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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

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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.

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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

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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

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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

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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

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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 40000Section Distance

0

100

200

300

Elevation

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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

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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

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GSFLOW – INTEGRATED GW/SW MODELLING

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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”

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USGS-GSFLOW

S o i l w a t e r

U n s a t u r a t e d

z o n e P r e c i p i t a t i o n

E v a p o t r a n s p i r a t i o n

S t r e a m S t r e a m

E v a p o r a t i o n

P r e c i p i t a t i o n

I n f i l t r a t i o n

G r a v i t y d r a i n a g e

R e c h a r g e

G r o u n d - w a t e r f l o w

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

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GSFLOW SW/GW/SW Components

► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)

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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

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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

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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

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Aquifer Head vs. Stream Stage

• Groundwater discharging to the stream, except during large flow events

• Example stream gauge

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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

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GW Feedback: Surface Discharge and Saturation Excess

Rejected Recharge

S o i l w a t e r

U n s a t u r a t e d

z o n e P r e c i p i t a t i o n

E v a p o t r a n s p i r a t i o n

S t r e a m S t r e a m

E v a p o r a t i o n

P r e c i p i t a t i o n

I n f i l t r a t i o n

G r a v i t y d r a i n a g e

R e c h a r g e

G r o u n d - w a t e r f l o w

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

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

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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

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YORK TIER 3 MODEL DEVELOPMENT AND CALIBRATION: OVERVIEW

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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

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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

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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

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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

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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

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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

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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 Recharge Discharge to Streams

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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

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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

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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

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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

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TIER 3 MODEL APPLICATIONS

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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

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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

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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

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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

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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

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DROUGHT ANALYSIS

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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

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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)

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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

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CONCLUSIONS

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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)