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1. 1
Integrated surface water/groundwater
modelling to simulate drought and climate
change impacts from the reach to the
watershed scale
IAH-CNC – Waterloo 2015
P.J. Thompson, E.J. Wexler,
M.G.S. Takeda, Dirk Kassenaar
Earthfx Incorporated, Toronto, Ontario
Special thanks:
Shelly Cuddy and Katie Howson
Lake Simcoe Conservation Authority

2. 2
Lake Simcoe Restoration and Protection
► Fourth largest lake in Ontario and
has history of environmental stress.
► Watershed is under pressure from
increased development
► Lake Simcoe Protection Act (2008)
requires that every subwatershed be
studied to assess:
 current water demand,
 effect of future land-use change and
increased water demand
 response to drought
 response to future climate change
► Approach: develop fully integrated
GW/SW models using USGS GSFLOW
code
Lake Simcoe
Watershed

3. 3
GSFLOW - Integrated GW/SW Model
► GSFLOW combines MODFLOW-NWT with the PRMS hydrologic model
 PRMS code can be used as a distributed (cell-based) model
 Cascade method used to route overland runoff between cells
 Runoff can re-infiltrate downslope
 UZF module for unsaturated flow and GW ET
 Additional modules simulate GW interaction with lakes and streams

4. 4
Oro Moraine Study Area
Oro Moraine
Study sub-
watersheds
► Study focused on three
subwatersheds on NW shore
of Lake Simcoe
 Oro Creeks North
 Hawkestone Creek
 Oro Creeks South
► Oro Moraine is a high-
recharge surficial deposit that
feeds many headwater
streams.
► Model encompassed all
catchments fed by the Oro
Moraine.
Model Boundary

5. 5
Surficial
Geology
► The Oro Moraine
sits on top of
regional till plains
► Tunnel Channels -
tills have been
eroded by sub-
glacial flow
► Sands plains are
remnants of glacial
Lake Algonquin
► Best viewed in
section
Oro Moraine
Tunnel Channel
Sand Plain
Till Plain

6. 6
Hydrogeologic Model
► A complex 3-D geologic model was available from the OGS
► Provide very detailed mapping of shallow aquifer system
► Formed basis of the groundwater sub-model layers
► Shows the Oro Moraine, regional till plains, and infilled tunnel channels

7. 7
Surface Water
System
► Study area has numerous
streams and wetlands
(PSWs)
► Flow routed through all
stream segments as
shown
► 85 lakes and wetlands
also represented
► Four stream gauges to
calibrate GSFLOW model
7
Stream Gage

8. 8
Hydrologic Model
Inputs/Outputs
► PRMS Sub-model Inputs
 Daily Climate Data
► Precipitation (NEXRAD)
► Temperature
► Solar radiation
 Topography
 Land cover
 Soil properties
► Model computes daily water
budget components
 Snowmelt, Interception, Overland
flow, Infiltration, ET, Recharge
8
PRMS Flow Chart

9. 9
► Results for Coldwater
River (02ED007)
► Validated against
historical low flow
periods
9
Calibration to Daily and Monthly Flows
Observed (blue) Simulated (red)

10. 10
Simulated
Recharge
► PRMS run using uniform
grid with 50 m cells
► Results show average
annual recharge from a
32-yr simulation
► Shows high recharge on
Oro Moraine.
► Results dominated by soil
properties
► Results from PRMS
passed to MODFLOW
10

11. 11
Simulated Groundwater Heads
11
► Shallow system show influence of topography and streams. Deeper
system (below regional tills) is more subdued

12. DROUGHT ASSESSMENT
12

13. 13
10-Year Historic Drought Period
13
1953-1967
► Used daily climate data from 1956-1967 drought
to analyze subwatersheds response
► Model demonstrated a good match to available
historic streamflow records (1965-1967 records at
Coldwater Creek)

