sedExnerFoam 2412: a 3D Exner-based sediment transport and morphodynamics model

Abstract

Predicting the complex interplay between flow hydrodynamics, sediment transport, and morphological evolution is a key challenge in hydraulic and coastal engineering. This paper presents an open-source numerical model for sediment transport and morphological evolution called sedExnerFoam. Implemented in the C++ multi-physics simulation toolkit OpenFOAM, the model combines high-resolution hydrodynamics with a transport equation for suspended sediment concentration, as well as a morphological evolution module based on the Exner equation. The sediment bed is one of the computational domain's boundaries, and its geometry varies over time. In turn, the evolution of the bed position affects the hydrodynamics through mesh deformation. Following a thorough description of the model, a series of benchmark tests is presented to evaluate its performance and demonstrate its capabilities. These benchmarks consist of a set of simplified simulations designed to validate each model component independently. These include a turbulent suspension case in an equilibrium channel, a case in which the flow transitions from a rigid starved bed to an erodible bed, becoming progressively laden with suspended sediments, and an idealized dune migration scenario that is decoupled from flow hydrodynamics. Finally, two deposition tests validate the model's mass conservation capability and highlight the avalanche mechanism that prevents excessive bed slope steepness. After the model has been validated, an application to the migration of a single dune under the influence of a steady flow is presented. Incorporating spatial bedload flux saturation is essential for achieving stable simulations and quantitative comparisons with experimental data in this application. The work presented in this manuscript represents a significant initial step in the development of a fully operational open-source model. Nevertheless, many improvements are still required. The article lists guidelines for future developments to inform future work.