2025 CSDMS meeting-131
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Future projections of compaction-induced subsidence on the Ganges-Brahmaputra Delta
Mike Steckler,
LDEO, Columbia University Pallisades New York, United States. steckler@ldeo.columbia.edu
Like many densely populated deltas worldwide, the Ganges-Brahmaputra Delta faces cascading flood and salinization hazards associated with relative sea-level rise (RSLR). One of the greatest uncertainties in future RSLR projections stems from the compaction of unconsolidated sediments, which causes land to subside with significant spatiotemporal variations. Here we constrain compaction variations on the Ganges Brahmaputra Delta, using a state-of-the-art 1D compaction model based upon fundamental principles of porous-media mechanics and groundwater flow; as well as constitutive relations for porosity and edaphic factors (e.g., roots, burrows). The model accurately reproduces field observations from GNSS, RSET-MH, and optical fiber strainmeters with compaction-induced subsidence rates of 1–30 mm/y depending upon local thickness and lithology of underlying Holocene deposits, forest tree density, and sedimentation rate. Sedimentation drives a dynamic compaction response over timescales of 10–100 years, such that floodplains cut off from sediment after 1950’s embankment construction have undergone significant elevation loss and are now experiencing a gradual subsidence slowdown. Updated RSLR projections informed by our model indicate that compaction-induced subsidence will be responsible for up to 50% of twenty-first-century RSLR, and exert a first-order control on hotspots of flooding and salinization hazards.
