Indicadores de vulnerabilidade de erosão costeira: Um estudo de caso no Norte de Portugal

Resumo

Coastal management is challenging given the increasing vulnerability due to impacts of human activities, like tourism, growing settlements and development of infrastructures, associated with the growing risk of climate change impacts. Integrated Coastal Zone Management thus requires an evaluation of coastal vulnerability and risks for climate change scenarios, which predict sea-level rise and an increase in the frequency and intensity of extreme events. In this work, we present the methodology used to quantify several morphometric and morphodynamic vulnerability indicators in the scope of the MarRisk project. Indicators are determined based on beach classification and on digital terrain and surface models, derived from LiDAR and aerial photography survey data, collected in 2011, 2017 and 2018. Results obtained for the Northern-Portuguese coast are presented and discussed. The applied methodology resulted in high-resolution imagery (orthophotos) and in morphometric (shoreline position, beach and dune width and volume, shoreface slope) and morphodynamic (changes of shoreline position and beach/dune volume between surveys) indicators for the study area. On average, and for the whole area studied, the coastline was stable between 2011 and 2017, but retreated more than 17 m between 2017 and 2018, which can be partly attributed to seasonal effects. The beach/dune volume (apparently) increased by 10% between 2011 and 2017 and decreased by 2% between 2017 and 2018. However, we found that the digital terrain model based on the LiDAR data cannot be directly compared to the digital elevation models obtained during the project, as, at least part of the observed increase in volume is due to differences in the method and not to real accretion. The implementation of a preventive monitoring plan is suggested, which should use normalized methods, defined according to the knowledge acquired about the dynamics established in the region.