What is coastal subsidence?

Törnqvist, Torbjörn E.; Blum, Michael D.

doi:10.1017/cft.2024.1

Cited by 3 publications

(1 citation statement)

References 32 publications

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“…However, by combining multiple measurements, we can approach a more complete understanding of what is happening. Knowing the current balance of sediment deposition, sediment compaction, tectonic land movement, and isostatic loading is critical for understanding elevation and sediment dynamics in deltas around the world (Tornqvist and Blum, 2024). Here, we focus on the Ganges-Brahmaputra Delta (GBD) and the prospect for nearfuture land loss and salinization in this megadelta that is home to >200 million people.…”

Section: Introductionmentioning

confidence: 99%

Contribution of campaign GNSS toward parsing subsidence rates by time and depth in coastal Bangladesh

Steckler,

Jaman,

Grall

et al. 2024

Front. Earth Sci.

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Coastal regions are vulnerable to rising seas, increasing storm magnitude, and decimation of ecologically-fragile areas. Deltas are particularly sensitive to the balance between sea-level rise, land subsidence and sedimentation that determine relative elevation. Bangladesh has been highlighted as being at risk from sea-level rise. Integrating measurements from different methods can approach a more complete understanding of factors controlling areally and temporally varying subsidence rates. To augment our compilation of rates from stratigraphic wells, historic buildings, vertical strainmeters, RSET-MH, and continuous Global Navigation Satellite System, we resurveyed 48 geodetic monuments in coastal Bangladesh ∼18 years after the monuments were installed. A later resurvey of 4 sites showed that some sites with higher subsidence may be unstable, but we consider the subsidence pattern of all the sites. Sites with rates <2 mm/yr overlie thin (≤35 m), sandy Holocene deposits located along interfluves between the main paleo-river valleys. As Holocene strata thicken seaward and become muddier, subsidence rates increase to 20–25 mm/y. Sites in incised valleys of the Ganges, Brahmaputra and Meghna Rivers, with Holocene sediments >100 m show subsidence rates of 20 ± 10 mm/y, with a slight seaward increase. Overall, subsidence rates increase with Holocene sediment thickness and the seaward shift from sandy to muddy sediments. Together with earlier measurements, we parse the different rates and mechanisms of subsidence. Earlier models show 2–3 mm/yr correspond to deep processes, such as isostasy. Within the shallow Holocene (<10 m), we estimate 5–8 mm/yr of subsidence from shallow, edaphic effects (tree roots, burrows, organic matter decomposition) and shallow (≤10 m) sediment consolidation on short timescales. Below this, we estimate 3–6 mm/yr from compaction of the upper Holocene strata, with 2–5 mm/yr occurring in deeper Holocene strata. Subsidence rates in areas of active sedimentation, such as rice fields and mangrove forests, are greater than buildings and structures with deep foundations. Subsidence on timescales >300 y, which do not include edaphic effects, are up to ∼5 mm/y. We note subsidence can be offset by active deltaic sedimentation, and does not necessarily indicate elevation loss. Collectively, the integration of these approaches allows us to begin quantifying the varied contributions to land subsidence from edaphic effects, Holocene sediment compaction, lithology, and time. Similar factors may contribute to the highly variable subsidence rates observed at other deltas worldwide.

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Section: Introductionmentioning

confidence: 99%

Contribution of campaign GNSS toward parsing subsidence rates by time and depth in coastal Bangladesh

Steckler,

Jaman,

Grall

et al. 2024

Front. Earth Sci.

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Subtle Land Subsidence Elevates Future Storm Surge Risks Along the Gulf Coast of the United States

Wang,

Chen,

Valseth

et al. 2024

JGR Earth Surface

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We developed a robust InSAR processing strategy that can effectively mitigate severe decorrelation noise in a large volume of InSAR data. We mapped the average land subsidence rate (2017–2020) over the 131,572 km2 Upper Texas and Louisiana coasts from Sentinel‐1 data, with ∼2 mm/yr accuracy based on independent GPS and tide gauge validation at 189 locations. The improved InSAR observations reveal widespread subsidence that was previously undetected in coastal wetlands and rural areas with small communities. Our InSAR surface deformation map is at the spatial scale that overlaps with the scale of hydrodynamic model grids. This allows us to integrate InSAR observations into operational storm surge models to analyze future flooding risks due to relative sea level change. We found that these subtle millimeter‐to‐centimeter subsidence features can substantially increase hurricane‐induced inundation, and passive flood mapping (known as the “bathtub” approach) can lead to inaccurate flood risk predictions.

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Coastal Flooding in Asian Megadeltas: Recent Advances, Persistent Challenges, and Call for Actions Amidst Local and Global Changes

Becker,

Seeger,

Paszkowski

et al. 2024

Reviews of Geophysics

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Asian megadeltas, specifically the Ganges‐Brahmaputra‐Meghna, Irrawaddy, Chao Phraya, Mekong, and Red River deltas host half of the world's deltaic population and are vital for Asian countries' ecosystems and food production. These deltas are extremely vulnerable to global change. Accelerating relative sea‐level rise, combined with rapid socio‐economic development intensifies these vulnerabilities and calls for a comprehensive understanding of current and future coastal flood dynamics. Here we provide a state‐of‐the‐art on the current knowledge and recent advances in quantifying and understanding the drivers of coastal flood‐related hazards in these deltas. We discuss the environmental and physical drivers, including climate influence, hydrology, oceanography, geomorphology, and geophysical processes and how they interact from short to long‐term changes, including during extreme events. We also jointly examine how human disturbances, with catchment interventions, land use changes and resource exploitations, contribute to coastal flooding in the deltas. Through a systems perspective, we characterize the current state of the deltaic systems and provide essential insights for shaping their sustainable future trajectories regarding the multifaceted challenges of coastal flooding.

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What is coastal subsidence?

Cited by 3 publications

References 32 publications

Contribution of campaign GNSS toward parsing subsidence rates by time and depth in coastal Bangladesh

Contribution of campaign GNSS toward parsing subsidence rates by time and depth in coastal Bangladesh

Subtle Land Subsidence Elevates Future Storm Surge Risks Along the Gulf Coast of the United States

Coastal Flooding in Asian Megadeltas: Recent Advances, Persistent Challenges, and Call for Actions Amidst Local and Global Changes

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