Salt Water Intrusion from a Tidal Estuary
Abstract
The North Stockton Sandbeds are located on the coastal fringe of Newcastle Bight immediately north-east of the city of Newcastle. The aquifer is located within the coastal barrier system that forms the shore line of the Newcastle Bight and is bounded by the Tasman Sea to the south and by the tidal estuary known as Tilligerry Creek to the north. Investigations into the safe extractive yield of the North Stockton Sandbeds have included drilling and testing of boreholes and numerical groundwater modelling. Field investigations have identified the existence of saline water in the shallow aquifer on the southern margins of Tilligerry Creek. Electrical conductivity measurements in boreholes indicate that the saline water has migrated several hundreds of metres southward from the estuary. A combination of three dimensional groundwater flow and two dimensional density dependent solute transport modelling has been used to assess the processes that have given rise to the salt water intrusion and to predict the movement of the fresh water – salt water interface under various pumping regimes. The study has identified the construction of shallow surface drains, levee banks and tidal flap gates on the southern shores of the estuary as the principal cause of the saline water migration from the estuary that has occurred to date.
Authors
Brian Barnett, Brendan Berghout & Redha Beddek