Study On Gravel Transportation Of Non-uniform Flow In The Tail Of Reservoir

According to the research on Three Gorges fluctuating backwater area and the collected measured data, the end of the backwater area of river bed is mainly consist of gravel and sand, and hinders features for navigation is mainly caused by gravel movement quality during the drawdown period. The Three Gorges reservoir tail area is encountered with hinders navigation problems caused by gravel beach regenerating process, which caused a great impact on the tail section of the library navigation, while one of the objectives of the construction of the Three Gorges Project is navigation, so it is necessary to research the gravel transport characteristics in the reservoir Tail flow status.The research background is based on “Sediment Transport researches on end section of the Three Gorges Reservoir” which is in the "Waterway Management of the end section of the Three Gorges Reservoir fluctuating backwater area(2012BAB05B03)" and it is included in the national “the twelfth five” scientific and technological support projects. The lab flume experiment provides long-term theoretical basis to solve hinders navigation problem in Three Gorges reservoir caused by gravel transportation.In the process of researching non-uniform flow gravel transport characteristics, with the basis of previous research methods, two new attempts were made. Firstly, on the sediment transport rate measurement technology, the shortage of the impact of the previous measurement instruments on water flow has been changed; instead, the image recognition method for measuring sediment transport rate was used. Secondly, based on the pervious drainage experiment that only sediment transport rate in the tail area was measured, and then we selected a few sections to measure sediment transport rate under the same flow conditions. The characteristics of gravel transportation in non-uniform flow area were preliminary derived.Based on flume experiments of gravel transport in non-uniform flow, the following conclusions were reached:First, the method based on image recognition to measure the sediment transport rate along the section has the advantages of no interference to flow, more convenient data collection, simple and real-time, etc., and compared with the previous sand transport rate method, the measurement results are closer to the actual state of motion.Second, according to observations obtained during the flume experiments, for the sediment transport in non-uniform tail area, the non-uniformity of flow is growing along with increasing depth, which leading to the entire amount of sediment transport along the waterway getting smaller and smaller. When the flow is lower than 0.026, Thus began deposition forming gravel pile.Third, Due to siltation gradually increase over time, the tailgate backwater range extends towards upstream, which changes flow conditions, along the flow non-uniformity is gradually increased, the speed of gravel siltation to downstream become more and more slowly.Then, compare flume experiments data with existing bedload formula and according to the of existing formula in the form of a typical transport rate, combined with the results of the flume experiments, we derived the interpolated the sediment transport rate formula containing non-uniformity coefficienta(0H=Ha,H is the depth of the non-uniform flow,0H is normal depth) for gravel transportation under non-uniform flow pattern.