Frequency Analysis of Low-Flows in the Large Karoun River Basin in Iran

ABSTRACT: Frequency analysis is one of the suitable statistical methods in assessing the amounts of low-flow in various return periods which could be obtained using statistical distribution theories and choosing proper probability law or distribution function. The purpose of this study is a frequency analysis for low-flows of Karoun, Dez, and the Large Karoun river basin in Iran , find the dominant probability distribution functions and the low-flowsʹ values until their behaviors in 1-day to 30-day periods could be determined. The observed statistics and information from three hydrometric stations were used in this investigation, namely, Polshaloo as the inflow to the Karoun-3 storage dam, Talezang as the inflow to the Dez storage dam, and Ahvaz as the performance location of the Large Karoun system. The results from this study showed the low-flow generation in Karoun basin (Polshaloo) and the Dez basin (Talezang) are closed together in low probabilities. Analysis of daily to monthly low-flows of the Large Karoun River in Ahvaz station varies between 190 to 250 m3/s. These values for 80% frequencies are between 143 to 183 m3/s. The time series analysis of 1-day to 30-day low-flows of this station shows that flow during the first 15-year period prior 1969 had been normal and during the following years it was affected by the basin’s soil and water resources development plans.