A three-dimensional process-based morphodynamic model on orthogonal unstructured grids for coastal applications

This study presents a 3D process-based morphodynamic model that uses orthogonal unstructured grids. It is designed for coastal applications involving complex bathymetry and varying spatial scales. The model extends the Delft3D-FM framework by incorporating full 3D representation of wave, wind, and density-driven effects in the short-wave-averaged, non-linear shallow water equations. The framework includes expressions for wave and roller effects on flow forcing, turbulence, and bed shear stress, and integrates sediment transport and morphodynamic feedback. Multi-fraction sediment transport is supported, and the model tracks stratigraphy through a layered bed composition framework. Features such as infragravity wave dynamics, sediment mass slumping, swash zone slope nudging and morphological acceleration techniques are incorporated to better capture long-term morphological trends as well as storm erosion. The framework supports in-memory model coupling and is fully parallelized, enabling efficient, large-scale simulations. Model verifications presented here include analytical benchmarks and comparisons with laboratory and field observations, demonstrating reliable reproduction of wave–current interaction, sediment transport rates, and bed level changes. The model has the potential to bridge the gap between high-resolution event-scale modelling and long-term morphodynamic prediction, offering a flexible framework to study coastal sedimentary dynamics.