ELUCIDATING SEA-LEVEL RISE, SUBSIDENCE, AND SEDIMENT ACCRETION IN THE GANGES-BRAHMAPUTRA (G-B) TIDAL DELTAPLAIN

2016 ◽  
Author(s):  
Carol A. Wilson ◽  
◽  
Michael Steckler ◽  
Steven L. Goodbred ◽  
Richard Hale ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Sediment Accretion ◽  
The Ganges

scholarly journals CAN MANGROVES HELP COMBAT SEA LEVEL RISE THROUGH SEDIMENT ACCRETION AND ACCUMULATION?

2015 ◽  
Vol 34 (1) ◽  
pp. 78-86 ◽  
Author(s):  
Hoque M.M. ◽  
Abu Hena M. K. ◽  
Ahmed O. H. ◽  
Idris M. H. ◽  
Hoque A. T. M. ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Sediment Accretion

The physical sustainability of the coastal zone of the Ganges-Brahmaputra-Meghna delta under climatic and anthropogenic stresses

2021 ◽  
Author(s):  
Stephen Darby ◽  
Md. Munsur Rahman ◽  
Anisul Haque ◽  
Robert Nicholls ◽  
Frances Dunn
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Average Rate ◽  
River Management ◽  
Tidal River ◽  
Natural Conditions ◽  
Fluvial Sediment ◽  
Average Value ◽  
Delta Plain ◽  
The Ganges

<p>The Ganges-Brahmaputra-Meghna (GBM) delta is one of the world’s largest deltas, and consists of large areas of low flat lands formed by the deposition of sediment from the GBM rivers. However, recent estimates have projected between 200~1000 mm of climate-driven sea-level rise by the end of the 21st century, at an average rate of ~6 mm/yr. Eustatic sea-level rise is further compounded by  subsidence of the delta, which in the coastal fringes varies from 0.2 to 7.5 mm/yr, at an average value of ~2.0 mm/yr. Therefore, the combined effect of sea-level rise and subsidence (termed relative sea-level rise, RSLR) is around 8.0 mm/yr. Such high values of RSLR raise the question of whether sediment deposition on the surface of the delta is sufficient to maintain the delta surface above sea level. Moreover, as the total fluvial sediment influx to the GBM delta system is known to be decreasing, the retained portion of fluvial sediment on the delta surface is also likely decreasing, reducing the potential to offset RSLR. Within this context, the potential of various interventions geared at promoting greater retention of sediment on the delta surface is explored using numerical experiments under different flow-sediment regime and anthropogenic interventions.  We find that for the existing, highly managed, conditions, the retained portion of fluvial sediment on the delta surface varies between 22% and 50% during average (when about 20% of the total floodplain in the country is inundated) and extreme (> 60% of the total floodplain in the country is inundated) flood years, respectively. However, the degree to which sediment has the potential to be deposited on the delta surface increases by up to 10% when existing anthropogenic interventions such as polders that act as barriers to delta-plain sedimentation are removed. While dismantling existing interventions is not a politically realistic proposition, more quasi-natural conditions can be reestablished through local- sediment management using tidal river management, cross dams, dredging, bandal-like structures and/or combinations of the above measures.</p>

scholarly journals The Dominant Climate Change Event for Salinity Intrusion in the GBM Delta

Climate ◽  
2019 ◽  
Vol 7 (5) ◽  
pp. 69 ◽  
Author(s):  
Rabeya Akter ◽  
Tansir Zaman Asik ◽  
Mohiuddin Sakib ◽  
Marin Akter ◽  
Mostofa Najmus Sakib ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Saltwater Intrusion ◽  
Climatic Conditions ◽  
Salinity Intrusion ◽  
Surface Water Salinity ◽  
The Ganges ◽  
The Impact ◽  
Change Event ◽  
Different Levels

Salinity intrusion through the estuaries in low-lying tide-dominated deltas is a serious threat that is expected to worsen in changing climatic conditions. This research makes a comparative analysis on the impact of salinity intrusion due to a reduced upstream discharge, a sea level rise, and cyclonic conditions to find which one of these event dominates the salinity intrusion. A calibrated and validated salinity model (Delft3D) and storm surge model (Delft Dashboard) are used to simulate the surface water salinity for different climatic conditions. Results show that the effects of the reduced upstream discharge, a sea level rise, and cyclones cause different levels of impacts in the Ganges-Brahmaputra-Meghna (GBM) delta along the Bangladesh coast. Reduced upstream discharge causes an increased saltwater intrusion in the entire region. A rising sea level causes increased salinity in the shallower coast. The cyclonic impact on saltwater intrusion is confined within the landfall zone. These outcomes suggest that, for a tide dominated delta, if a sea level rise (SLR) or cyclone occurred, the impact would be conditional and local. However, if the upstream discharge reduces, the impact would be gradual and along the entire coast.

