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.
Highlights
Sandbars are omnipresent patterns along river estuaries that interact with waves
The tidal currents, waves, and sediment are governed by the two-dimensional shallow water grid
The tidal currents, waves, and sediment are governed by the two-dimensional shallow water equations, the action density balance equation, and the advection-diffusion equation, respectively
Summary
Sandbars are omnipresent patterns along river estuaries that interact with waves. Their local morphology is expressed in terms of an underwater barrier [1]. Could take into account the coupling effect among tidal currents, waves and sediments, which has been shown to be an important dynamic factor that drives estuary sediment transport. Those process-based models still have some limitations. Wave height varies consistently with the tide level inside the mouth bar, while wave height has a phase lag of about one-quarter of the tidal period outside the mouth bar [13] Those complex coupling effects among tidal currents, waves, salinity and sediments should be fully considered by models. Morphodynamic approaches based on the coupled wave-current-sediment transport model [14] should be adopted for sandbar simulation in the Modaomen Estuary.
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