Effect of flow and electrolyte on the flocculation-settling of cohesive sediment

To explore the effect of flow and water salinity on the flocculation-settling of cohesive sediment in estuary and coastal region, we took sediment concentration and floc diameter as parameters, and used a self-made rotary cylinder and electrolyte added method to examine the flocculation-settling process under six flow intensities (0 s^-1, 1.38 s^-1, 2.54 s^-1, 4.67 s^-1, 7.19 s^-1, 13.2 s^-1, 20.3 s^-1) and three electrolytes (NaCl, CaCl₂, AlCl₃). The results showed that: ① The effect of flow on flocculation-settling of cohesive sediment is related to flow intensity. Low intensity flow improves the flocculation-settling at early stage and hinders it at the other stages, while high intensity flow always retards it because of the strong shear stress and turbulent mixing. ② The existence of electrolyte has a net expansionary effect on the action of low intensity flow and a contractile effect for high intensity flow. In the same concentration, when the cation valence of electrolyte becomes from +1 to +3, the influence of flow becomes greater, especially at stabilization period.