Evolution of rip channel systems under morphodynamic state constraints

Beach state classification models are widely applied in rip current hazard assessment. However, these frameworks primarily represent time-averaged beach conditions, and the correspondence between beach state and specific hydrodynamic–sedimentary evolutionary processes remains uncertain. In this context, this study treats beach state as a background constraint and integrates process-based numerical simulations with field observations and controlled experiments from 54 representative headland beaches in southern China. By introducing a quantitative indicator of rip channel three-dimensionality, rip channel evolutionary efficiency is evaluated under varying shoreline curvature and wave incidence conditions. The results indicate that curvature and wave direction, which are not explicitly considered in traditional assessment frameworks, both influence the three-dimensional evolution of rip channels. Among these factors, curvature exerts a more pronounced modulation, as its presence reduces the dependence of rip currents on pronounced three-dimensional morphological relief. Furthermore, even under identical beach state conditions, different wave–sediment parameter combinations lead to markedly different rip channel evolutionary responses, demonstrating that a single beach state parameter is insufficient to uniquely characterize rip channel evolutionary efficiency. These findings suggest that improving beach state–based rip current hazard assessment frameworks requires the explicit incorporation of process-related factors, including shoreline geometry, wave direction, and parameter pathway effects.