Numerical study on surface water leakage replenishment of the Fenhe 2nd reservoir into the Jinci spring system

Due to the construction of the Fenhe 2nd Reservoir, some essential conditions about surface water leakage into karst groundwater system have changed in the Jinci spring area, which affects the regional karst water flow field changes in future. In this study, based upon systematic analysis of formation lithology and water level in the Fenhe 2nd Reservoir area, the contribution of reservoir leakage to the Jinci spring has been determined. Then, a three-dimensional groundwater flow model has been built to investigate the impacts of reservoir leakage into karst groundwater flow system, and the groundwater level change trend at outlet of the Jinci spring is predicted when the Fenhe 2nd reservoir runs in the different scenarios. The results showed that, the leakage into the Jinci spring area increases with the rise of the reservoir water level, and its proportion changes non-linearly, which lowest is 92.8% and stabilizes at 93.7% after water level reaches 902 m.The groundwater level rise is mainly affected by the recharge distance from the leakage zone. The runoff zone of Jinci spring karst water system is most significantly affected by reservoir leakage, followed by the discharge area and the northern recharge area. Besides, it is concluded that, the groundwater level near the Jinci spring can reach to its spring outlet elevation by July,2021 and January,2023 when the reservoir water level stays at designed level of 905.7 m and the level in 2017, respectively.