Offshore Freshened Groundwater Systems
In recent times, tremendous pressure has been exerted on freshwater resources due to natural and anthropogenic activities globally. Several major coastal cities are seriously facing the water crisis, in recent years, Cape Town in South Africa and Chennai in India are a prime example of this. Therefore, alternative sources of freshwaters are urgently needed to fulfill the need for potable water in the future. Several regions (e.g. Australia, the USA, South America, New Zealand, Indonesia, Japan, Israel) of the world have offshore fresh groundwater (OFG) reserves.
In recent years, researchers across the globe have shown their keen interest in it because OFG systems can be potential sources of potable water that can be used for drinking and domestic purposes. Hence, quantitative mapping of OFG resources could be significant for the major coastal cities of different countries to supply freshwater sustainably in future.
Based on this, a study has been carried out by a group of researchers on the “3D characterisation and quantification of an offshore freshened groundwater system in the Canterbury Bight, New Zealand”( see Fig. 1) as part of the MARCAN Project. This project is funded by the European Research Council and led by Prof. Aaron Micallef from the University of Malta, Malta and GEOMAR, Germany.
The objectives of MARCAN are to:
- define the characteristics and dynamics of topographically-driven meteoric groundwater systems in passive continental margins, and
- demonstrate that topographically-driven meteoric groundwater is an important geomorphic agent in passive continental margins.
The OFG system near Canterbury, New Zealand, consists of one main and two smaller low salinity groundwater bodies. The main body extends up to 60 km from the coast and a seawater depth of 110 m. The outcome of the modelling results suggests that the majority of the OFG was emplaced via topographically driven flow during sea level lowstands in the last 300 ka in the area. Moreover, the geochemically analysed pore water from borehole U1353 indicate freshwater mixing in the depth range of 59.7–75 mbsf. These observations are significant contributions to the understanding of OFG systems across the globe.
This was the first time an OFG has been investigated in 3D. In the case of New Zealand, the OFG is found offshore of the driest part of the country, which needs lots of water for irrigation purposes. Similar studies have been carried out offshore New Jersey and Israel, and the main challenge has always been the ambiguity of the geophysical data and the measurement of the geological parameters that can reduce such ambiguity.
Fig. 1 Study area. Three-dimensional digital elevation model of the Canterbury Basin (Source: https://data/linz.govt.nz). The location of the rivers, onshore gravel aquifer, onshore well Ealing 1, CSEM and multichannel seismic reflection lines, and boreholes U1353 and U1354, is shown. https://www.nature.com/articles/s41467-020-14770-7