Author(s): G. S. De Costa; M. Porter; A. Jones
Linked Author(s): Gregory De Costa
Keywords: Salinity intrusion; Ground water quality
Abstract: The Waiwhetu aquifer provides the main water supply for the greater Wellington area. This paper explores the susceptibility of the aquifer to degradation through the intrusion of saline water. Long-term variations in salinity levels are analysed at three locations adjacent to the coast. It is concluded that there is no appreciable salinity impact at this point in time. However, the aquifer water does exhibit some evidence of salinity intrusion. It is predicted that on the basis of past trends the water quality at Seaview will cross the category threshold from Fresh to Saline water by the year 2025. The potential to control future quality degradations by active management of the aquifer is estimated by comparison with a similar aquifer's performance in Bundaberg, Australia. This aquifer has been used for irrigation over many years with abstractions in excess of the longterm sustainable levels. There is a saline wedge evident in the aquifer from seawater intrusion. It appears that this wedge has been stabilised by active management in recent years. This stability has occurred even though locations nearer to the coast have tended to increase in salinity while those upstream of the wedge have decreased in salinity. The behaviour of the two aquifers are compared and contrasted in this paper.