Abstract
The medium-term seabed evolution of Piraquê-Açú/Piraquê-Mirim estuary (ES/Brazil) is studied numerically in this work. The hydrodynamics is induced by the tide, the river discharges, and the incident water wave. The wave-tide-current interactions are obtained by coupling the shallow water equations with the radiation stress tensor introduced by Longuet-Higgins & Stewart (1960). In this way, the influence of both the tidal current and the current induced by gravity waves on the sediment transport are taken into account. We utilized the Exner (1925) equation, based on the conservation of seabed sediment mass, to calculate the morphological evolution. Seabed morphological changes are accelerated by introducing a time scale factor. Four bedload sediment transport formulations were tested and compared. We found an excellent agreement when numerical results are compared with currents measured in the upper estuary and with sediment transport rates measured at the river’s mouth when using the Engelund and Hansen (1967) sediment transport formulation. We also found that the main morphological changes occurring at the estuary mouth are due to the action of gravity waves. Between the head and mouth of the estuary, the sediment transport rate and morphological seabed changes are controlled exclusively by the tidal currents and the river discharge. In this latter case, we found that the large sandbank located at the estuary mouth is responsible for the absence of wave.
Highlights
Worldwide estuaries have a great importance for many human activities, e.g., harbor and navigation, fishing and aquaculture, tourism, and provide many other ecological services such as coastline protection, flood defense, and biodiversity conservation
Understanding the estuarine morphodynamics is crucial for the protection of coastal structures, logistic and management of water, living resources, and require a vast knowledge of various hydrodynamics processes acting in the estuary, like tidal induced currents, wave-current interactions, river discharges and sediment transport
Several studies of the hydrodynamics and morphological changes in estuaries have focused on the effect of river discharge and tidal flow in the absence of waves
Summary
We set up the Delft3D numerical model using the coupled hydrodynamics and waves effects to compute the sediment transport and medium-term seabed evolution at the PiraquêAçú/Piraquê-Mirim estuary. The Delft3D is a finite difference model who solves the 3D or depthaveraged mass and momentum conservation equations in a staggered grid. This model includes the main hydrodynamic processes that modify the coastal morphology, such as tidal flow, wave-current interaction, wave induced currents, wind drag, density flow, etc
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