Northwest Coast of Portugal – Past behavior and future coastal defense options

Abstract

Portugal's northwest coast, between Ovar and Marinha Grande presents an\nimportant sediment deficit, mainly due to rivers sediments supply\nreduction and harbors' constrains. The sediment transport capacity\nresulting from the wave's action (mainly from the northwest) is\nnourished with the sand of the up drift beaches, leading to the\nshoreline's erosion and retreat. The shoreline retreat represents\nconflicts with the land use and human occupation, and the protection of\npeople and properties becomes essential. Thus, coastal interventions\n(seawalls and groins), try to constrain the shoreline evolution,\nconducting to an artificial coast and site aesthetical deterioration.\nThis work's objective is to present an analysis of the shoreline\nevolution, in order to select a suitable model of coastal intervention.\nThus, the current paper aimed a diagnostic based in the shoreline\nevolution indicators in the period between 1994-2011: a) average rate of\nshoreline retreat; b) number of coastal defense structures implemented;\nc) number of coastal emergency works and interventions; and d) number of\nregistered events related to shoreline retreat (overtopping, dune system\nand coastal structures partial destruction). This analysis highlights\nthe location of the most vulnerable areas. Furthermore, different\nscenarios of coastal defense interventions are discussed, having as\nvariable the associated investment costs, which represents different\nstrategies and impacts, namely: a) maintain the existent coastal defense\nstructures; b) adapt the existent coastal defense structures; c) perform\nartificial nourishments; and d) propose new coastal defense solutions.