Prediction of groundwater seepage caused by unclogging of fractures and grout curtain dimensions changes via numerical double-porosity model in the Karun IV River Basin (Iran)

Water tightness of the reservoir is considered not only a common problem; but also it is time-consuming and expensive when constructing a dam. The water seepage of Karun IV was observed at the initial impounding stage. The dam site consists of highly heterogeneous karst terrain. 2D dual-porosity numerical model with the geometry-based finite element is used to investigate the performance of the grout curtain, drainage tunnels, as well as proposed curtain length for seepage control. The model is calibrated before and after impounding for the dam site aquifer, to achieve the best possible fit between the calculated and observed groundwater heads, and variations of the reservoir water level. The obtained hydraulic conductivity of the site has indicated the existence of very high heterogeneity and few conduits coinciding with the faults. The water seepage mainly occurs in the left abutment; the faults which have been centered near the river in the right abutment play a significant role in the water seepage rate as well. The swing of the curtain is crucial to the impervious layers in both horizontal and vertical directions to reduce the seepage. The results have indicated that there may be a conduit(s) which does not coincide with the position of the fault, or reported the opening of core logs, or the water seepage may be due to the improper sealing of the site.