Morphodynamics of Brazilian river mouths and delta shorelines

Deltas are important systems that host large populations, contributing to biodiversity, coastal protection, and socio-economic activities. Understanding their evolving morphodynamics is crucial for managing the impacts of climate change, anthropogenic influences and natural variability. Several deltas formed along the Brazilian coast during the Quaternary due to the combination of sediment-rich rivers with specific geologic and oceanographic conditions. Despite studies on their geological evolution, research investigating the modern morphodynamics of Brazilian delta shorelines and associated river mouths remains relatively limited. This thesis addresses this gap by analysing the morphodynamic behaviour of three wave-influenced deltas (São Francisco, Jequitinhonha and Doce) on Brazil’s east coast, focusing on their shoreline dynamics, wave climate variability, coastal change and sediment transport processes over years to decades. Analysis of the spatiotemporal dynamics of delta shorelines, using satellite imagery and shoreline change calculations, revealed that river mouths are erosion hotspots. These coastlines are highly sensitive to wave climate variability, leading to distinct wave-driven longshore sediment transport rates between 1984 and 2023, highlighting how shifts in wave patterns affect sediment distribution along the deltaic coasts. At a local scale, sediment analysis along the Doce delta coast based on field survey and laboratory work found beach sediment grain sizes ranging mostly from fine to very coarse sand, with an average of 0.92 mm (coarse sand). Geochemical data revealed significant alongshore variability in element concentrations and distribution between the bounded sediment cell regions. A focused study of the Doce River mouth morphodynamics over intra- and inter-annual timescales across four decades demonstrated a complex interplay between metocean conditions, coastal processes, and hydrological drivers. Different forces (fluvial vs. marine) dominate at different times, reshaping the river mouth morphology. This thesis offers a novel framework to understand and quantify shoreline and river mouth morphodynamics along Brazilian delta coasts over multidecadal timescale. By considering both short-term variability and long-term trends, this research offers valuable insights to inform future research and support sustainable coastal management.