Karst leakage analysis of Roudbal Dam, southwestern Iran, using geological, hydrogeological, hydrochemical and stable-isotopic approaches

Understanding the leakage routes plays an important role in a successful remediation of water loss by consequently reducing its cost and time. Among the common methods for reducing uncertainty in leakage analysis, the geology, hydrochemistry, environmental isotopes, grouting analysis, water-balance calculations, and water level monitoring are applied at this study to find the dominant leakage routes at the Roudbal Dam site. Results show that two leakage routes are probable, through the karstic limestone at the right bank of reservoir. Leakage along the first route is based on the following evidence: (a) the occurrence of bedding plane conduits; (b) the appearance of leakage in the access gallery down gradient of grout curtain; (c) the similarity of water chemistry and isotopic content; (d) the close correlation of water-level response in open boreholes to fluctuation in reservoir water levels; and (e) inadequate sealeing of grout curtain in depth and length. For the second route, leakage evidence is based on: (a) the interpreted hydraulic connectivity of karst aquifers especially by the presence of springs at transverse faults; (b) the elevation of discharge zones approximately 300 m lower than reservoir water level; (c) the similar water chemistry and isotopic content; (d) the results of water-balance calculations; and (e) no grout curtain was constructed on this route. To reduce uncertainty along any proposed leakage route, a thorough hydrogeological investigations (including spring monitoring, tracer test, borehole drilling and karst assessment) and geophysical evaluation (particularly in sites with complex structure) are needed. It is concluded that to reduce uncertainty in the addressing leakage routes, the applied approach at each dam site must be based specifically on the local geological and hydrogeological conditions.