Recent morphodynamics of the Indus delta shore and shelf

Giosan, Liviu; Constantinescu, Stefan N.; Clift, Peter D.; Tabrez, All R.; Danish, M.; Inam, Asif

doi:10.1016/j.csr.2006.05.009

Cited by 170 publications

(118 citation statements)

References 28 publications

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“…River diversions into agricultural canals also offer an effective way to reduce a river's sediment load (e.g. Indus River [31]), as does the hardening of riverbanks by raft and concrete [32].…”

Section: Supply and Flux Of Sediment Along Hydrological Pathwaysmentioning

confidence: 99%

Sediment flux and the Anthropocene

Syvitski

Kettner

2011

Phil. Trans. R. Soc. A.

505

293

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Data and computer simulations are reviewed to help better define the timing and magnitude of human influence on sediment flux—the Anthropocene epoch. Impacts on the Earth surface processes are not spatially or temporally homogeneous. Human influences on this sediment flux have a secondary effect on floodplain and delta-plain functions and sediment dispersal into the coastal ocean. Human impact on sediment production began 3000 years ago but accelerated more widely 1000 years ago. By the sixteenth century, societies were already engineering their environment. Early twentieth century mechanization has led to global signals of increased sediment flux in most large rivers. By the 1950s, this sediment disturbance signal reversed for many rivers owing to the proliferation of dams, and sediment load reduction below pristine conditions is the dominant signal today. A delta subsidence signal began in the 1930s and is now a dominant signal in terms of sea level for many coastal environments, overwhelming even the global warming imprint on sea level. Humans have engineered how most water and sediment are discharged into the coastal ocean. Hyperpycnal flow events have become more common for some rivers, and less common for other rivers. Bottom trawling is now widespread, suggesting that even continental shelves have received a significant but as yet quantified Anthropocene impact. The Anthropocene attains the level of a geological climate event, such as that seen in the transition between the Pleistocene and the Holocene.

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Section: Supply and Flux Of Sediment Along Hydrological Pathwaysmentioning

confidence: 99%

Sediment flux and the Anthropocene

Syvitski

Kettner

2011

Phil. Trans. R. Soc. A.

505

293

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“…Of this total sediment flux, ~70% or ~13 x 10 9 tons is believed to discharge from the eastern and southern Asian Pacific and oceanic margins alone (Milliman and Meade, 1983;Milliman and Syvitski, 1992;Ludwig et al, 1996;Milliman, 1995). In eastern and southern Asia, about one-third to one-half of river-derived sediments are trapped in the river's low reaches and contribute to extensive floodplain and delta plain development, for example the Yellow (Saito et al, 2000), Yangtze (Hori et al, 2002), Pearl (Zong et al, 2009), Red (Tanabe et al, 2003); Mekong (Nguyen et al, 2000;Ta et al, 2002), Ganges-Brahmaputra (G-B) (Goodbred et al, 2003), and Indus (Giosan et al, 2006). Among the remaining sediments delivered to the ocean, how much is trapped near the river mouth, and how much is able to reach the deep ocean is still not completely clear.…”

Section: Introductionmentioning

confidence: 99%

Fate of sediments delivered to the sea by Asian large rivers: Long-distance transport and formation of remote alongshore clinothems

Liu¹,

Xue²,

Ross³

et al. 2009

TSR

159

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Recent studies show that the global flux of river-derived sediment reaching the coasts and oceans is about 15-19 x 10 9 tons per year. New sediment budgets for the major Asian river systems (e.g.,Yellow, Yangtze, Mekong, Ganges-Brahmaputra, etc.) suggest that 30-50% of their sediment load has been retained in the lower channel reaches to form an extensive subaerial delta plain, while the rest is discharged to the sea. Of the sediment load reaching the ocean, about half has been found to accumulate near the river mouth as a proximal subaqueous delta clinothem. However, the remaining sediment is found to be transported up to 600-800 km alongshore, ultimately being deposited as a shore-parallel middle-shelf clinothem.These clinoform deposits are generally <100 km in across-shelf width, 20-40 m thick nearshore, and pinch-out gradually seaward at 40-90 m water depth.A secondary nearshore depocenter can usually be found along the shelf away from the river mouth, with mud-lobe accumulation up to 40-50 m thick locally. Except for a few systems with shelf-indenting canyons (e.g., Ganges-Brahmaputra and Indus), most of Asian riverderived sediments are trapped on the inner and middle shelf, unable to reach the deep ocean (i.e., >150 m) despite having been transported hundreds of kilometers from their mouths.

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“…In contrast, the amplified tidal currents in the Gulf of Mottama efficiently redistributed the significantly larger amount of Ayeyawady sediment that escaped beyond the energy fence together with sediments from Sittaung and Thanlwin to form the mid-shelf clinoform there. The offshore-directed tidal pumping leading to the formation of the Mottama clinoform is reminiscent of the situation on the eastern Indus shelf where strong tidal currents from the Gulf of Kutch built a mid-shelf clinoform with Indus sediments escaping eastward (Giosan et al, 2006). Such clinoforms, which are of purely tidal origin and do not front a subaerial deltaic counterpart per se, may have been more common in sediment-rich macrotidal environments during faster transgressive conditions in the past.…”

Section: Discussionmentioning

confidence: 96%

On the Holocene evolution of the Ayeyawady megadelta

et al. 2018

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Abstract. The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe) was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe) is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven by tectonic-hydrodynamic feedbacks as the extensionally lowered shelf block of the Gulf of Mottama amplifies tidal currents relative to the western part of the shelf. This situation probably activates a perennial shear front between the two regions that acts as a leaky energy fence. Just as importantly, the strong currents in the Gulf of Mottama act as an offshore-directed tidal pump that helps build the deep mid-shelf Mottama clinoform with mixed sediments from the Ayeyawady, Sittaung and Thanlwin rivers. The highly energetic tidal, wind and wave regime of the northern Andaman Sea thus exports most sediment offshore despite the large load of the Ayeyawady River.

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Recent morphodynamics of the Indus delta shore and shelf

Cited by 170 publications

References 28 publications

Sediment flux and the Anthropocene

Sediment flux and the Anthropocene

Fate of sediments delivered to the sea by Asian large rivers: Long-distance transport and formation of remote alongshore clinothems

On the Holocene evolution of the Ayeyawady megadelta

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