Worldwide treasure hunt for scarce fresh groundwater with fresh-saline mapping technology from the Netherlands

Published: 16 May 2017

An electromagnetic 'cigar' has been used to map the presence of fresh, brackish and saline groundwater from the air in the Dutch Province of Zeeland. The information includes how many billion cubic metres of fresh groundwater are present, and the depths where the water is located. Evidence has even been found for the presence of 'old fresh groundwater'. The maps are available online at www.zeeland.nl/water/zoet-water/zoet-zoutverdeling-zeeuwse-ondergrond.

Within the Zeeland-project FRESHEM and together with TNO and BGR, Deltares developed the method for converting electromagnetic measurements into information about fresh, brackish and salinet groundwater. ‘By combining saltwater-freshwater data with a broader knowledge of groundwater systems, we can make predictions about climate change and sea-level rise. As a result, we are able to make predictions about the availability of fresh groundwater in the future’, says Deltares-researcher Esther van Baaren. ‘That brings promising solutions closer to be implemented, such as the underground storage of fresh surfacewater. These solutions are needed to protect the freshwater resources’, adds researcher Gualbert Oude Essink. ‘Those solutions have already been tested and proven in Zeeland in the GO-FRESH project’.

This new knowledge makes it possible to protect the availability of fresh water, not only in Zeeland and other Dutch coastal areas but also in deltas worldwide. Deltares is already using the fresh-saline mapping approach with similar technologies in Belgium and Vietnam. There is also interest from the Nile Delta.

Few or no options for fresh water supply

The mapping was done on behalf of de Province Zeeland, Waterboard Scheldestromen, ZLTO, Evides, Rijkswaterstaat, the Vlaams-Nederlandse Scheldecommissie, Zeeland-municipalities and the Delta Fund.

Many areas of Zeeland have few, or even no, options for supplying their own fresh water for domestic and Agricultural use. Over the year as a whole, there is more precipitation than evaporation but the situation is reversed in the summer, when there is simply not enough water available. This imbalance is being exacerbate by climate change. ‘In the long run, that will cause problems for the availability of fresh water in Zeeland. That is why the province stimulates a number of initiatives for storage of and more efficient use of fresh water’, says Ben de Reu, Deputy Water of the Province of Zeeland.

‘Knowing where there’s water availability will be of increasing importance’, emphasizes dikereef Luc Magnus of Waterboard Scheldestromen. ‘We can already use this information for a sustainable fresh water supply for the stakeholders. For instance, by attributing permits for who can extract groundwater or for infiltration.’

Mapping of the fresh-saline groundwater reserves help Zeeland

The fresh-saline mapping results are also helping farmers in Zeeland to store fresh water underground when rainfall is plenty in locations that have been identified as promising by the measurements. Farmers and nature managers now know where the subsurface is saline and how saline it is exactly.
Although some information was already available in that respect, it is now possible to explain why some areas have only salt nature and why farmers are unable to irrigate their crops due to the absence of fresh water, and to show where they can grow salt-tolerant crops. Landscape architects and planners can now make decisions about which functions are more, or less, appropriate for a particular area.

‘Old fresh water’

Although it was suspected that ‘old fresh groundwater’ was present, the survey in Zeeland also provided information about where exactly large volumes of this water were located. These reserves were created when enormous amounts flowed to these locations over many thousands of years. They are hidden deep below saltier, relatively impermeable, layers.

Treasure hunt for fresh groundwater elsewhere in the world

The urgency in Zeeland is also felt elsewhere in the world. Deltas and islands are the most densely populated areas on earth. The consequences of climate change, land subsidence, population growth and related salinisation and water shortages are increasingly apparent to local people. Because Deltares works worldwide, they are already using the charting technology outside the boundaries of Zeeland. And that starts just across the Dutch border.
From May 2017 onwards, Deltares,  SkyTEM, Gent University, TNO, Inagro and De Watergroep will map the fresh-brackish-salt distribution of groundwater from the air in the Flemish coastal area. SkyTEM’s ‘hoop’ will be suspended under a helicopter to collect electromagnetic data. The first flights are expected to between mid-June and mid-July 2017. The aim is to identify promising agricultural sites for the underground storage of fresh water. Measures will then be designed with the farmers to improve the availability of fresh water.

This project is on behalf of the Vlaamse Milieumaatschappij within the European project TOPSOIL. Data acquisition will be executed in joint cooperation with the MOW-department Maritieme Toegang, The Antwerp Harbour, Maatschappij Linkerscheldeoever and het Agentschap voor Natuur en Bos.

Vietnam

Further away, in the Mekong delta in Vietnam, fresh groundwater is also urgently needed. Every day, about 2.3 million m3 of groundwater is extracted from tens of thousands of small extraction wells for agriculture and aquaculture. The overexploitation of the wells results in salinisation of the fresh groundwater and substantial land subsidence. Deltares is using similar technology to map the fresh-brackish-salt distribution in the Vietnamese subsurface. It’s a WalkTEM survey conducted by walking over the subsurface with a ‘hoop’ to collect data. Deltares has come to the conclusion that the distribution is extremely heterogeneous: at large depths down to at least 200 metres, fresh groundwater can be found next to salt water. That knowledge also creates opportunities for protecting and increasing supplies of precious fresh groundwater. Deltares works together with NWO, Utrecht University, the Danish Aarhus University, TNO en The Vietnamese Division for Water Resources Planning and Investigation for the South of Viet Nam.

Relevant for water-guzzling industry

It makes sense to know where fresh groundwater is located, and in what amounts, not only for agriculture, but also for the industries that need a lot of water, such as the energy sector, the food and drinks sector, and for gas, oil and mining industry. These industries often extract large quantities of water at a single location. These extractions are generally located close to urban areas where water demand is already high, and where they already often pump up fresh groundwater from deeper below the surface. It is expected that they will run up against more and more difficulties in terms of maintaining access to adequate water supplies of the right quality for their activities. Particularly in regions that suffer from ‘water stress’, places where water consumption is high in relation to the available reserves.

More information

The maps are available online.

FRESHEM Zeeland is the abbreviation for FREsh Salt groundwater distribution by Helicopter ElectroMagnetic Survey in the Province of Zeeland and it is a research programme run by Deltares, TNO and the German research institute BGR.
The clients are: the Province of Zeeland, Evides Water Company, Rijkswaterstaat Sea & Delta, Association of Zeeland Municipalities, Flemish-Dutch Scheldt Commission (VNSC), the Scheldstromen water authority, the Southern Agriculture and Horticultural Organisation (ZLTO) and the Delta Fund.

The charting in Zeeland is not the first project of its kind, but it is one of the largest saltwater-freshwater charting operations worldwide. It has also led to the best possible results because:
a) many different types of data from Zeeland have been used to translate the measurements into 3D fresh-brackish-salt distribution of the groundwater and
b) the quantification of various types of uncertainties means that Deltares can make statements about the likelihood of finding fresh, brackish or salt groundwater.