Sand dynamics in the Mekong River channel and export to the coastal ocean

Stephens, J. Drew; Leonardo, D. R. Di; Weathers, H. Dallon; Ogston, A. S.; McLachlan, Robin; Xing, Fei; Meselhe, E. A.

doi:10.1016/j.csr.2017.08.004

Cited by 26 publications

(21 citation statements)

References 38 publications

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“…The estimated rates of suspended transport are in agreement with results from previous years 48 . Calculated bed load transport rates are similar to reported rates for the Hau River branch 39 . Bed load transport rates were indirectly calculated based on dune fields DF01 and DF02 , which were located downstream from most of the investigated sand mining sites.…”

Section: Discussionsupporting

confidence: 74%

“…According to ref. 39, the annual suspended sand fluxes within the Tien River are of the order of 3.8 Mt/yr, representing around 44% of the observed sand extraction. Only a fraction of this suspended load effectively contributes to the refilling process, depending on the local sediment and flow characteristics as well as the geometry of dredging pits.…”

Section: Discussionmentioning

confidence: 99%

“…Estimates for the total yearly sediment discharge to the South China Sea vary from 40 to 160 Mt/yr 36–38 . Sand, transported as suspended load, contributes 6.5 1.6 Mt/yr to the total sediment transport 39 . Available data of bed load transport rates at Kratie and for the Hau River branch indicate that sand, transported as bed load, accounts for around 1 to 3% of the local sediment transport 39,40 .…”

Section: Hydro- Morpho- and Sedimentological Regime Of The Mekong Rimentioning

confidence: 99%

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Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

Jordan

Tiede

Lojek

et al. 2019

Sci Rep

117

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The delta of the Mekong River in Vietnam has been heavily impacted by anthropogenic stresses in recent years, such as upstream dam construction and sand mining within the main and distributary channels, leading to riverbank and coastal erosion. Intensive bathymetric surveys, conducted within the Tien River branch during the dry and wet season 2018, reveal a high magnitude of sand mining activities. For the year 2018, an analysis of bathymetric maps and the local refilling processes leads to an estimated sand extraction volume of 4.64 0.31 Mm/yr in the study area, which covered around 20 km. Reported statistics of sand mining for all of the Mekong’s channels within the delta, which have a cumulative length of several hundred kilometres, are 17.77 Mm/yr for this period. Results from this study highlight that these statistics are likely too conservative. It is also shown that natural sediment supplies from upper reaches of the Mekong are insufficient to compensate for the loss of extracted bed aggregates, illustrating the non-sustainable nature of the local sand mining practices.

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Section: Discussionsupporting

confidence: 74%

Section: Discussionmentioning

confidence: 99%

Section: Hydro- Morpho- and Sedimentological Regime Of The Mekong Rimentioning

confidence: 99%

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Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

Jordan

Tiede

Lojek

et al. 2019

Sci Rep

117

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“…Because the formation of alternating bars will affect flow and sediment division at the junction, the channel depth and upstream-prescribed river discharge were chosen such that the system was in the overdamped bar regime (Struiksma et al, 1985). To this end, we conservatively followed the empirical classification proposed by Kleinhans and van den Berg (2011).…”

Section: Model Set-upmentioning

confidence: 99%

Morphological evolution of bifurcations in tide-influenced deltas

2020

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Abstract. In river-dominated deltas, bifurcations often develop an asymmetrical morphology; i.e. one of the downstream channels silts up, while the other becomes the dominant one. In tide-influenced systems, bifurcations are thought to be less asymmetric and both downstream channels of the bifurcation remain open. The main aim of this study is to understand how tides influence the morphological development of bifurcations. By using a depth-averaged (2DH, two-dimensional horizontal) morphodynamic model (Delft3D), we simulated the morphological development of tide-influenced bifurcations on millennial timescales. The schematized bifurcation consists of an upstream channel forced by river discharge and two downstream channels forced by tides. Two different cases were examined. In the first case, the downstream channels started with unequal depth or length but had equal tidal forcing, while in the second case the morphology was initially symmetric but the downstream channels were forced with unequal tides. Furthermore, we studied the sensitivity of results to the relative role of river flow and tides. We find that with increasing influence of tides over river, the morphology of the downstream channels becomes less asymmetric. Increasing tidal influence can be achieved by either reduced river flow with respect to the tidal flow or by asymmetrical tidal forcing of the downstream channels. The main reason for this behaviour is that tidal flows tend to be less unequal than river flows when geometry is asymmetric. For increasing tidal influence, this causes less asymmetric sediment mobility and therefore transport in both downstream channels. Furthermore, our results show that bedload tends to divide less asymmetrically compared to suspended load and confirm the stabilizing effect of lateral bed slopes on morphological evolution as was also found in previous studies. We show that the more tide-dominated systems tend to have a larger ratio of bedload-to-suspended-load transport due to periodic low sediment mobility conditions during a transition between ebb and flood. Our results explain why distributary channel networks on deltas with strong tidal influence are more stable than river-dominated ones.

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“…For example, the main dams in the Lancang River occupy sediment trapping efficiencies between 30% and 70% because of the high sediment yield in the Lancang-Mekong River's mainstream and sub-basins [20]. Some estimate the sediment flux of the Mekong, the pre-dam sediment flux into the South China Sea, has been estimated from 40 to 160 Mt/year [21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Assessment of Hydrology and Sediment Yield in the Mekong River Basin Using SWAT Model

Sok

Oeurng

Ich

et al. 2020

Water

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The Mekong River Basin (MRB) in Southeast Asia is among the world’s ten largest rivers, both in terms of its discharge and sediment load. The spatial and temporal resolution to accurately determine the sediment load/yield from tributaries and sub-basin that enters the Mekong mainstream still lacks from the large-scale model. In this study, the SWAT model was applied to the MRB to assess long-term basin hydrology and to quantify the sediment load and spatial sediment yield in the MRB. The model was calibrated and validated (1985–2016) at a monthly time step. The overall proportions of streamflow in the Mekong River were 34% from surface runoff, 21% from lateral flow, 45% from groundwater contribution. The average annual sediments yield presented 1295 t/km2/year in the upper part of the basin, 218 t/km2/year in the middle, 78 t/km2/year in the intensive agricultural area and 138 t/km2/year in the highland area in the lower part. The annual average sediment yield for the Mekong River was 310 t/km2/year from upper 80% of the total MRB before entering the delta. The derived sediment yield and a spatial soil erosion map can explicitly illustrate the identification and prioritization of the critical soil erosion-prone areas of the MR sub-basins.

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Sand dynamics in the Mekong River channel and export to the coastal ocean

Cited by 26 publications

References 38 publications

Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

Sand mining in the Mekong Delta revisited - current scales of local sediment deficits

Morphological evolution of bifurcations in tide-influenced deltas

Assessment of Hydrology and Sediment Yield in the Mekong River Basin Using SWAT Model

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