Numerical simulation for the evolution of the overflow spring in fracture-karst aquifer system

Based on discontinuous fracture network medium model, coupled hydrodynamic conditions and the dynamic conditions of carbonate dissolution, this paper established a mathematical model and take numerical method to simulate and analyze the evolution of fracture-karst aquifer system. On the basis of established numerical model, two sets of instance model are constructed(one fracture-karst aquifer system recharged by precipitation and the other one recharged by river) to study the early evolution of overflow spring in the fracture-karst system. It is found that with the evolution of fracture-karst aquifer system, the fractures are constantly corroded and widened, which lead to water table declines and many springs being drained out. Moreover, since the variance dissolution, corrosions are quicker at the water table and in the vicinity of the dominant fracture, while the other location is relatively slow, and a karst dominant tube is gradually formed which captures most of the water in the system and develops large spring. Comparing the two instance models, it is also found that in rainfall infiltration recharged system, the springs develop from the sink to the source; while in river infiltration recharged system, the springs develop from the source to the sink.