Frequency Analysis of Monthly Runoff in Intermittent Rivers

Frequency analysis of runoff is one of the major approaches in modeling and estimating the probabilistic behavior of discharge in rivers. Two intermittent rivers, one in Turkey another in Iran, Shahar-Chay and Akarcay both located between 30°-40° Northing latitude are selected for comparative investigations. Both rivers show similar behavior in moments and properties of distribution. A set of common 40 year of monthly recorded data between 1961-2000 is selected. Comparative frequency analysis is done on the data by dividing the time series into two-time intervals between 1961-1980 and between 1981-2000. Results indicate an alteration in low and medium range flows in Akarcay. Both stations show that droughts are becoming more frequent while the frequency and the magnitude of the extreme events are increasing. It is also concluded that the seasonal properties of partial-auto-correlation and auto-correlation coefficients have been altered for both of rivers.