Synergistic use of bathymetric measurements, ADCP, and SSP for hydromorphological monitoring of the navigable lower Danube River

Study region The study investigates the Corabia – Turnu Măgurele sector (rKm 601 – rKm626) of the Lower Danube River in Romania. This is a hydromorphologically dynamic area of regional importance for navigation. Spatial and temporal dynamics modify its hydrodynamic behaviour, sediment transport, and channel morphology, changing it into a critical navigation sector. Study focus Modern hydrographic and acoustic survey equipment was used to describe the study area's hydromorphological characteristics. The synergistic use of MBES, ADCP, and SSP delineated five morphological areas grouped into three broad classes: shallow-water zones associated with sandbar formation; moderate-depth sections characterized by relatively stable hydrodynamic conditions and requiring long-term monitoring; and deep-water zones within the main navigable channel, characterized by enhanced erosion and sediment transport. Principal component analysis, K-means clustering, and spatial principal component analysis were used to classify areas with different hydromorphological characteristics. The analysis offers insights into water flow patterns and areas for this regional critical area where the sedimentation rate is excessive. New hydrological insights for the region The integrated analysis identified water-flow patterns and zones of excessive sedimentation. 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 (PCA, K-means, spatial PCA) grouped datasets into three types of areas with different hydro-morphological characteristics. Under extreme low-flow conditions, water depths within the navigable channel often locally drop below 2 m, imposing operational limitations on vessel draught and increasing the risk of navigation disruption. The proposed approach provides a valuable method to understand the importance of the synergistic application of bathymetric, hydrodynamic, and sedimentological analysis, contributes to increasing the level of knowledge on sediment dynamics in regional river systems, such as the Lower Danube, and provides support in decision-making regarding the prioritization of dredging interventions.