Mechanics Of River Course Response To River Environment Change And Control Strategy--for The Ning-Mong Section Of The Yellow River

The place around Ningxia-inner Mongolia river bend of the Yellow River (Ning-Mong section in short) is a relative developed place within west China, where live ethnic minorities as the Hui, Manchu and Mongolian. Since the last 20 years, climate change and human activities there have affected the river environment in the results of the river serious shrinkage and frequent ice flood disasters, which bring great loss of people properties and big influence in society. Therefore, debates are caused from the local requirement for the development of water resources. One of the focuses is on which measure can be adopted in good use water resources and at same time in improving the river shrinking situation and even the whole flood control system of the Yellow River. However, since the research work has been down before long, the existing research results are unable to answer the above question due to lack of adequate knowledge on the laws of the riverbed scour and deposition. Apart from that, river of the Ning-Mong section is a medium scale sediment river and a coarse river as well. It should have different sediment transport characteristics from that of the downstream channelof the Yellow River or a river of small sediment concentration. Studying the interaction of river flow with sediment and river deformation process is meaningful not only to enrich river mechanics and riverbed evolution, but also to support theoretically a method research for water table forecasting of an alluvial river. Especially, it would be more important practical meaning if a soundly measure of the shrinkage control is proposed from the study.For the reasons above and considering strong riverbed deformation occurring in flood season, this thesis focused on studying the interaction process among flow, sediment and bed form happening in flood including ice flood period. The research work started at demarcating the river sediment fraction and sediment mobility instead of a tradition that starts at analyzing sediment delivery rate and sediment transportation equilibrium based riverbed scour-and-fill amount, and then found and brought the river environment causes of the shrinkage into order. Finally, the availability of proposed shrinkage control measures for the Ning-Mong section was discussed in detail. Meanwhile, in connection with the shortage existing in the sediment transportation equilibrium based quantification of an amount of scouring and deposition, a new method should be found by this thesis in order to show the river cross section deformation in quantification following flood process.The practical research results gained from this thesis are listed as follow.(1) Based on sediment mechanics and hypothesis test, the sediment fraction, mobility and motion style had been qualified.(2) Put forward the physical process mode of riverbed scour-and-fill during flood, which had been shown existed in nature by observations. This is helpful to know the nature of heavily burdened coarse river change.(3) Indicated the characteristics of sediment transport in ice flood and its formation mechanics.(4) Found out the environmental causes of the shrinkage and put them into order.(5) Proven the measure of manmade flood for the Ning-Mong section deposition control to be unavailable on five aspects which are the basic theory, the difference of sediment conditions from that in the downstream of the Yellow River, effect of medium and normal flood on bed form, the ship of manmade flood effect and sediment-scouring water volume.(6) From the laws of sediment motion and the characteristics of ice flood sediment transport, an idea about the river deposition control was brought out which is to deal with coarse and fine particles differently. Therefore a measure which is a new desilting gallery used with low temperature water flow was proposed to evacuate coarse in a river or in a cannel, or in a reservoir. Its prospect had also been showed with proposed application in the Xiaolangdi reservoir desilting as example.This thesis's key innovative points include:1) Throw a light on the "hump" phenomenon in the downstream of the Yellow River with the theory of momentum and taxis of an alluvial river motion to equilibrium.2) Propose a new method to calculate the change quantity of cross section area leading from scouring or deposition at any time in flood period, which can be traditionally gained by measuring the section after flood. Compare with the traditional method of sediment load balance, the new method would not be influenced by missing sediment load near bed and by uncertainty from lacking agreement between upstream and downstream hydrographs.3) Exploit the Wang's scouring rate formula to calculate sediment-scouring water volume. In this way, factors as flow, particle size and boundary ship can be considered.