Evaluating the impact of dredging strategies at tidal inlets: Performance assessment

Despite relevant advances achieved in recent years, sediment transport and sedimentation problems at tidal inlets are still worldwide issues to be addressed. Furthermore, 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. This work proposes a new dredging strategy for tidal inlets and analyzes its morphodynamic evolution by means of numerical modeling. This numerical model, used to perform hydro-morphodynamic simulations, is applied to a highly altered tidal inlet (Punta Umbría inlet, Southern Spain) with a navigational capacity being continuously compromised. After calibrated and tested, the model is applied to different dredging strategies, including channel deepening, littoral drift barrier and shoal removal. Among these strategies, the shoal removal, which is a new soft-engineering strategy, is found to be the most efficient to improve the navigational channel operativity, defined as the percentage of navigable hours per year for different vessel drafts; this operativity improves up to 60% compared to the other strategies. This solution, which reduce the frequency of maintenance interventions and hence the environmental impacts, may be suitable for other inlets with compromised navigational capacities due to the presence of ebb shoals. The relation between the main maritime drivers and the morphodynamic changes is analyzed, concluding that the morphodynamic evolution of the navigational channels is closely related not only to the wave energetic content, but largely to the wave directionality. Finally, the shoal removal also increases the flow velocities at the inlet modifying the stability of the mouth and hampering its long-term closure. The potential environmental impacts derived from the shoal removal are also discussed.