Sediment properties in the fluvial and estuarine environments of the Mekong River

Abstract

The Mekong river, located in Southeast Asia, is one of the largest rivers in the world. It is facing serious problems related to sediment transport, e.g. the reduction of sediment volume supply to the delta and estuary. This study focuses on the physical properties of suspended particles in the upstream fluvial section (Luang Prabang, Laos) and in the region of tidal influence (Song Hau estuary, Vietnam). These sites are respectively the upper and lower limits of the Lower Mekong River (LMR), which are experiencing contrasted transport modes. The main objective of this study is to quantify the proportion of inert sand and of cohesive particles in the water through comprehensive measurements of particle size, settling velocity and flocculation in the water column. Two field campaigns were undertaken in the summer monsoon season. The results point out the predominance of flocculi, with sizes of 18 ± 5 µm in the fluvial environment and 15 ± 5 µm in the estuary and the similarities in patterns, mixture of sand (12 ± 5 %) and mud (88 ± 5 %). They also provide a statistically representative set of suspended particle populations in the upstream and downstream regions that could be used for improving numerical models.

Modeling of Hydrodynamics and Sediment Transport in the Mekong Delta

“…The w was set to 5x10 -5 m/s and 3.5x10 -4 m/s for fresh and saline waters, respectively, with interpolated values for brackish environments. Recent measurements by Gratiot et al (2017) and Le et al (2018) have reasonable agreement with these settling velocities.…”

“…Specifically, the settling velocity and the critical shear stresses were estimated based on available measured data. The settling velocities in fresh water and saltwater are well measured and applied in numerical modeling (Le et al, 2018;Vinh et al, 2016). We calibrated to lower the sediment flux by increasing the critical shear stress and decreasing the erosion rate.…”

“…Roughness coefficients are not an efficient calibrated parameter for sediment model because they are evaluated in hydrodynamic calibration and this eliminates a free variable in sediment calibration (Gibson et al, 2017). The settling velocity was not considered as calibration parameter, because it is well measured and successfully used in other numerical studies (Gratiot et al, 2017;Le et al, 2018;Marchesiello et al, 2019;Tu et al, 2019;Vinh et al, 2016). The w was set to 5x10 -5 m/s and 3.5x10 -4 m/s for fresh and saline waters, respectively, with interpolated values for brackish environments.…”

A numerical investigation on the suspended sediment dynamics and sediment budget in the Mekong Delta

“…Specifically, the settling velocity and the critical shear stresses were estimated based on available measured data. The settling velocities in fresh water and saltwater are well measured and applied in numerical modeling (Le et al, 2018;Thanh et al, 2017;Vinh et al, 2016). We calibrated to lower the sediment flux by increasing the critical shear stress and decreasing the erosion rate.…”

Comparative Assessment of Fluvial Suspended Sediment Concentration Analysis Methods

“…[41] This is very useful, as determining the PSD is rather difficult and time-consuming otherwise. An example of the application of LISST-Portable|XR for determining PSD can be found in [42].…”