Abstract
In 1997, in front of the Pescara Harbour (Italy), a detached breakwater was constructed. In the successive years, the sediment transport due to the combined action of waves and coastal currents, in the area between the detached breakwater and the entrance of the Pescara Harbour, produced an accumulation of about 40,000 m 3 of sediment per year. In this paper, the causes of the accretion of the bottom elevation in front of the Pescara Harbour entrance and the effects produced by the existing detached breakwater are investigated. The effects on the sediment transport of the introduction of a new submerged breakwater designed to protect the entrance of the harbour from sediment siltation are investigated. In particular, the ability of the designed submerged breakwater, located orthogonally to the longshore current, to intercept the aforementioned solid material and to significantly reduce the accretion of the bottom in the area in front of the harbour entrance, was numerically verified. Numerical simulations were carried out by means of a model of the bottom-change composed of two sub-models: a two-dimensional phase resolving model that is used to calculate the fluid dynamic variables changing inside the wave period and a second sediment transport sub-model to simulate the bottom changes, in which the suspended sediment concentration is calculated by the wave-averaged advection–diffusion equation. The equations of motion, in which the vector and tensor quantities are expressed in Cartesian components, are written in a generalised curvilinear coordinate system. The fully nonlinear Boussinesq equations are written in an integral form and used to simulate the velocity fields.
Highlights
In the literature [1,2], the simulation of sea bottom changes produced by a coastal defence structure are usually carried out by simulating the hydrodynamic fields and the concentration of the suspended solid particles
We present a simulation model for the sea bottom modifications, composed by two sub-models: the hydrodynamic modifications are simulated by means of a two-dimensional phase-resolving model that considers the variation of the variables inside the wave period and takes into account the undertow and the sea bottom modifications are simulated by means of a second sub-model that calculates the suspended sediment concentration by means of the wave-averaged advection–diffusion equation
The Italian Ministry of Public Works has considered the possible construction of a submerged breakwater that is able to act as an obstacle to the flow of solid material carried by the longshore current coming from northwest
Summary
In the literature [1,2], the simulation of sea bottom changes produced by a coastal defence structure are usually carried out by simulating the hydrodynamic fields and the concentration of the suspended solid particles. In the framework of coastal sediment transport, 3D models for the simulation of the hydrodynamic fields [3,4,5,6] require considerable computational time, due to the long-time scale of the sea bottom variations. For this reason, in the context of morphodynamic simulations, the hydrodynamic equations [7,8,9,10,11,12,13] and the suspended sediment concentration equation are usually depth averaged [14]. The variability of the hydrodynamic field and the wave–current interactions over the wave period are taken into account in FNBE models
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