Short-term morphodynamic changes in a fetch limited beach at the Ebro delta (Spain), under low wave-energy conditions

Abstract

Sandy beaches in fetch-limited environments are protected from large ocean-generated swell waves, and fetch characteristics allow local wind-generated waves and currents to develop and drive the main morphodynamic processes. The morphodynamics of these low-energy beaches present a peculiar behaviour since there is not a dominant forcing mechanism inducing the beach changes. The main objective of this work is to describe and quantify the observed morphodynamic changes at the barred, quasi longshore-uniform beach of the Trabucador Bar at the Ebro Delta (Spain) under low-energy conditions. A nine-day field campaign was carried out within the framework of the European project FANS (Fluxes Across Narrow Shelves. The Ebro Delta Case) supported by the EC MAST-III Research Programme, (Contract No. MAS3-CT95-0037, DG12 – ESCY) and the measurements included a detailed topo-bathymetric surveying at the beginning and at the end of the campaign, video recordings covering the whole domain of the study area, surf zone waves and currents time series obtained at different positions and depths, nearshore pressure and horizontal velocities time series outside the surf zone. The results show that the beach underwent important longshore and cross-shore (the breaching of the submerged bar) morphodynamic changes under low-energy conditions. The observations suggest that the low-energy wave field and the beach profile played a key role in the generation of low frequency oscillations and rip currents that reshaped the whole study zone.