290-1 Future projections of compaction-induced subsidence on the Ganges-Brahmaputra Delta

Session: Delta Evolution from Rivers to the Shelf: Past, Present and Future Perspectives for Society

Presenting Author:

Austin Chadwick

Authors:

Chadwick, Austin J¹, Steckler, Michael S.², Wilson, Carol A.³, Goodbred, Steven L.⁴, Rana, Masud⁵, Akter, Sharmin⁶, Bhuiyan, Md. Anwar Hossain⁷, Camargo, Suzana J.⁸, Larochelle, Stacy⁹, Hossain, Md. Jakir¹⁰, Mahmud, Sheak Sazzad¹¹, Tanvir, Ashraful A.¹², Ahmed, Zohur¹³, Mim, Afroza¹⁴

(1) Lamont Doherty Earth Observatory, Columbia University, New York, NY, USA, (2) Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA, (3) Louisiana State University, Geology and Geophysics, Baton Rouge, LA, USA, (4) Vanderbilt University, Nashville, TN, USA, (5) Geography and Environment Discipline, Bangladesh Open University, Gazipur, Bangladesh, (6) Department of Geology, University of Dhaka, Dhaka, Bangladesh, (7) Department of Geology, University of Dhaka, Dhaka, USA, (8) Columbia Climate School, Columbia University, New York, NY, USA, (9) Lamont-Doherty Earth Observatory, Columbia University, New York, NY, USA, (10) Massachusetts Institute of Technology, Cambridge, MA, USA, (11) Department of Geology, University of Dhaka, Dhaka, USA, (12) Department of Geology, University of Dhaka, Dhaka, Bangladesh, (13) Department of Geology, University of Dhaka, Dhaka, Bangladesh, (14) Department of Geology and Mining, University of Barishal, Barishal, USA,

Abstract:

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 (GNSS, RSET-MH, optical-fiber compaction meters, auger cores), showing 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 embankment construction in the 1960s have undergone significant elevation loss, but are now experiencing a gradual subsidence slowdown. Some of the fastest subsidence rates can be attributed to buried Pleistocene paleovalleys infilled with thick Holocene sediments, portending a legacy of ancient sea-level changes on future RSLR hazards. 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

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-5530

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