For more information about our work please feel free to visit our website at http://earthfx.com/

1. 1
Assessing Sensitivity to
Drought and Climate Change
with an
Integrated Surface Water/Groundwater Model
at the Subwatershed Scale
MODFLOW and More 2015
E.J. Wexler, P.J. Thompson,
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
 High water table contributes to Dunnian runoff and higher ET
 UZF module for unsaturated flow and GW ET
 LAK and SFR2 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
► Flow routed through all
stream segments as
shown
► 85 lakes and wetlands
also represented
► Four gages to calibrate
GSFLOW model
7
Stream Gage

8. 8
Hydrologic Model
Inputs/Outputs
► PRMS Sub-model Inputs
 Daily Climate Data
► Rainfall (NEXRAD)
► max/min temp.
► Solar radiation
 Topography (DEM)
 Land cover (% imperv)
 Soil properties (n, fc,wp)
► Model computes daily water
budget components
 Net P, Snowmelt, Interception,
RO, Infiltration, ET, Recharge
8
PRMS Flow Chart

9. 9
► Results for Coldwater
River (02ED007)
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 Heads: Layer 1 and 7
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
► Three prior years used for model start-up

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. 1616
Section line is through the two watersheds.
Differences in the till thickness and the aquifer
continuity affect the behavior of the streams in
Hawkstone and Oro South
Hawkstone Creek runs along the base of the moraine
cutting off flow to South Oro

17. CLIMATE CHANGE
ASSESSMENT
17

18. 18
GCM models of Climate Change
► Climate predictions are done
with Global Circulation
Models (GCM).
► Many different GCMs with
different assumptions.
► Predictions of annual Temp
and Precip change cover a
wide range
► Most show 1.5 - 4 C
increase by 2070 for
Southern Ontario
► Most show increase in winter
Precip and decrease in
summer/fall Precip
► GW/SW models can be
run with a range of GCM
predictions to bracket
range of likely outcomes
Increase in Mean Annual Temperature (C)
%ChangeinMeanAnnualPrecipitation
Selected by Percentile Method
Modelled for this Study

19. 19
Change Field Method - Baseline versus CGCM3T63
Shift in Month Temperature
Values shifted by 1 to 5 C
Percent Change in Monthly Precipitation
Values scaled by -45 to 45%
► Many methods for downscaling GCM outputs for local-scale models
► Change Field method selected for this analysis
 Shift observed Temp by predicted monthly increase for each GCM scenario
 Multiply local observed Precip values by monthly scale factor
► Selected approach does not change frequency or intensity of storms

20. 20
Comparison of Low Flow Change – North vs South Oro
• CGMC3T63 scenario shows more flow in winter months. Spring freshet is earlier
• Reduction in summer flows due to lower rainfall and longer recession period.
• Summer flow change in South Oro more pronounced due to poor connection
Shellswell Creek (South Oro)
Bluffs Creek (North Oro)

21. 2121
Change in Total 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.

22. 22
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 be further stressed in summer
► Understanding the underlying geology is essential
 Shallow geology is important
 Interconnection of streams to recharge feature is key factor
 Oro Moraine also provides high storage
► GSFLOW proved extremely useful for analyzing GW/SW
response under a variety of climatic conditions.

23. 23
Baseline Click for animation CGCM3T63
Thank you!
Questions or Comments?