Abstract: To evaluate the capacity of a reservoir system operated presently in the Sishui River System of Dongting against historical extreme floods, this study develops a VIC-WUR distributed hydrological model coupled with a reservoir operation module. This model simulates and compares the 1954 basin-wide catastrophic flood events under the scenarios with and without reservoir regulation. The results demonstrate the reservoir group generates significant attenuation to flood peaks, with a maximum peak flow reduction of 62.5% (the Zaoshi Reservoir on the Lishui River), and the longest peak lag of 177.0 hours. The regulatory efficacy features significant spatial variations, subject to the storage capacity, geographical location, and coordinated operation. In the joint operation case of the Zaoshi and Jiangya reservoirs on the Lishui River, the average peak reduction rate is increased up to 56.6%. This study reveals quantitatively the spatiotemporal regulation patterns of reservoir groups against extreme floods, laying a basis critical for managing flood risks in the middle Yangtze and decision making of its collaborative reservoir operation.

Key words: reservoir regulation, flood control efficacy, VIC-WUR model, 1954 catastrophic flood, Sishui River System of Dongting Lake