The Development of 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 pre-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 non-cohesive sediment transport model MOHID sand. The operational wave model was previously calibrated and validated 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, which exchanges files between the two models every hour, forces the wave model with current velocity and water level output from SOMA and forces SOMA with results of significant wave height, mean wave direction, mean wave period, bottom orbital velocity, and radiation stress from SWAN. Results of the coupling revealed that the impact of current velocity and water level forcing on the wave model was statistically significant, with surface current velocity yielding results most similar to observations as opposed to depth-averaged velocities. Improvements in current velocity and water levels were also found with the forcing of wave parameters on the hydrodynamic model. A non-cohesive sediment transport model is now being run inside the fully two-way coupled system to compute the sediment transport rates due to the effects of wave-current interaction. The final results are being used to evaluate in real-time risks at the B24 site, which can further be applied to other UCH sites. This forecasting system will be included in the decision support system of the THETIDA platform.