Hydrogeological characterization of Dasht-e-Arjan Lake (Zagros Mountains, Iran): clarifying a long-time question

Dasht-e-Arjan Lake is located in the southern Zagros mountain ranges of Iran. It is a tectonic karst polje, fed by a single spring plus local surface runoff, and drained by a single ponor. The fate of sinking water from the ponor had not been determined before this study. Previous investigations suggested two alternatives: (1) underground flow ~ 24 km southwest to Parishan Lake and/or springs in the Kazeron area, and (2) underground flow ~ 20 km southeast to springs at Domeasb Gorge. To clarify this question, an integrated hydrogeological study including a dye tracer test was undertaken. Comparison of the discharge into the Arjan ponor and the discharge of the Domeasb springs shows a reliable correlation. Further, annual water balance analysis reveals that the discharge at the Domeasb springs is too great for its topographic catchment, requiring a major additional source. The dye tracer test, using 5 kg of uranine, was detected only at the Domeasb springs. Flow through time after the dye injection was 210 h. The tracer breakthrough curves are very simple and sharp, with a clear peak concentration of 7 ppb. The total tracer mass recovery and groundwater flow velocity were estimated to be 58% and 105 m h⁻¹, respectively. The results indicate a simple and direct limestone karst hydraulic connection along the geologic strike between Dasht-e-Arjan Lake and the Domeasb springs. The results clearly suggest the possibility of designing a dam around the ponor to protect drying up the lake during drought periods.