Analysis on the return period of the rainstorm in the Qinhe River basin on July 11, 2021

According to the Table 1 and Table 2 of Maximum Rainfall Data of Different Periods over the historical years and the “7·11” rainstorm in 2021 in the Qinhe River basin, the rainfall frequency curves of three representative periods of fourteen long series stations are established by using P-Ⅲ distribution, and the rainfall return period of “7·11” with maximum 24 h greater than 100 mm, maximum 6 h greater than 100 mm and maximum 1 h greater than 50 mm is calculated. According to the historical survey flood and the maximum peak discharge over the years, the frequency curves are established, and the return period of peak discharge of Wulongkou, Shanluping and Wuzhi hydrology stations are calculated. The results show that: (1) The return period of the largest 24 h rainfall reaching 351 mm in Yaotou station is about 3,000 years, that of the largest 6 h rainfall reaching 328.5 mm in Yaotou station is about 10,000 years, and that of the largest 1 h rainfall in the first three stations, Yaotou, Lizhai and Hexi, is 200~300 years. (2) The return periods of flood peak discharge of Wulongkou, Shanluping and Wuzhi stations are equivalent to 30 years, 10~15 years and 10 years, respectively. The results can provide technical support for flood control operation in the Qinhe River basin and the lower Yellow River.