Conceptualization and numerical simulation of a karst subterranean river and its outlets using MODFLOW

Abstract

Objective In the set of 3D seepage simulation programs of MODFLOW, the Conduit Flow Process (CFP) module has been widely used to represent karst conduits and karst aquifers and provides an important tool for groundwater simulation in karst areas. Methods When using CFP module to conceptualize the subterranean river conduits and their outlets, there are two schemes for the conceptualization of the outlets: setting the subterranean river outlet in the conduit model (FH scheme) or in the equivalent porous medium (Dr scheme), whose simulation effects are to be evaluated. In this paper, a groundwater numerical model with conduit flow was constructed, taking the Jiangjia Subterranean River in Jinyun Mountain, Chongqing as an example. The outlets of the subterranean river were conceptualized by the aforementioned two schemes, and then the differences between the subsequent two simulations were analyzed and compared. Results The results show that the FH scheme is better than the Dr scheme. The fixed head setting in the FH scheme can achieve the effect of groundwater discharge in all segments of the subterranean river, while the drain setting in the Dr scheme only discharges groundwater in the upstream of the subterranean river conduit, then recharges the aquifer in the downstream, and finally, the groundwater is discharged in the drain unit. Conclusion The water balance analysis also demonstrates the advantage of the FH scheme in terms of the capacity of groundwater discharge and the function of aquifer storage.

Keywords

• karst conduit
• conduit equivalent porous medium coupling model
• modflow-cfp
• subterranean river