Assessing the impact of Koohrang III tunnel on the hydrogeological settings using stable isotopes and hydrochemical methods

Water seepage into the tunnels may cause technical problems as well as springs flow rate decrease which may lead to environmental, social, and technical problems. This study aims to assess the impact of the Koohrang III tunnel, Iran, on contiguous springs' that provide water for drinking and agricultural activities. This tunnel with a length of 23.3 km aims to provide part of the water shortage in the central region of Iran for drinking, industry, and agriculture purposes (similar to 120 million cubic meters per year, MCM/year). Prior to tunnel sealing, the amount of water seeping into the tunnel was estimated at 11.6 MCM/year, with the highest seepage occurring in karstic formations. However, after sealing the tunnel, the total water seeping into the tunnel is about 5.1 MCM/year. Koohrang III tunnel, which transfers surface water from Karun catchment to Zayandehrud catchment through extremely complex geologic settings, has caused decrease in flow of some springs. In order to determine the source of water seeping into the tunnel and to investigate the effect of tunnel excavation on the flow rate of springs, two sampling campaigns were conducted during wet and dry seasons, 2018-2019. Samples were taken from the seeps within the tunnel, groundwater, and precipitation and analyzed for isotopic and hydrochemical evaluations. The results show that groundwater enters the tunnel from the catchment area of several karstic springs in the study area.

Automated summary

This study assesses the impact of the Koohrang III tunnel in Iran on the contiguous springs that provide water for drinking and agricultural activities. Prior to tunnel sealing, water seepage into the tunnel was estimated at 11.6 MCM/year, with the highest seepage occurring in karstic formations. After sealing, the total water seeping into the tunnel decreased to about 5.1 MCM/year. The tunnel excavation has caused a decrease in the flow of some springs.