% 3.15 22% 4 529 431 8% 2.07 15% 5 29 266 5% 1.43 10% 6 16 112 2% 0.61 4% 7 7 66 1% 0.6 4% Total 7995 5078 14.26 Strahler Classes Baseflow Pickup
  16. 16. 16 GSFLOW Total Flow Routing ► White-blue gradation indicates total streamflow  Green-orange gradation indicates topography ► All streams, including key headwater springs are simulated Click for Animation
  17. 17. 1717 Aquifer Head vs. Stream Stage • Groundwater discharging to the stream, except during large flow events • Example stream gauge
  18. 18. 18 Benefits of Integrated Stream Routing ► Head dependent leakage based on total flow stream levels  In a GW only model, the leakage is based on baseflow levels only  High stream levels after a storm can drive SW into the GW system ► Upstream flow can infiltrate downstream to the GW system  Full 3D “routing” of both SW and GW ► Analysis of the entire water budget, including SW takings, SW discharges and stream diversions ► Model calibration to a field measurable parameter (total streamflow)  No need to guesstimate baseflow ► Direct baseflow measurement is nearly impossible (seepage meters?) ► Baseflow separation is, at best, an unscientific empirical estimate
  19. 19. 19 GW Feedback: Surface Discharge and Saturation Excess Rejected Recharge Soil water Unsaturated zone Precipitation Evapotranspiration StreamStream Evaporation Precipitation Infiltration Gravity drainage Recharge Ground-water flow Soil-zone base Surface Discharge ► Surface Discharge is the movement of water from the GW system to the soil zone, where it can become interflow or surface runoff ► Saturated soils can reject recharge: groundwater feedback
  20. 20. 20 Dunnian Runoff Generation ► Dunnian runoff occurs where depth to water table is at or near surface
  21. 21. 21 GSFLOW Conclusions ► GSFLOW features:  Streams can be incised in the GW system layers  Interaction is conceptually similar to MODFLOW Rivers, but with total flow routing  Streams can dry up and later rewet  Every component of the stream flow can be identified and visualized ► Limitations: Stream routing simplified when compared to storm water models  Timing and channel flow representation not ideal for peak flow or flood modelling  (However, GW interaction is likely not significant during peak flow analysis) ► Overall benefits for water budgeting and cumulative impact:  Full accounting of gains and losses to the stream network  Ideal for simulation of impact during low flow conditions  Allows calibration to total measured streamflow at the gauge ► Much more direct than trying to calibrate to a baseflow estimate
  23. 23. 23 York Tier 3 Model Development Phases ► Step 1: Steady State MODFLOW and PRMS model: initial calibration  Objective is to get the models up and running and internally consistent ► Step 2: Fully integrated transient calibration  Core calibration period included average (2006), dry (2007) and wet (2008) years ► Good water use, water levels, climate and streamflow data for calibration  Dry/Wet year transition provides insight into both seasonal and longer term storage ► Tier 3 Applications: 10 Year Drought Simulation: 1958-1967  Multiple scenarios with different takings and land use (each scenario is 1 TB in size!)  Each 10 year run is a “Scenario” with historic climate and current water taking  Results processed to evaluate both water level and stream sensitivities and Tier 3 issues ► Ecological impacts assessment of future water use and land develop  Simulation outputs include all components of accumulated total streamflow (baseflow and runoff) throughout the entire steam network
  24. 24. 24 Conceptual Geologic Model Update ► Updated Conceptual Model:  Description accompanied by schematics of key geologic settings and processes ► Updated 3D model surfaces considered:  New boreholes, seismic data, geophysical logs  Earlier conceptual models (GSC/CAMC/Earthfx) ► All surfaces completely re-gridded and rebuilt, with:  ORAC silts  Upper/Lower Newmarket Till N-S Section along Bayview Ave
  25. 25. 25 Step 1: Steady-State GW Model ► Model inputs include average pumping at municipal and private wells. ► Steady state recharge based on results of long-term average of PRMS step 1 simulation ► Model calibrated to match static water levels in WWIS database and average heads in wells with continuous record. ► Model matched observed water levels and groundwater flow patterns well Simulated heads in INS/Lower ORAC
  26. 26. 26 Step 1: Steady-State Baseflow Simulation ► Steady-state model only routes baseflow ► Model was calibrated to match estimated baseflow at EC gauges ► Red zones show areas of surface discharge Simulated groundwater discharge to streams and wetlands
  27. 27. 27 PRMS: 3D Hydrology Simulation ► Cascade routes overland flow and interflow downslope to streams  Allows infiltration of run-on ► Used a modified SCS CN method for Hortonian flow estimate  Initial abstraction calculated by PRMS.  CN values updated daily based on antecedent moisture conditions ► Dunnian runoff calculated based on soil moisture Overland flow network from 100-m DEM
