Geoindicadores de vulnerabilidade à erosão em praias estuarinas, costa amazônica, Pará.

Abstract

The coastal zone (CZ) is a region responsible for various ecological functions, and also object of concern due to its uses and anthropic pressures, which affect its balance and environmental integrity. The beach is one of the most important environments in CZ, due to its intense use by the human population, having ecological function for many organisms and being a natural protection against physical forcers (waves, tides and chains). The anthropogenic occupation on a particular beach can aggravate coastal erosion (natural process of the morphological amendment of the environment, due to the interaction with physical agents). This occurs on the island of Mosqueiro, object of study of this work, where erosive processes have been intensified in recent decades, combined with urbanization. Observing this problem, the present research aims to analyze vulnerability to erosion on the Amazonian estuarine beaches of the Mosqueiro Island, well as evaluating the degree of coastal risk to which they are exposed. Using geoindicators, index and classification of local vulnerability were obtained. Being the index composed of coastal variables: morphology and granulometry of the beach, sedimentary swing, variation of the coast line, cliffs, natural barriers; and continental variables: land elevation, vegetation, coastal engineering structures, percentage of occupation and soil permeability. Then it was carried out: (a) collection of topographic data and sealing samples on 16 beaches; (b) observational analysis with Checklist of geoindicators of coastal erosion in loco and through satellite images; c) treatment of data collected in the field and by remote sensing; d) Use of the coastal vulnerability index to evaluate erosion on the beaches; and, e) identification of risk degree in these beaches. The results demonstrate that 8 of the 16 analyzed beaches are classified with high vulnerability (IVC: 5,0-7,4) and accentuated coastal risk, and that the presence of active cliffs, wall of arrimation and high occupation next the beaches stood out as favoring ones for this result. The data indicated high human occupation (> 70% on most beaches), since several forms of land use are frequent on the island, whether for homes or establishments (shops, restaurants, inns), which raises local risk for the occurrence of damage caused by erosion. In general, the adapted method of this study for Amazonian estuarine beaches, proved to be an interesting tool to be used in urban planning and to minimize future impacts of coastal erosion. It provides information that can aid in decision-making focused on coastal management and choosing which mitigatory measures can be carried out. Thus, the importance of this analysis and continuous coastal monitoring is reinforced through the use of geoindicators.