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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
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
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
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
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
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
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
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
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

10. 10
GSFLOW – INTEGRATED
GW/SW MODELLING
10

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
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
GSFLOW SW/GW/SW Components
► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)

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
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
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. 1717
Aquifer Head vs. Stream Stage
• Groundwater
discharging to the
stream, except during
large flow events
• Example stream gauge

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
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
Dunnian Runoff Generation
► Dunnian runoff occurs where depth to water table is at or near surface

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

22. 22
YORK TIER 3 MODEL
DEVELOPMENT AND
CALIBRATION: OVERVIEW
22

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
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
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
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
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
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
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
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
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
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
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

34. 34
TIER 3 MODEL
APPLICATIONS
34

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
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
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
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
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
DROUGHT ANALYSIS
40

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
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
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
CONCLUSIONS
44

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)