Quantitative Analyses of Saeed - Abad- Chay Basin Run off

Saeed–Abad – Chay basin is one of the basins which is situated in the northern hillside of the Sahand Mountains ranges in north-west of Iran. The area of this basin is about 215 square kilometers and is a sub-basin of Aji–chay which leads towards the orumiyyeh Lake.In this study, medium isorain lines and also isorain lines with return periods of 25 and 100 years, have been prepared for the purpose of analyzing the amount of rainfall.Regarding the difficulty of determining the effective elements on run off such as evaporation, transpiration, cesspool storage, interception, infiltration and the moisture of the soil, long –term period was selected to estimate the amount of run off since the effect of various elements is approximately constant in this period.To study the relationship between seasonal and annual rainfall and run off of Saeed–Abad Chay basin, the statistical period of common rainfall and run off in (1970-1971) to (1996-1997) has been used except for (1995-1996) because of unavailability of statistics. To obtain models prevailing on seasonal and annual rainfall and run off of Saeed–Abad Chay basin, different kinds of models have been used such as: simple process model, simple temporal series model, multisentential model, simple linear model (SLM), and run off coefficient model with seasonal changes. In most cases, second and third degree multi-sentential have revealed a better fitting comparing with the other equations.