Mapping and modeling coastal flood dynamics using remote sensing and hydrodynamic models

This study presents an integrated and multidisciplinary methodology for investigating coastal flooding and morphodynamic processes in low-lying coastal environments, with a comparative application to two geomorphologically distinct Mediterranean coastal plains: the Volturno Plain and the Fondi Plain. The methodological framework combines high-resolution topographic and bathymetric datasets, aerial remote sensing, sedimentological analyses, statistical wave climate assessment, numerical hydrodynamic modelling, and relative sea-level rise scenarios that incorporate both eustatic trends and local vertical land movements. This approach enables a robust evaluation of how differing coastal configurations influence flooding susceptibility under extreme marine conditions.

For both study areas, the topographic baseline was derived from 2 m resolution LiDAR-based Digital Terrain Models, subsequently refined using site-specific datasets. In the Volturno Plain, extensive GNSS field surveys were conducted along the beach between Volturno and Regi Lagni river mouths. In the Fondi Plain, DTM refinement relied on aerial drone surveys carried out over the beach sector between the Canneto and Sant’Anastasia river mouths. Photogrammetric processing of aerial imagery allowed the generation of high-resolution surface models, which were integrated with the existing LiDAR DTM to enhance the depiction of subtle morphological features critical for flood propagation.

Sedimentological characterization was performed to constrain morphodynamic responses. Granulometric samples were collected along cross-shore transects at elevations ranging from −1.5 m to +2 m. Grain-size distribution analyses supported the calibration and interpretation of sediment transport and wave dissipation processes within numerical models.

Bathymetric modelling was based on high-precision single-beam echo-sounder surveys, with depth data corrected for tidal variations using official tide-gauge records. Emerged and submerged datasets were merged into continuous topo-bathymetric models, ensuring consistency in vertical reference systems and numerical stability.

Marine storms were identified through the analysis of offshore buoy records using a Peak Over Threshold approach. Storm events were classified into five classes using their Storm Power Index calculated by combining significant wave height and event duration. Representative events were selected as boundary conditions for coupled hydrodynamic simulations performed with Delft3D and XBeach. Simulations were run for future scenarios based on high-emission IPCC projections (SSP 5-8.5), integrating local sea-level rise, local subsidence rates, and highest tidal and surge levels.

A comparative analysis of the simulation outcomes highlights marked differences between the two coastal plains. The Volturno Plain results highly prone to inundation, with storm surges overtopping dune systems and propagating inland due to low elevations, local subsidence, and limited effectiveness of existing coastal defenses. Conversely, the Fondi Plain exhibits significantly reduced flood penetration. The presence of a wide bar system, coupled with efficient coastal defense structures, promotes substantial dissipation of incoming wave energy. As a result, even under intense storm conditions, inundation remains confined to a narrow coastal strip immediately landward of the beach.

Overall, the comparative methodological application demonstrates how coastal morphology, sedimentological properties, and defense systems critically control flood dynamics. The proposed framework provides a transferable and decision-oriented tool for assessing coastal vulnerability and supporting adaptation strategies in heterogeneous low-lying coastal settings under climate change pressure.