| Dams are the masterpiece that man develop the water resource and conquer the nature. It advance and ensure the development of human civilizations. The impact of dams on river and society has dualism. On the one hand, the built of dams advance the exertion of river serving function and improve the environment. On the other hand, it produces negative effect. Once the effects exceed the endurance of river system, it not only block exertion of serving function, but also lead maladjustment or degradation of river ecosystem and destroy river health. Deteriorative environment has become the main obstacle of society development in some district. Dams affect the river by alter the nature flow &sediment regime essentially. It lead the variation of flow & sediment transportation and alteration of rive boundary, which is the complex process of different time and space scales and has various expression form. It not only induce the different response of riverine ecosystem, but also has various affect on all kinds of serving function. These results of adjustment directly decide the condition of river health. Thus, it is necessary and significant to carry out the research on the regulation dynamic of dam downstream river system to maintain and restore river system health, or to achieve the sustainable development in watershed scale.For a long time, geomorphologists and ecologist have done comprehensive and intensive researches in correlative field. However,the recognition for the change of flow & sediment transportation and the corresponding adjustment of channel form is still insufficient. The research on the relationship between fluvial process and riverine ecosystem is few. The necessary intersection and amalgamation of different disciplines is scarce. All of them constraint understand of adjustment mechanism and trend prediction of downstream river system and the establishment of regulation and control system of flow &sediment.In this paper, taking the downstream flow & sediment variation as the claw, the researcher tries to reveal the change of flow & sediment transportation and the corresponding adjustment of channel form, find the linkage between fluvial process and riverine ecosystem adjustment. The research feature is that the essence of dams impact on the river system and the dynamic relationship between flow & sediment process, channel form and ecosystem is considered, which is the fundamental works for prediction of the downstream river system adjustment, maintain the system health and the establishment of regulation and control system of flow &sediment. Main work included: the adjustment law of some factors is analyzed, including the changes of flow &sediment regime due to dam alternation and feature of downstream sediment transportation, channel morphology change, such as lateral adjustment process, change of continent and shoal, flood feature. Base of it, the relationship between ecosystem and factors mentioned above is discussed and the frame for downstream riverine ecosystem model is presented. It is the preliminary try for the amalgamation of riverine ecology and river dynamics.The key issues discussed in this paper are shown as follows:(1) The origination, background and significance of the topics are described. It is clearly show that a series of variation downstream dam come down to the alteration of flow & sediment. It is necessary to regulate flow & sediment regime to maintain and restore river system health, or to utilize the serving function of river system. It is important fundament of achieving flow & sediment regulation that deeply to research the change of flow & sediment transportation and the corresponding adjustment of channel form, finding the linkage between fluvial process and riverine ecosystem adjustment. Summarize the previous research and draw out the main research contents(2) Summarize the general feature of flow & sediment below of dams. In view of the absent knowledge of sediment transportation character downstream dams, through analyzing the change character of the flow energy and sediment before and after dam establishment, it is show that the downstream sediment transport capacity decreases obviously. Base of it, combined with the field data of several worldwide reservoirs, it is conclude that for any grain size, post-dam sediment transport rates cannot exceed its pre-dam level at any location along the downstream alluvial channel. (3) Through analyzing the factors leading to the channel lateral adjustment, it is show that the flow energy and bank material is the decisive factors. After the dam built, the change of different factors makes the channel adjustment toward to the stable state. According to the change of channel width and migration rate, although the width is narrowed and the migration rate is decreased finally because flow energy reduce and the capability of river bank to resist erosion increase, during the adjustment, the direction of change is not single and often fluctuate, which depend on the comparison between flow acting force and bank resistance or the ratio of bank and bed resistance. Based on the feature of the flow & sediment regime and channel boundary downstream TGP, the probable lateral adjustment is outlined. For the Upper reach of Jingjiang River, because the flow energy increase and riverbed become coarse quickly, it will threaten bank stabilization of some weak point. For the down reach of Jingjiang River, because the flow energy increases a few and the capability of river bank to resist erosion is weak, the width of local channel will be wider. The bar-braided reach downstream Chenglingji is unlikely to experience any notable change for the unaltered flow &sediment regime. (4) Based on the field data, summarize the character of the local channel morphology response to the variation of flow & sediment. Taking Shashi reach in the middle Yangtze River as example, the characteristics of the shoal fluvial process before and after dam are analyzed. Then, based on the change character of flow and sediment, a plane 2-D flow and sediment mathematical model is used to predict the dynamic variation process of continent and shoal after Three Gorges Reservoir impoundment. The results show that the mathematical model can simulate the characteristics of flow and sediment transport and the rule of continent and shoal fluvial process well. The prediction result is in good agreement with field data. It has reference to the research on other braided and shoal reach after Three Gorges Reservoir impoundment.(5) Summarize the change character of flood magnitude, timing and duration downstream dam. Taking the reach from Luoshan to Hankou in the middle Yangtze River as the example, the change flood process owing to the alteration of channel bed degradation or aggradations before and after dam is analyzed. It shows that flood frequency is increase due to sediment deposition. During 20 years of TGP regulation, the flood level changes little with the small deposition amount in the reach.(6) Analyze the relationship between riverine ecosystem and key factors mentioned above. The scope and intensity of dam impact are discussed. Based on its, according to the dynamic relationship between fluvial process and ecosystem, the frame of riverine ecosystem model downstream dam is presented. Based on the relationship between geomorphology and ecosystem, the riverine ecosystem is divided into different hierarchy. The methods for different hierarchy and the integration of model are discussed.
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