In this study, critical extreme events affecting salt intrusion are investigated using an unstructured 3D hydrodynamic model applied to a coastal system comprising the Po River Delta and the nearby Emilia-Romagna coast located in the Northern Adriatic Sea (Italy). River–sea systems respond to severe floods and droughts through two mechanisms: enhanced saltwater intrusion (SWI) under conditions of reduced freshwater availability, and the formation of buoyant freshwater plumes (FWPs) during flood events, which modify coastal stratification and transport processes. During the 2022 drought, along-river salinity profiles confirmed that the model captured the vertical structure and inland propagation of the salt wedge, although the maximum saltwater intrusion was locally underestimated by a few kilometers. During drought conditions, reduced river discharge led to enhanced SWI, with saline water propagating several kilometers inland on the main distributary branches, together with a strong vertical stratification and persistent bottom salinity; while flood conditions generate short but intense freshwater pulses that propagate offshore over several kilometers, generating multiple coalescing river plumes, altering coastal stratification and mixing patterns. These contrasting responses highlight the sensitivity of river–sea systems to extreme forcing and their implications for water resources, ecosystem dynamics, and coastal processes. This work provides an integrated assessment of SWI and FWP dynamics under real extreme events, demonstrating how tools like process-based models can inform the prediction and management of hydroclimatic extremes in transitional environments.

This study introduces an innovative, accurate and open source approach to the detection of the thalweg, by leveraging an iterative path-finding algorithm, enriched with a loop-prevention mechanism. The tool has been applied to the bathymetric datasets interpolated onto a triangular mesh of a finite-element model used to numerically solve the river–sea continuum system of two test cases i.e. the Po and the Tiber deltas. The detected thalweg shows a strong agreement with deepest-point observed along cross-sections. Further improvements were obtained after optimization. The tool proved to be effective even in data-scarce branches with nearly uniform bathymetry and in presence of meanders, islands and lateral water bodies. A second tool has been developed and applied downstream of the thalweg detection to estimate the salt wedge intrusion length along delta branches by processing the salinity field produced by a river–sea continuum modeling systems. Both tools can support model practitioners and end users in managing modeling datasets and operational decision-support systems, such as drought early-warning applications.

This study investigates the response of salt intrusion and Turbidity Maximum Zone (TMZ) to changes in the river discharge, tides and coastal conditions. The study is carried out in the Weser Estuary, a typical funnel-shaped tidal estuary in the North Sea. The results show that the estuary does not respond immediately to changes in external forcing. Significant spatial and temporal lags are found in response to changes in drivers. There is a hysteresis between discharge and salt intrusion and TMZ location. The estuary follows different pathways while adjusting to increasing and decreasing flows. Changes in river discharge produce the largest shifts, whereas changes in tidal range have a smaller and more rapid effect. Storm surges can cause substantial, but short-term variations. Overall, the findings highlight that estuaries are in a continuous state of adjustment.

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). The SCOR WG members Nadia Pinardi, from the University of Bologna (Italy), and Manuel Díez-Minguito, from the University of Granada (Spain), participated in the Evaluation Committee acting as external referees.

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.

This study provides preliminary estimates of Total Exchange Flow (TEF) along the Guadalquivir  Estuary (Spain) during low river flows. The analysis combines 3 years of observations with an analytical exchange flow scenario featuring a sectionally-homogeneous M2+M4 oscillating tidal flow and salinity. The results indicate that the largest net incoming water volume transport, on the order of 300 m³ s⁻¹, is attained at the lower part of the estuary, near where the largest salinity gradient and currents are observed. This value is about 12-fold the normal river flow from the head dam at Alcalá del Río. The covariance between M2 salinity and current seems to play a more important role in exchange flow in the Guadalquivir estuary than the effects due to tidal asymmetry. Overall, the inclusion of the M4 improves TEF estimates in ∼ 10 % in the Guadalquivir estuary. A sensitivity analysis shows that in other estuaries and semi-enclosed basins the effects of the M4 could be even larger.

The SALTWATER SCOR Working Group 172 met in person in Glasgow.

Please find here the Schedule! 

Dates (local time): 

    – February 21, 2026, Saturday, from 14:00 to 18:30

    – February 22, 2026, Sunday, from 09:00 to 13:00

Venue:

    – Room LT907. Livingstone Tower (LT), 26 Richmond St. The venue is at walking distance from Queen St. Station and George Square in Glasgow city centre.

In this study, a type of artificial intelligence called Long Short-Term Memory (LSTM) networks is used to predict how far saltwater moves into estuaries. Different data types (such as salinity, water levels, wind, and river flow) are combined with computer model outputs to train LSTM networks. Once the network is trained, it is applied to the same data to predict saltwater movements quickly and accurately. The approach is tested on two tidal estuaries and shows that the network works even when some data is missing. However, predicting further into the future is more challenging because short-term events affect saltwater movement. This study shows that LSTM networks can make fast and accurate predictions of saltwater entering estuaries, helping with real-time monitoring and decision-making for coastal protection and water management.

Observations of estuarine salt intrusion dynamics during a prolonged drought event in the Rhine‐Meuse Delta

This study shows that the salt intrusion length mainly depends on the Rhine River discharge. Water level variations associated with storm surges contribute to shortterm variations in salt intrusion length. However, the tidal variations, caused by the spring‐neap cycle do not alter the tidally averaged salt intrusion length. Side branches behave differently from the main river, and their salt intrusion length mainly depends on the downstream salinity. The findings highlight the importance of understanding how
forcing conditions influence salt intrusion in a complex, branched delta.

The severe drought that affected large areas of Europe in Spring and Summer 2022 hit the Po valley (northern Italy) with an intense water scarcity crisis. Productive activities, particularly agriculture, suffered the consequences of water shortage, and the coastal regions of the Po Delta underwent extensive saltwater intrusion. By relying on observed discharge records and on precipitation data from reanalysis and climate models, we analyse the 2022 event in the framework of the recent past statistics and in future scenarios. Alongside with a projection of future rainfall regimes on the Po River basin in two climate change scenarios, our analysis shows that persistent negative rainfall anomalies like the ones that characterised the 2022 event, though unlikely to become a typical feature of future climate, could remarkably increase their frequency, particularly in a severe climate change condition. Moreover, their impacts will be magnified by rising temperatures and, in coastal areas, by rising sea level, enhancing the salinisation of agricultural lands and altering the dynamics of transitional ecosystems. While providing a first quantitative assessment of an event that struck a strategic productive and environmental region of the Italian territory, this brief communication points out the importance of a multi-disciplinary, basin-scale approach to climate change adaptation.