Groundwater naturally flows towards the coast, where it discharges to the sea. The freshwater and seawater meet each other at a position called the saltwater interface.
Generally, the saltwater interface is found slightly inland from the coastline.
If groundwater abstractions from the aquifer are excessive, particularly near the coastline, the saline interface can move inland.
This has the potential to affect the potability of groundwater in the coastal area, but has not occurred to date.
Council maintains a network of sentinel wells along the coastline that monitor the conductivity (a measure of salts in the water) of groundwater, to provide early warning of an inland migration of the saltwater interface.
In addition, resource consents in areas of concern have specific management controls or conditions in place to restrict water use and arrest the onset of seawater intrusion. The drawing is a conceptual view of groundwater flow at the Te Koko-o-Kupe/Cloudy Bay coast.