3D transient numerical flow simulation of groundwater bypass seepage at the dam site of Dongzhuang hydro-junction

Hydrogeological conditions at the Dongzhuang Hydro-Junction site are complex and include underground water divides, a hanging river and hydraulic drops along faults. The site suffers from seepage because of its location in karst terrain. This study addresses dam bypass leakage at the Dongzhuang site and deficiencies in the regional groundwater seepage model. A hydrological conceptual model is generated, as well as a regional numerical simulation of groundwater flow based on analysis of the geology and hydrogeology of the dam site and surrounding area. From the analysis, a detailed 3D model of the groundwater flow field at the dam site is established, in which permeability and precipitation infiltration parameters are corrected using the inversion method. Leakage quantities are calculated for three different conditions: natural state, regular dam impoundment with an impervious curtain, and regular dam impoundment without an impervious curtain. The results show that underground water flows from west to east during all three conditions. The leakage quantity bypassing the dam region without anti-seepage treatment is 220,000 m3/d, with seepage concentrated around the dam foundation, dam abutments and the river bend of the reservoir head. Leakage in these areas accounts for 72% of the total leakage in the study area. However, when an impervious curtain is included in the model, the total leakage quantity is reduced to 51,000 m3/d and seepage concentrates along the banks of the reservoir. The 3D numerical model of regional groundwater flow is promising in that it can simulate complex hydrogeological conditions, and the accuracy and confidence levels improve when a detailed 3D model of groundwater flow at the dam site is added to the regional model.