Sustainability of Water Resources in Karst Undermined by Tunneling: A Case Example

Drago Dvanajščak,Jože Ratej,Vojkan Jovičić

doi:10.3390/su14020732

Abstract

Water resources in karsts are scarce due to the high cavernosity in the otherwise low-permeability limestone rock mass. The highly variable porosity and transmissivity of karst aquifers are caused by a network of channels, caverns, and caves that typically act as water-bearing, connected vessels. Tunneling in a karst environment can severely deplete an aquifer and undermine the sustainability of water resources over the long term. A research study was carried out to elaborate and develop measures for the sustainable preservation of the water resources in a Slovenian karst, in which two approximately 7 km-long tunnels will be driven as part of the construction of the new Divača–Koper railway line. Hydrogeological site investigations were carried out with an aim to evaluate the transmissivity and spatial spreading of the karst aquifer along the route of the tunnels, including the observation of the long-term variation of the groundwater levels and trace experiments. The main findings, which are presented in this paper, were used to develop a methodology for the selection of adequate measures for tunnel construction with an aim of ensuring the sustainability of water resources in karst aquifers. The construction measures comprise limiting the inflows using injection grouting, obscuring the groundwater intake by undrained sections of the tunnel, and constructing bypasses around the tunnel to preserve the current groundwater flow regime. The presented methodology of dynamically accommodating the preventive measures to the actual hydrogeological conditions onsite is generally applicable for common cases in which the state of the karst aquifer could not be pre-determined with a sufficient accuracy of tens of meters to a meter. The spatially and temporally continuous hydrogeological investigations and decision-making charts to reduce the tunnelling’s impact on the karst aquifer are explained in detail in this paper.

Highlights

According to some estimations, karst regions cover 7–12% of the Earth’s continental area, and their aquifers are at least a partial source of drinking water supply to almost one quarter of the world’s population [1]
The main findings, which are presented in this paper, were used to develop a methodology for the selection of adequate measures for tunnel construction with an aim of ensuring the sustainability of water resources in karst aquifers
The presented methodology of dynamically accommodating the preventive measures to the actual hydrogeological conditions onsite is generally applicable for common cases in which the state of the karst aquifer could not be pre-determined with a sufficient accuracy of tens of meters to a meter

Summary

Introduction

Karst regions cover 7–12% of the Earth’s continental area, and their aquifers are at least a partial source of drinking water supply to almost one quarter of the world’s population [1]. 50% of the surface area is karstified and more than 50% of the drinking water comes from groundwater from karstic aquifers. A methodology integrating structural, geological, hydrogeological, and karstological data as well as groundwater protection demands was developed to obtain the sustainability of the water resources undermined by the new Divača–Koper railway line. The development of the methodology started in 2007 following the early stages of the planning procedure and continued throughout additional field investigation over the following decade; the need for this was identified by the described method and is extending into and beyond the end Sustainability 2022, 14, 732.

Objectives

Methods

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Discussion

Conclusion