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1
Simulating hydrologic response to climate
change and drought with an
integrated surface water/groundwater
model
Lake Sim...
2
Drought and Climate Change
Analysis with Integrated GW/SW Models
► The Water Budget drought assessment component of the ...
3
Integrated GW/SW Modelling
► Water simply does not care
what we call it (SW or GW) and
it moves seamlessly between
domai...
4
USGS-GSFLOW
Soil water
Unsaturated
zone
Precipitation
Evapotranspiration
StreamStream
Evaporation
Precipitation
Infiltra...
5
GSFLOW SW/GW/SW Components
► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)
6
Oro Moraine Study Area
► Under the LSPP, a water-budget model was needed for the
Oro North, Oro South, and Hawkestone Cr...
7
Oro Moraine Study Area
Oro Moraine
Study
watersheds
► Three watersheds
contributing to the
northwestern shores
of Lake S...
8
Geology
► The Oro Moraine
has high
groundwater
recharge but also
high groundwater
storage
Oro Moraine
9
Hydrogeologic Model Layers
► A complex 3D geologic model was available from the OGS
► Too often, hydrogeologists need to...
10
Hydraulics and Eco-Feature Representation
► Our approach was to
represent all streams in
the model, even the
intermitte...
11
Hydrology: Precipitation
► Calibrated hourly NEXRAD
radar data was found to
provide the best estimate of
distributed pr...
12
Hydrology: Topography and Runoff
► 50-m DEM used to generate
cascade flow paths to route
overland runoff to streams
► S...
13
Hydrology: Predicted Average Recharge
► Average recharge
from a 32-yr
simulation
13
14
Predicted GW Levels: Layer 1 and 7
14
15
► Coldwater River at
Coldwater (02ED007)
15
Continuous Streamflow Simulation
Observed (blue) Predicted (red)
1616
Aquifer Head vs. Stream Stage
Groundwater
discharging to the
stream, except
during large events
Hydrograph at Oro-Haw...
17
Model Development Conclusions
► The integrated GSFLOW model represents the entire
SW+GW system, including:
 Very detai...
18
DROUGHT ASSESSMENT
18
19
Selected 10-Year Drought Period
► Recent and relatively prolonged drought
 More climate and streamflow data than the 1...
2020
Predicted monthly flows before and during 10-year drought
0
2000
4000
6000
8000
10000
12000
14000
16000 Jan-54
Jul-54...
2121
August 1957 November 1964
Monthly flows before and during 10-year drought
Many of smaller tributaries have dried up. ...
22
10-Year Drought
► Figure shows decrease
in average monthly
flow at worst point in
drought compared to
start of drought
...
23
10-Year Drought
► Limited drought
impact in Oro North
► Moderate change in
Hawkstone tribs
► Large, severe
change in Or...
24
GW Discharge to Wetlands
Soil water
Unsaturated
zone
Precipitation
Evapotranspiration
StreamStream
Evaporation
Precipit...
2525
Contributing Area/GW Feedback
• Areas of high water table (red) contribute Dunnian runoff to streams.
• Significant s...
2626
Areas of high Water Table and Stream Flow
• Areas of high water table contribute Dunnian runoff to streams.
2727
Groundwater Seepage to Hawkestone Creek
• GW seepage (green lines) in the reach near the Hawkestone WSC
stream gauge....
2828
Hydrograph shows groundwater seepage along Hawkestone Creek.
Seepage is controlled by till thickness and aquifer geom...
2929
Section line is through the two watersheds.
Differences in the till thickness and the aquifer
continuity affect the b...
30
Drought Simulation Conclusions
► Changes in simulated flows at the gauge don’t always tell
the whole story
► Change in ...
31
CLIMATE CHANGE
ASSESSMENT
31
32
Building on the Drought Analysis
► Simulation of recent droughts provides an excellent
foundation for climate change an...
33
Climate Change in Ontario
► Average of 30 GCM-scenarios a show 2 to 4C temp. increase by 2050.
 About double the glob...
34
GCM models of Climate Change
► Many different
climate models.
► Predictions of
annual temperature
and precipitation
inc...
35
Downscaling GCM Models
► Climate predictions are done with Global Circulation Models (GCM).
 Grid scale is large (250 ...
36
Temperature - Baseline versus CGCM3T63
Daily and Monthly Baseline Temperature versus CGCM3T63
Values shifted by 1.4 to ...
37
Precipitation - Baseline versus CGCM3T63
Daily and Monthly Baseline Precipitation versus CGCM3T63
Values scaled by -15 ...
3838
Change in Total Streamflow – Bluffs Creek (North Oro)
• More flow in winter months.
• Spring freshet is earlier
• Ver...
3939
Change in Total Streamflow - Hawkestone Creek
• More flow in winter months.
• Spring freshet is earlier
• Not much ch...
4040
Change in Total Flow – Shellswell Creek (South Oro)
• Similar results.
– More flow in winter months.
– Spring freshet...
4141
Change in Total Streamflow – Oro South
• Log Scale: Shows significant reduction in summer flows
4242
Simulated Change in Total Streamflow - Coldwater River
Again, reduction in summer flows, but not as severe
given cont...
4343
Comparison of Low Flow Change – Bluffs vs Shellswell Creek
• Similar change in winter patterns, change in South
Oro C...
44
Comparison of Flow Change – Bluffs vs Shellswell Creek
Shellswell Creek (South Oro)Bluffs Creek (North Oro)
• Little ch...
4545
Change in Baseflow (Hyporheic Exchange) -
Hawkestone Creek
• GSFLOW simulates the true baseflow component of total st...
4646
Contributing Area: High Water Table GW Feedback
• Areas of high water table (red) contribute Dunnian runoff to stream...
4747
Areas of high Water Table and Stream Flow
• Areas of high water table contribute Dunnian runoff to streams.
48
Climate Change: Conclusions
► As with the drought analysis, changes in simulated flows at
the gauge don’t always tell t...
49
Integrated Modelling: Conclusions
► Integrated modelling can provide locally detailed insights
into the behaviour of sp...
50
Baseline Click for Animation CGCM3T63
Thank you!
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Simulating hydrologic response to climate change and drought with an integrated surface water/groundwater model Lake Simcoe watershed

