Investigation of Chehel-Chay River and groundwater interaction in the Eastern part of Gorgan Plain

The present study was conducted to investigate the interaction between river and groundwater in the eastern part of Gorgan Plain. For this purpose, first, the flow of Chehel-Chay River was measured at four stations with specific intervals. Then, the relationship between the fluctuations of the river discharge and the groundwater level in the deep and semi-deep wells around it was investigated using graphical and statistical methods. The results of direct discharge measurement revealed that that the river recharges the aquifer in the first, second and fourth stations. But in the third station, the amount of flow rate increases, which indicates that the river drains the aquifer in this part of river. Results of the relationship between Chehel-Chay River discharge and water level of semi-deep wells based on Pearson's correlation test showed that there is a significant relationship between the changes in monthly river discharges and the monthly water level in 7 out of 19 semi-deep wells and 2 out of 5 deep wells. But, no significant relationship was observed in the rest of the wells. At the beginning of the river's entry into the plain, the curvature of the groundwater level curves is in the direction of Chehel-Chay River movement. But in the future, the shape of the curvature of the groundwater level changes and gradually turns against the direction of the Chehel-Chay River, which indicates that the aquifer feeds the river.