Processes controlling morphodynamics of artificially breached barriers

Abstract

Naturally and artificially breached tidal inlets can promote fast morphological changes along the adjacent detrital barriers, as they evolve in response to the contemporaneous wave regime. Inlet migration results in downdrift barrier erosion, while updrift sand accumulation and concomitant barrier extension are commonly observed.This study addresses the performance of placement of a sandfill designed to create an artificial dune along the updrift tip of a sand barrier aiming to constrain inlet migration, stabilize its location and reduce sand transfers from the ocean into the lagoon induced by storm overtopping of the barrier. Herein, we investigate the patterns of inlet drifting and processes regulating the progressive loss of efficiency of this soft engineering solution.We show that, besides updrift inlet migration, which occurs with temporary reversal of the prevailing direction of drift currents, meandering of the ebb-channels that envelop the flood delta is quite effective in triggering or enhancing erosion of the updrift barrier tip in periods when the inlet main channel is migrating in the opposite direction. This additional erosional process, which acts along the back-barrier façade, is responsible for the increase of the erosion rate of the artificial dune and regardless of the direction of wave-induced drift direction of the inlet. This finding discloses the relevance of taking into account not only the oceanic processes (waves) but also processes operating on the lagoonal side of the barriers in future engineering operations designed for tidal inlet management.