Instantaneous Runoff Coefficient and Water Table Relationship and Stream Flow Reduction Mechanism along River (Case Study: Ajabshir Basin)

Nowadays, water scarcity and frequent occurrence of droughts in Middle East countries including Iran create many problems for population of these regions. Drying off Salty Lake Urmia and its consequences is very important form the Iran and Middle East water industries. The main reason of Lake Urmia crisis is streamflow reduction of rivers leading to the lake due to excessive extraction of water resources in recent decades. Since the river-aquifer is a system with two interrelated elements, therefore, investigation of streamflow coefficient versus groundwater table relationship is necessary for streamflow forecasting. In this study, instantaneous runoff coefficient (events) and water table fluctuation relationship was checked out in two hydrometric stations located at the beginning and ending sections of Ghaleh-Chayriver which discharges water to the Lake Urmia. Then, the mechanism of stream flow loss (flow reduction process) due to water level draw down was studied along the river profiles. The results of this study showed a direct relation between the runoff coefficient and the water table level. Correlation coefficient value (R) between these two factors was observed 0.9 for Yengejeh station located at the beginning section of the river and 0.84 for Shishavan station at the ending section of river. Evaluating the stream flow losses trend along the river indicates that this flow has been naturally diverted to saturate the transition zone (the zone between the water table level and stream bed).