The Study Of Physicochemical Process Of Sediment Movement In River

River sediment erosion from the upper reaches, riverway sediment transportation, and estuary sediment deposition; are all closely related to river physicochemical process. With further research on sediment movement, it is necessary to settle the sediment problems in environment based upon the study of the river chemical condition. Especially with the degradation of water quality, the variation of hydrochemistry changes the basic modes of sediment movement, which influences the sediment transportation in the whole catchments. So, both from the points view of sediment researches development, and of the sediment problems in changed environment, it is significant to do further research on the relation between sediment movement and river physicochemical processIn this thesis, the physical chemistry problem in the sediment research is summarized. Based on the basic theory of sediment science and physical chemistry, this thesis presents the physicochemical process of sediment movement and the main content of the process, which includes three points. One is the catchments soil erosion, sediment yield and ion transport. Second is the physical chemistry effect in sediment transport process. The last is the thermodynamic process in sediment transport. The first two contents are mainly discussed in this thesis. Firstly, from the angle of chemical erosion process, the relation between catchments flow & sediment variation and ion transport is studied. Then, the mechanism of microphysical chemistry effect on sediment particle surface is analyzed according to the microstructure characteristic on sediment particle surface. Finally, the micro mechanism is used to reveal some special phenomena and rule in the sedimentation and movement process of cohesive sediments.The principal contents about the research include the following:According to the study of physical chemistry action and chemical reaction process of the sediment erosion process, it is concluded that there exists the accompanying characteristic between the sediment erosion and ion erosion. Then, the environment condition and catchments characteristics, which influence the sediment erosion and ion erosion, are discussed. And the erosion process under different geologic conditions and environment is analyzed. The results show that it is the discrepancy of the erosion process that leads to different chemical components of flow & sediment between different catchments. According to the comparison of sediment elements and chemical components in the major rivers of China, we analyze the ion components, concentration variation, and so on.Based on the data from Water Year Book about the main river of Yangtze river and Jia Ling river, the relationship of sediment transport and ion transport is studied. The results show that there exists positive correlation between the sediment transport and ion transport, and the equation is established between them. The correlativity of ion transport and sediment transport is varied if the ion category changes. In the Yangtze river the ions of Ca²+ and HCO₃^- are most important ions in relation to sediment transportation. If the conditions change, the correlativity between ions and sediment will change too. As far as the reservoir constructing and the branch affluxing areconcerned, the correlativity between ion and sediment transportation in the downstream will get lower.The thesis proposes that the physical chemistry action of the sediment transport process is the macroscopical embodiment of microphysical chemistry effect on sediment particle surface. According to the microscopic morphology action of sediment particle, this thesis studies the physical chemistry action of sediment particle surface, and concludes that sediment surface has the electrochemical property and water film property. Finally, based on the results of colloid theory and sediment science, a surface joint model is established. This thesis also studies the effect of water condition variation on particle surface joint structure and microscopic morphology action. At the same time it analyzes the micro-force on the particle surface joint.Based on the experiments of sediment settling in water, the relationship between the settling velocity in flocculation and cations concentration is revealed. And the results indicate that: when the concentration of positively charged ion increases, the settling velocity will obviously increase, and there exists a critical cation concentration in course of increase. If the concentrations of positively charged ions exceed the critical value, the settling velocity will not change or change little as the concentration increases. The processes of influence on the settling velocity in different sediment concentration are the same, but the extent is different. Namely, when the concentration of different positively charged ions is the same, the ion with more electric charge has more effect on sediment settlement.Comparing the ion concentration in the natural rivers (Yangtze River> Yellow River) with that in the laboratory, it is concluded that in natural rivers ,to calculate the sediment settling velocity, it is necessary to consider the influence of the concentration of positively charged ions. The most important ions are positively charged ions with double electrovalence, and the representative ions which affect the settling velocity in different rivers are confirmed. Besides these, the experiments of sediment settling under different sediment concentration and ion concentration are done, and the results indicate that when the sediment concentration increases, the settling velocity will increase to the maximum, and then begin to reduce. And under different ion concentration, the changing courses of sediment concentration vary a lot.Based upon the analysis of the difference between colloid congregation and sediment flocculation, the thesis points out that the study about sediment flocculation can't directly cite the theories and results of colloid science. Using surface transitional layer model, the author investigates the variation of surface action when particles collide and separate, and it indicates that collision between cohesive particles isn't flexible and the process includes cohesive action. By applying this particular collision process, we can put up detailed explanation about cations influence on sediment flocculation process. Moreover, according to the settlement process of floes, taking Ca2+ as an example, the flocculation settlement equation about cohesive sediment, which includes ion parameters, is established.The movement law of the cohesive sediment in weak dynamical conditions is studied by using dynamic flumes, and it is concluded that there will be a particularmode of sediment movement in weak dynamical condition—layered movement. The appearance of layered movement is closely interrelated with conditions of flow, sediment and ions. We consider the respective influence of different magnitude of flow, different sediment concentration and different ion condition on the layered movement, and point out that the layered movement needs determinate range of flow condition in given sediment concentration, thus we concluded that the layered movement will form in a certain range of sediment concentration, but it will disappear out of the range (more than or less than certain values). The range of the layered movement changes along with the sediment concentration. When sediment concentration increases, the intensity of the flow which forms the layered movement also increases. The formation of the layered movement is also effected by the cations in water column. And the increase of the cations concentration will facilitate the formation of the layered movement as the flow and sediment concentration are the same.