As the critical water source of large cities such as Hong Kong and Guangzhou

the East River is influenced significantly in the hydrological processes by the Xinfengjiang

Fengshuba and Baipenzhu reservoirs. Copula functions are used to analyze the possibly-synchronous occurrence of high- and low-flow regimes in the East River. The results indicate that: ① The marginal distribution with the highest goodness-of-fit is log-normal distribution and generalized extreme value distribution. Meanwhile

the Gumbel Hougaard Copula has the best fitting efficacy for the inflow series of the hydrological stations; ② Three water-reservoirs have great impact on the synchronous occurrence of high and low flow events at 6 pairs of hydrological stations in the downstream

the reservoirs have the filling valley and modulating peak effects which cause flattened hydrological processes when compared to those in the upper and middle East River basin. Besides

the synchronous occurrences of normal vs. normal flows in the upper and the middle East River basin show an increasing trend

causing flattened hydrological variation of the East River basin; ③ The hydrological processes at the Longchuan

Lingyuan

Lingxia and Boluo stations are heavily influenced by hydraulic facilities and scare occurrences can be observed for the peak flood flow and flood discharge

which greatly reduced the flood risks; ④ The construction of water reservoirs can flatten the hydrological processes and reduce the occurrence frequency of high and low flows

being beneficial for flood mitigation.