Objective/Mission
Drs. Steckler and Chadwick’s efforts have focused on quantifying subsidence and elevation changes in coastal Bangladesh. Using a combination of field data collection, data analysis, and physics-based poroelastic modeling, Steckler and Chadwick are identifying ongoing trends and predicting future changes in coastal subsidence and land-surface elevation, as well as their response to climate change and land use. They are sharing this information across the Jameel Observatory CREWSnet team, where it complements and enhances efforts across all three Flagship Initiatives.
Approach in Year 3
Steckler and Chadwick are utilizing an extensive network of field stations that utilize a variety of instruments and methods (Figure 14), including Continuous and Campaign GNSS, Rod Surface Elevation Tables with Marker Horizons (RSET-MH), Optical-fiber strainmeters, stratigraphic wells with C14 dating, investigation of archeological sites, and Interferometric Synthetic-Aperture Radar (InSAR). Year 3 Efforts have been focused on maintaining this network with modern measurements, data analysis, and the development of a predictive model to understand ongoing trends and future changes.
Progress in Year 3
In Year 3, Steckler and Chadwick have continued to maintain the network of field stations (Figure 14) for monitoring coastal subsidence and elevation change. Year 3 maintenance has primarily been accomplished through remote communication with collaborators and scientists at Dhaka University, as well as a field trip led by Steckler. Jameel Observatory CREWSnet funds have been used to service the RSET-MH and continuous GNSS stations.
During Year 3, Steckler published a first-author manuscript on the latest subsidence analysis associated with Campaign GNSS stations (https://doi.org/10.3389/feart.2024.1354686) The published analysis provides a comprehensive look at subsidence patterns across the country, including subsidence hotspots coinciding with buried paleo-valleys of the Ganges and Brahmaputra rivers carved during the last ice age (11,000+ years ago). This finding points to an important legacy of ancient climate change on future climate hazards, which intersect with the effects of modern land-use (e.g., groundwater extraction, deforestation). These subsidence hotspots partially overlap with Jameel Observatory CREWSnet focus areas (parts of Assasuni and Shyamnagar).
Foundational/internal modeling
In Year 3, Chadwick and Steckler built a predictive model for coastal subsidence and elevation change designed to resolve the observed variations (Figure 15) and disentangle the effects of climate change and human activities. The model is built upon fundamental principles of effective stress, conservation of mass, and Darcy flow; as well as constitutive relations for sediment porosity and shallow-subsurface ecology (e.g., tree roots, animal burrows). As input, the model uses stratigraphic data for the recent (Holocene) sedimentary deposits, near-surface soil properties, and sedimentation rate for a designated site. As output, the model generates a time-series of subsidence and surface-elevation change, which can be directly compared to field measurements and projected into the future (Figure 15).
Chadwick and Steckler validated the model region of Polder 32 in coastal Bangladesh, which boasts a dense clustering of field measurements (Figure 15). Results show the model can accurately resolve twenty-first-century subsidence dynamics within +/- 5 mm/yr., including local amplification of subsidence hazards in response to land use and climate change (Figure 15). A manuscript presenting the model and its publicly available, open-source components is in preparation for publication at a peer-reviewed scientific journal. The outcome of this work will allow for the generation of new, dynamic Digital Elevation Models (DEMs), which can be utilized across the Jameel Observatory CREWSnet efforts to improve predictions of where water will flow during floods and where waterlogging will occur during intense rains.
Data Hub and Decision Support Tool
In Year 3, Chadwick and Steckler uploaded the subsidence and elevation-change field measurements (Figure 15) to the Data Hub, and will upload the complementary subsidence-model predictions and their associated DEMs once completed. These data are excellent candidates for direct visualization using the Decision-Support Tool, to assess inundation risks due to sinking of the land surface, which in coastal Bangladesh often exceed the rate of gradual sea-level rise.
Summary of Potential Impact and Extensibility
The model enables a projection of elevation and elevations changes for the future that will improve estimates of waterlogging and necessary crop adjustments, and areas most susceptible to flooding from cyclones or other climatic events. If successful in Bangladesh, this approach can be used in other deltaic regions across the globe.
Learn more about Michael’s field work on Geohazards in Bangladesh