evaluation of base flow index in lake urmia basin using one parameter digital filter method

Lake urmia is a terminal hyper-saline lake, designated as a unesco biosphere and wetland of international importance. recent sharp decline in the lake water level is mainly addressed to the changes in the runoff patterns by means of climate changes and construction of more than 70 dams within the basin. in this study the main statistical characteristics of the runoff records in the most downstream hydrometric stations along the rivers that ends up to the lake is analyzed. then, one parameter digital filter method is used to separate the base-flow from direct flow in runoff time series. it is concluded that the main source of runoff in the basin is base-flow provided by the groundwater which also is the main resource of water for rural, industrial and domestic use in the basin. it is obvious that the over consumption of the groundwater resources within the basin will put huge stress on the surface water as well as lake water level in the basin.