Geoscience Reference
In-Depth Information
Cohesive sediment transport
modeling
Fine-grained sediments, such as clay and fine silt, widely exist in rivers, lakes,
reservoirs, estuaries, and coastal waters. They generally exhibit cohesive properties
and undergo a number of complex mechanical, physicochemical, and biochemical pro-
cesses. Fundamentals and methodologies for simulation of cohesive sediment transport
and the associated morphodynamic processes are presented in this chapter.
11.1 COHESIVE SEDIMENT TRANSPORT PROCESSES
11.1.1 General transport patterns
Fig. 11.1 shows the general transport pattern of cohesive sediments in estuaries and
coastal waters. Similar patterns can be found in rivers, reservoirs, and lakes, except
for the effects of salinity and tide. Because of the action of electrostatical forces that
are comparable to or larger than the gravity forces, fine sediment particles may stick
together and form flocs or aggregates when they collide, as shown in Fig. 11.2. This
process is called “flocculation.” The flocs may be transported by convection (due
to river flows, currents, and waves), turbulent diffusion, and gravitational settling.
They may move in suspended load or bed load, depending on their sizes; however,
suspension is usually presumed to be the main transport mode. Variations in flow
conditions may cause sediment erosion and deposition, whereas the settled cohesive
deposits may consolidate, due to gravity and the overlying water pressure.
Figure 11.1
Cohesive sediment transport in estuary.
