Indications of tunnel water inrush to the origin of large karst springs in Southwest China and water environmental effects

Objective The Kuncheng Tunnel of the Central Yunnan Water Diversion Project crosses the Heilongtan and Bailongtan areas, the major headwater regions in the Chenggong District of Kunming City. Methods Tunnel water inrush may seriously threaten the safety of the urban water supply. In this paper, based on hydrodynamic data and hydrochemical data during tunnel construction, the characteristics of the karst water system, the origin of the springs, and the impact of tunnel construction were analysed. Then, a three-dimensional groundwater flow model for the Heilongtan-Bailongtan Section was developed and calibrated to simulate and predict groundwater level changes during the construction of the Kuncheng Tunnel, and the water environment effect of tunnel construction was evaluated. Results The results show that both the Heilongtan and Bailongtan springs are mainly recharged by the same karst P1q+m aquifer. However, controlled by aquitard P1d and the Hunshuitang fault downstream of the Sanjiacun Depression, the two springs actually belong to two relatively independent karst water systems. In addition, the excavation of the Kuncheng Tunnel has changed the regional groundwater flow field and cut off the flow of Bailongtan, while it has negligible impact on Heilongtan. Conclusion This study discusses the genetic relationship of karst spring, and quantitatively analyzes the impact of tunnel excavation on water environment, which has reference significance for preventing water inrush in tunnel construction.