scholarly journals Water level changes, subsidence, and sea level rise in the Ganges–Brahmaputra–Meghna delta

2020 ◽  
Vol 117 (4) ◽  
pp. 1867-1876 ◽  
Author(s):  
Mélanie Becker ◽  
Fabrice Papa ◽  
Mikhail Karpytchev ◽  
Caroline Delebecque ◽  
Yann Krien ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Water Level ◽  
Sea Level ◽  
El Niño ◽  
El Nino ◽  
Southern Oscillation ◽  
Climate Mitigation ◽  
Vertical Land Motion ◽  
The Ganges ◽  
And Sea Level

Being one of the most vulnerable regions in the world, the Ganges–Brahmaputra–Meghna delta presents a major challenge for climate change adaptation of nearly 200 million inhabitants. It is often considered as a delta mostly exposed to sea-level rise and exacerbated by land subsidence, even if the local vertical land movement rates remain uncertain. Here, we reconstruct the water-level (WL) changes over 1968 to 2012, using an unprecedented set of 101 water-level gauges across the delta. Over the last 45 y, WL in the delta increased slightly faster (∼3 mm/y), than global mean sea level (∼2 mm/y). However, from 2005 onward, we observe an acceleration in the WL rise in the west of the delta. The interannual WL fluctuations are strongly modulated by El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) variability, with WL lower than average by 30 to 60 cm during co-occurrent El Niño and positive IOD events and higher-than-average WL, by 16 to 35 cm, during La Niña years. Using satellite altimetry and WL reconstructions, we estimate that the maximum expected rates of delta subsidence during 1993 to 2012 range from 1 to 7 mm/y. By 2100, even under a greenhouse gas emission mitigation scenario (Representative Concentration Pathway [RCP] 4.5), the subsidence could double the projected sea-level rise, making it reach 85 to 140 cm across the delta. This study provides a robust regional estimate of contemporary relative WL changes in the delta induced by continental freshwater dynamics, vertical land motion, and sea-level rise, giving a basis for developing climate mitigation strategies.

Recent measurements of subsidence in the Ganges-Brahmaputra Delta, Bangladesh

2021 ◽  
Author(s):  
Michael S. Steckler ◽  
Bar Oryan ◽  
Md. Hasnat Jaman ◽  
Dhiman R. Mondal ◽  
Céline Grall ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Land Subsidence ◽  
Anthropogenic Activity ◽  
Relative Sea Level ◽  
The North ◽  
Active Tectonic ◽  
Relative Sea Level Rise ◽  
Tectonic Boundaries ◽  
The Ganges

<p>Deltas, the low-lying land at rivers 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 in the GBD 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 compaction and subsidence in the GBD in order to better evaluate the processes controlling it and the pattern of relative sea level rise in this vulnerable region.</p><p>With support from the Bangladesh Water Development Board, we have rehabilitated previously installed GNSS and installed new GNSS co-located with Rod Surface Elevation Tables (RSET) to better understand the balance of subsidence and sedimentation in the coastal zone in SW Bangladesh, which is less affected by the active tectonic boundaries to the north and the east. The continuous GNSSs installed in 2003 and 2012 were mounted on reinforced concrete building roofs. GPS stations in the area yield subsidence rate estimates of 3-7 mm/y.  To densify the subsidence data, in early 2020 we resurveyed 48 concrete Survey of Bangladesh geodetic monuments in SW Bangladesh that were installed in 2002. Although only measured at the start and end of the period, the time span between the two measurements is ~18 years enabling us to estimate subsidence over this timespan.</p><p>Preliminary results show that about ½ the sites yielded very high subsidence rates; repeat measurements confirm the suspicion that the monuments at these sites are unstable and have undergone localized subsidence from settling or anthropogenic activity. The remaining sites show an increase in subsidence from the NW to the SE, consistent with estimates of average Holocene subsidence (Grall et al., 2018). However, rates from the campaign stations are much higher than those from continuous GNSS sites, but only slightly higher than an RSET site. We interpret that the continuous building GNSS omit very shallow compaction-related subsidence, while RSETs neglect deep subsidence. This is further reinforced by results from a compaction meter consisting of 6 wells from 20 to 300 m depth with vertical optical fiber strainmeters in each well. They show a decrease in compaction with depth. While initial results require further investigation, we highlight the importance of multiple methodologies for interpreting subsidence rates--deep, shallow, natural, anthropogenic--in vulnerable delta regions.</p>

scholarly journals Modelling the increased frequency of extreme sea levels in the Ganges–Brahmaputra–Meghna delta due to sea level rise and other effects of climate change

2015 ◽  
Vol 17 (7) ◽  
pp. 1311-1322 ◽  
Author(s):  
S. Kay ◽  
J. Caesar ◽  
J. Wolf ◽  
L. Bricheno ◽  
R. J. Nicholls ◽  
...  
Keyword(s):  
Climate Change ◽  
Sea Level Rise ◽  
Sea Level ◽  
21St Century ◽  
Bay Of Bengal ◽  
Hydrodynamic Model ◽  
Sea Levels ◽  
Extreme Sea Levels ◽  
The Ganges

