Engineering Applications of Cohesive Sediment Dynamics
This chapter discusses the engineering applications of cohesive sediment dynamics. Problems related to cohesive sediments can be classified in three general categories of hydraulic engineering design of open channels safe against scouring and deposition. These categories are control of deposition in closed conduits is also a related problem, prediction and control of shoaling in navigable coastal and estuarine waterways for maintaining desirable navigable depths, and control of environmental pollution. It is in the second category where the erosional and depositional behavior of cohesive sediments is particularly applicable. The need for a rational control of shoaling in estuarial navigable waterways is one of the primary motivations for most of the recent fundamental and applied research work on the subject. In the discussion of the physicochemical aspects of cohesive soils, it becomes apparent that several factors may drastically affect the erosive resistance of a soil of a particular consistency. Chemical composition of the water, desiccation, compaction, and disturbances of various kinds are some of these factors. Changes of sediment distribution due to dredging and to various other solid waste disposals may have several unfavorable environmental impacts, of which two are the most obvious: excessive deposition on the feeding grounds and an increase in turbidity to a point prohibiting sufficient light for the development of plankton, one of the basic nutrients for marine life. Interaction of suspended cohesive sediments with organic matter and various dissolved chemicals from industrial and domestic sewers may become a major problem. The very same physicochemical forces acting on the surfaces of the fine particles are responsible for flocculation.