Abstract: As a fundamental issue of river dynamics, the resistance of river bed is closely related to the discharge capacity and sediment carrying capacity of river. The distribution of river bed resistance in different reaches was analyzed by calculating the sand particle resistance and sand wave resistance based on data acquired synchronously using multi-beam measurement system, ADCP, and particle size data from Jiujiang to Hekou in 2014-2016. The relations of bed resistance against ratio of width to depth, particle size, and flow velocity were examined. Furthermore, the bed resistance and influencing factors for main segments before and after the impoundment of Three Gorges Project (TGP) were also compared. Results concluded that: around the impoundment of the TGP, the maximum and average sand particle resistance from Jiujiang to Wusongkou decreased by 57% and 63%, respectively. Meanwhile, sand particle resistance was the dominant resistance, while sand wave resistance accounted for less than 1% and even tended to decline along with the operation of TGP. Before the impoundment of TGP, bed resistance in the lower reach of the Yangtze River was the most significantly correlated with particle size, followed by velocity and width to depth ratio; and the corresponding average correlation coefficients was 0.48, 0.30, and 0.25, respectively. After the impoundment of TGP, the correlation ranked from flow velocity, width to depth ratio to particle size in sequence; and the corresponding average correlation coefficients was 0.71, 0.41, and 0.30, respectively. The main influential factors of bed resistance in different reaches varied with time period.

Key words: the lower reach of Yangtze River, riverbed resistance, distribution characteristics, ratio of width to depth, particle size, flow velocity, impoundment of Three Gorges Project