Fresh groundwater occurs within submerged fringes of continents globally. These offshore fresh groundwater reserves can form via connections to modern day onshore hydrological systems. Offshore fresh groundwater may also be paleo-groundwater emplaced during previous glacial periods when lower sea levels drove fresh water into exposed continental shelves. Offshore aquifer research is an emerging field that is becoming increasingly important as population growth and climate change put pressure on coastal water resources. The objective of this study is to document evidence for New Zealand aquifer systems that extend offshore and that likely contain significant volumes of low salinity groundwater.
Design and methodology
The study involves a review of previous work on coastal aquifers and adjacent continental shelf geology in New Zealand. Onshore and offshore geological and hydrogeological data, marine geophysical data and seafloor fluid seepage indicators are combined to develop conceptual models for onshore-offshore aquifers. Analytic and numerical modelling is used to provide a preliminary estimate of offshore fresh groundwater extent at selected locations.
Original data and results
There is evidence for offshore fresh groundwater systems in South Canterbury and Wellington. Preliminary analysis suggests there is potential for offshore fresh groundwater systems at many locations along the east coast of the South and North Islands, including but not limited to Dunedin, North Canterbury and Hawkes Bay.
Our review documents multiple lines of evidence for offshore fresh groundwater systems at several locations in New Zealand. Some of this is direct evidence for fresh or low salinity submarine groundwater, some is indirect via geophysical imaging of the offshore continuation of aquifers where freshwater occurs up to the coastline. In the longer term, offshore drilling will be required to prove freshwater resources however this regional scoping study is a first step towards that goal.