Karoline Rummel obtained her PhD with honors (“summa cum laude“)  on “Salt Intrusion Dynamics and Data-Driven Forecasting in Estuaries”.

The PhD was supervised by Hans Burchard, from the Leibniz Institute for Baltic Sea Research Warnemünde (IOW).

The defense took place on July 10, 2026, at Lecture Hall 1 of the Teaching Building at the Institute of Physics (Albert-Einstein-Str. 24, 18059 Rostock) of the University of Rostock (Germany). 

Key results of this Thesis were given on:

• Which mechanisms dominate the advective salt transport in estuaries (in particular, in the Weser estuary, Germany) and how spatial variability in these mechanisms is shaped by flow-bathymetry interactions.

• Anthropic effects, namely deepening of the navigational channel by dredging, on salt transports mechanisms.

• Machine learning algorithms aimed to replicate salinity observations and improve projections from hydrodynamic and transport numerical models in estuaries.

The Thesis extends spatially an advective salt transport decomposition approach. Her approach allows identifying the spatial and temporal variability of the main transport mechanisms, which are subtidal depth-averaged transport, tidally-correlated depth-averaged transport, subtidal shear transport, and tidally-correlated shear transport. Remarkable differences between dominating mechanisms in the channel and shoals are found. The thesis also implements a Long Short-Term Memory (LSTM) neural network that can accurately replicate the spatial extent of the salt intrusion point (X2) from limited and fragmented station data.

Overall, this Thesis provides a mathematically rigorous foundation for analyzing salinity intrusion transport mechanisms. Furthermore, beyond advancing estuarine physics, the results serve as a practical tool for more effective estuary management.

About two-thirds of global freshwater comes from surface waters like tidal estuaries, which are increasingly affected by saltwater intrusion due to factors such as droughts, sea-level rise, river floods, tides, storm surges, and human interventions like channel modifications and water management. However, the combined impact of these factors—especially during prolonged drought—remains poorly understood. This knowledge gap has gained public attention through reports of salt-contaminated drinking water in tidal rivers. The SCOR Working Group 172 “SALTWATER” aims to address this issue by advancing interdisciplinary research and developing a global synthesis. We welcome contributions on estuarine salt intrusion using theoretical, observational, modeling, or machine learning methods.

We invite contributions highlighting new findings on estuarine salt intrusion processes, using theoretical, observational, numerical, statistical or Machine Learning approaches.