Abstract: As a large number of flood control and soil-water conservation projects have been constructed in
the Haihe River Basin, the underlying surface conditions and the characteristics of the runoff yield and
concentration are changed, which leads to the nonstationarity of the reservoir inflow flood time series.
Hence it is very necessary to revise the previous design flood. In this paper, the annual flood peak discharge
series and the annual maximum flood volume series of Wangkuai Reservoir, which lies in the Shahe, the
south branch of the Daqing River, were used as the basic data. The mixed distribution method and the
conditional probability distribution method were used to directly analyze the frequency of the non-stationary
flood time series based on their respective change point diagnosis results. The design flood calculated with
these two methods were compared to the 1985 design flood which was approved by the WRHPDGI (Water
Resources and Hydropower Planning and Design General Institute) in 1985, and to the design flood
calculated by the P-Ⅲ curve which considers the flood time series as stationary. The results reveal that the
design values with different return periods are reduced to some extent compared with the 1985 design flood,
with a decrease of about 15% to 30% for annual flood peak discharge, and about 5% to 30% for annual
maximum flood volume; Compared with the P-Ⅲ curve results, the decrease of annual flood peak
discharge and annual maximum flood volume(1-day and 6-day) are less than 10%, the decrease of annual
maximum flood volume(3-day) is about 1% to 15% . The results may lay a basis for the revision of the
design flood in the Daqing River Basin.