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Pukekawa aquifer: groundwater flow modelling

TR 2017/18

Report: TR 2017/18

Author: Blair Thornburrow (Pattle Delamore Partners Ltd)

About this report

Waikato Regional Council commissioned this study to develop a groundwater flow model for the Pukekawa volcanic cone in the Lower Waikato catchment.

The primary objective was to characterise the spatial and temporal pattern of this groundwater-surface water interaction. Pukekawa aquifer is one of the stressed aquifer in the Waikato region. This aquifer sustains stream flows around the cone and the abstraction of groundwater is known to reduce the surface water flow.

The model showed that the impact of focused seasonal pumping activities in a summer was spread out over the year. The use of this model will guide Council’s water allocation decisions and support the surface water allocation calculator (WAC).

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Pukekawa aquifer: groundwater flow modelling [PDF, 4.5 MB]

Contents

  Executive summary
1 Introduction
1.1 Background
1.2 Objectives
1.3 Previous studies
2 Conceptual hydrogeology
2.1 Climate and rainfall
2.2 Geology
2.3 Groundwater levels
2.4 Recharge and discharge
2.5 Aquifer hydraulic properties
2.6 Groundwater abstraction and use
2.7 Expected outcomes
3 Model design and construction
3.1 Model domain
3.2 Mesh and layer structure
3.3 Stresses and boundary conditions
3.4 Time stepping 
3.5 Representation of confined / unconfined conditions
4 Calibration and sensitivity analysis
4.1 Approach to model calibration
4.2 Calibration to flow data
4.3 Calibration to groundwater levels
4.4 Calibrated model parameters
4.5 Calibrated model results
4.6 Sensititivy analysis
5 Predictive simulations
5.1 Scenarios
5.2 Simulated drawdown
5.3 Impacts on surface water discharges
5.4 Predictive uncertainty
6 Discussion
6.1 Allocation limit setting
6.2 Management zone delineation
6.3 Groundwater take restrictions
6.4 Surface water flow monitoring as consent condtions
7 Conclusions
Appendices
Appendix A: Modelling data inputs
Appendix B: Recharge model methodology
Appendix C: Model design and construction
Appendix D: Model calibration and sensitivity analysis