Development of Low Flow Duration-Frequency Curves by Hybrid Frequency Analysis

In this study, duration-frequency curves were developed for D = 1, 7, 14, 30, 90 and 273-day low flows corresponding to the 2, 5, 10, 25, 50 and 100-year return periods. For this, daily data acquired from streamflow gauging stations with minimized anthropogenic effects were used. A hybrid frequency analysis coupled with the total probability theorem was applied on D-day low sequences to accommodate zero values. Among the tested probability distribution functions, Generalized Extreme Value was found the best in fitting low flows for majority of cases. Low flow discharge increases with increasing duration while it decreases with increasing return period for a given duration. Low flow duration-frequency curves can be considered one among significant tools to be used by the hydrological community in water resources planning and management.