Abstract: To obtain the change trends of runoff and sediment in the Chabagou catchment, we expound the sediment transport dynamics in single flood event by analyzing the sediment load in 98 flood events during 1970-2016. Results show that the hysteresis curve patterns(denoted by the C-Q relation) of flood and sediment transport in the Chabagou catchment over the past five decades mainly include four types: clockwise, counterclockwise, 8-shaped, and complex. Among the four modes, the counterclockwise type has the largest proportion and the largest amount of sediment transported by flood, while the clockwise type has the smallest proportion but the highest average peak flow and highest average sediment peak, whereas complex pattern has the longest average duration. In temporal scale, the hysteresis curve of flood and sediment transport in 1980-1989 is mainly counterclockwise, followed by complex pattern. Since 2006, the number of counterclockwise pattern flood and complex pattern flood has decreased significantly, while the number of 8-shaped pattern has increased. This phenomenon can be accounted for the following facts: comprehensive management of small watersheds has been carried out since the 1970s, and various soil and water conservation measures have had strong effects in 1970-1989; however, after 2000, due to depositions and damages after long-term use, the effectiveness gradually reduced, affecting the overall water and sediment transport mode in the Chabagou catchment.

Key words: hysteretic relation between water and sediment, runoff, sediment load, soil and water conservation measures, single flood event, Chabagou catchment