Helicopter surveys provide 3D image of salinisation and the subsurface
Where are fresh and saline groundwater located and at what depth? And where are the clay layers that protect the underlying groundwater? This is important information for provincial authorities, water managers, water authorities, farmers and nature managers. To establish a picture, measurements will be made with a helicopter from August this year until February next year in the southern, western and northern Netherlands.
The helicopter surveys are being carried out as part of the FRESHEM-NL project. The research institutes TNO Geological Survey of the Netherlands (TNO GDN) and Deltares are working closely with seven provincial authorities, seven water authorities and five water companies in this project. The national government is contributing to funding from the Freshwater Delta Programme, which was established to make the Netherlands more resilient to freshwater shortages.
Three-dimensional images down to a depth of 200 metres
The measurements are made with an instrument suspended below a helicopter. The results are used to produce a three-dimensional image down to a depth of 200 metres, providing researchers with information about the salinity of groundwater at different depths, as well as the location and thickness of clay layers. The survey is being conducted for parts of Noord-Brabant, Zeeland, Zuid-Holland, Noord-Holland, Friesland, Groningen and Drenthe. “The results are important for, among others, farmers, and water and nature managers. They provide a clearer insight that makes it possible to work with water in a sustainable and responsible way,” says Jan Gunnink of TNO Geological Survey of the Netherlands. “Using helicopters makes it possible to map large areas from Zeeland to Groningen, and parties will soon be able to draw on the results of this project for years to come,” says Geert-Jan Nijsten of Deltares. The results of the project will be publicly available.
A treasure trove of information about freshwater and salinisation
Climate change is leading to alterations in the availability of fresh water, of which we are also using more and more. Because of the country’s location by the sea, some of the groundwater in the Netherlands is saline. Sea level rise is gradually making groundwater in coastal areas saltier, and saline groundwater is also flowing upwards below deep polders. That process of salinisation harms agriculture and nature. “So it is important to have an insight into the salinity of the groundwater,” argues Jan Gunnink.
Geert-Jan Nijsten: “In addition, it is also important to know more about where clay layers are located. They protect the groundwater below them against pollution from above. Knowledge about clay layers is also needed to understand groundwater flows better, as well as the potential impacts of climate change and interventions in the water system. To ensure that, in time, nature, agriculture and businesses will be damaged as little as possible by salinisation and that adequate supplies of drinking water will continue to be available, it is important to have a clear picture of the subsurface and groundwater. With the wealth of information from the FRESHEM project, we are making an important contribution in that respect.”
Helicopter flights
The helicopter used to make the measurements flies at a height of about 80 metres at a speed of 60 to 80 kilometres an hour. There are daytime flights only and, of course, the strict regulations about flying low with a helicopter are respected. There are no flights during the nesting season and there are specific regulations for nature areas. Before flights begin in early August, the area will be informed about the exact schedule.
