Frequency analysis of low flows in intermittent and non-intermittent rivers from hydrological basins in Turkey

Abstract

This study attempts to find out the best-fit probability distribution function to low flows using the up-to-date data of intermittent and non-intermittent rivers in four hydrological basins from different regions in Turkey. Frequency analysis of D = 1, 7, 14, 30, 90 and 273-day low flows calculated from the daily flow time series of each stream gauge was performed. Weibull (W2), Gamma (G2), Generalized Extreme Value (GEV) and Log-Normal (LN2) are selected among the 2-parameter probability distribution functions together with the Weibull (W3), Gamma (G3) and Log-Normal (LN3) from the 3-parameter probability distribution functions family. Selected probability distribution functions are checked for their suitability to fit each D -day low flow sequence. LN3 mostly conforms low flows by being the best-fit among the selected probability distribution functions in three out of four hydrological basins while W3 fits low flows in one basin. With the use of the best-fit probability distribution function, the low flow-duration-frequency curves are determined which has the ability to provide the end-users with any D -day low flow discharge of any given return period.