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Geomorphology of a tropical river delta under pressure: the Rufiji delta, Tanzania—context, channel connectivity and alongshore morpho-sedimentary and hydrodynamic variability

Abstract : The geomorphology of the Rufiji River delta was investigated with emphasis on the influence of the delta's context, including the river basin, and remote-sensed delta-plain channel connectivity and shoreline morphological, sedimentary and hydrodynamic variations. The Rufiji is influenced by its East African Rift Valley tectonic context, high inter-annual water discharge variability and large mud-dominated sediment supply. The delta exhibits 14 distributary channels, only five of which are currently functional and all debouching presently in a low-energy muddy north sector, probably in response to NE tectonic tilting of the coastal basin of Tanzania. The south sector is characterized by a clear loss of distributary connectivity with the main stem but this appears to have occurred gradually over time, and is not a product of sudden avulsion. This loss is manifested by stronger meandering and numerous meander cut-offs indicative of a weaker overall delta-plain gradient, and may reflect the influence of the aforementioned tilting. This sector also has more abundant beach-ridge deposits than the north sector. The difference in shoreline facies between the dominantly muddy north sector and the dominantly sandy south sector appears to reflect primarily exposure to wave energy determined by an archipelago fronting the delta, and this difference is presently reinforced by preferential channel sediment routing to the north and sectorial sediment sequestration. The Rufiji River basin and its delta represent important stakes in the development of Tanzania under the country's rapid demographic growth, hydropower dam development and climate change. Eventual expected delta retreat caused by fluvial sediment shortage from the basin due to current and projected hydropower dams could be temporarily mitigated by sediment release by deforestation and by the relatively sheltered hydrodynamic setting of this delta.
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Submitted on : Friday, August 20, 2021 - 12:11:11 PM
Last modification on : Tuesday, September 7, 2021 - 3:44:18 PM

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Edward Anthony, Manon Besset, Florin Zainescu, Marc Goichot. Geomorphology of a tropical river delta under pressure: the Rufiji delta, Tanzania—context, channel connectivity and alongshore morpho-sedimentary and hydrodynamic variability. Geo-Marine Letters, Springer Verlag, 2021, 41 (2), ⟨10.1007/s00367-021-00695-7⟩. ⟨hal-03323098⟩

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