Salinity indicator as a monitoring intstrument for salinisation in the Bruges Polders and Yser river basin

Due to climate change, coastal and polder areas are increasingly confronted with salinisation during droughts. VITO supports governments and other stakeholders in mapping the salinisation with sensor data. Together with the Flemish Environment Agency (VMM), VITO developed a salinisation indicator for the Yser river basin and the Bruges Polders.


Electrical conductivity
Salinisation is measured using conductivity data from a sensor network in the catchment of Yser river and in the region of the Bruges Polders. The electrical conductivity is proven to be a good indicator of the salt concentration in the water. The data are collected by sensor measurement points from the Flemish Environment Agency (VMM) and from the project Internet of Water Flanders

The salinity indicator is an instrument that responds to the need for easy interpretation of sensor data. The indicator converts all measurement results into accessible information on the current status and evolution. The interpreted data are presented in a user-friendly web tool, developed by VITO within Internet of Water Flanders. The water managers and other stakeholders involved can thus better monitor the situation and take appropriate measures. 

The indicator is now used actively by the Drought Advisory Group as a (decision-making) tool to give advice to the Coordinating Committee for Integrated Water Policy. 


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The indicator brings an overview of the locations where increased salt concentrations are measured. Additionally, it indicates whether the salinity of the water is stable, declining or increasing.

A colour code is used to indicate the situation at each measurement point at a given time: green is favourable; orange indicates that a first threshold is exceeded, and an increased value is detected; red means that a second threshold is exceeded and that the location has a problematic high salinity.


Reliable threshold values

While the salinity indicator relies on data from the sensor networks, the threshold values used rely both on sensor data and the results of grab samples from the past decades.

Frie Van Bauwel, researcher Digital Water Services at VITO, explains how the threshold values are determined: “The thresholds are chosen based on a previous time series for a specific location. The more data are available, the better this threshold can distinguish normal or exceptional situations for a given location.

For some watercourses, the time series are not yet long enough to derive a reliable threshold from the sensor data. If possible, grab sample results are then used to determine a threshold value.

Once sufficient sensor data are available, robust threshold values can be derived and established for all monitoring sites."