A hydrodynamic model of the Bay of Bengal has been used to explore increasing frequency of extreme sea levels in the Ganges–Brahmaputra–Meghna delta over the 21st century.

scholarly journals Modeling complex flow dynamics of fluvial floods exacerbated by sea level rise in the Ganges–Brahmaputra–Meghna Delta

2015 ◽  
Vol 10 (12) ◽  
pp. 124011 ◽  
Author(s):  
Hiroaki Ikeuchi ◽  
Yukiko Hirabayashi ◽  
Dai Yamazaki ◽  
Masashi Kiguchi ◽  
Sujan Koirala ◽  
...  
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Flow Dynamics ◽  
Complex Flow ◽  
The Ganges

scholarly journals Recent trends in groundwater levels in a highly seasonal hydrological system: the Ganges-Brahmaputra-Meghna Delta

2009 ◽  
Vol 6 (3) ◽  
pp. 4125-4154 ◽  
Author(s):  
M. Shamsudduha ◽  
R. E. Chandler ◽  
R. G. Taylor ◽  
K. M. Ahmed
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Urban Areas ◽  
Shallow Aquifers ◽  
Groundwater Levels ◽  
Decomposition Procedure ◽  
Hydrological System ◽  
Recent Trends ◽  
The Ganges ◽  
First Time

Abstract. Groundwater levels in shallow aquifers underlying Asian mega-deltas are characterized by strong seasonal variations associated with monsoon rainfall. To resolve trend and seasonal components in weekly groundwater levels in the Ganges-Brahmaputra-Meghna (GBM) Delta, we apply a nonparametric seasonal-trend decomposition procedure (STL) to observations compiled from 1985 to 2005 in Bangladesh. Seasonality dominates observed variance in groundwater levels but declining groundwater levels (>1 m/yr) are detected in urban and peri-urban areas around Dhaka as well as in north-central, northwestern, and southwestern parts of the country (0.1 to 0.5 m/yr) where intensive abstraction of groundwater is conducted for dry-season rice cultivation. Rising groundwater levels (0.5 to 2.5 cm/yr) are observed in the estuarine and southern coastal regions. This novel application of the STL procedure reveals, for the first time, the unsustainability of irrigation supplied by shallow aquifers in some areas of the GBM Delta and the hydrological impact of seawater intrusion of coastal aquifers associated with sea-level rise. Our findings provide important insight into the hydrological impacts of groundwater-fed irrigation and sea-level rise in other Asian mega-deltas where monitoring data are limited.

scholarly journals Effects of a large-scale, natural sediment deposition event on plant cover in a Massachusetts salt marsh

PLoS ONE ◽  
2021 ◽  
Vol 16 (1) ◽  
pp. e0245564
Author(s):  
G. E. Moore ◽  
D. M. Burdick ◽  
M. R. Routhier ◽  
A. B. Novak ◽  
A. R. Payne
Keyword(s):  
Sea Level Rise ◽  
Sea Level ◽  
Large Scale ◽  
Plant Cover ◽  
Sediment Deposition ◽  
Natural Phenomenon ◽  
Percent Cover ◽  
Sediment Thickness ◽  
Sediment Accretion ◽  
Natural Sediment

In mid-winter 2018, an unprecedented sediment deposition event occurred throughout portions of the Great Marsh in Massachusetts. Evaluation of this event in distinct marsh areas spanning three towns (Essex, Ipswich, and Newbury) revealed deposition covering 29.2 hectares with an average thickness of 30.1±2.1 mm measured shortly after deposition. While sediment deposition helps marshes survive sea level rise by building elevation, effects of such a large-scale deposition on New England marshes are unknown. This natural event provided an opportunity to study effects of large-scale sediment addition on plant cover and soil chemistry, with implications for marsh resilience. Sediment thickness did not differ significantly between winter and summer, indicating sediment is not eroding or compacting. The deposited sediment at each site had similar characteristics to that of the adjacent mudflat (e.g., texture, bivalve shells), suggesting that deposited materials resulted from ice rafting from adjacent flats, a natural phenomenon noted by other authors. Vegetative cover was significantly lower in plots with rafted sediment (75.6±2.3%) than sediment-free controls (93.1±1.6%) after one growing season. When sorted by sediment thickness categories, the low thickness level (1–19 mm) had significantly greater percent cover than medium (20–39 mm) and high (40–90 mm) categories. Given that sediment accretion in the Great Marsh was found to average 2.7 mm per year, the sediment thickness documented herein represents ~11 years of sediment accretion with only a 25% reduction in plant cover, suggesting this natural sediment event will likely increase long-term marsh resilience to sea level rise.

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