Groundwater Inflow Assessment For Deep Basement Excavations: A Case Study

Approvals for proposed building developments in Sydney are granted by the consent authority with input on groundwater-related matters from NSW Office of Water. Developments with deep basements require approval for construction dewatering. NSW Office of Water input considers the requirements of the NSW Aquifer Interference Policy, including assessment of the excavation’s “groundwater take” and potential impacts associated with dewatering.

In order to adequately assess the potential impacts associated with construction dewatering, and to design appropriate construction dewatering systems, it is important to accurately estimate groundwater inflow rates to deep basement excavations during construction.

This paper discusses and compares established methods to assess groundwater inflows to deep basement excavations, including analytical, analogue and numerical approaches. A case study for a proposed development in Sydney is used to demonstrate differences in estimated inflow based on these approaches, and highlight the benefits and disadvantages of each approach. Consideration is given to geological structures, basement design, and uncertainty in conceptual models and aquifer parameters that can complicate accurate assessment.