Experiments On Flow Characteristics And Deposition Behavior Of Suspended Load Under Backwater

Backwater flow is the basic form of water movement in reservoir-area rivers. With the increaseof the flow depth along reservoir-area rivers, the backwater level increases and the sediment carryingcapacity of the flow decreases, resulting reservoir sedimentation. The flow in backwater conditionbelongs to non-uniform flow and the sediment transport belongs to non-equilibrium sedimenttransport. Currently scholars have made a progress in understanding the flow characteristics ofnon-uniform flow. However when it goes to the suspended sediment deposition, relevant researcheson mechanism is relatively little, compared with the observed data analysis and the calculation ofmathematical model et. al. In this paper, flume experimental studies are conducted to observe thewater and sediment movement under backwater condition, which could broad the research areas ofnon-uniform flow and non-equilibrium sediment transport, enrich non-equilibrium sedimenttransport theory, and provide theoretical and technical support to the improvement of the eiffciencyof the reservoir utilization and sedimentation reduction.Firstly, take the three gorges reservoir as an example, river flow characters along thereservoir-area river are analyzed. The longitudinal velocity along the depth is in accord with thelogarithmic distribution law, and influenced by the downstream terrain; vertical distribution of flowturbulence intensity is different from that in uniform flow，and the difference is larger in the verticalturbulent intensity distribution. It has been found out that the traiffc increases, while the totalsediment concentration and grouping sediment concentration decrease along the main stream of thereservoir-area river. The larger the particle size is，the greater the percentage of silt will be; the closerto the dam, the greater siltation intensity would be; sedimentation problem becomes serious after theflood season.Analysis of the flow characteristics under different backwater flow conditions on a smooth bedis carried out made through flume experiments. This paper explores the law of flow characteristicsand the degree of roughness variation with backwater under three condition, including the same flowrate, bottom slope different water depths condition, the same flow rate, depth different bottom slopecondition, and the same water depth, bottom slope different traiffc condition. The longitudinalvelocity of non uniform flow along the depth exists partition structure. The inner area abide by alogarithmic distribution and the outside area deviate to the logarithmic law; vertical velocitydistribution along the depth is a convex distribution; roughness coefifcient increases with the degreeof a backwater increasing; bottom slope has little effect on the flow characteristics; a friction velocityformula under backwater flow is given in this paper.A suspended sediment deposition flume experiments under backwater condition is carried out. Calibration is made to measure the sediment concentration using adv. It could be inferred that thevertical distribution of sediment concentration under backwater condition meet (I) type distribution(a inflection point preset near bed); suspended targets decrease as backwater degree coefficientincreases; the dimensionless suspended-stop shear parameter of suspended load is not constant, and itvaries with the particle size; the relationship of dimensionless particle size parameter and flowstrength parameter is obtained by iftting the experiment data.