Author(s): Yarko Nino; Id Hillmer
Linked Author(s): Yarko Niño
Keywords: Wind induced flow; Sediment suspension; K-εmodel; Sediment concentration
Abstract: Results of a numerical simulation of wind induced sediment resuspension from the bed of a body of water are presented and discussed. This phenomenon is modelled using a one-dimensional version of the Reynolds averaged equations, coupled with the k-εturbulence closure, and the sediment continuity equation. The model resolves the vertical structure of the flow induced by the wind and also the vertical distribution of suspended sediment concentration. The mathematical model is solved numerically using the method of control volumes. The simulations of the flow velocity induced by the wind reproduce experimental data adequately. Seiches associated with the oscillation of the pressure gradient in the direction of the wind cause damped oscillations of both, the flow velocity vertical distribution and also of the bed shear stress, until an equilibrium condition is reached asymptotically in time. Due to the circulation induced by the finite length of the water body, the bed shear stress in equilibrium conditions points in the direction opposite to that of the wind. The bed shear stress causes the suspension of bed material. The simulated values of such stress are used to estimate the sediment concentration near the bed by means of an empirically based entrainment relationship. This represents a reference concentration that is used to compute the vertical distribution of suspended sediment. The results are presented in dimensionless terms using the ratio between the particle fall velocity and the wind induced shear velocity as a parameter. A relationship between the ratio of surface to bed shear stresses and a Reynolds number based on the wind induced shear velocity and the depth of the water body, is obtained from the analysis of the numerical results. This is used to propose a relationship to estimate the wind induced sediment concentration near the bed as a function of the wind shear velocity, the sediment size and the depth of the water body.