Modern sedimentation and morphology of the subaqueous Mekong Delta, Southern Vietnam

Unverricht, Daniel; Szczuciński, Witold; Stattegger, Karl; Jagodziński, Robert; Le, Xuan Thuyen; Kwong, L. Liong Wee

doi:10.1016/j.gloplacha.2012.12.009

Cited by 65 publications

(27 citation statements)

References 46 publications

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“…saline water is congruent with the weak southwesterly waves and low winds at the coast during the summer monsoon [Hu et al, 2000], though the shallow depth ( 5 m) of the subaqueous delta topset [Unverricht et al, 2013] suggests that even moderate waves could resuspend sediment there.…”

Section: 1002/2015jc010754mentioning

confidence: 99%

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

et al. 2015

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A better understanding of flow and sediment dynamics in the lowermost portions of large‐tropical rivers is essential to constraining estimates of worldwide sediment delivery to the ocean. Flow velocity, salinity, and suspended‐sediment concentration were measured for 25 h at three cross sections in the tidal Song Hau distributary of the Mekong River, Vietnam. Two campaigns took place during comparatively high‐seasonal and low‐seasonal discharge, and estuarine conditions varied dramatically between them. The system transitioned from a tidal river with ephemeral presence of a salt wedge during high flow to a partially mixed estuary during low flow. The changing freshwater input, sediment sources, and estuarine characteristics resulted in seaward sediment export during high flow and landward import during low flow. The Dinh An channel of the Song Hau distributary exported sediment to the coast at a rate of about 1 t s−1 during high flow and imported sediment in a spatially varying manner at approximately 0.3 t s−1 during low flow. Scaling these values results in a yearly Mekong sediment discharge estimate about 65% smaller than a generally accepted estimate of 110 Mt yr−1, although the limited temporal and spatial nature of this study implies a relatively high degree of uncertainty for the new estimate. Fluvial advection of sediment was primarily responsible for the high‐flow sediment export. Exchange‐flow and tidal processes, including local resuspension, were principally responsible for the low‐flow import. The resulting bed‐sediment grain size was coarser and more variable during high flow and finer during low, and the residual flow patterns support the maintenance of mid‐channel islands.

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Section: 1002/2015jc010754mentioning

confidence: 99%

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

et al. 2015

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“…The wet season (from June to October) alternates with a dry season (November-May) and accounts for 85%-90% of the total yearly rainfall. In South Vietnam, the annual rainfall ranges between 1600 and 2000 mm [34,35]. Rainfall is higher (2000-2400 mm per year) in the Western region than in the Eastern (1600-1800 mm) and in the central delta (1200-1600 mm) [36].…”

Section: Climate and Rainfallmentioning

confidence: 99%

“…The total water discharge of the Mekong is~500 km 3 yr´1, of which 85% flows in flood season (from September to November) and 15% in low flow season (from December to August) [21,35]. In the delta, the flood season occurs later than the local rainy season, since the water flux mainly comes from the upper and central Mekong basin and is partially regulated by the dynamics of the Tonle Sap in Cambodia.…”

Section: Hydrological Regimes and Sediment Transportmentioning

confidence: 99%

Numerical Simulations of Suspended Sediment Dynamics Due to Seasonal Forcing in the Mekong Coastal Area

