Synthesis of the distribution of subsidence of the lower Ganges-Brahmaputra Delta, Bangladesh

Michael Steckler (1) , Bar Oryan (1) , Carol Wilson (2) , Céline Grall (1, 3) , Scott Nooner (4, 5) , Dhiman Mondal (6) , S. Humayun Akhter (7) , Scott Dewolf (8) , Steve Goodbred

1 LDEO - Lamont-Doherty Earth Observatory
2 LSU - Louisiana State University
3 LIENSs - LIttoral ENvironnement et Sociétés
4 Department of Psychology [University North Carolina Wilmington]
5 UNC - University of North Carolina [Wilmington]
6 MIT Haystack Observatory
7 University of Dhaka
8 Clemson University

Deltas, the low-lying land at river mouths, are sensitive to the delicate balance between sea level rise, land subsidence and sedimentation. Bangladesh and the Ganges-Brahmaputra Delta (GBD) have been highlighted as a region at risk from sea-level rise, but reliable estimates of land subsidence have been limited. While early studies suggested high rates of relative sea-level rise, recent papers estimate more modest rates. Our objective is to better quantify the magnitude, spatial variability, and depth variation of sediment compaction and land subsidence in the lower GBD to better evaluate the processes controlling them and the pattern of relative sea level rise in this vulnerable region. We combine subsidence and compaction estimates from hand-drilled tube wells and historic sites (1–5 mm/y), GNSS and river gauges (4–8 mm/y) and RSET-MH and borehole vertical strainmeters (9–10 mm/y) in SW Bangladesh. The differences between the different types of measurements reflect the different timescales, spatial distribution and depth sensitivity of the different observations. Rates are lower for times >300y providing data on the timescale of compaction. We also observe differences related to the degree to which different devices measure shallow and deep subsidence. Higher values reflect a greater component of subsidence from young shallow deposits from soil compaction and organic matter degradation. Thus, we observe different rates for different environments and physical settings. These differences indicate that in planning adaptation for rising sea level, hard construction with a solid foundation may experience different subsidence rates than open fields or reclaimed land with recent natural or anthropogenic sedimentation.

Mots clés: land subsidence; deltas; Bangladesh; compaction; sediments; sustainability

Domaines: Sciences de la Terre; Interfaces continentales, environnement

Michael Steckler, Bar Oryan, Carol Wilson, Céline Grall, Scott Nooner, et al.. Synthesis of the distribution of subsidence of the lower Ganges-Brahmaputra Delta, Bangladesh. Earth-Science Reviews, 2022, 224, pp.103887. ⟨10.1016/j.earscirev.2021.103887⟩. ⟨hal-03482391⟩