Groundwater modelling of the Omaha aquifer system

Abstract

The Omaha aquifer is one of the most highly utilised aquifer systems in the Auckland Region. It is therefore under increasing pressure for controlled resource management to promote sustainable use. This study reports on the construction of a two layered, finite difference model incorporating base parameter information from an earlier study, while extending and refining a conceptual model into an interactive two layered numerical model of the system. The study includes the creation of an initial steady state model, using the MOD FLOW groundwater modelling package. The model, once calibrated, is then investigated by a sensitivity analysis. The results show how the model behaves under stressed conditions for the following parameters: the degree of hydraulic connectivity between the two layers; the rates and distribution of recharge of the model; the interaction of the Tamahunga River with the groundwater system; and the interaction with the tidal waters, the harbour and the Omaha Spit. From the various simulations of the model an assortment of recommendations have been made on how to further improve the knowledge of how the Omaha aquifer system works.