Sediment flocculation in the Mekong River estuary, Vietnam, an important driver of geomorphological changes

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

“…In the estuarine environment, the mixing between freshwater from land and salt water from the ocean generates a complex situation, with the formation of vertical stratifications in the water column. This was clearly observed during our field survey in October 2016 (graph not shown), and was also reported by [12] from field surveys conducted in December 2015 and March 2016 ( Fig. 2 of their paper).…”

“…The PSD measurement shows the median size of sediment particles in the fluvial section is 13 -23 µm. In their recent study, [12] were in agreement with the PSD results measured by [6,7]. The dominant particle population in the estuary was flocculi, accounting for 80 -100 % of the total volume with a median size of 10 -15 µm.…”

“…Each sample was measured in two steps, before and after two minutes of sonication. Hence, it is possible to evaluate the proportion of sand and flocs because large-size particles built by smaller cohesive particles (silt or clay) are dispersed by sonication [12].…”

“…The SCAF instrument (System for the Characterization of Aggregates and Flocs), was used to measure the settling velocity of particles [12,13]. It is an optical settling column, equipped with a vertical array of sixteen optical sensors, each separated by one cm.…”

“…Measurements taken in the eight upper centimetres provided an estimate of flocs' settling velocity under quiescent conditions ws,q. Measurements made in the eight centimetres near the bottom of the settling tube provided an estimation of settling velocity after flocculation under settling dominated conditions, the latter velocity being ws,≠ [12].…”