Saltwater intrusion

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What is saltwater intrusion

In the 2001 drought, saltwater intrusion occurred in the lower reaches of the Waimea River and was threatening to migrate further inland. In March Tasman District Council opened talks to consider options to protect the dry riverbed. Because the river had no flows, no river water was flushing the saltwater out and it was instead accumulating on the estuary. The Council discussed building a bund across the river and drilling monitoring bores to better monitor how the saltwater contamination was migrating inland, including to the urban supply bores. Ultimately, three urban supply wells were shut down over this period and two were decommissioned at the end of the drought.

Saltwater intrusion is a threat to coastal communities. Once saltwater has entered an underground freshwater system (aquifer) and contaminates it, it can cost much more to treat it for consumption or simply render the supply unusable. For people along the Waimea Plains who rely on bores for their water supply, saltwater intrusion is a real issue.

A drought isn’t the only way saltwater intrusion can occur. When freshwater is withdrawn at a faster rate than it can be replenished, a draw-down of the water table occurs. This can also cause saltwater to enter coastal areas where the water level is similar to that of the groundwater supply.

Vegetation is highly susceptible to saltwater intrusion because these plants are often unable to cope with high salt concentrations. If saltwater enters the low-lying land areas, it’s likely most of the native plant life could be destroyed. In some cases, plant root systems holding the soil together could even see rapid erosion following loss of plant life. Irrigating with salt-contaminated water also poses a significant threat to crops. Saltwater can also cause damage to the soil structure and affect the overlying soil quality.