Sediment moves in the Ganges-Brahmaputra delta, measured by Swot

The Ganges-Brahmaputra delta is an especially active environment, submitted to the rivers' flow variations (including in monsoon periods) and to tropical cyclones, and the storm surges they induce. The intertidal zones, covering more that 1200 km2, are submitted in addition to tides and tidal currents. They are also home for a large number of vulnerable people in this region. However, in situ observation there are scarce, and estimating the rapid coastal evolution in these zones is challenging.
Swot enables to measure water height. But wet soil also reflect back the radar signal, so that digital elevation model of intertidal areas can be made (as foreseen, see Apr. 2020: Arcachon Bay between tides). Moreover, it can be reassessed regularly, whenever measurements are made at low tide.
A study from La Rochelle Université examines the intertidal zones of the Ganges-Brahmaputra delta in 2024 and 2025 from Swot Pixel cloud data, specifically processed for such surfaces. The analysis reveals distinct island-scale and local-scale sediment redistribution patterns, some areas losing heights, others gaining, with an overall net gain, consistent with long-term observations of land gain in the Meghna Estuary. Between 2024 and 2025, this area experienced approximately 117 megatons of net sediment accretion and 47 megatons of net sediment erosion, with height variations frequently reaching 1 m (plus or minus) and, locally, extreme changes exceeding 2 m, and with surface area changes of approximately 60 km² emerging versus 80 km² submerged, both quantities detected by Swot, and allowing for the deduction of volume variations.
With longer time series available from Swot, seasonal or at least annual assessments will be possible. It could also help in modelling such rapidly evolving estuarine systems.