Study On Deposition Sediment Of Three Gorges Reservoir In Initial Stage

Three Gorges Project is the key projects that comprehensively develops the Yangtze River and reservoir management. The project has a huge economic benefits such as flood control, power generation and shipping. After the impoundment, the water level of the reservoir has raise, the velocity reduces, and the flow characteristics of the reservoir aera has changed. It has a great impact on the sediment deposition and erosion, channel morphology, and flow velocity of the reservoir area. So learning about the laws of reservoir sediment transport is directly related to the management, development, protection of the Three Gorges project.Based on the analysis of the observational data about the Three Gorges Reservoir after impoundment, established the mathematical models to used to research the morphology, conditions and the law of sediment deposition in the reservoir area.Through analyzing the change of runoff and sediment process, scouring-deposition in quantity and the process of deposit distribution which before and after the three gorges project in typical hydrological station. we known that the basin runoff change rarely in recent years, and sediment discharge reduced obviously, the particle size is diminution. Before the impoundment, scouring and deposition is balanced basically in reach. After the impoundment, it is deposition.Secondly, take the series of the 135-139m water storage operation phases of the Three Gorges Project(TGP)as an example. According to the different water depth as well as different forms of scouring or deposition, the river channel of the reservoir is divided into three sections: deep-water section, shallow section and the backwater areas. Deposition form in deep-water section is horizontal deposition in the groove of river; in shallow section, the silting is related with the riverway morphology; the backwater areas is alternately deposition and scouring. Besides, this thesis also summaries the rules of river bed change that sediment deposition in all sections. As to deep-section of the reservoir, the maximum critical flow velocity is 1.2m/s, if the value is smaller than that, deposition will happen. As to the shallow section of the reservoir, When the critical velocity is greater then 2.1m/s, deposition will not occur; When the value is smaller then 1.2m/s, the section is deposition;When the velocity in between 1.2m/s and 2.1m/s, if there are continuous river bend or branching channels, siltation will be occurs, otherwise it doesn't happened. As for the backwater areas, because of there is not alternately deposition, we can only judged that when the average velocity is greater then 2.1m/s, the deposition does not occur.Finally, according to deposition of the shallow section in reservoir. Established the three dimension mathematical model for continuous river bend. Combined with fixed measuremented section analysis: the circulation flow will make the small particles sediment from mainstream,and with circulation flow move. because of the mainstream will be "go straight" in continuous curve reach, when the quantity of flow. So the sediment will carry over to small velocity areas, it located in convex bank of downstream in the continuous river bend reach and sink down.