Vulnerabilidade do litoral do município de Paulista-PE à erosão costeira

Abstract

Coastal erosion is a serious social and economic problem that affects several coastal stretches in Brazil and in the world. Its occurrence is related to several factors, both natural and anthropic. Erosive processes in the state of Pernambuco date back to at least the middle of the 20th century. The objective of this study is to estimate the vulnerability to erosion in the municipality of Paulista/PE, located north of the municipalities of Recife and Olinda, both heavily affected by erosive processes. The vulnerability was estimated to 29 points distributed along the coast of the municipality that is divided into three beaches (from south to north): Janga, Pau Amarelo and Maria Farinha. The methodology used to calculate the index was the one proposed by Mallmann (2010), which divides the vulnerability index into partial indices - related to coastal morphology, natural attributes, marine influence, coastal processes and anthropic influence - before an overall index is obtained. To calculate the vulnerability, coastlines were mapped between 1975 and 2018 to obtain medium-term coastline displacement rates. Two field studies were also carried out to collect information and also to identify the current conditions of erosion in the municipality. In addition, the evolution of the implementation of coastal defence structures was analyzed and the coastal transport in the municipality was calculated using the SMC-Brasil software. The results showed that on the beaches of Janga and southern part of the beach of Pau Amarelo there is a medium-term trend of erosion, while in the northern portion of the beach of Pau Amarelo and on the beach of Maria Farinha the trend is of progradation. It was also observed that even with the construction of coastal defence structures, in particular on the beaches of Janga and Pau Amarelo, the erosion indicators are still present in the municipality, in addition to the fact that in a large part of the coast the beach does not present recreational conditions at high tide. Between the many kinds of coastal defence structures present in the municipality, such as seawalls, bagwalls, etc., the best results against erosion were obtained by the breakwaters, built on the beach of Janga, because they allowed a certain accumulation of sediments, forming tombolos. Global vulnerability indices have shown that the southern portion of the municipality is the most vulnerable to erosion, a vulnerability that decreases to the north, especially on the beach of Maria Farinha, with the exception of a stretch on this beach where vulnerability is maximum, apparently caused by an irregular occupation on the beach. The coastal transport along the entire municipality is to the north, which seems to corroborate with the idea that the chronic erosion of Paulista is related to the presence of the port of Recife, which has already long triggered erosive processes in Olinda. Possibly also, the coastal erosion defence structures of Olinda aggravate erosion in the municipality of Paulista. Despite the strong anthropic factor causing erosive processes in Paulista, the partial vulnerability index associated with anthropic influence was low, which indicates a weakness in the method of calculating the index, although the overall result was satisfactory.