Effects of tunnel excavation on slope runoff and soil erosion in a karst trough valley

Karst groundwater systems have been destroyed because of the excavation of tunnels. However, the effects of the tunnel excavation on soil erosion in karst areas remain largely unknown. This study aims at investigating disciplines and processes of slope runoff, interflow and surface soil erosion in two runoff plots where are or are not affected by tunnel excavation, respectively, in a karst trough valley, SW, China based on high-resolution hydrological data and isotopic values(δD-H2O and δ18O-H2O). The results show that the annual coefficient of slope runoff is 0.027 and soil erosion modulus is 16.68 km-2 a-1 in the tunnel-influenced plot where the slope runoff responds faster to precipitation, while the corresponding values in the tunnel-free plot were 0.013 and 7.73 km-2 a-1, respectively. In contrast, the interflow in the tunnel-influenced plot is only 31% of that in the tunnel-free plot. The monitoring values of δD-H2O and δ18O-H2O were similar in slope runoff but different in interflow during a storm event. The contributions of rainwater to both the slope runoff and interflow increased in the tunnel-influenced plot based on the stable isotope mixing model. These discrepancies could be due to a decrease in the soil moisture and differences in the soil structures, as the soil clay content is higher and the original loose and sticky layers in the soil profile are damaged in the tunnel-influenced plot, leading to the decrease in the infiltration capability but an increase in the slope runoff. In general, the tunnel excavation increased the slope runoff and soil erosion and decreased the interflow in the karst trough valley. Our study can provide fundamental data on soil erosion and water loss resulting from tunnel construction in karst areas and shed light on the protection and management of karst environments.