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1. 1
Simulating hydrologic response to climate
change and drought with an
integrated surface water/groundwater
model
Lake Simcoe watershed
CWRA 2014
E.J. Wexler1, P.J. Thompson1, S.E. Cuddy2, K.N. Howson2,
M.G.S. Takeda1, Dirk Kassenaar1
¹Earthfx Incorporated, Toronto, Ontario
²Lake Simcoe Conservation Authority, Newmarket, Ontario
Presented by
Dirk Kassenaar, Earthfx Inc.

2. 2
Drought and Climate Change
Analysis with Integrated GW/SW Models
► The Water Budget drought assessment component of the Source
Water Protection program has driven the analysis of water supply
sustainability in Ontario
 Some Tier 3 studies have utilized powerful fully integrated SW/GW models to
complete this assessment
► The Lake Simcoe Protection Plan (LSPP) has adopted key elements of
the SWP drought assessment approach
► The purpose of this presentation is to show how the insights from an
integrated LSPP model, developed for drought analysis, can be
extended to provide further insights into the assessment of climate
change

3. 3
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”

4. 4
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 the USGS’s preferred tool for Climate Change Assessment
 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 free and open source model

5. 5
GSFLOW SW/GW/SW Components
► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)

6. 6
Oro Moraine Study Area
► Under the LSPP, a water-budget model was needed for the
Oro North, Oro South, and Hawkestone Creek
subwatersheds
► The Oro Moraine is a sand and gravel deposit that feeds
the headwaters of these catchments.
► Proposed approach:
 Develop a fully-integrated GSFLOW model representing the
hydrology, GW flow, stream and wetland hydraulics of the entire
moraine

7. 7
Oro Moraine Study Area
Oro Moraine
Study
watersheds
► Three watersheds
contributing to the
northwestern shores
of Lake Simcoe
 Oro North
 Hawkestone
 Oro South

8. 8
Geology
► The Oro Moraine
has high
groundwater
recharge but also
high groundwater
storage
Oro Moraine

9. 9
Hydrogeologic Model Layers
► A complex 3D geologic model was available from the OGS
► Too often, hydrogeologists need to simplify the shallow aquifer systems
because of model stability and unsaturated model performance issues
► GSFLOW provides a GW submodel that can simulate seepage faces,
springs, and thin surficial sand deposits that can be seasonally important
 Particularly for important for vernal pools, wetlands and headwater creeks

10. 10
Hydraulics and Eco-Feature Representation
► Our approach was to
represent all streams in
the model, even the
intermittent Strahler Class 1
streams
► Over 85 Lakes, Ponds, and
Lake/Wetlands
► Wetlands accounted for
both hydraulically (LAK) and
hydrologically (Soil Moisture
Accounting package)
► Continuous fully coupled
GW/SW interaction
10
Oro Moraine

11. 11
Hydrology: Precipitation
► Calibrated hourly NEXRAD
radar data was found to
provide the best estimate of
distributed precipitation
► NEXRAD cells represented as
Virtual Climate Stations (VSCs)
spaced ~4.5 km apart across
the study area
11
NEXRAD VCS

12. 12
Hydrology: Topography and Runoff
► 50-m DEM used to generate
cascade flow paths to route
overland runoff to streams
► Slope aspect used for ET and
snowmelt modules

13. 13
Hydrology: Predicted Average Recharge
► Average recharge
from a 32-yr
simulation
13

14. 14
Predicted GW Levels: Layer 1 and 7
14

15. 15
► Coldwater River at
Coldwater (02ED007)
15
Continuous Streamflow Simulation
Observed (blue) Predicted (red)

16. 1616
Aquifer Head vs. Stream Stage
Groundwater
discharging to the
stream, except
during large events
Hydrograph at Oro-Hawkstone stream gauge

17. 17
Model Development Conclusions
► The integrated GSFLOW model represents the entire
SW+GW system, including:
 Very detailed geologic layering, including complex partially
saturated shallow aquifers
 Fully distributed hydrology, overland flow and interflow
 Hourly NEXRAD precip inputs.
 All streams and wetlands, including even the smallest intermittent
streams and headwater springs
 Full stream routing, with complex GW/SW discharge reversals
during storm events.

