Assessment of Dredging Scenarios for a Tidal Inlet in a High-Energy Coast

Sandra Fernández-Fernández,Caroline C Ferreira,Paulo A Silva,Xavier Bertin,Soraia Romão,Paulo Baptista,Tiago Abreu,Ángela Fontán-Bouzas

doi:10.3390/jmse7110395

Abstract

The high energetic wave climate of the North Atlantic Ocean causes important morphological changes at Figueira da Foz coastal system (W Portugal), which is comprised of sandy beaches and the Mondego estuary-inlet. The submerged sandbar at the inlet mouth is highly dynamic inducing short waves shoaling and breaking processes that can entail navigation problems towards the local harbor. Therefore, coastal dredging operations are performed to guarantee safe navigation. Nevertheless, these operations have a limited temporal effectiveness and require a high annual budget to be accomplished. The goal of this research is to seek long-life dredging alternatives using modeling tools (i.e., Delft3D model suite). Delft3D model is used to simulate the morphological evolution of five dredging scenarios during a three-month winter period under three wave climate scenarios. The bed level differences at the dredged area and at the inlet mouth for each scenario are analyzed in comparison with numerical solutions obtained in a reference scenario (i.e., no-dredging). Results highlight morphological changes at the dredged inlet and surrounding areas and their effectiveness in extending the operational lifetime of inlet dredged operations on dredging configuration and wave climate conditions. These findings are the basis for selecting the most suitable dredging scenario to this coastal region under current wave climate conditions.

Highlights

Tidal inlets establish a connection between the coastal ocean and the sheltered back-barrier environment, such as lagoons, estuaries, bays, and marshes
The dredging effectiveness to retain sediment was determined by wave climate conditions and dredging operation configuration
The DRD and DRE dredging scenarios, with dredged sediment volumes of Vdo = 1065 × 103 and 2925 × 103 m3, respectively, promoted a huge sediment retention inside the sedimentation basin and can avoid shoaling at the tidal inlet mouth. Detailed analysis of these results revealed that the small sedimentation basins (DRO and DRA dredging scenarios) were only effective under low-energy wave conditions whereas, under high-energy wave conditions, few solutions corresponding to high volume of dredged sediment (DRD and DRE dredging scenarios) drive results that guarantee a safe navigation bed level at the tidal inlet mouth (z ≤ 9 m)

Summary

Introduction

Tidal inlets establish a connection between the coastal ocean and the sheltered back-barrier environment, such as lagoons, estuaries, bays, and marshes. They allow the exchange of water, sediments, nutrients, organisms, and pollutants between these systems and provide a waterway towards the harbors located at the back-barrier environments. For these reasons, tidal inlets are regarded as environments with high ecologic and socio-economic values. Stakeholders are aware of the importance of their correct management to increase their resilience This task requires a large effort because tidal inlets are highly dynamic morphological environments. Their behavior is the result of the interplay between oceanic processes, such as waves, tides and mean sea level, fluvial/estuarine processes, such as river discharges, and geological constraints on varying spatial and temporal scales [1,2]

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