Efficient dredging strategy in a tidal inlet based on an energetic approach

Despite relevant advances in the study of inlet morphodynamics during the last decades, there is still a lack of knowledge regarding the effects of dredging interventions into these systems and their role into the mid-term stability. In this work the case of Punta Umbría, a deeply human-altered inlet in Southwestern Spain, was studied. To ensure the operational capacity and safe navigation throughout the inlet, five dredging works have been done since 2002, according to three alternative navigation channels designs. Given the siltation of the dredged channels and their associated high economic and environmental impacts, regional managers are demanding a more efficient alternative in time with a longer life cycle. The objective of this study is to relate the observed morphological activity to the forcings' dynamics to quantitatively assess the morphodynamic response of the tidal inlet. To this purpose, 18 high-resolution bathymetries of the inlet were analyzed in order to compute the morphological activity of the bed. The Delft3D numerical model was implemented to reproduce the total energy flux, obtained as the sum of both tidal and wave energy fluxes. The model was then calibrated and validated with hydrodynamic measurements from a monitoring network. Results show that the spatial divergence of the total energy flux explains the observed morphological activity patterns in the inlet, where locations with larger sedimentation correspond to those with higher convergence in the total energy flux. Through the reduction of the bed slope a more efficient design was obtained, since it minimizes the divergence of the energy fluxes and hence the bed activity, in contrast to former channel designs. This methodology can be extended to other systems, and therefore improve the efficiency in time of dredging interventions in tidal inlets.