Analysis of Hourly Storms for the Purpose of Extracting Design Hyetographs using the Huff Method

This study aims at plotting the Huff curves and designing storm hyetographs in the stations of Izeh, Idonak, Abdolkhan and Ahvaz. A total of 1811 recorded storms in the period 1966-2016 in different seasons were classified into five distinct time groups according to their rainfall duration. The Huff curves were plotted for each class in each of the seasons using the whole set of storms. Results showed that classification of storms led to a better distinction of rainfall pattern in different seasons and durations. In order to compare the time distribution of rainfalls, three indices of S, I, and Q were defined that consider the ratios of non-dimensional cumulative rainfall curves from the 10% probability Huff curve obtained in the 25%, 50%, and 75% of time durations to their corresponding values from the 50% probability Huff curve. The results showed that in the four mentioned stations, the values of S index were greater than I, and both of them were greater than Q. The range of S index varied from 1.47 (in Idonak station for spring storms having the duration between 12-24 hours) to 9.63 (in Abdolkhan station for spring storms with the duration of less than 2 hours). Whereas the range of Q index varied from 1.03 (in Ahvaz station for spring and winter rainfalls having the duration of less than two hours, and in Idonak station for spring storms with the duration of less than two hours) to 1.44 (in Abdolkhan station for spring storms with the duration of 6-12 hours). The range of I index varied from 1.07 (in Ahvaz for spring storms with the duration of 2-6 hours) to 2.12 (in Abdolkhan for winter storms with the duration of less than two hours). For each of the Huff curves, design storm hyetographs were derived and presented using the 50% probability Huff curve.