Cartografia de suscetibilidade a deslizamentos e unidades territoriais de risco à escala regional: o caso da região Figueira da Foz – Nazaré

Abstract

Este trabalho faz uma análise da suscetibilidade a deslizamentos na área da plataforma litoral entre a Figueira da Foz e a Nazaré. Pretende-se efetuar uma cartografia de suscetibilidade, pelo método de análise hierárquica de pa‑ res, que constitua um instrumento para o ordenamento do território e para a gestão de risco, permitindo definir áreas prioritárias para estudos de pormenor. Poderemos enunciar, para a área estudada, diferentes tipos de processos perigosos naturais: sismos, erosão litoral, inundações, incêndios florestais, movimentos de massa (deslizamentos, desabamentos e fluxos). Estes afetam desigualmente as diferentes unidades territoriais, tendo por base as suas características físicas e de uso dos solos: Serras calcárias, Colinas gresosas, Planícies aluviais, Campo dunar eólico, Faixa litoral, Corredores neotectónicos (alinhamen‑ tos tectónicos e núcleos diapíricos).

Ce travail porte sur l’analyse de la susceptibilité à glissements de terrain dans la plateforme côtière entre Figueira da Foz et Nazaré. On veux faire une cartographie de la susceptibilité à glissement, par la méthode d’analyse hiérarchique de pairs, qui constitue un outil important pour la planification et la gestion des risques, ce qui permet de définir des domaines prioritaires pour des études détaillées. Nous pouvons énoncer, dans la région étudiée, différents types de processes dangeroux naturels : sismes, l’érosion côtière, inondations, incendies, glissements de terrain, coulées de boue et des flux qui affectent inégalement les diverses unités territoriales du risque, fondée sur les caractéristiques physiques et l’utilisation des terres: collines calcaires, collines greseuses, plaines alluviaux, champ des dunes, zone côtière, zones de alignements neotectoniques.

The coastal plain located betwen Figueira da Foz and Nazaré (western Portugal) has a general low slope towards west, presents elevations below 200 m a.s.l. and constitutes an important geomophological unit in this area. Towards north, east and south the platform is limited by the limestone relieves of the Serra da Boa Viagem – Verride arc, Sicó Massif and Estremenho Massif, respectivelly. These relieves are characterized by high slope values and also higher altitudes (> 200 m). The area comprises the terminal portion of the hydrographic basins of the Mondego and Lis rivers. Regionally six territorial units were distinguished which, given the characteristics of natural systems and the development of human activities, determine different areas of risk: the limestone hills, the sandy hills, floodplains, coastal plain the coastline and the probable neotectonic structures. The limestone hills are particularly sensitive to mass movements (mainly landslides), the sandy hills are vulnerable not only to movements and fluvial erosion, but also to forest fires. Alluvial plains are vulnerable to floods and overflooding, coastal plain and its eolian dune field could be very vulnerable to forest fires, the coastline presents high vulnerability to erosion of different types according to morphology of the coast and, finally, the active tectonic structures, particularly those that are related with diapirs, are a source of seismic risk. It is our goal with this study, to create a GIS project covering diverse thematic mapping (lithologies, tectonics, slopes, hydrology, land use), to do data spatial analysis, particularly in anticipation of the hypothetical scenarios of rising sea level, floods, forest fires and slope movements.