Morphological variability of sandy beaches due to variable oceanographic conditions: a study case of oceanic beaches of Rio de Janeiro city (Brazil)

Abstract

Due to their overall east-west orientation, the Rio de Janeiro oceanic urban beaches are exposed to high energy meteoceanographic events, exhibiting large spatial and temporal morphodynamic variability that affect their use and functionality. The main goals of this study are to describe the morphology of these sandy beaches and to evaluate their response to different oceanographic conditions. Between 2016 and 2018 quasi-monthly monitoring surveys, comprising topographic and sedimentological sampling, were carried out at 21 sites distributed along Macumba, Recreio-Barra da Tijuca, Sao Conrado, Leblon-Ipanema-Arpoador and Copacabana-Leme beaches. During this period, 29 storm events were recorded by an oceanographic buoy near the study area (~20 m depth). The most energetic event occurred between 11 and 14 August 2017 and caused widespread morphological changes, as the 45 m retreat at the Recreio-Barra beach eastern sector. Overall, mean grain size decreases from west to east varying from coarse to medium sand. The topographic record shows decreasing slope and increasing width from west to east, except in the Leblon-Ipanema-Arpoador beaches, where beach rotation was documented. The main findings were the interannual variability trends to beach morphometric records, the period each beach needs to recover its mean width after erosional events and how severe are storm impacts. Besides contributing to the morphodynamic understanding of the studied beaches, new understandings of the impacts of storm events and the subsequent recovery of sandy beaches are presented.