Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: Implications for delta management and sustainability
Richard Hale, Rachel Bain, Steven Goodbred, Jim Best
Geography and Geographic Information Science
Mechanical Science and Engineering
The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges-Brahmaputra-Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.
10.5194/esurf-7-231-2019
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sediments Physics & Astronomy
plains Physics & Astronomy
mass transport Earth & Environmental Sciences
plain Earth & Environmental Sciences
sustainability Earth & Environmental Sciences
scaling Physics & Astronomy
rivers Physics & Astronomy
tides Physics & Astronomy
Hale, R., Bain, R., Goodbred, S., & Best, J. (2019). Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: Implications for delta management and sustainability. Earth Surface Dynamics, 7(1), 231-245. https://doi.org/10.5194/esurf-7-231-2019
Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain : Implications for delta management and sustainability. / Hale, Richard; Bain, Rachel; Goodbred, Steven; Best, Jim.
In: Earth Surface Dynamics, Vol. 7, No. 1, 12.03.2019, p. 231-245.
Hale, R, Bain, R, Goodbred, S & Best, J 2019, 'Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: Implications for delta management and sustainability', Earth Surface Dynamics, vol. 7, no. 1, pp. 231-245. https://doi.org/10.5194/esurf-7-231-2019
Hale R, Bain R, Goodbred S, Best J. Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: Implications for delta management and sustainability. Earth Surface Dynamics. 2019 Mar 12;7(1):231-245. https://doi.org/10.5194/esurf-7-231-2019
Hale, Richard ; Bain, Rachel ; Goodbred, Steven ; Best, Jim. / Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain : Implications for delta management and sustainability. In: Earth Surface Dynamics. 2019 ; Vol. 7, No. 1. pp. 231-245.
@article{e3da781d74704082ac85ed42ebd943fa,
title = "Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain: Implications for delta management and sustainability",
abstract = "The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges-Brahmaputra-Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.",
author = "Richard Hale and Rachel Bain and Steven Goodbred and Jim Best",
note = "Funding Information: Acknowledgements. This work would not be possible without the support of our local collaborators, Kazi Matin Ahmed and Syed Humayun Akchter from Dhaka University, who oversaw in-country logistics and offered local guidance. We would also like to thank Abu Naser Hossain of the Forestry Crime Department for his help with permitting, Nasrul Islam Bachchu of Pugmark Tours, and the captain and crew of the M/V Bawali and M/L Mawali for their seemingly endless patience with our field logistics. We would also like to thank Md. Saddam Hossain, Abrar Hossain, Mynul Hassan, Carol Wilson, and Mike Reed for their field support. This research was supported by the US Office of Naval Research (N00014-11-1-0683) and the National Science Foundation (Coastal SEES no. 1600319). We are grateful to the external reviewers, Mead Allison and John Shaw, for their valuable insights and contributions to the strength of the final paper.",
doi = "10.5194/esurf-7-231-2019",
journal = "Earth Surface Dynamics",
publisher = "Copernicus Publications",
T1 - Observations and scaling of tidal mass transport across the lower Ganges-Brahmaputra delta plain
T2 - Implications for delta management and sustainability
AU - Hale, Richard
AU - Bain, Rachel
AU - Goodbred, Steven
AU - Best, Jim
N1 - Funding Information: Acknowledgements. This work would not be possible without the support of our local collaborators, Kazi Matin Ahmed and Syed Humayun Akchter from Dhaka University, who oversaw in-country logistics and offered local guidance. We would also like to thank Abu Naser Hossain of the Forestry Crime Department for his help with permitting, Nasrul Islam Bachchu of Pugmark Tours, and the captain and crew of the M/V Bawali and M/L Mawali for their seemingly endless patience with our field logistics. We would also like to thank Md. Saddam Hossain, Abrar Hossain, Mynul Hassan, Carol Wilson, and Mike Reed for their field support. This research was supported by the US Office of Naval Research (N00014-11-1-0683) and the National Science Foundation (Coastal SEES no. 1600319). We are grateful to the external reviewers, Mead Allison and John Shaw, for their valuable insights and contributions to the strength of the final paper.
N2 - The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges-Brahmaputra-Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.
AB - The landscape of southwest Bangladesh, a region constructed primarily by fluvial processes associated with the Ganges River and Brahmaputra River, is now maintained almost exclusively by tidal processes as the fluvial system has migrated east and eliminated the most direct fluvial input. In natural areas such as the Sundarbans National Forest, year-round inundation during spring high tides delivers sufficient sediment that enables vertical accretion to keep pace with relative sea-level rise. However, recent human modification of the landscape in the form of embankment construction has terminated this pathway of sediment delivery for much of the region, resulting in a startling elevation imbalance, with inhabited areas often sitting >1 m below mean high water. Restoring this landscape, or preventing land loss in the natural system, requires an understanding of how rates of water and sediment flux vary across timescales ranging from hours to months. In this study, we combine time series observations of water level, salinity, and suspended sediment concentration with ship-based measurements of large tidal-channel hydrodynamics and sediment transport. To capture the greatest possible range of variability, cross-channel transects designed to encompass a 12.4h tidal cycle were performed in both dry and wet seasons during spring and neap tides. Regional suspended sediment concentration begins to increase in August, coincident with a decrease in local salinity, indicating the arrival of the sediment-laden, freshwater plume of the combined Ganges-Brahmaputra-Meghna rivers. We observe profound seasonality in sediment transport, despite comparatively modest seasonal variability in the magnitude of water discharge. These observations emphasize the importance of seasonal sediment delivery from the main-stem rivers to this remote tidal region. On tidal timescales, spring tides transport an order of magnitude more sediment than neap tides in both the wet and dry seasons. In aggregate, sediment transport is flood oriented, likely as a result of tidal pumping. Finally, we note that rates of sediment and water discharge in the tidal channels are of the same scale as the annually averaged values for the Ganges and Brahmaputra rivers. These observations provide context for examining the relative importance of fluvial and tidal processes in what has been defined as a quintessentially tidally influenced delta in the classification scheme of Galloway (1975). These data also inform critical questions regarding the timing and magnitude of sediment delivery to the region, which are especially important in predicting and preparing for responses of the natural system to ongoing environmental change.
U2 - 10.5194/esurf-7-231-2019
DO - 10.5194/esurf-7-231-2019
JO - Earth Surface Dynamics
JF - Earth Surface Dynamics