Vinh¹,

Ouillon

Thao³

et al. 2016

Water

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Abstract:The Mekong River is ranked as the 8th in terms of water discharge and as the 10th in terms of sediment load in the world. During the last 4500 years, its delta prograded more than 250 km to the south due to a tremendous amount of sediments deposited, and turned from a "tide-dominated" delta into a "wave-and-tide dominated" delta. This study aims at completing our knowledge on the fate of sediments that may be stored in estuarine or coastal systems, or dispersed over the continental shelf and slope. Sediment transport in the Mekong River Delta (MRD) coastal area was studied by numerical simulations using the Delft3D model. The model configuration was calibrated and validated from data collected in situ during 4 periods from 2012 to 2014. Then, 50 scenarios corresponding to different wave conditions (derived from the wave climate) and river discharge values typical of low flow and flood seasons enabled us to quantify the dispersal patterns of fluvial sediments close to the mouths and along the coast. Sediments mostly settled in the estuary and close to the mouths under calm conditions, and suspended sediment with higher concentrations extend further offshore with higher waves. Waves from the Southeast enhanced the concentration all along the MRD coastal zone. Waves from the South and Southwest induced coastal erosion, higher suspended sediment concentrations in front of the southern delta, and a net transport towards the Northeast of the delta. Because of episodes of Southern and Southwestern waves during the low flow season, the net alongshore suspended sediment transport is oriented Northeastward and decreases from the Southwestern part of the coastal zone (~960ˆ10 3 t yr´1) to the Northeastern part (~650ˆ10 3 t yr´1).

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“…Above storm‐wave base, wave processes are typically more influential such that the sedimentological and ichnological character of shallow‐water deltaic deposits is determined by waves (e.g. Walsh & Nittrouer, ; Xue et al ., ; Dashtgard, ; Tamura et al ., ; Unverricht et al ., ). Below storm‐wave base, the development of deep‐water asymmetrical deltas is not restricted by bathymetry; tidal current deposits have been documented as deep as 3000 m (Cowan et al ., ; Shanmugam, ; Shanmugam et al ., ), and contourites commonly accumulate in >1000 m of water where ocean currents transport and deposit sediments (Stow & Lovell, ; Faugères et al ., ).…”

Section: Discussionmentioning

confidence: 99%

Asymmetrical deltas below wave base: Insights from the Fraser River Delta, Canada

Ayrancı

Dashtgard

2015

Sedimentology

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The Fraser River Delta exhibits distinct asymmetry in the sedimentological and neoichnological characteristics of the updrift (south) and downdrift (north) sides of the main distributary channel in water depths below storm‐wave base. The asymmetry is the result of net northward tidal flow. Tides erode sediments across the updrift delta front, whereas the downdrift delta front is an area of net deposition. A submarine channel prevents sand eroded from the updrift delta front from reaching the downdrift delta. The updrift delta front and updrift upper prodelta are composed of sand or heterolithic sand and mud that show a low density of burrowing (Bioturbation Index 0 to 3) and are dominated by simple traces. The downdrift delta front and prodelta, and the updrift lower prodelta are composed of homogeneous muds with significantly higher bioturbation intensities (Bioturbation Index 3 to 6), and a more diverse suite of traces akin to Cruziana Ichnofacies. Using the Fraser River Delta as an archetype and comparing the Fraser to the Amazon River Delta, a preliminary model for deep‐water (below storm‐wave base: ca 20 m) asymmetrical deltas is proposed. Firstly, deep‐water asymmetrical deltas are recognized from sediments deposited below storm‐wave base. At these depths, tidal and ocean currents are more likely to impact sediment transport, but wave processes are less effective as a sediment transport mechanism. Sediments deposited below storm‐wave base in deep‐water asymmetrical deltas will display the following: (i) the updrift delta front will be coarser‐grained (for example, sand‐dominated or heterolithic sand and mud), than the downdrift delta front (for example, mud‐dominated); and (ii) the updrift delta front should show low‐diversity suites of simple burrows. Depending on sedimentation rates, the downdrift delta front and prodelta may show either high diversity suites of traces that are dominated by both complex and simple burrows (low sedimentation rates) or low density and diversity suites akin to the updrift delta front (high sedimentation rates).

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Modern sedimentation and morphology of the subaqueous Mekong Delta, Southern Vietnam

Cited by 65 publications

References 46 publications

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

Sediment dynamics in the lowerMekongRiver: Transition from tidal river to estuary

Numerical Simulations of Suspended Sediment Dynamics Due to Seasonal Forcing in the Mekong Coastal Area

Asymmetrical deltas below wave base: Insights from the Fraser River Delta, Canada

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