On Flocculation Of Cohesive Sediment And Its Ecology Effect In Estuaries

The flocculation and sedimentation processes of cohesive fine sediment particles, under the interactive actions of electro-chemical surface forces and gravitational force, can greatly influence the rheological behavior of hyper-concentrated sediment flow, the micro-structure of sediment deposits, and the incipient motion and scour of consolidated cohesive sediment lump. The flocculation and sedimentation mechanics and dynamics of cohesive sediment are essential and substantial to investigate the phenomena such as the siltation in channels, harbours and reservoirs, the evolutions of submarine delta and costal beach, the transportation of fluid mud, and the hyperconcentrated sediment flow, which are all important issues in the harness of rivers and lakes, the construction of hydro-projects, and the maintenance of harbours and channels. Together with theoretical analysis, laboratory and field experiments, as well as mathematical modeling, the flocculation-sedimentation processes of cohesive sediment particles and its ecology effect in estuary environment are investigated and explored, and four main issues are discussed in this paper.1. Based upon theories on DLVO and colloidal stability analysis deployed traditionally in colloidal subjects, the cohesion mechanism of fine particles is researched, and the estimation of the interaction between two fine particles is developed by limited-track method. The key parameter—collision effectiveness, is studied and calculated systematically, and the results fitted well with the engineering knowledge about the cohesive sediment.2. Series of experiments are carried out to study the influences of concentrations of the sediment and electrolyte, the valence of cation, on the flocculation. Micro-photographics are made to observe the morphological structures of the flocs. 3. Modified Smoluchowski equations that describe the kinetics of the particle aggregation incorporating gravitational settling down of flocs are proposed, and then they are numerically integrated using the second-order splitting operator method.4. Field experiments are carried out to collect the fluid silt and silt in the estuarine district of Haihe River. The group analysis and statistics of the meiofauna in the silt were made in the lab. Two main groups, named as nematodes and harpacticoida, are found out, which are both quite appropriate indicting genres. Then the relation between the flocculation and the ecology in estuary is further discussed.