Introduction: Studying the changes in surface water storage and exchanges with groundwater in the hydrological system of rivers is a prerequisite for water resources management in the basin. In this paper, Zayandehrood River has been studied and the historical series of flow has been used in six hydrographic stations located downstream the Zayandehrood Dam.
Materials and Methods: Based on the surface water balance and considering monthly inflows and outflows in each river reach, a general equation for water outflow was extracted for each month, in which the net interaction of surface water with the water in the air and groundwater are in the form of a polynomial of the inflows and a constant.
Results: The obtained equations showed that in two reaches, surface water was increased by groundwater and in the other three reaches, surface water fed the groundwater. The results showed that in normal conditions, 1613 million cubic meters of surface water resources were consumed in the reaches under study. In the event of severe drought, except for the first three reaches (from the sadtanzimi to Lenj), the remaining reaches (downstream Lenj) faced water shortage. The results showed that increasing surface water by groundwater is very important for water supply in drought condition.
Conclusion: Based on the results, the proposed method is an appropriate tool for investigating the exchange of surface water with groundwater.