Abstract：The bedded structure of the left abutment of the Xiaolangdi Reservoir Dam on Yellow River has a low dip and the quantity of seepage into the 30# drainage gallery is quite large even with grouting curtain. The permeability of the bedded structure is analyzed and the modern tracer theory and analysis method are applied to get the result of seepage，which shows that the seepage pathway to the 30# drainage gallery is quite different. The seepage from the drainage boreholes at the north side of the gallery is very large，and the seepage penetrates the impervious layer through bed-cutting fissures，flows into the permeable layer and finally reaches the drainage bore holes. According to water connection tests between boreholes，it is confirmed that flow in the fissure network has formed a concentrated seepage pathway. The water inflow from other drainage bore holes is relatively small. It is recommended to apply this modern tracer theory and method to solve complex seepage and leakage problems in the key hydraulic projects.
