An Operational Numerical Framework for Assessing Risks to Underwater Cultural Heritage

Underwater cultural heritage (UCH) sites provide insight into past human behavior and history and thus their preservation is crucial. Within the scope of THETIDA, a Horizon Europe project dedicated to developing technologies and methods to protect coastal and underwater cultural heritage, this work aims to predict the physical processes that can put UCH at risk. This risk assessment is applied to a specific site in the Algarve, Portugal where a WWII U.S. B24 bomber plane crashed approximately 3 km offshore Praia de Faro. The plane now sits 21 m deep on the coastal shelf, which consists mainly of sand. The site is exposed to dominant, more energetic waves coming from W-SW and sheltered from less energetic E-SE waves. The mean significant wave height is 0.9 m, but it can rise to above 3 m with the occurrence of storms. As the site is located in the open ocean, a highly energetic environment, the site is subject to risks caused by wave-induced currents and sediment transport. To analyze and predict these risks in real time a numerical framework integrating three operational process-based models was developed. The numerical system is composed of: 1) the wave model SWAN, 2) the hydrodynamic model MOHID, and 3) the sediment transport model MOHID sediment. The operational wave model uses bathymetric data from EMODNET and is forced with wind conditions from the Skiron Atmospheric Modeling and Weather Forecasting Group in Athens and wave conditions at the boundary from the Copernicus Marine Environmental Monitoring Service (CMEMS). The model was calibrated by testing various formulas for the physical parameters attributed to wave propagation. A statistical analysis was completed to determine the best physics formulas to use for the model by comparing the results of each calibration setting with in-situ buoy measurements. SWAN was then two-way coupled to the hydrodynamic modeling system SOMA (Algarve Operational Modeling and Monitoring System), which is powered by MOHID. The coupling mechanism forces the wave model with velocities and water level output from SOMA and forces SOMA with wave results from SWAN. Preliminary results of the coupling revealed that the impact of current velocity and water levels on wave propagation in the study area is negligible in deeper areas, where the observations used for model validation lie. Further investigations are been conducted to analyze the effects of the two-way coupling in nearshore areas such as the location of the B24. The wave-hydrodynamic coupled system is now being used to develop a non-cohesive sediment transport model, which will be used to evaluate in real-time risks on UCH. This forecasting system will be included in the decision support system of the THETIDA platform.