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Rainfall intensity, duration and frequency of 24 consecutive hours or longer (48h, 72h, 96h) are very essential for the assessment of flood risk and the design of the reservoirs and dams in Huong Khe district, Ha Tinh province. | VNU Journal of Science: Earth and Environmental Sciences, Vol. 33, No. 2 (2017) 48-59 Study on the Frequency of Heavy Rainfall in Huong Khe District, Ha Tinh Province Nguyen Van Loi1, Le Quang Dao2,*, Dong Thu Van2, Pham Lan Hoa2, Le Thanh Tung2 1 2 Center for Water Resources Consultant and Technology Transfer-MARD Institute for Geological Sciences-Vietnam Academy of Science and Technology Received 15 March 2017 Revised 15 April 2017; Accepted 28 June 2017 Abstract: Rainfall intensity, duration and frequency of 24 consecutive hours or longer (48h, 72h, 96h) are very essential for the assessment of flood risk and the design of the reservoirs and dams in Huong Khe district, Ha Tinh province. The analysis of flood-causing rainfall and the actual floods from 1990 to 2012 has shown that floods usually occur when: a) 24-hour continuous rainfall reacheds 710.6mm or more; b) Heavy rains which lasted longer than 24 hours and reached 548.9mm/24h to 630.2mm/48h or more; c) Heavy rains lasted from 72 hours to 96 hours and reached from 534.5mm/72h to 575.6mm/96h. The following conclusions have been drawn from analysis results of development of the empirical and theoretical exceedance frequencies of Pearson III distribution of 24h-96h heavy rainfall: a) All the theoretical and empirical frequency data have very high correlation coefficient from 0.891 (24h rainfall) to about 0.948 (72h-96h rainfall); b) For 24h rainfall, the actual rainfall of the empirical P of 13% to 26% is about 40mm lower than the theoretical rainfall, while the actual rainfall of the empirical P of 8.7% is about 80mm higher than the theoretical value, and that of the empirical P of 4.35% is about 175mm higher than the theoretical value; the actual rainfall at empirical P of 8.7% is corresponding to theoretical P of 4.5%, and actual rainfall at empirical P of 4.35% is corresponding to theoretical P of ~1%; c) For 48h and 72h rainfall, the empirical and theoretical frequency data are very close to each .
