Oral Presentation NCGRT/IAH Australasian Groundwater Conference 2019

Practical examples of numerical modelling techniques to inform groundwater impact assessments for major infrastructure projects (89)

Rikito Gresswell 1
  1. GHD, Melbourne, VIC, Australia

Objective

Groundwater impact assessments for major projects rely on the outputs from numerical groundwater modelling to quantify potential project-induced changes to groundwater levels and fluxes. For major infrastructure projects, groundwater modellers are often required to accurately simulate the geometry of complex engineering structures and their interaction with the geology and hydrological features. Additionally, predictions are commonly required for stresses larger than those of the natural range of seasonal variations and for a period of time longer than the period of historical observations. This presentation provides practical examples of modelling techniques applied to assist with the preparation of Environmental Effects Statements for major infrastructure projects in Victoria.

Methodology

The presentation will draw on GHD’s recent experience with the following two projects:

  1. Edithvale-Bonbeach Level Crossing Removal Project which will involve the construction of pile walls near Ramsar listed wetlands of high ecological importance.
  2. Northeast Link Project which will involve the construction of 6 km long twin tunnels, mined tunnels and cut and cover excavations.

Data and results

The presentation will provide an overview of:

  • The use of unstructured grids to accurately simulate the geometry of engineering structures, geology and hydrological features within regional model domains.
  • Loose coupling of MODFLOW-USG with SOURCE to simulate interactions between groundwater and wetlands.
  • Rigorous automated calibration in a highly parallelized computing environment using PEST_HP.
  • Predictive uncertainty analysis based on PEST’s Null-Space Monte Carlo methodology.
  • Climate change impact assessment using Victorian Government’s climate change guidelines, with benchmarking of the model against long term historical climate data.

Conclusion

Recent advances in modelling capabilities provide modellers with the opportunity to assess groundwater impacts in greater detail, including probabilistic outcomes that are particularly suited to the risk assessment framework adopted in major infrastructure projects.