Study On Regularity Of Riverbed Evolution In Fluctuating Backwater Area Of Xiujiang River, Guangxi Province

With the methods of statistic and calculation, theory analysis, logic reasoning, etc, this dissertation mostly studies on the problem of riverbed evolution in fluctuating backwater area, appearing in the resailing project of Xiujiang River. By concretely analysis of typical reach and shoal, it opens out the common regulation of riverbed evolution in fluctuating backwater area of medium and small hydropower plant building on alluvial river in mountainous area. Based on it, regulation principles of waterway are suggested. The main achievements are as follows:(1) Hydraulic characteristics in fluctuating backwater area. Mainly affected by operating level of the Plant, fluctuating backwater area appeared characteristics of reservoir region during low water period, and those of river channel during flood period in consequence of upstream incomings of water and sediment. In this area, water surface slope was influenced by upstream runoff and downstream reservoir operation. With the same operating water level, water surface slope increased with larger flow rate, and decreased with higher operating level on condition of the same flow rate.(2) Evolution characteristics of riverbed in fluctuating backwater area. Generally the flow released freely during flood period; as stage in reservoir region fell, water surface slope and sediment transport capacity increased, which would result in riverbed erosion. During post-freshet period, water level increased before the dam, and water surface slope decreased with higher operating-level with the same flow rate, thus siltation in fluctuating backwater area could be seen due to post-freshet period and high operating-level.(3 ) Regulation principles of waterway in fluctuating backwater area. According to the river regime, the slightly-sinuous unichannel should be rationally planned, and regulation combined with dredging, also the regulation projects should be designed to improve the silt-carrying capacity during median-low water period in fluctuating backwater area.