Variabilidade da resposta da linha de costa aos condicionantes hidrodinâmicos e às oscilações do nível do mar no litoral sul fluminense.

Abstract

The shoreline outlines a transition interface between continent and ocean and due to this its behavior may be used as a tool to understand trends followed by exposed coastal systems. In this regard, two compartments of Rio de Janeiro southern coastline, SE Brazil, were evaluated concerning shoreline response to long and medium-term meteo-oceanographic forcings. Thereafter, environmental and social data compilation provided inputs to assess coastal vulnerability due to erosion and inundation. The analyzed compartments correspond to restinga da Marambaia , a 40 km barrier island with sparse urban occupation, and Macumba and Recreio-Barra beach arcs, a highly urbanized 20 km-long sector. Long-term temporal scale (1986 to 2018) analysis comprised Landsat satellite imagery, WaveWatch3 model reanalyzes data, metereological register from the Instituto Nacional de Meteorologia do Brasil (INMET) station and sea level measures from a tidal gauge located at Rio de Janeiro city. Additionally, comparisons with climatic indices, such as Southern, Pacific Decadal and Atlantic Multidecadal Oscillations, were evaluated to access possible teleconnections. On the other hand, medium-term scale (2016 to 2018) estimations involved monthly survey of eleven topographic profiles and shoreface sediment samples at Macumba and Recreio-Barra beaches. Oceanographic buoy registers, from deep and shallow waters, were acquired in order to characterize the hydrodynamic conditions during those surveys. These informations allowed to estimate the longshore sediment transport (LST) through three models: CERC, Kamphuis and Bayram. Lastly, both long and medium-term information enabled the construction of a Coastal Vulnerability Index due coastal erosion and inundation for the study area. Overall, 28% of the coastline is under erosion, 32% is stable and 40% is advancing. During the studied period, just above four-hundred storm events were computed, of which during La Niña years the events were more energetic and erosive, especially at Marambaia. The sea level at Rio de Janeiro coastline is rising (2.4 mm/yr), presenting a decelerating trend between 1989 and 2017 (1.9 mm/yr). Regarding the LST rates, it is noticed eastern and western transports related to SW and SE waves, respectively. Also higher values of LST are associated to storminess waves. In terms of vulnerability, Marambaia Western sector exhibits low values owing to its urban occupation level, whereas at Central and Eastern sectors the vulnerability is high. At Macumba, low coastal vulnerability characterizes the Western sector, as opposed to the Eastern zone, where is very high vulnerable. Finally, at Recreio-Barra beach, vulnerability outlines an increasing pattern from west (moderate) to east (very high). In conclusion, these results indicate the important role played by the anthropic influence in areas naturally prone to high coastal vulnerability, demanding a better comprehension of natural conditions associated to anthropic intervations.