Impacts of human interventions on the evolution of the Ria Formosa barrier island system (S. Portugal)

Human interventions on sandy barriers disturb natural barrier dynamics, to the extent of having become key forces in modifying geomorphological evolution. This work identifies natural and human-induced drivers and analyses their importance to the multi-decadal evolution of the Ria Formosa barrier island system, in South Portugal. Aerial photographs from the last six decades and historical maps are used to assess changes in cross shore rates, morphological characteristics (barrier and dune widths, inlet morphology and migration) and barrier areas, through systematic methods that can be easily transferred to other barrier systems. Interventions, and especially hard engineering ones (jetties, inlet stabilisations), affected barrier evolution trends. Shore perpendicular works increased shoreline progradation updrift and initiated coastal retreat downdrift, with strongest erosive impacts along the edges of the system. Inlet stabilisations changed tidal inlet hydrodynamics and initiated ebb-shoal attachment to the barriers on either side of a non-migrating inlet that experienced loss of tidal prism. This shoal attachment was the main factor for the increase in total barrier area of Ria Formosa during the 60 years of analysis. Barrier growth after 2005 was slower, which could indicate that the system is reaching morphodynamic stability. (C) 2019 Elsevier B.V. All rights reserved.