Abstract:
The Patagh Dam is under construction in the Kermanshah province in the west of Iran. The right abutment of the dam is located on Ilam-Sarvak limestone, which has the potential of karstification. This limestone is drained by several springs including Gelodareh Spring. In order to study possible leakage through the dam, a dye tracing test was organized in borehole PC208 near the dam. The recession coefficients and hydrochemical data of the Gelodareh Spring show that the flow regime of the area is of diffuse type. The dye appeared in the water samples from borehole PC206 and Gelodareh Spring, which are located downstream of the dam. This demonstrates a hydraulic connection between the injection well and these points. Therefore, there is the potential for seepage through the right abutment of the dam. The measured mean flow velocity to borehole PC206 (0.86 m/h) indicates a diffuse flow regime. The breakthrough curve of the Gelodareh Spring shows multiple peaks without significant tail except the last one. Additionally, the high flow velocity (11.8 m/h) is at odds with a diffuse flow regime. The ambiguous behaviour of the dye breakthrough curve of the Gelodareh Spring is explained by a combination of siphon and diffuse flow systems. Existence of a siphon flow system explains the multiple periodic peaks of the breakthrough curve and the lack of tails. The tail on the last peak is the result of diffuse flow system. A neck, close to the spring or the main conduit, which conveys water to the spring, might be causing the pseudo-steady state behaviour of spring discharge and diminishes the periodic discharge fluctuation, which is created by a siphon. It is probable that the siphon level is situated in the zone of water level fluctuation.