Barred beach profile equilibrium investigated with a process-based numerical model

The Equilibrium Beach Profile (EBP) means a profile along which local, time-averaged net cross-shore sediment transport is everywhere nil under a given wave condition and water level for a sufficiently long time. Analysis of the equilibrium profile of a sandy beach is important for coastal engineering design. Previous studies focused on establishing empirical beach shape relations, which do not support us to understand the underlying equilibrium morphodynamic mechanisms. In this study, detailed hydraulic and sediment transport processes on an equilibrium profile are revealed based on a process-based numerical model. It is found that the equilibrium is achieved by the balance between onshore sediment transport induced by wave nonlinearity and current-induced offshore transport. A dimensionless parameter is proposed so that we can measure the ‘distance’ from equilibrium for a beach based on sufficient wave recordings. These findings can enrich basic hydrodynamics theory and guide coastal engineering and practice.