An Unstructured-Grid Based Morphodynamic Model for Sandbar Simulation in the Modaomen Estuary, China

Abstract

The Modaomen Estuary is the most important passageway in discharging flood and sediment of the Pearl River Delta, which is one of the most complex estuarine systems in China. Due to the coupling effect among tidal currents, waves, and sediments, an immense sandbar area evolved in the outer subaqueous delta, impeding the flood releasing during wet season, as well as salinity intrusion during the dry season. In this work, an unstructured-grid based morphodynamic model was proposed to simulate the sandbar evolution process in the Modaomen Estuary. The proposed model was constructed by using the two-dimensional shallow water equations for tidal flow, the advection-diffusion equations for salinity and suspended sediment transport, and the non-equilibrium formulation of the Exner equation for bed evolution. To simulate the wave-induced longshore currents in the Modaomen Estuary, an adaptive time-stepping approach was proposed to couple the unstructured-grid based Simulating WAves Nearshore (SWAN) model and the shallow flow model. An integrated solver is proposed for computing flow, salinity, and sediment transport fluxes simultaneously, and then the shallow water equations and advection-diffusion equations are jointly solved by a high-resolution, unstructured-grid Godunov method. Application of the model to the Modaomen Estuary, using calibrated parameter values, gives results comparable to the measured data. The butterfly shape of the sandbar in the Modaomen Estuary is considerably well simulated by the proposed model, which matches well with the measured topography.

Alternate erosion and deposition in the Yangtze Estuary and the future change

“…The classical Zhang's Formula of sediment transport capacity, which is widely accepted by researchers to calculate the capacity of water to carry sediment in rivers (Tan et al, 2018), can be used to further interpret the mechanism under high and low river water discharges. Although the formula may need to consider marine influences when using in estuarine areas, as many researchers have done over the past years (Xie and Yan, 2011;Mo et al, 2012;Hu et al, 2018), the main terms of the modified forms are still similar to the original Zhang's Formula. In addition, since we are mainly concerning the sediment transport capacity of river water discharge here, it is acceptable to employ the original Zhang's Formula to simplify the deduction.…”

Modeling Hydro-Dynamics in a Harbor Area in the Daishan Island, China

“…In Equation 5, α is the settlement probability of sediment, varying from 0.67 to 0.84; ω is the settling velocity of SPM; M is the coefficient of scouring, which is determined by sediment model verification; τ b is bed shear stress in τ b = ρU 2 * (ρ is the water density and U * is the shear velocity); τ e is the critical shear stress for sediment resuspension in τe = ρU 2 * e (U * e is the critical shear velocity for sediment resuspension); τ d is the critical shear stress for sediment deposition in τ d = ρU [37], Hu et al [38] and Xie et al [39].…”

Laboratory Experimental Investigation on the Hydrodynamic Responses of an Extra-Large Electrical Platform in Wave and Storm Conditions

“…The present results could reflect the dynamic responses of the offshore electrical platform. Due to high efficiency and accuracy, numerical simulation has been widely used in the fields of coastal and offshore engineering [19][20][21][22]. In the future work, the results of physical model test will be taken as the benchmark for the development of finite element model.…”