A One-dimensional Model of Cohesive Sediment Transport in Open Channels

Book excerpt: Abstract: Fine-grained, cohesive sediments, widely existing in rivers, lakes, reservoirs, estuaries, etc., not only harmfully influence environment and ecosystems, but also cause problems to many types of structures, e.g., siltation in harbor entrance channels, docks and reservoirs. It has been recognized that when the fraction of fine-grained sediments is larger than about 10%, sediment mixtures consisting of cohesive and non-cohesive particles may exhibit cohesive properties, which gives a result that transport that transport processes of such mixtures are more complicated than those of coarse grained, non cohesive sediments. In an effort to understand and quantitatively predict the transport of sediment mixtures with cohesive and non-cohesive particles, a one-dimensional cohesive sediment transport model has been developed and integrated with the existing CCHE1D non-cohesive sediment transport model into a new sediment transport module, which calculates the concentrations of both cohesive and non-cohesive sediments using the same solver. Thereafter, the new sediment transport module has been incorporated with the hydrodynamic model into a newly enhanced CCHE1D model framework. A detailed mathematical description, numerical discretization, and solutions of the governing equations of the new sediment transport model are presented in this thesis. The cohesive sediment transport model simulates the deposition and erosion of cohesive sediments considering the effects of flocculation and consolidation. It relates the flocculation to the sediment size, sediment concentration, salinity, and turbulence intensity, and represents the consolidation of cohesive bed material through the temporal variation of dry bed density. The new sediment transport model takes into account the interactions between cohesive and non-cohesive sediments exceeds certain limits. The developed cohesive sediment transport model has been validated using two single-sized cohesive transport experiments conducted by Hayter (1983) and Dixit ((1982). The entire integrated sediment transport model has been tested by three real-world cases: the lower Fox River in Wisconsin, U.S., the Three Gorges Reservoir in China, and the Danjiangkou Reservoir in China. The model shows a good agreement between simulated results and measured data. After having been validated by a variety of laboratory and field cases, the new model can be applied to studies of real-world problems related to cohesive and non-cohesive sediments, with high efficiency and reliability.