groundwater management modelling and science an example … · 2020. 3. 2. · groundwater...
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Groundwater management modelling and science – an example from the Surat Basin
QWMN Forum 2020
Sanjeev Pandey
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Outline
• The modelling drivers - some background and context
• Surat impact model for assessing coal seam gas impacts
• How the model is used for resource management purposes
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Background
Office of Groundwater Impact Assessment (OGIA)
• Cumulative impact assessment and management
• 3 years reporting cycle
3 year cycle
monitor, model, report
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Surat CMA
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Why model?
Context
• Complex multilayered aquifer system
• Multiple stresses (20,000 CSG wells)
Explicit objective
• Assess impacts from depressurisation – time
and space
• Underpin proactive management arrangements
for:
• Impacted water bores
• Environmental values (springs, watercourses, etc)
Implicit objective
• Stakeholder communication and engagement
• Information for regulators for compliance
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2019 OGIA GW Model
• 3D geological model
• MODFLOW-USG
• 34 layers, 22 faults
• ~1,3 million cells
• 1.5 km x 1.5 km cells
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Regional CSG modelling challenges
1. Dual-phase flow
2. Local data assimilation
3. CSG well operations
4. Faults
5. Model calibration
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Local data assimilation
Stochastic Lithology Permeability Models
Kh and Kv for 2019 Model
Geophysical logs, Pumping
Tests, Core Tests, DST’s
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Uncertainty analysis
• Null Space Monte Carlo (Tonkin
& Doherty, 2008)
• 450 sets of parameters + predictions
Coal compressibility Walloon Coal Measures
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Key outputs for GW impact management
• Impacts on water bores and springs
• Loss in fluxes to alluvial aquifers
Walloon Coal Measures
Impact
[m]
5 m threshold 0.2 m threshold
Impact
[m]
Lucky Last spring complexWater bore – Springbok Sandstone
95th Percentile
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How are predictions used?
• Proactive ‘make good’ of water supply bores
• Monitoring network
• Spring impact mitigation and monitoring
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Make-good bores
• 100 bores impacted in the short-term (next 3 years)
• Responsible tenure holders are assigned
• Proactive bore assessment and make-good will follow
Bore assessment
Establish impairment
Make good
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Groundwater monitoring
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Spring impact management
• 8 spring groups impacted
• 6 require mitigation actions
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So what did we learn in the process?
• Every model has its purpose – a specific purpose
• Stakeholder buy-in is essential
A sound model with academic seal of approval
vs
An appropriate model trusted by stakeholders
• Trust in model depends on:
• Trust in data
• Trust in conceptualisation and science
• Ongoing improvement cycle
• Simple is beautiful…but…complex might do the trick
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Thank you
Sanjeev Pandey
Executive Director, Office of Groundwater Impact Assessment