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Simulating hydrologic response to climate change and drought with an integrated surface water/groundwater model Lake Simcoe watershed

  1. 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. 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. 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. 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. 5 GSFLOW SW/GW/SW Components ► Hydrology (PRMS) GW (MODFLOW-NWT) Hydraulics (SFR2)
  6. 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. 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. 8 Geology ► The Oro Moraine has high groundwater recharge but also high groundwater storage Oro Moraine
  9. 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. 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. 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. 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. 13 Hydrology: Predicted Average Recharge ► Average recharge from a 32-yr simulation 13
  14. 14. 14 Predicted GW Levels: Layer 1 and 7 14
  15. 15. 15 ► Coldwater River at Coldwater (02ED007) 15 Continuous Streamflow Simulation Observed (blue) Predicted (red)
  16. 16. 1616 Aquifer Head vs. Stream Stage Groundwater discharging to the stream, except during large events Hydrograph at Oro-Hawkstone stream gauge
  17. 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. 18 DROUGHT ASSESSMENT 18
  19. 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. 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. 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. 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. 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. 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. 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. 26. 2626 Areas of high Water Table and Stream Flow • Areas of high water table contribute Dunnian runoff to streams.
  27. 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. 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. 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. 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. 31 CLIMATE CHANGE ASSESSMENT 31
  32. 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. 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. 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. 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. 36 Temperature - Baseline versus CGCM3T63 Daily and Monthly Baseline Temperature versus CGCM3T63 Values shifted by 1.4 to 4.6 C
  37. 37. 37 Precipitation - Baseline versus CGCM3T63 Daily and Monthly Baseline Precipitation versus CGCM3T63 Values scaled by -15 to 46%
  38. 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. 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. 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. 41. 4141 Change in Total Streamflow – Oro South • Log Scale: Shows significant reduction in summer flows
  42. 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. 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. 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. 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. 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. 47. 4747 Areas of high Water Table and Stream Flow • Areas of high water table contribute Dunnian runoff to streams.
  48. 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. 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. 50 Baseline Click for Animation CGCM3T63 Thank you! Questions or Comments?

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