Effect of hydrodynamics factors on sediment flocculation processes in estuaries

Abstract

Purpose Cohesive sediment is able to flocculate and create flocs, which are larger than individual particles and less dense. The phenomenon of flocculation has an important role in sediment transport processes such as settling, deposition and erosion. In this study, laboratory experiments were performed to investigate the effect of key hydrodynamic parameters such as suspended sediment concentration and salinity on floc size and settling velocity. Results were compared with previous laboratory and field studies at different estuaries. Materials and methods Experimental tests were conducted in a 1-L glass beaker of 11-cm diameter using suspended sediment samples from the Severn Estuary. A particle image velocimetry system and image processing routine were used to measure the floc size distribution and settling velocity. Results and discussion The settling velocity was found to range from 0.2 to 1.2 mm s −1. Settling velocity changed in the case of increasing suspended sediment concentration and was controlled by the salinity. The faster settling velocity occurred when sediment concentration is higher or the salinity is lower than 2.5. On the other hand, at salinities higher than 20, in addition to increasing SSC, it was found that the situation was reversed, i.e. the lower the sediment concentration, the faster the settling velocity. Conclusions Sediment flocculation is enhanced with increasing sediment concentration but not with increasing salinity.

Flocculation of Riverine Sediment Draining to the Great Barrier Reef, Implications for Monitoring and Modeling of Sediment Dispersal Across Continental Shelves

“…We stress that the application of a nominal floc fractal dimension is only to demonstrate the importance of considering floc parameters in the estimation of particle size distributions by mass. In practice, floc fractal dimension may vary within a sample, across catchments, and with time (Fall et al., 2021; Guo et al., 2021; Manning & Dyer, 2007; Mhashhash et al., 2018; Mikkelsenand Perjup, 2001; Sahin et al., 2017). The primary particle size for each river was computed as the median of median particle size by volume ( D 50v ) from laboratory samples.…”

Sediment–water interface and water toxicity tests with mysids (Crustacea, Mysidacea) to assess the quality of tropical estuaries.

“…Although P3 is close to the channel that drains untreated sewage, no toxicity was observed in water samples from this site, probably due to its proximity to the ocean and the high hydrodynamic flow that may promote pollutant dispersion. In contrast, the SWI test with sediment collected in a rainy month showed toxicity at all collection sites, suggesting that the pollutants released into the water may have settled out into the sediment due to contact between the freshwater and seawater flow (Mhashhash et al 2018). There are several studies on the of precipitation on pollutant sedimentation and toxicity (Biati et al 2010, Casadio et al 2010, Hassani et al 2017, Li et al 2010.…”

The Role of Mangroves in Coastal and Estuarine Sedimentary Accretion in Southeast Asia

“…However, salinity has an inverse relationship with settling velocity of the suspended particles. Laboratory analysis by Mhashhash et al [31] reveals that settling velocity becomes faster with the increase in sediment concentration and decrease in salinity (Figure 2).…”