Medium-term coastal response at the Ebro delta, Spain

Abstract

Measurements of shoreline displacements along the Ebro delta coast have been used to estimate the medium-term evolution of the coastline. Aerial photographs and beach profile surveys covering the last 35 years have been used. Shoreline data obtained from beach surveys have been analysed using a linear regression technique in order to filter out short-term components. The medium-term scale has been derived from the asymptotic trend with this filtered analysis. Results have been compared with trends observed in the past and a similar qualitative behaviour has been found. Rates of change have decreased because the shoreline has slowly evolved towards a more stable configuration. A profile closure depth of 7 m has been estimated based on morphological changes in the submerged profiles and then used to convert shoreline displacements into yolume changes. From these, a medium-term sediment budget has been calculated. Based on the available evidence it has been assumed that these changes are mainly due to wave-induced longshore transport gradients. Assuming proper boundary conditions, the net longshore transport scheme has been estimated for each hemidelta. The results obtained using this method are in good agreement with the longshore transport rates predicted by well-known transport formulae.