Numerical simulation for the evolution of covered karst fissure system between rivers

Initial media characteristics and boundary conditions of a karst system determine its evolution process. The purpose of this study is to reveal the development of a concealed karst aquifer system under different boundary conditions and medium characteristics. Based on groundwater seepage and carbonate dissolution theory, we construct a karst fissure network dissolution propagation model of coupled fracture network seepage and carbonate dissolution, and conduct simulation on the evolution process of the concealed karst aquifer system between rivers. The results show that the flow changes during the development of the karst system have three stages. The first stage is a slow laminar flow with a flow rate increase of 2.2×10 -6 mL·(s·a) -1, with a duration logarithmically related with the initial head difference. The second stage is a very fast turbulent with a flow rate increase of 5.5×10 2 mL·(s·a) -1, and the duration is linearly related with the initial head difference. Stage III is a fast turbulent with a flow rate increase of 26 mL·(s·a) -1. The existence of dominant cracks accelerates the dissolution of karst fracture network. The time for the heterogeneous system entering the extremely fast turbulence phase is 53% shorter than that of the homogeneous system, and the dissolution rate of cracks is accelerated by 12.5%.