Hazard assessment in Galé - Olhos de Água sea cliffs: a tool for coastal management

Dissertação de mest., Gestão da Água e da Costa, Univ. do Algarve, 2007

Coastal hazards are a function of the interaction between human activities and naturally induced coastal processes. The conflicts arising from this interaction require new approaches that integrate the complex geodynamic environment of rocky coasts. Aiming to develop a method for assessing hazard in sea cliffs suitable for coastal management, the research presented combines the assessment of sea cliff evolution forcing mechanisms along with protection factors. The method considers wave exposure, mass movements and cliff face lithology and profile as factors of increased susceptibility to erosion in sea cliffs, while the presence of beaches and shore platforms protects cliffs from erosion. The method combines digital photogrammetry techniques and GIS analysis, based on a weighted factors approach, attributing weights according to different classes within each factor, in order to obtain a final hazard index that aggregates all factors. The method was applied to the rocky sea cliffs between Galé and Olhos de Água (Algarve, Portugal). High and very high hazard are dominant along the study area, representing more than 90% of the coastline studied. They occur predominantly in the absence of protective beaches and shore platforms. Moderate and low hazard have reduced expression but, even where they have been reported, hazard is not inexistent. The method presents cliff erosion hazards along the study area, being a suitable tool for cliff hazard assessment and useful for coastal management.