Monitoring network maps salt content of Lauwersmeer lake
July 14, 2025
In the coming months, the Noorderzijlvest Water Authority will be launching a special project in the Lauwersmeer area: the construction of an extensive monitoring network to map the salinity levels. Why is this important, how does it work exactly, and what are the benefits? Hydrologist Meike Coonen and Johan Draaier, data and monitoring network management consultant, give us a glimpse behind the scenes.
A more natural Lauwersmeer
The Lauwersmeer Future Agenda stipulates that the northern part of the lake may become more brackish in order to improve its ecological quality. At the same time, the southern part will remain fresh, which is important for agriculture.
We are investigating how we can achieve a gradual transition from fresh to salt water between Lauwersmeer and the Wadden Sea," says Meike. "The new monitoring network is a first step in this direction."
Where is the salt?
Johan explains why measurement is so important:
We want to know where the salt water is located, how it flows and mixes with the fresh water, and how we can quickly drain it away again. To do this, we need reliable data.
The monitoring network will consist of around fifty measuring points spread across the area. Some existing measuring locations will be reused, but many new ones will also be added. These include monitoring wells for groundwater measurements, measuring buoys in the lake, and fixed installations on the waterfront. The measuring points will be located on agricultural land and in Lauwersmeer itself, among other places. We also want to install new measuring points in areas managed by Staatsbosbeheer (the Dutch Forestry Commission) and on the De Marnewaard defense site.
Smart measurement, together with Rijkswaterstaat
The water board is working with Rijkswaterstaat to install measuring buoys in the lake. "They already have experience with this," says Johan. "For example, with measuring in shipping channels, where salt water—which is heavier than fresh water—moves across the bottom. At some locations, we use a smart construction in which a sensor descends to the bottom via a guide rail. This way, we don't interfere with shipping."
Suitable measurement locations are also being sought at the Cleveringsluizen. "We want to measure how much salt water enters or is discharged there," explains Meike. "This fall, we are organizing a sailing measurement campaign together with Rijkswaterstaat to map flow velocities and chloride levels."
What are we actually measuring?
Although the project is known as a "saltwater monitoring network," the sensors actually measure the electrical conductivity (EC) of the water. In general, the higher the EC, the more ions there are, and therefore the saltier the water.
From data to insight
Data collection takes place over a long period of time and under various conditions. "Wind, drought, and management choices influence the spread of salt water," says Meike. "That's why we take measurements in all seasons and at different depths."
The data we collect helps us better understand how salt water spreads in the area, as well as the extent to which this can be controlled. "With this information, we can also improve the models that predict what will happen if we allow salt water in," says Johan. "This allows us to analyze different scenarios and investigate which solutions work well without disrupting other functions of the Lauwersmeer. Based on this, we choose the best ways (variants) to achieve a natural transition from fresh to salt water."
More information
We are setting up a monitoring network to determine the salinity in and around the lake. This will enable us, together with our regional partners, to learn more about the water system in the area. Read more about the saltwater monitoring network.