Doce River mouth dynamics and morphological changes over recent years

Deltaic river mouths are dynamic coastal environments and often exhibit significant morphological changes over different timescales. One of these environments is located at the mouth of the Doce River delta (southeastern Brazil) on a coastline dominated by wave processes. This study focuses on delineating and analysing recent changes in the Doce River mouth morphology over monthly timescales. Investigations were undertaken using Sentinel-2 data for the period between April 2017 and March 2022. Exposed river mouth bars and shoreline positions adjacent to the main channel (5 km to the north and to the south) were detected and the morphological changes were quantified. Analysing the changes between the initial and final dates, it was observed that the sand bars located in the Doce River mouth occupied an area of 301,457 m² in 2017, while this area decreased to 213,630 m² in 2022. The shapes of these morphologies also changed considerably during this period, with a sand bar dominating the central portion of the river mouth in 2017, leaving only two narrow stretches (66 and 87 meters) for the riverine and coastal interaction; in 2022, however, the river mouth width was 684 m. This increase in inlet width could contribute to changes in tidal incursion and fluvial-marine interactions in this system. Considering the adjacent shorelines, it was verified a dominance of erosional processes nearby the river mouth, with a maximum retreat of the shoreline position around 130 m in the south bar; the north bar, conversely, moved towards the sea between this time period. Considering the 10 km of shoreline analysed near the Doce river mouth, it was found that the erosional behaviour changed to accretional after the kilometer 3.8 in the north margin and after the kilometer 4.3 in the south margin, indicating greater dominance of erosional processes in the south margin of this river. Further investigations are in progress to identify the forcings shaping the river mouth and reworking the sediment along the adjacent shorelines. This will allow an integrated understanding of sediment availability and transport processes controlling this river mouth and associated shorelines over the recent years.