Modelling of stem-scale turbulence and sediment suspension in vegetated flow

Abstract

This paper presents a vegetated flow and sediment transport model for investigating flow–vegetation–sediment interactions. Vegetation-induced turbulence is simulated by a turbulence closure, in which shear and stem-scale wake turbulent kinetic energies are solved separately. The model simulates both unidirectional and oscillatory flows as well as turbulence structures reasonably well with the model skill greater than 0.8 and the coefficient of determination greater than 0.95, and better agreements between simulations and measurements are observed in cases with large stem Reynolds number. To account for sediment suspension induced by wake turbulence within the canopy, a modified Shields parameter based on turbulence intensity is introduced. Compared to the traditional Shields number model in which sediment suspension is related to mean flow, the proposed model can more reasonably simulate sediment suspension in a dense vegetation canopy with the model skill greater than 0.8 and the coefficient of determination greater than 0.75, where mean flow is weak and stem-scale wake turbulence is dominant. The model uncertainties are evaluated by conducting sensitivity tests on the new coefficients introduced in the turbulence and sediment models. The influence of vegetation density on sediment suspension is also investigated. It is found that suspended sediment concentration is generally higher with higher vegetation density within the canopy, and lower with increasing vegetation density above the canopy.