Applications of Integrated Models to Watershed and Sub- Watershed Scale Analysis: A Canadian Context E.J. Wexler, P.J. Thompson, J.D.C. Kassenaar, M. Takeda Earthfx Incorporated XXI International Conference Computational Methods in Water Resources, June 2016
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Applications of Integrated Models to Watershed and Sub-Watershed Scale Analysis: A Canadian Context
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Applications of Integrated Models to Watershed and Sub-Watershed Scale Analysis: A Canadian Context
E.J. Wexler, P.J. Thompson, J.D.C. Kassenaar, M. Takeda Earthfx Incorporated XXI International Conference Computational Methods in Water Resources, June 2016
Watershed-Scale Integrated Modelling in a Canadian Context
Historical Perspective: Ontario
1990 – 2000 ▪ Groundwater models rarely used for engineering design or
impact assessment. Simple water budgets and aquifer tests
2001-2003 ▪ Steady state groundwater models for Ontario Municipal Groundwater
Studies and some quarry impact studies
▪ After Walkerton disaster, Source Water Protection called for multi-tiered assessment of watersheds and municipal supply
2003 – Present ▪ Loosely-coupled hydrologic/groundwater models for Tier 2 and 3
Key questions at Tier 3 level: ▪ Impact of municipal wells on wetlands and coldwater streams
▪ Impact of drought on municipal wells
▪ Impact of future development on groundwater recharge
▪ We developed 7 integrated models for Tier 3 watershed assessments to answer these questions
2 - History in Ontario/Canada
CMWR 2016
Integrated Watershed Models by
Earthfx
Watershed-Scale Integrated Modelling in a Canadian Context
Integrated Models: Canadian Applications
Watershed Management ▪ Water Budgets (Current/Future)
▪ Source Water Protection
▪ Irrigation demand management
▪ Ecological Flow Needs
Land Development ▪ Cumulative impact of development
▪ Low Impact Design alternatives
Resource Extraction ▪ Quarry/Mine impact
▪ In-Situ oil sands development
▪ Mine-site management
Climate Change Adaptation
3 - Model Applications
Watershed-Scale Integrated Modelling in a Canadian Context
Integrated Models
Integrated models consider both groundwater and surface water flow.
Feedback between the two systems can dominate in some hydrologic settings
For example, shallow water table influences:
▪ Evapotranspiration rates
▪ Dunnian (saturation excess) runoff
▪ Key for representing groundwater interaction with streams, lakes, and wetlands.
4 - Definitions
U n s a t u r a t e d
z o n e
S t r e a m S t r e a m
G r a v i t y d r a i n a g e
R e c h a r g e
G r o u n d - w a t e r f l o w
Interflow
ET
Dunnian Runoff
Watershed-Scale Integrated Modelling in a Canadian Context
USGS GSFLOW Code
Many integrated modelling codes
We use the USGS integrated GSFLOW code for watershed and engineering-scale studies: ▪ Open-source, proven, and very well documented
▪ Combines two USGS models: MODFLOW and PRMS (Precipitation-Runoff Modeling System)
▪ Fully-distributed: cell-based representation of hydrology and groundwater
Good balance of hydrology, hydraulics, and groundwater flow
5 - GSFLOW
Watershed-Scale Integrated Modelling in a Canadian Context
Watershed-Scale Integrated Modelling in a Canadian Context
Case Study 5 – York Region Water Budget
Used an integrated model to assess the sustainability of wellfields that supply about 200,000 residents
30 - York Region
CMWR 2016
Watershed-Scale Integrated Modelling in a Canadian Context 31 - Case Study 5
Drawdown Impacts on Wetlands Percent Decrease in Baseflow
Under Future Pumping Study looked at effect
of drought on wells
Also looked at effect of wells on wetlands and coldwater streams
Study showed that streamflow affected mainly within 1-m drawdown line
Few wetlands and coldwater streams remained within 1-m drawdown
Case Study 5 – York Region Water Budget
Watershed-Scale Integrated Modelling in a Canadian Context
Watershed-Scale Integrated Modelling in a Canadian Context
CONCLUSIONS
32 - Wrap Up
Watershed-Scale Integrated Modelling in a Canadian Context
Challenges in Integrated Modelling
33 - Wrap Up
Calibration ▪ Good calibration is mandatory for predictive, engineering studies
Model run times ▪ PRMS is fast but GSFLOW runs can take days
▪ Need faster MODFLOW solvers
▪ Better yet, need parallel solvers so models can run on multi-core machines
Model stability
Data limitations ▪ Continuous groundwater level and streamflow data can be sparse
Staffing ▪ Integrated, multidisciplinary teams are a must!
Watershed-Scale Integrated Modelling in a Canadian Context
Overall Conclusions:
34 - Wrap Up
Integrated models are effective, practical tools to evaluate complex, challenging problems from the watershed to the engineering scale
Models provide insights for complex systems
Canada is moving ahead in the application of integrated modelling
There are ongoing challenges, but transient, integrated modelling is becoming the standard for impact assessments, water budgets, climate change predictions, drought assessments, and eco-hydrology studies