A New Soft-Engineering Alternative to Traditional Dredging Strategies

Sediment transport and sedimentation problems at tidal inlets and navigational channels are still worldwide issues to be addressed. Furthermore, future challenges such as climate change and the adaptation of coastal areas increase the uncertainties of the future evolution of these systems. However, dredging strategies are carried out following traditional layouts, such as channel deepening, lasting short periods of time despite the high economic expenditures and the potential environmental impacts derived from the increase on water turbidity and dispersion of contaminants. This work proposes a new soft-engineering dredging strategy for tidal inlets, analyzing its morphodynamic evolution by means of numerical modeling. The model, used to obtain the hydro-morphodynamic evolution of the inlet, is applied to Punta Umbría inlet (Southern Spain), which is a highly altered system for which the navigational capacity is continuously compromised. The simulations were successfully calibrated and tested both for hydrodynamics and morphodynamics and later applied to different dredging strategies, including traditional alternatives, such as channel deepening and littoral drift barrier, and a new soft-engineering solution based on shoal removal. Among these strategies, the shoal removal, which is designed to minimize the energy gradients at the navigational channel, is found to be the most efficient on the basis of the operativity of the channel for different vessel draughts; being this operativity improved up to 60% compared to the traditional strategies. This solution, which reduces the frequency of the maintenance of the channel depths, may be suitable for other inlets with compromised navigational capacities due to the presence of ebb shoals. Furthermore, it reduces the frequency of high turbidity and contaminant concentration episodes, which is of major interest in areas, such as Punta Umbría inlet, where the pollution derived from the soil content of heavy metals is important. After the analysis of the correlations between the main maritime drivers and the morphodynamic changes, we conclude that the morphodynamic evolution of the navigational channels is closely related not only to the energetic content of ocean waves, but also (and significantly) to the wave directionality. Finally, the analysis of the hydrodynamic impacts of the shoal removal shows that this alternative also increases the flow velocities at the inlet, which in turn modifies the stability of the mouth and hampers the closure of the mouth in the long-term.