Abstract:Ecological base flow (EBF) is a minimum channel flow to maintain a healthy river system and to avoid deteriorating its functions. A case study was conducted in the Yuanhe River which belongs to the Ganjiang River

a branch river of the Yangtze River.In this study

a distributed hydrological model of SWAT was adopted to simulate runoffs and base flows based on daily precipitations and designed scenarios of rainfalls. According to the concept of EBF and the content of base flows

the EBF at the important ecological function zones of the middle to the upper stream of the Yuanhe River was analyzed. Results showed that the EBF at the Luxi and Maozhou hydrological stations is 1.25 m3/s and 17.0 m^3/s

respectively

accounting for 11.14% and 17.39% of their averaged annual flows

respectively.These results are close to the results calculated by other methods.In addition

EBFs based on a distributed hydrological model of SWAT have the mechanism of water cycle and should be more reasonable than the values determined by other methods.