Estimation of Monthly Low Flow Rates During Different Return Periods in Rivers of Ardabil Province

Considering the harmful effects of drought, it is important to recognize and evaluate the frequency of low flow. Analysis of low flow is a method for estimating hydrologic drought. In this study, 33 hydrometric stations used in Ardebil province for hydrological droughts survey. The purpose of this study was to analyze the intensity of the low flow (hydrologic drought) using the gamma distribution of two parameter and the relationship between low flow with the percentage of occurrences and the return periods and plotting the curves in different basins have discharge statistics in Ardebil province. The results of this study showed, with increasing the return period, the intensity of the low flow decreases and the severity of drought increases. The discharge values at the two-year return period change from 0.01 to 0.95 at the stations of the booran and atashghah respectively. In the return period of 100 years, the low flow rate at Bouran and Nair stations are the lowest (0) and maximum (0.21) of the value respectively. Since the occurrence of drought causes significant damage to the economic, social, political and environmental sectors of the country, consideration of this phenomenon is necessary in order to achieve the goals of sustainable development.