The Geheyan Hydropower Project is located in a highly karstified limestone area. The Shilongdong limestone of the foundation bedrock is strongly karstified. Over 600 karst caves of different sizes were discovered in the project area, with a total volume of more than 60,000 m 3 . Faults parallel to the river are quite developed and karstification is intensified along the faults and their intersections. Exploration adits following the fault zones show a linear karstification ratio of 50%. Therefore, the potential karst leakage under the dam foundation and around both dam abutments is potentially problematic. Thanks to a proper investigation program and a large amount of geological investigations and analysis the karst conditions and major karst zones in the dam site had been identified before the construction commenced. Accordingly, the optimum grouting route was chosen and appropriate seepage control measures were adopted. During the construction, the pre-construction investigation results were well confirmed. Up to now, the project has been in good operation for nine years and the engineering treatment are proved to be very effective.