Analysis of the effect of unsteady reservoir flow and sand excavation on the channel conditions of the Yangtze River (Yibin-Chongqing)

Abstract

This paper systematically describes the current research methods for analyzing unsteady flows in an open channel. In particular, it focuses on elaborating a discrete method to solve the one-dimensional Saint–Venant equations for unsteady flow in an open channel, compares the advantages and disadvantages of different discrete methods, and proposes a new implicit iterative mathematical model applicable to the calculation of the multiwavelength unsteady flow in the Yangtze River from Yibin to Chongqing. This paper also simulates three typical unsteady flow processes and analyzes the effect of sand excavation on the water level in the upper reaches of the Yangtze River from Yibin to Chongqing considering flood, normal-water, and low-water conditions. The spreading characteristics of the daily adjusted unsteady flow were obtained in the Shuifu-Chongqing river reach. Under the conditions of the daily minimum unsteady discharge flow rate, the designed water level of the reach from Yibin to Chongqing increases by 0.19 m compared to the natural water level. With the increase in concentrated sand excavation in the upper reaches of the Yangtze River, a large number of shingle beaches have disappeared, and the riverbed has been drastically lowered. Affected by the excessive and unordered sand excavation in the river channel, the water level of the upper reaches of the Yangtze River from Chongqing to Yibin has decreased by 0.5–2.0 m.