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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. [ABSTRACT FROM AUTHOR]

As international concern for the survival of deltas grows, the Mekong River delta, the world's third largest delta, densely populated, considered as Southeast Asia's most important food basket, and rich in biodiversity at the world scale, is also increasingly affected by human activities and exposed to subsidence and coastal erosion. Several dams have been constructed upstream of the delta and many more are now planned. We quantify from high-resolution SPOT 5 satellite images largescale shoreline erosion and land loss between 2003 and 2012 that now affect over 50% of the once strongly advancing >600 km-long delta shoreline. Erosion, with no identified change in the river's discharge and in wave and wind conditions over this recent period, is consistent with: (1) a reported significant decrease in coastal surface suspended sediment from the Mekong that may be linked to dam retention of its sediment, (2) large-scale commercial sand mining in the river and delta channels, and (3) subsidence due to groundwater extraction. Shoreline erosion is already responsible for displacement of coastal populations. It is an additional hazard to the integrity of this Asian mega delta now considered particularly vulnerable to accelerated subsidence and sea-level rise, and will be exacerbated by future hydropower dams. [ABSTRACT FROM AUTHOR]