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1
Assessing Sensitivity to
Drought and Climate Change
with an
Integrated Surface Water/Groundwater Model
at the Subwatersh...
2
Lake Simcoe Restoration and Protection
► Fourth largest lake in Ontario and
has history of environmental stress.
► Water...
3
GSFLOW - Integrated GW/SW Model
► GSFLOW combines MODFLOW-NWT with the PRMS hydrologic model
 PRMS code can be used as ...
4
Oro Moraine Study Area
Oro Moraine
Study sub-
watersheds
► Study focused on three
subwatersheds on NW shore
of Lake Simc...
5
Surficial
Geology
► The Oro Moraine
sits on top of
regional till plains
► Tunnel Channels -
tills have been
eroded by su...
6
Hydrogeologic Model
► A complex 3-D geologic model was available from the OGS
► Provide very detailed mapping of shallow...
7
Surface Water
System
► Study area has numerous
streams and wetlands
► Flow routed through all
stream segments as
shown
►...
8
Hydrologic Model
Inputs/Outputs
► PRMS Sub-model Inputs
 Daily Climate Data
► Rainfall (NEXRAD)
► max/min temp.
► Solar...
9
► Results for Coldwater
River (02ED007)
9
Calibration to Daily and Monthly Flows
Observed (blue) Simulated (red)
10
Simulated
Recharge
► PRMS run using uniform
grid with 50 m cells
► Results show average
annual recharge from a
32-yr si...
11
Simulated Heads: Layer 1 and 7
11
► Shallow system show influence of topography and streams. Deeper
system (below regio...
DROUGHT ASSESSMENT
12
13
10-Year Historic Drought Period
13
1953-1967
► Used daily climate data from 1956-1967 drought to analyze
subwatersheds ...
14
Drought Impact on
Streamflow
► Limited drought
impact in Oro North
► Moderate change in
Hawkstone tribs
► Large change ...
15
Pathline
Analysis
► Endpoints from forward
tracking confirm that Oro
Moraine feeds headwater
streams and wetlands
along...
1616
Section line is through the two watersheds.
Differences in the till thickness and the aquifer
continuity affect the b...
CLIMATE CHANGE
ASSESSMENT
17
18
GCM models of Climate Change
► Climate predictions are done
with Global Circulation
Models (GCM).
► Many different GCMs...
19
Change Field Method - Baseline versus CGCM3T63
Shift in Month Temperature
Values shifted by 1 to 5 C
Percent Change in...
20
Comparison of Low Flow Change – North vs South Oro
• CGMC3T63 scenario shows more flow in winter months. Spring freshet...
2121
Change in Total Streamflow – Oro South
• Ensemble of models show consistent results
• Log scale highlights significan...
22
Climate Change: Conclusions
► Climate effects in Southern Ontario:
 More recharge and baseflow discharge in the winter...
23
Baseline Click for animation CGCM3T63
Thank you!
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Assessing Sensitivity to Drought and Climate Change with an Integrated Surface Water/Groundwater Model at the Subwatershed Scale

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Assessing Sensitivity to Drought and Climate Change with an Integrated Surface Water/Groundwater Model at the Subwatershed Scale

  1. 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. 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. 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. 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. 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. 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. 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. 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. 9 ► Results for Coldwater River (02ED007) 9 Calibration to Daily and Monthly Flows Observed (blue) Simulated (red)
  10. 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. 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. 12. DROUGHT ASSESSMENT 12
  13. 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. 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. 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. 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. 17. CLIMATE CHANGE ASSESSMENT 17
  18. 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. 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. 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. 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. 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. 23 Baseline Click for animation CGCM3T63 Thank you! Questions or Comments?

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