Research On The Transport Rate And Bed Form Of Sand-gravel Bimodal Sediment

Sediment motion laws have long been an important subject in the study of riverdynamics. The study of sediment motion starts from uniform sediment. However,uniform sand almost does not exist in natural rivers. So it’s necessary to introduce theresearch of laws of non-uniform sediment motion. Sand-gravel bimodal sediment, onetype of specific non-uniform sand, the motion characteristics of which are particular insome degree, compared to ordinary non-uniform sediment. But there existsfew studiesfocusing on motion characteristics of the sand-gravel bimodal sediment. So to exploremotion characteristics of sand-gravel bimodal sediment on the basis of non-uniformsediment is to enrich non-uniform sediment movement theory and to providetheoretical and technical support for the forecast of river evolution.Firstly，the research results at home and abroad of the sediment transportcharacteristic and form of sand wave were analyzed, and the existed studies on thesand-gravel bimodal sediment were summarized in this paper. For the sand-gravelbimodal sediment, gravel was easier to move compared with uniform sediment of thesame grain size, sand was more difficult to move compared with uniform sediment ofthe same grain size, which indicated the mutual hiding and exposure effect betweensand and gravel. Wang formula of uniform sediment, Guo Yakun’s formula of bimodalsediment transport rate and Sun Zhilin’s fractional bedload formula of non-uniformsediment used to calculate sediment transport rate of the sand-gravel bimodal sedimentwere analysed and compared in this paper. The method of using Wang’s formula(2007)grouped to calculate sediment transport rate of the sand-gravel bimodal sediment wasobtained by taking heterogeneity into consideration. Though error comparison, thecomputing method of using Wang’s formula (considering heterogeneity) was provedreasonable.54sets of flume experiments had been done to research the development process,formation mechanism and Sand wave scales of the bed form of sand-gravel bimodalsediment. Experimental results showed that whether there will be sand ripples duringthe development process of the bed form of sand-gravel bimodal sediment or notdepends on the particle size and proportion of the sand. During the experiment, therewasn’t any sand ripple when the sand (with a medium diameter of0.286mm)proportion is25%, and the sand bed transferred directly from smooth bed to sand ridges; while there were sand ripples when the sand proportion is50%and75%, andthe sand bed developed from smooth bed to sand ripples and finally to sand ridges, butthere existed difference among the sand ripples. Single factor method was used for theanalysis of the relationship between sand wave and composition of sand-gravelbimodal sediment and various parameters of flow conditions, and the expressions ofthe sand wave, wave length and the wave speed were finally reached.