18. 18
DROUGHT ASSESSMENT
18

19. 19
Selected 10-Year Drought Period
► Recent and relatively prolonged drought
 More climate and streamflow data than the 1930’s
 Similar land use
► Hourly climate data from local MNR In-filled Climate
Stations (BARRIE WPCC, COLDWATER WARMINSTER, MIDHURST, ORILLIA BRAIN)
19
1953-1967

20. 2020
Predicted monthly flows before and during 10-year drought
0
2000
4000
6000
8000
10000
12000
14000
16000 Jan-54
Jul-54
Jan-55
Jul-55
Jan-56
Jul-56
Jan-57
Jul-57
Jan-58
Jul-58
Jan-59
Jul-59
Jan-60
Jul-60
Jan-61
Jul-61
Jan-62
Jul-62
Jan-63
Jul-63
Jan-64
Jul-64
Jan-65
Jul-65
Jan-66
Jul-66
Jan-67
MonthlyAverageGroundwaterDischargetoStreams
(m3/day)
Hawkstone Oro South Oro North
Compares typical late summer flows with drought flows

21. 2121
August 1957 November 1964
Monthly flows before and during 10-year drought
Many of smaller tributaries have dried up. Oro South Creeks
affected most because they are not fed directly by Oro Moraine.

22. 22
10-Year Drought
► Figure shows decrease
in average monthly
flow at worst point in
drought compared to
start of drought
► Decreases occur in all
tributaries
► Change in flow or
minimum flows can be
set as drought triggers
► Flows can be used to
estimate effects on
fish habitat
Decrease in average monthly streamflow (m3/s)

23. 23
10-Year Drought
► Limited drought
impact in Oro North
► Moderate change in
Hawkstone tribs
► Large, severe
change in Oro
South tribs and
main branch
► Drought sensitivity
depends on
whether streams
are linked to Oro
Moraine or
recharged locally
Percent change in average monthly streamflow

24. 24
GW Discharge to Wetlands
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

25. 2525
Contributing Area/GW Feedback
• Areas of high water table (red) contribute Dunnian runoff to streams.
• Significant seasonal and drought change in contributing area

26. 2626
Areas of high Water Table and Stream Flow
• Areas of high water table contribute Dunnian runoff to streams.

27. 2727
Groundwater Seepage to Hawkestone Creek
• GW seepage (green lines) in the reach near the Hawkestone WSC
stream gauge.
• Not much change during drought. Other reaches more sensitive
• Daily seepage shows reversal of gradients (seepage losses) during
periods of high streamflow (blue line) and stream stage.
• Gradients restored after peak stage passes.

28. 2828
Hydrograph shows groundwater seepage along Hawkestone Creek.
Seepage is controlled by till thickness and aquifer geometry. Seepage
decreases during drought.
August 1957
November 1964
GW discharge where aquifer pinches
and forces water to surface

29. 2929
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 runs along the base of the moraine
cutting off flow to South Oro

30. 30
Drought Simulation Conclusions
► Changes in simulated flows at the gauge don’t always tell
the whole story
► Change in tributary response can be very different
between apparently similar catchments
 South Oro – Major change in both tributary and main branch
response
 Hawkstone – Significant change in tributaries
 North Oro – Little change in trib or main branch drought flows
► Understanding the underlying geology is essential

31. 31
CLIMATE CHANGE
ASSESSMENT
31

32. 32
Building on the Drought Analysis
► Simulation of recent droughts provides an excellent
foundation for climate change analysis
► The drought analysis provides:
 Insights into the complex behaviour at both the watershed and
tributary scale
 An excellent “stress test” for the model
► We now have a good understanding of the system, and a
framework for climate change assessment

33. 33
Climate Change in Ontario
► Average of 30 GCM-scenarios a show 2 to 4C temp. increase by 2050.
 About double the global estimate.
► Changes in extreme warm temperatures expected to be greater than
changes in annual mean temperature
 Number of days above 30°C to double
 More heat wave and droughts.
► Annual precip. will increase up to 10% in S. Ontario, but
 Summer and fall total rainfall may decrease by up to 10%
 Winter precip. may increase up to 10% in south
 Less precipitation as snow; more lake effect snow though.
 Rainfall intensity and frequency of intense events likely to increase
► How will the Oro watersheds respond?

