There is increasing interest in the use of nature-based approaches for mitigation of storm surges along coasts, deltas, and estuaries. However, very few studies have quantified the effectiveness of storm surge height reduction by a real-existing, estuarine-scale, nature-based, and engineered flood defense system, under specific storm surge conditions. Here, we present data and modelling results from a specific storm surge in the Scheldt estuary (Belgium), where a hybrid flood defense system is implemented, consisting of flood control areas, of which some are restored into tidal marsh ecosystems, by use of culvert constructions that allow daily reduced tidal in- and outflow. We present a hindcast simulation of the storm surge of 6 December 2013, using a TELEMAC-3D model of the Scheldt estuary, and model scenarios showing that the hybrid flood defense system resulted in a storm surge height reduction of up to half a meter in the estuary. An important aspect of the work was the implementation of model formulations for calculating flow through culverts of restored marshes. The latter was validated comparing simulated and measured discharges through a physical scale model of a culvert, and through a real-scale culvert of an existing restored marsh during the storm surge.

High-lying vegetated marshes and low-lying bare mudflats have been suggested to be two stable states in intertidal ecosystems. Being able to identify the conditions enabling the shifts between these two stable states is of great importance for ecosystem management in general and the restoration of tidal marsh ecosystems in particular. However, the number of studies investigating the conditions for state shifts from bare mudflats to vegetated marshes remains relatively low. We developed a GIS approach to identify the locations of expected shifts from bare intertidal flats to vegetated marshes along a large estuary (Western Scheldt estuary, SW Netherlands), by analyzing the interactions between spatial patterns of vegetation biomass, elevation, tidal currents, and wind waves. We analyzed false-color aerial images for locating marshes, LIDAR-based digital elevation models, and spatial model simulations of tidal currents and wind waves at the whole estuary scale (~326 km²). Our results demonstrate that: (1) Bimodality in vegetation biomass and intertidal elevation co-occur; (2) the tidal currents and wind waves change abruptly at the transitions between the low-elevation bare state and high-elevation vegetated state. These findings suggest that biogeomorphic feedback between vegetation growth, currents, waves, and sediment dynamics causes the state shifts from bare mudflats to vegetated marshes. Our findings are translated into a GIS approach (logistic regression) to identify the locations of shifts from bare to vegetated states during the studied period based on spatial patterns of elevation, current, and wave orbital velocities. This GIS approach can provide a scientific basis for the management and restoration of tidal marshes.

The spatial and temporal dynamics modify the hydrodynamic behavior, sediment transport, and morphological evolution on rivers. This study utilizes modern survey equipment to describe and analyze the Danube River hydromorphological features. The synergistic use of MBES, ADCP, and SSP delineates five distinct morphological areas on Corabia-Turnu - Magurele section, Danube River – Romania: shallow water area (small sandbars), , moderate depth sections (stable hydrodynamics condition), and require long term monitoring activities, deep water zone (excessive depth erosion and sediment transport). The analysis offers insights into water flow patterns and areas where the sedimentation rate is excessive. The bathymetric surveys and ADCP measurements were complemented by sediment suspended profiling. The result reveals that the majority of sediment particles fall within the 100–1000 µm range (fine to medium sands). A dominant fraction (100–300 µm) underscores the prevalence of fine sand, indicative of moderate-energy depositional behavior. The low content of fine particles (<10 µm) reflects limited silt and clay retention. The statistical analysis grouped datasets into three types of areas with different hydro-morphological characteristics. Our proposed approach provides a valuable method to use integrated bathymetric, hydrodynamic, and sedimentological analyses, wich contributes to the increseing baseline of knowledge on sediment dynamics in riverine systems, such as the Danube River, and highlights the value of spatially resolved morpho-sedimentary data for sustainable river basin management.