  28. 28. 28 Distributed Modelling - PRMS ► Soil water balance calculated on a cell- by cell basis. ► Unique inputs for each model cell  Climate data interpolated over grid  Topography from DEM ► slope and slope aspect ► Parsimony  Regionally consistent values for vegetative cover, % impervious for land use classes  Regionally consistent values for soil properties by surficial geology class Land Use Class Assigned to Grid % Impervious based on Land Use Class
  29. 29. 29 PRMS Model Results ► Model calibrated to match flows at EC Gauges ► Daily outputs for each cell  Can be averaged monthly, annually, and over study period  Hydrographs can be generated for each cell. Net Precipitation Cascade Flow Actual ET GW RechargeDischarge to Streams
  30. 30. 30 Recharge Change ► Future land use  % impervious and vegetative cover were modified  Results subtracted to show areas with significant change to GW Recharge and other water balance components Change in GW Recharge - Future Land Use
  31. 31. 31 Step 2: Integrated GSFLOW Stream Gauge Calibration ► All mapped streams in York/TRCA area represented in model ► Model calibrated to observed total flows measured at EC gauges
  32. 32. 32 GSFLOW Stream Response ► Gradational Stream Color: Total accumulated stream flow along reach ► Blue shading: Overland runoff from rainfall events ► Animation shows headwater tributaries flowing after a storm and then drying up during the dry periods ► Storm of August 19, 2005 produces large overland and stream flows Click for Animation
  33. 33. 33 GSFLOW Comparison to TRCA Sport Flows ► Check of simulated summer flows to low flows measured by TRCA in 2002 ► Gradational Stream Color: Total accumulated stream flow along reach. Note log scale ► Colour-coded diamonds show measured flows. Comparison of mid-September 2005 to TRCA baseflows
  35. 35. 35 Risk Assessment: Vulnerable Areas ► Scenario G(2) looked at changes in heads due to future pumping (municipal and non-municipal consumptive use) ► WHPA-Q1 defined by 1-m drawdown from no-pumping condition ► Simulated steady-state heads with future pumping subtracted from heads with no pumping. The simulated drawdown cone is continuous. ► Change in land use had no effect on extent of WHPA-Q1 Maximum extent of 1-m drawdown due to all takings
  36. 36. 36 Risk Assessment Scenarios ► For example, Scenario G(2) looked at incremental changes in heads due to future increases in municipal pumping ► Simulated steady-state heads with future pumping subtracted from heads with existing pumping. Extent of 1-m drawdown in the TAC
  37. 37. 37 Impact on Other Uses ► Scenario G(2) also looked at incremental changes in baseflow due to future increases in municipal pumping ► Simulated baseflow with future pumping subtracted from baseflow with existing pumping. ► Change occurs mostly within 1-m drawdown cone % decrease in baseflow due to increase in municipal pumping
  38. 38. 38 Impact on Other Uses ► Changes above 20% of baseflow in coldwater streams caused by planned systems is considered significant risk ► Changes above 10% of baseflow in coldwater streams caused by increase from existing to allocated demand for existing systems is considered moderate risk ► Reaches with 50% decrease in flow to warm water streams (red circle) ► Also looked at 1-m decrease in heads below wetlands and at other permitted takings % decrease in baseflow due to increase in municipal pumping
  39. 39. 39 SGRA Analysis ► Tier 3 model to estimate average groundwater recharge ► Clipped and infilled areas based on procedures followed in LSRCA and TRCA Tier 1 studies SGRAs defined for LSRCA and TRCA
  40. 40. 40 DROUGHT ANALYSIS 40
  41. 41. 41 Drought Analysis ► Simulations considered the 10-year drought of WY1957- WY1966. Added two years for model startup ► Scenario D simulated drought with existing pumping and land use ► Scenario H(1) simulated drought with increased pumping and land use change ► Low heads in Summer 1965. Simulated heads – Location D – Scenario D
  42. 42. 42 Drought Analysis ► Model run starts with a steady-state Scenario C simulation. ► Two year simulation (average years) run to set up transient model conditions (i.e. get soil moisture to average levels etc.) ► Drought reference level - September 1956 - provides reasonable average conditions. ► Drawdowns are change from simulated heads at start of drought to heads on worst date Decrease in TAC heads due to 10-year drought – Scenario D Decrease in TAC heads due to 10-year drought – Scenario H(1)
  43. 43. 43 Drought Analysis ► Also looked at changes in streamflow under drought conditions ► Change primarily occur in headwater streams % decrease in streamflow due to 10-year drought
  44. 44. 44 CONCLUSIONS 44
  45. 45. 45 Summary ► The York Tier 3 project is complete with Peer Review sign-off ► Project report: 953 pages  Warning: may cause drowsiness ► The project represent a significant improvement over the previous Core Model, and should be an excellent foundation for York and TRCA moving forward. ► Special thanks to all the staff at Earthfx, our partner agencies and peer reveiwers! Click for Animation Monthly average flows – Scenario H(1)