Coastal analysis of river deltas in northeastern Brazil: A case study of parnaiba, jequitinhonha and São Francisco river delta

Abstract

Deltas, essential economic hubs, are increasingly vulnerable to coastal erosion driven by anthropogenic pressures within coastal zones. This study examines shoreline changes in three northeastern Brazilian deltas—São Francisco, Parnaíba, and Jequitinhonha—over the period 1984–2021, with a focus on natural processes and human activities, particularly dam construction. Utilizing multispectral imagery and hydro-climatic data, distinct shoreline alteration patterns were identified across the deltas. The Parnaíba Delta showed substantial sediment deposition at its mouth, with progradation rates exceeding 20 m/yr and sedimentary gains of 2.2 km², especially during flooding periods in the Parnaíba River (1991–2005). In contrast, the Jequitinhonha Delta experienced erosion at the mouth (rates below 10 m/yr). The limited correlation of active coastal area (R² = 0.49) suggests that eroded sediments are transported, via bidirectional currents, to the delta's margins. The São Francisco Delta, most anthropized delta, exhibited high erosion rates (above 20 m/yr) and greater loss of sedimentary area at its mouth (2.2 km²). In both the Jequitinhonha and São Francisco deltas, dam construction closes to the coast during the 90's (e.g., Itapebi and Xingó dam) contributed to increased shoreline erosion by reducing the annual/monthly variability of river flow and riverbank erosion potential. Conversely, the Parnaíba Delta, with the distant Boa Esperança dam, showed minimal human impact and remains relatively pristine. Over the last two decades, reduced rainfall—around 30% across these deltas—has likely diminished sediment transport capacity. Persistent drought and the planned expansion of mining activities may exacerbate erosion in the future. Over the last two decades, reduced rainfall— around 30% across these deltas—has likely diminished sediment transport capacity. Persistent drought and potential mining and dredging activities may exacerbate erosion in the future.