Evaluation of the effect of groundwater abstraction on changes in discharges of Sezar river

IntroductionSezar River of the main branches of Dez River and long term streamflow predicting of the river is important, in order to optimal operation of Dez Dam Reservoir. MethodsIn this research initially, streamflow trend of Sezar River evaluated with TFPW-MK method at statistical period 1970-1971 to 2008-2009 that is a period without trend of the basin precipitation. The results showed, streamflow of Sezar River has a significant negative trend. Then in order to evalution streamflow reduction causes of the river, were evaluated, three basic factors affecting on river streamflow, that is precipitation, inter and intra basin withdrawals from surface water resources of basin and withdrawals from groundwater resources of basin. ConclusionThe results showed, main cause of streamflow reduction of the river is excessive harvesting of groundwater. Finally, predicted long term streamflow of Sezar River. The results showed, average of prediction streamflow time series of Sezar River, about 22.42 m3/s is lower than average of streamflow time series of the river in the case of excessive withdrawals from groundwater resourses are not that cause the interaction of surface water and groundwater is not. The data used is include, data of 3 hydrometric stations and 15 pluviometry stations of Sezar basin, information of development projects inside and outside basin surface water resources, and data of digging year and coordinates of waterwells in the basin.