An Integrated Multi-Observation Study of Coastal Dynamic Processes Near the Tiber River Mouth

Given the ocean’s dynamic and fragile nature, innovative observing approaches are required to enhance spatio-temporal data coverage and to support integrated analyses of coastal hydrodynamics driven by interacting processes across multiple spatial and temporal scales. In the vicinity of river mouths, these dynamics become particularly complex, as wave-induced motion, wind-driven circulation, and baroclinic processes associated with horizontal density gradients interact with river discharge, which acts as a source of momentum and buoyancy through the input of fresher, less dense water into the marine environment.This complexity is especially pronounced at the Tiber River mouth, where freshwater enters the Tyrrhenian Sea through a bifurcated estuarine system consisting of the northern Traiano Canal and the southern Fiumara Grande. In this area, river discharge plays a key role in modulating local circulation and plume dynamics.Investigating such processes therefore requires the integration of high-resolution coastal observing systems with numerical models capable of resolving fine-scale hydrodynamic variability. Within this framework, the present study focuses on quantifying the relative contribution of the main physical forcings governing river plume dynamics in the vicinity of the Traiano Canal.To this end, a combined observational and modelling approach was adopted, including: (i) hydrometric stations along the Tiber River for continuous measurements of water level and discharge; (ii) a fixed coastal station near the Traiano Canal mouth for continuous monitoring of total suspended matter (TSM); (iii) a meteorological station providing wind speed and direction, atmospheric pressure, incoming solar radiation, relative humidity, precipitation, and air temperature; (iv) an X-band marine radar for monitoring wave fields and surface currents during storm events; (v) an upward-looking Acoustic Doppler Current Profiler (ADCP), deployed near the seabed, to continuously profile current velocity and TSM throughout the water column and to estimate wave spectral properties; and (vi) coupled hydrodynamic and wave numerical models implemented within an ocean–sea–river continuum framework.A dedicated field experiment, involving the simultaneous operation of all observing systems, was conducted between February and March 2025 in the coastal area adjacent to the Traiano Canal mouth. In the first phase, the performance of the WW3 wave model was evaluated by comparing simulated and observed statistical wave parameters and directional wave spectra, with particular attention to bimodal wave conditions. Subsequently, surface and depth-resolved current measurements were used to validate the three-dimensional hydrodynamic model SHYFEM-MPI, both in stand-alone mode and coupled with WW3, in order to quantify the contribution of wave forcing to coastal circulation during storm events.Finally, the optimal model configuration identified during the validation phase was applied to investigate the relative role of wind forcing, wave action, river discharge, and coastal morphology in controlling river plume dynamics in the vicinity of the Traiano Canal mouth.