Reginal flood frequency and study of empirical flood estimation methods in Western zarbaijan for aplacation of tbe suitable method in unguged watershed

The lack of enough hydrometrical stations on rivers and their branches, have made some problems for hydrologists in calculating designing discharge of watershed management projects, water resources, river engineering and small water hydropower plans. This research work was carried out in catchments located in middle parts of west Azarbaijan province with similar physical and climatic characteristies , in order to ob tain suitable methods for regional conditions and are based on measured data. To do this, six main rivers with 23 hydrometry' stations were selected and were evatuated in 4 face based on surface area by using 8 different methods. Measured data of peak discharge during 25 years were analyzed by these methods : Griker , Diken, Regional, Fuller , Index flood Method (IFM) and multifactrol correlation. Then the amount of surface runoff was calculated for return period of 2 years by comparing measured .and estimaed amounts and the statistical method of cross validation was used in order to select the most suitable relationship. The data of hydrometrical stations was considered in 4 face as follows; 1) Catchments with the surface area of less than 500 km 2) Catchments with the surface area of more than 1000 km 3) Catchments with the surface area of more than 1000 km 4)All catchments without considering their area. Results showed that the method of method of multiple linear corrolation using two factors of surface area and mean annual rainfall of catchmentsis are sultable to calculate designed peak discharge with return period of 2 years. So it is recommonded , to estimate flood with necessary return period , the relationship Amoung 2 years returne period and other data with different return periods, that have high corrolation , could be used. For catchments with surface area less than 100km2 , carryling out another research work like Slope- Area are recommonded, Some main problems were also reccognized in estimating of exact surface runoff in catchments that includes less density of rainfall and river muoff guages , lack of snowrneter stations, overgrazing of rangelands and miss management of watersheds.