Effect of reservoir construction on suspended sediment load in a large river system: Thresholds and complex response

摘要

Dam construction greatly alters the channel boundary of rivers, making the dammed river system a human-controlled system. Based on hydrometric data in the upper Changjiang River basin, the change in behaviour of sediment transport of some dammed rivers was studied. As a result, some phenomena of threshold and complex response were found. When the coefficient (C_(r,a)) of actual runoff regulation by reservoirs, defined as the ratio of total capacity of reservoirs to annual runoff input, is smaller than 10%, suspended sediment load at Yichang station, the control station of the Changjiang River, shows a mild decreasing trend. When this coefficient becomes larger than 10%, suspended sediment load decreases sharply. The coefficient of 10% can be regarded as a threshold. The C_(r,a) of 10% is also a threshold, when the variation of suspended sediment concentration (SSC) with C_(r,a) at Yichang station is considered. The impacts of reservoir construction can be divided into several stages, including road construction, dam building and closure, water storage and sediment trapping. During these stages, some complex response was identified. At the station below the dam, SSC increases and reaches a maximum, and then declines sharply. This phenomenon was found on the main-stem and several major tributaries of the upper Changjiang River. In the Minjiang River, where a series of dams were built successively, the response of SSC is more complicated.