Numerical modelling investigation of finite-amplitude subaqueous dune saturation

Abstract

Observations of bedform development under various flow conditions show that an initially flatbed evolves through different phases leading to a fully developed dune field. However, the mechanisms limiting dune growth in flows with limited depth and suspended sediment transport are not fully understood. This paper presents a novel methodology to characterise the evolution of phase shifts in bed shear stress and sediment flux maxima in relation to finite-amplitude bedform crests, using a 2D Reynolds-averaged Navier–Stokes model (RANS) to simulate dune profile evolution. Our results indicate that increasing both profile wavelength and height enhances turbulent mixing, thereby reducing flow inertia and decreasing the phase advance of bed shear stress. We then demonstrate that increased turbulent kinetic energy levels entrain significant amounts of suspended sediment in the water column, eventually leading to profile saturation at specific parameter thresholds. This research sheds light on important mechanisms controlling the equilibrium dimensions of finite-amplitude dunes. The various saturation modes presented in this paper provide deeper insights into the diverse dune profiles found in nature.