Study On Characteristics Of Density Current In Xiaolangdi Reservoir

The discharging sediment with density current is an only measure to reduce reservoir region' s deposition in the reservoir with storage operation on the overloaded river and an important mode to discharge sediment for deposition reduction as well. To reduce deposition in the Lower Yellow River is one of main development tasks in Xiaolangdi Reservoir. Its effect of deposition reduction is mainly depended by trapping sediment and regulating water-sediment operation with reservoir. In the early stage of water storage of Xiaolangdi Reservoir, it can basically retain all of sediment out of Sanmenxia Reservoir, its mode of discharging sediment is mainly depended by discharging sediment with density flow. For reservoirs on different rivers, the water-sediment condition, bed condition, reservoir operation mode and discharge construction are different, the producing, movement and discharging sediment characteristics of density current are also different. To study common law of producing, transporting and discharging sediment of density flow in Xiaolangdi reservoir is convenient to using density current better for serving the production and providing scientific basis for regulating water-sediment in Xiaolangdi Reservoir. Simultaneously it has an important reference value for storage operation of reservoir on the overloaded river and provides valuable data for theory development of density current.Based on the relative data of density flow in Xiaolangdi Reservoir in flood period of 2001, and through analyzing on water-sediment condition of density flow formed and movement element of density current, the common movement law and special phenomenon on forming, operating and discharging sediment of density flow in Xiaolangdi Reservoir have been clarified in this paper. The relationship of sediment transport of density flow has been explored combining with theory analysis and formula deduction. It is shown from the research thatthe talent condition of density flow in Xiaolangdi Reservoir can use Froude coefficient equal to 0.78 as a distinguishing standard, Froude coefficient and critical depth formula by Ashida, K are suitable to density flow in Xiaolangdi Reservoir; Density flow is non-steady flow, water-sediment factor is not stable. On the whole the density flow has a tendency with velocity reducing and sediment concentration increasing along the distance. The propagation velocity of density flow is 1.17m/s, without obvious climbing phenomenon in front the dam. After forming the reservoir with muddy water, the interface between clear water and muddy water is settling slowly; in the free flow section of density flow, the comprehensive resistance coefficient is 0.022 on an average, close to that with flume experiment and Guanting Reservoir. It is proved that the universality of resistance computation formula is in agreement on comprehensive resistance coefficient of density flow; the deposition along the distance occurs in reservoir' s section of density flow operation, the slope in front of dam is gently and the cross-section is rising horizontally. During the density flow measurement in Xiaolangdi Reservoir, the ratio of discharging sediment is small. Finally the formula of unit sediment rate of density flow in Xiaolangdi Reservoir has been pointed out and the data of other reservoirs has been verified.