Mobilidade do limite praia duna no balneário Mostardense - RS : monitoramento por drone

Abstract

conjuntamente com a revisão da bibliografia regional, apontam para um processo erosivo acentuado no balneário Mostardense. As taxas de variação de linha de costa no referido balneário, foram próximas as encontradas em dois "hotspots" erosivos, bastante conhecidos na costa do RS (Balneário Hermenegildo e Farol da Conceição). Embora também tenham sido encontrados valores de recomposição do limite praia duna em alguns períodos, estes foram muito inferiores aos valores erosivos. Os resultados permitem identificar que os processos erosivos das dunas frontais ocorrem por ondas de alta energia, tendo destaque para a erosão ocorrida em outubro de 2016. Este conjunto de informações também demonstra o comportamento não linear do limite praia duna, podendo apresentar estabilidade durante todo ano, e sofrer considerada erosão em um único evento com duração de um a dois dias. Atualmente as dunas estão sendo obliteradas, ou seja, destruídas por ação marinha, sendo progressivamente suprimidas entre o pós praia e as edificações. Processos de recomposição são ocasionados pela ação de vento nordeste embora não tenha havido relação direta com a sazonalidade destes processos. Por fim, foi possível analisar a situação das edificações a beira mar em relação aos processos de erosão costeira e movimentação eólica a partir de um produto cartográfico síntese. Os dados revelam que as edificações, sobretudo as mais próximas ao mar, estão ameaçadas pelos processos marinhos e eólicos atuantes.

This document analyzed the mobility of the beach-dune limit facing of the Mostardense's Beach, municipality of Mostardas, in the middle coast of Rio Grande do Sul. Previous works has revealed that there are problems in this urban site and adjacent areas related to coastal erosion and the dune transgression towards to the continent, sometimes burying houses. To identify these processes better, were performed a collect of orbital imagery available in the Google Earth Pro software, added to a monthly monitoring over a year, with the aid of an unnamed aerial vehicle (drone), in an attempt to provide vertical aerial photographs of the study área. Orbital images and mosaics of aerial photographs extracted by drone were processed and compared in Agisof Photoscan and ArcMap 10.3 softwares, which allowed the vectorization the beach dune limit, characterizing processes of erosion by marine action and recomposition by wind action. Oblique aerial photographs and ground photographs, were also used to aid in the understanding of the processes. Meteorological and oceanographic data were collected, allowing a better understanding of the processes responsible for the analyzed dynamics. The data produced together with the review of the regional bibliography, point to a marked erosion process in the Mostardenses Beach. The rates of variation of the coastline in this beach were close to those found in two erosive hotspots, well known on the RS coast (Baln. Hermenegildo and Farol da Conceição). Although values of recomposition of the beach dune limit were also found in some periods, these values were much lower than the erosive values. The results allow us to identify that the erosive processes of the frontal dunes occur through high energy waves, highlighting the erosion occurred in October 2016. This set of information also demonstrates the non linear behavior of the beach dune limit, being able to present stability throughout the year, and suffer erosion in a single event in one to two days. Currently the dunes are being obliterated, that is, destroyed by marine action, being progressively suppressed between the swash zone and the buildings. Reconstruction processes are caused by the action of northeast wind although there has been no direct relationship with the seasonality of these processes. Finally, it was possible to analyze the situation of the buildings on the seafront in relation to the processes of coastal erosion and wind movement from a cartographic product synthesis. The data show that the buildings, especially those closest to the sea, are threatened by the active marine and wind processes.