34. 34
GCM models of Climate Change
► Many different
climate models.
► Predictions of
annual temperature
and precipitation
increase cover a
wide range
► GW/SW models can
be run with a
range of CM
predictions to
bracket range of
likely outcomes
Selected by Percentile
Modelled for this Study

35. 35
Downscaling GCM Models
► Climate predictions are done with Global Circulation Models (GCM).
 Grid scale is large (250 - 400 km cells).
 Results are in terms of annual, seasonal, monthly change.
 Each model has different predictions based on different greenhouse gas
(GHG) emissions scenarios
► Different methods are available for downscaling GCM outputs for use in
local-scale models
 Change Field method was selected for this analysis
► Shift mean of local observed data (e.g. Temp)
► Multiply values by scale factor (e.g. Precip)
 Shift can be on a monthly, seasonal, or annual basis.
► Selected approach does not change frequency or intensity of storms

36. 36
Temperature - Baseline versus CGCM3T63
Daily and Monthly Baseline Temperature versus CGCM3T63
Values shifted by 1.4 to 4.6 C

37. 37
Precipitation - Baseline versus CGCM3T63
Daily and Monthly Baseline Precipitation versus CGCM3T63
Values scaled by -15 to 46%

38. 3838
Change in Total Streamflow – Bluffs Creek (North Oro)
• More flow in winter months.
• Spring freshet is earlier
• Very little change in summer flows
• Strongly GW dominated.

39. 3939
Change in Total Streamflow - Hawkestone Creek
• More flow in winter months.
• Spring freshet is earlier
• Not much change in summer flows – volumes are
similar
• Main branch has a significant GW component

40. 4040
Change in Total Flow – Shellswell Creek (South Oro)
• Similar results.
– More flow in winter months.
– Spring freshet is earlier
• However - Smaller change in summer flows

41. 4141
Change in Total Streamflow – Oro South
• Log Scale: Shows significant reduction in summer flows

42. 4242
Simulated Change in Total Streamflow - Coldwater River
Again, reduction in summer flows, but not as severe
given contact with the GW system

43. 4343
Comparison of Low Flow Change – Bluffs vs Shellswell Creek
• Similar change in winter patterns, change in South
Oro Creeks is more pronounced in summer
Shellswell Creek (South Oro)
Bluffs Creek (North Oro)

44. 44
Comparison of Flow Change – Bluffs vs Shellswell Creek
Shellswell Creek (South Oro)Bluffs Creek (North Oro)
• Little change in runoff events, change in low flow
conditions more pronounced in Oro South

45. 4545
Change in Baseflow (Hyporheic Exchange) -
Hawkestone Creek
• GSFLOW simulates the true baseflow component of total streamflow
• Baseflow analysis provides insight into GW storage and release.
• Much more baseflow in winter months.
• Some decrease in summer baseflow, but well connected to the Moraine
• Very significant change in the timing and quantity of groundwater
inflows during the spring months (no freshet to recharge the GW
system in the mid to late spring)

46. 4646
Contributing Area: High Water Table GW Feedback
• Areas of high water table (red) contribute Dunnian runoff to streams.
• Significant seasonal and drought change in contributing area

47. 4747
Areas of high Water Table and Stream Flow
• Areas of high water table contribute Dunnian runoff to streams.

48. 48
Climate Change: Conclusions
► As with the drought analysis, changes in simulated flows at
the gauge don’t always tell the whole story
 More recharge and baseflow discharge in the winter
 Drought sensitive reaches will be further stressed in the summer
 Marginal reaches will become even more marginal
► Understanding the underlying geology is essential
 Interconnection to aquifer storage is key

49. 49
Integrated Modelling: Conclusions
► Integrated modelling can provide locally detailed insights
into the behaviour of specific creeks and tributaries
 This example shows how three apparently similar creeks can
exhibit significantly different drought and climate change response.
► Integrated models built for drought or low flow analysis are
well suited for climate change assessment
 Logical extension of the SWP program work
► Other issues, such as eco-hydrology, ESGRA analysis,
LIDS, urbanization, recharge protection and even flow
regime assessment can be studied

50. 50
Baseline Click for Animation CGCM3T63
Thank you!
Questions or Comments?