Channel-forming discharge based on the extreme value identification of sediment-carrying capacity index

Channel-forming discharge (D_cf) is an important parameter in river management and reservoir flood regulation. Applying the methods for calculating D_cf to reaches downstream reservoirs characterized by drastic changes in water and sediment conditions and long-term scouring status is difficult. Based on the riverbed-shaping principle of sediment-laden water flow, while simultaneously considering the active action of water flow and response of the riverbed, this study proposes a new method for calculating D_cf by identifying the extreme value of the suspended sediment-carrying capacity index. The application of this method to the middle and lower reaches of the Yangtze River showed that after the impoundment of the Three Gorges Reservoir, D_cf in this section was reduced by an amplitude between 2500 and 4700 m³/s. The results can be used to guide the operation of the Three Gorges Reservoir and the management of the middle and lower reaches of the Yangtze River, thus providing reference for other river channels downstream of the reservoir.