Hazard mapping based on observed coastal erosion rates and definition of set-back lines to support coastal management plans in the north coast of Portugal

Abstract

Coastal zone management plans need to consider scenarios of coastline evolution and associated uncertainties. In this paper, the main causes of shoreline retreat and coastal erosion (natural and anthropogenic) in the north coast of Portugal are discussed. The importance of increasing knowledge on coastal dynamics to improve long-term predictions of coastline changes is highlighted since it is essential to establish proper management tools. It is also shown that the Portuguese coastal ecosystems are not resilient enough to extreme events and that the Portuguese coastal zone, like very many others worldwide, and will be severely affected by the effects of climate change. It is concluded that extreme events need to be properly characterized and their impacts assessed since they have important implications in terms of uses of either the coastal zone or the coastal waters. Without that analysis, coastal management plans will be lacking technical and scientific information and data that could help decision-makers define the best strategies to control erosion levels and the impact of extreme events related to climate change effects. Finally, a detailed assessment of the coastline evolution was performed for the new Caminha-Espinho coastal management program, for the time horizons 2050 and 2100, based on historical data. The methodology used for the evaluation of the rates of shoreline change, hazard mapping and definition of set-back lines is presented. Selected examples are given to demonstrate the potential of this methodology in supporting the development of coastal zone management plans, but also to highlight the limitations and uncertainties linked to the complexity of the phenomena under analysis.