Effective energy controls on flocculation under various wave-current regimes

Abstract

Transport of sediments is a critical process in the coastal zone because of its relation with coastal erosion, productivity and pollution. Of particular interest are the dynamics of suspended cohesive sediments, known as flocs, which can aggregate and break-up during the flocculation process. This changes their size, density, settling velocity and overall transport. Even though turbulence is widely accepted to be an important control on floc aggregation and break-up, specific and detailed floc behaviour is still not fully understood. The present study seeks to help in the understanding of the intra-tidal turbulence-induced flocculation under different current-wave regimes. Observations of floc size and currents at high sample rates are used to investigate the changes throughout a fortnightly cycle. The occurrence of waves at different stages during the sampling period enabled determination of three regimes of currents dominant, combined waves and currents,

Investigation of flocculation dynamics under changing hydrodynamic forcing on an intertidal mudflat

“…Numerous articles have confirmed that LISST worked reasonably well over a range of environmental conditions (e.g. Mikkelsen and Pejrup, 2001;Guo and He, 2011;Safak et al, 2013;Ramírez -Mendoza et al, 2016). The work of Chen et al (2005b) on a mud tidal flat~30 km downstream from our study site with a camera showed that the largest floc size was 290 ± 170 μm, indicating that the major portion of flocs in this area can be detected by the LISST-100C.…”

“…time scales for aggregation and break-up are different (e.g. Verney et al, 2011;Ramírez -Mendoza et al, 2016). In the laboratory research of Verney et al (2011), they found that for a given shear rate, larger flocs were observed under increasing shear than those under decreasing shear, because the disruption of flocs was rapid once the shear force exceeded floc bond strength, while the aggregation process depended not only on moderate shear force, but also on collision efficiency and hence took longer time.…”

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

“…With longshore currents in the GBR of 0.1–0.3 m/s (Wolanski et al., 2008; Wolanski & Pickard, 2018) the shear rate 1 m above the bed will be on the order of 1 s −1 . This suggests that flocs can persist throughout the GBR lagoon; however, we note that non‐linear wind‐wave interactions on turbulence and therefore other flocculation processes must also be considered (Ramírez‐Mendoza et al., 2016).…”

A comparison study on the sediment flocculation process between a bare tidal flat and a clam aquaculture mudflat: The important role of sediment concentration and biological processes

“…Many studies have focused on the relationships between floc size, shear stress due to current, and shear rate (Ramírez-Mendoza et al, 2016;Schwarz et al, 2017;Wang et al, 2013).…”

“…The flocculation processes were also mediated through direct and indirect influences of the waves. Ramírez-Mendoza et al (2016) suggested that using the effective kinetic energy due to combined currents and waves can improve the prediction of flocculation when compared to estimates based on shear stress due to currents. In this study, the wave-current shear rate, GCW -m , was used to consider the effect of combined waves and currents.…”