How does bed load transport influence the longitudinal profile of reservoir sedimentation?

Abstract

The construction of the reservoir has destroyed the equilibrium of the natural river and promoted the siltation of a large amount of sediment in the reservoir. The longitudinal profile after reservoir siltation will have a great impact on the amount of the reservoir siltation, the retention of effective reservoir capacity, and the raise of water elevation caused by the backwater effect. Therefore, the estimation of the longitudinal profile is of great significance to the calculation of the reservoir sedimentation. For mountain rivers, the amount of bed load usually accounts for a large proportion of the total sediment load, which affects the longitudinal bed profile after dam construction. Because the amount and gradation data of bed load are often not available, the effects of bed load transport on the longitudinal profile of reservoir sedimentation cannot be accurately simulated. Until now, how bed load transport influences the longitudinal profile of reservoir sedimentation has not been fully understood. The motivation of our study is to clarify the effects of bed load transport on the longitudinal bed profile of reservoir sedimentation.   We use a 1D mathematical model to study the evolution of the longitudinal bed profile after dam construction to answer the question. Various scenarios with different boundary conditions are considered to analyze the effects of bed load, such as the amount, gradation and distribution during the year, on the longitudinal bed profile after dam construction. Our results show the effect of the amount of bed load on the longitudinal bed profile of reservoir sedimentation.is greater than that of bed load gradation and distribution during the year. In the early stage of reservoir operation, the influence of the bed load transport on the longitudinal profile is negligible. With the increase of operation time, the effects of bed load becomes more and more significant. The larger the amount of bed load, the higher the bed elevation, and the larger the slope of the riverbed near the dam. For areas with large initial topographic slopes, the greater the bed load amount, the smaller the slope of the riverbed after siltation. In contrast, the effects of bed load gradation and distribution during the year.on the longitudinal bed profile of reservoir sedimentation is not significant.