Numerical Modeling of the Formation of Nearshore Transverse Sandbars by a Phase-Resolving Model

This study employs the FUNWAVE-TVD phase-resolving model to simulate the formation and evolution of Low-energy Transverse Finger Bars (LTFBs) under idealized conditions representative of El Trabucador beach in Spain. The objective is to investigate the underlying mechanisms driving sandbar development and the factors influencing their geometric characteristics. The results confirm that wave-induced cross-shore transport over gentler-than-equilibrium profiles plays a fundamental role in LTFB formation. Experiments conducted on non-erodible beds reveal that double circulation cells can emerge independently of sediment transport. In contrast, on erodible beds, these double circulation cells transition into single circulation cells due to wave refraction caused by the developing bar structures. This transition underscores the dynamic coupling between hydrodynamics and morphology. Sensitivity analyses of the bed friction coefficient show the complex interplay between hydrodynamics and morphodynamics: higher bed friction produces more regular, thinner bars closely aligned with flow patterns, whereas lower bed friction leads to irregular, shorter bars less connected to flow patterns. Despite computational constraints limiting the full replication of natural systems, this study successfully captures key features of LTFBs and supports the formation mechanism proposed in recent literature. The alongshore wavelengths of the simulated sandbars align well with the smallest transverse bars observed at El Trabucador and reported in previous numerical studies.