14. 14
Drought Impact on
Streamflow
► Limited drought
impact in Oro North
► Moderate change in
Hawkstone tribs
► Large change in Oro
South tribs and main
branch
► Similar patterns seen
in wetland response
► Drought sensitivity
depends on
whether streams
are linked to Oro
Moraine or
recharged locally
% change in average monthly streamflow at height of drought

15. 15
Pathline
Analysis
► Endpoints from forward
tracking confirm that Oro
Moraine feeds headwater
streams and wetlands
along flank
► Deep flow path emerge
far from the Moraine in
North Oro
► South Oro has little
connection to Moraine
compared to North Oro
and Hawkestone
15
End Points
Pathlines

16. 16
► Hawkestone Wetlands fed by the
Moraine, lower reaches are not in contact
► The drought scenarios allow the role of
storage to be evaluated under historical
stress conditions

17. CLIMATE CHANGE
ASSESSMENT
17

18. 18
Global Circulation Models of Climate Change
► Predictions of annual
temperature and
precipitation change cover a
wide range
► Most show 1.5 - 4 C
increase by 2070 for
Southern Ontario
► We picked a range of
GCM predictions to
bracket range of likely
outcomes
► Recommended approach as
per MNR guidelines (EBNFLO
& Aquaresources, 2010)
► Data available through the
Aquamapper website
(climate.aquamapper.com)Increase in Mean Annual Temperature (C)
%ChangeinMeanAnnualPrecipitation
Selected by Percentile Method
Modelled for this Study

19. 19
Change Field Method
Example - Baseline versus CGCM3T63
Values shifted by 1 to 5 C
► Shift observed
daily temperature
by predicted
monthly increase

20. 20
Predicted Monthly Changes
► Ensemble of GCM runs
shows monthly
precipitation increases
during the fall and winter
► Ensemble of GCM runs
shows a clear increase
in temperature over all
months

21. 21
Comparison of Low Flow Change – North vs South
Oro
• CGMC3T63 scenario shows more flow in winter months. Earlier spring freshet.
• Reduction in summer flows due to lower rainfall and longer recession period.
• Summer flow change in South Oro more pronounced due to poor connection with
the Moraine.
Shellswell Creek (South Oro) Drought Sensitive
Bluffs Creek (North Oro) Drought Insensitive

22. 2222
Simulated Change in Streamflow – Oro South
• Ensemble of models show consistent results.
• Log scale highlights significant reduction in summer flows
due to lower summer rainfall and longer recession period.
• This subwatershed was predicted to be drought sensitive
during the 10-drought simulation.
In poor contact
with the Moraine

23. 23
Simulated Change in Total Streamflow - Coldwater River
• Reduction in summer flows, but not as severe
given contact with the GW system.
• This subwatershed was predicted to be drought resilient
during the 10-drought simulation.
In good contact
with the Moraine

24. 24
Case Study #2 – Talbot
Watershed
► Talbot River watershed is dominated by
alvar plain.
► High recharge, low storage system.
► More pronounced response to future
change, but drought resilience still a good
indicator of climate change sensitivity.

25. 25
Climate Change: Conclusions
► Climate effects in Southern Ontario:
 More recharge and baseflow discharge in the winter
 Spring freshet earlier due to earlier snowmelt
 Drought sensitive reaches will experience increased/extended summer
low flow conditions.
► Understanding the underlying geology is essential.
 Shallow geology is important
 Interconnection of streams to recharge feature is key factor
 High groundwater storage features can mitigate the effect of low flow
extremes
► Drought and climate change response are best studied on
the reach to subwatershed scale.

26. 26
Integrated Modelling: Moving Forward
► Integrated modelling is a mature, developed technology to
understand watershed function and the hydrologic
response to drought.
► Drought assessment based on historical information can
validate the models’ ability to match extreme events.
► This can reduce uncertainty related to climate change
impact assessment.
► Integrated modelling can be used to develop practical
climate change policy and adaptation strategies.

27. 27
Baseline Click for Animation CGCM3T63
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