中文摘要：

首次采用圆形分布法计算洪水发生的集中期、集中度和高峰期的起止时间，由此确定汛期分期。三峡水库的计算结果表明，汛期分期结果合理可靠。统计试验显示，考虑洪水量级的圆形分布法效果最优。圆形分布法可以较好地描述洪水季节性特征，为洪水汛期分期计算提供了一条新的途径。

英文摘要：

Circular distribution was used to calculate flood concentration period and degree as well as the start and end time of flood peak hydrograph for the identification of flood seasonality. Application results of the Three Gorge Reservoir show that flood seasonality determined by proposed method is reasonable and reliable. Statistical experiment indicates that circular distribution with consideration of flood magnitudes performs best. The circular distribution method can describe seasonal flood characteristics well and provide a new approach for seasonal flood analysis.