Unique salt intrusion observations during the severe drought of 2022

Salt intrusion is becoming an urgent problem in many deltaic areas due to the increasing probability of droughts under climate change. Sea level rise is an additional consequence of climate change, exacerbating salt intrusion worldwide. Extensive field observations during extreme droughts are rare. One of the worst droughts ever experienced took place in Europe in 2022. 

Here we present unique observations carried out during a 17 week period in the summer and autumn of 2022 in the Dutch Rhine-Meuse Delta. The dataset includes measurements of velocity and salinity around the mouth of the Rhine River and salinity measurements at numerous locations within the estuary. Apart from the fixed measurement locations, a number of ship-borne surveys were carried out during the campaign period. 

The ship transects are analysed to evaluate the internal flow structure compared to normal and high discharge conditions. The ship transects show a vertically well-mixed structure in the shallower sections of the upstream estuary. A salt-wedge structure is still present in the downstream estuary as found in a normal year, however, instead of fresh water in the surface layer as found in a typical year, the upper layer has a salinity of up to 8 PSU.  

We will present the first analysis of this dataset, exploring how the stratification alters during the drought and impacts the salt transport mechanisms in the estuary. Furthermore, our aim is to analyse the coupling between the Rhine Region of Freshwater Influence and salt intrusion length, under varying forcing conditions by means of combining the offshore stations and the inland salinity stations.