Study On Movement Characteristics For Bimodal Sediment

Laws of sediment movement has been an important topic in the study of riverdynamics. Nonuniform sediment is widespread in the natural river. As a specific type ofsediment,the bimodal sediment has its own motion characteristics of motion. At presentresearch on this topic is little. The research on the motion characteristics of bimodalsediment can expand the scope of the study of sediment, enrich and strengthen its theory,and provide a theoretical and technological support for further research on the trend ofriver-bed evolution.This paper reviews the recent progress in research on nonuniform sediment,andsummaries the agent of bimodal sediment incipient motion.Existed experimental datashow that: for the bimodal sediment, large grain was much easier to start than the samesize uniform sediment, the small sand was much harder to start. The hidden and exposedeffect among the sediment particles were cognized gradually. Based on the twodimension relative hidden degree of Han Qiwei, this paper put forward threedimensiona relative hidden degree, and provided the formula of nonuniform sedimentrelative hidden degree on the statistical sense. what is more, the study of nonuniformsediment incipient motion was based on a rolling model, and the shear stress formulawas also constructed. Theoretically the bimodal sediment incipient motion was analyzed.Meanwhile，based on the relative flume experiment abroad the formula of Reference BedShear Stress was established.This paper conducted research on the developing process of the bed morphologyand its mechanisation through the flume experiment, the flume was arranged64runs ofexperiments, and the characteristics of motion of bimodal sediment wave wasresearched. The results of the flume experiment shows that： the sand wave did notemerge the ripple when the median size of sediment was more than1mm. Based on theSingle-Factor Method, the relationship between bimodal sediment sand wave and thebed material， flow conditions was researched.Meanwhile，the formula of wave height，wave length and wave velocity was established.