Numerical analysis of solute transport and longitudinal dispersion coefficients in vegetated flow

Reasonable estimates of longitudinal dispersion coefficients are essential for predicting solute dispersion processes. However, the current knowledge of solute dispersion processes in vegetated waters is limited. In this work, we coupled a refined hydrodynamic model with scalar transport equations to simulate the flow field and dispersion process of solutes in water under the effect of vegetation. First, the proposed numerical model was verified using laboratory experiments, revealing the excellent performance of the coupled model in complex conditions. Eight different cases were subsequently simulated to analyse the effects of the upstream flow rate and vegetation height on the streamwise velocity, solute concentration, and longitudinal dispersion coefficients. The simulation results show that the upstream flow variation exerts a marked effect on the streamwise velocity and flow field within the vegetation zone, with a velocity difference within the shear layer reaching 54.7 % for an upstream flow of 0.018 m³·s^-1. The height of the vegetation affects both the velocity profile and solute dispersion. Placing emergent vegetation upstream can enhance solute dispersion in the longitudinal direction. The correlation analysis reveals that the longitudinal dispersion coefficients obtained using the routing producer are close to those determined using the theoretical method, with correlation coefficients reaching 0.75. This work presents the appropriate application range and parameters that must be considered in deriving formulas for longitudinal dispersion coefficients.