Assessing the impact of tunnelling on karst groundwater balance by using lumped parameter models

Abstract

Tunnelling activities may significantly alter the groundwater balance in a karst aquifer, but assessment of this effect remains challenging due to the complex flow geometries and strong hydrogeological heterogeneity. In this study, based on extensive site characterization of an independent hydrogeological unit (HU) in which a deep-buried tunnel is under construction, we present a modified lumped model to evaluate the impact of tunnel construction on the discharge from the aquifer system. The lumped model consists of four interacting flow compartments and the associated water balance equations. A series of simplified models is then developed, by merging or removing some of the flow components that represent different mechanisms and relationships between recharge and discharge. The dominant hydrological processes in the HU are identified by comparing the performance of the models of different structures and by screening analysis of parameter sensitivities. It is found that the tunnel excavation captured a mean portion of 19% discharge from the aquifer system into the tunnel, which is comparable to the result predicted by 3D numerical simulations. This study evidences that as a first and simple approximation, the lumped models provide a useful tool for characterizing the dominant factors that govern the groundwater response and for evaluating the groundwater budget changes induced by anthropogenic activities such as tunnelling and underground mining in karst regions.