Abstract: Determining flood season stages and corresponding water levels in flood season stages rationally could help coordinate the contradiction between flood control benefit and power generation benefit of reservoirs, and is also of great significance to give full play to flood control and power generation capacity of reservoirs and improve the utilization rate of flood resources in flood season. In this paper, the flood season of cascade reservoirs(Wudongde,Baihetan,Xiluodu,and Xiangjiaba) in the lower reaches of Jinsha River is divided into stages according to the incoming flood using the improved fuzzy set analysis method, and the staged limit water level of cascade reservoirs is determined through the mapping relationship between membership degree and flood control capacity. The stages and corresponding limit flood levels are revised with intertemporal sampling method. Research results reveal that the pre-flood season of cascade reservoirs in the lower reaches of Jinsha River is July 1-July 14, main flood season July 15-September 16, and post-flood season September 17-October 24. The reasonable limit flood level for the four reservoirs is 962 m, 800 m, 575 m and 374 m, respectively. The staged limit flood levels are verified through the flood process of different typical floods. The staging results obtained in this study and the phased limit flood level of each reservoir could improve the economic benefits of reservoirs' power generation under the premise of flood control safety, and enhance the utilization rate of flood resources in flood season.

Key words: flood season staging, limit flood level, water resources utilization, fuzzy set analysis, intertemporal sampling method, cascade reservoirs in downstream Jinsha River