Coastal Erosion Risk Assessment, Shoreline Retreat Rates and Causes of Coastal Erosion Along the State of São Paulo Coast, Brazil

Abstract

Monitoring on coastal erosion problems along the São Paulo shoreline have been carrying out by the author since mid the 80’s, including almost 87% of the whole 430 km length of sandy beaches. Eleven types of indicators of coastal erosional processes have been recognized, which have been attributed to seventeen causes, among them ten correspond to natural mechanisms and seven are due to anthropogenic interference. In this paper is presented rates of shoreline retreat based on the Bruun Rule application for six of the most threatened beaches, for a period as long as 56 years. Risk assessment is also estimated for these six beaches based on two criteria: (i) the total number (sum) of types of coastal erosion indicators found along the shoreline (frequency among the 11 types) and (ii) general spatial distribution (percentage of surface area) of coastal erosion indicators along the shoreline. Causes and effects of the coastal erosional processes are discussed for these six beaches. Results reveal high rates of shoreline retreat, even in non-urbanized areas, as well demonstrate that the six beaches are at very-high risk. Moreover, they indicate that natural mechanisms are very important as cause of coastal erosional processes in São Paulo, sometimes most them the human-induced causes. These studies have widely been supporting the State Plan for Coastal Zone Management, in order to create special rules for occupation and some activities along the shoreline, including engineering works, building and sand beach exploration. Besides, results are being recorded in a geoenvironmental information system for the Coastal Zone of the State of São Paulo (Project SIIGAL), which is in phases of implantation.