Hydrogeological processes of large karst spring in southeastern Yunnan affected by the combined influence of natural and engineering disturbances

HUANG Jingyu; LI Chunyu; XU Mo; WEI Qiyang

doi:10.11932/karst20250601

Abstract：Large karst springs are important surface water resources and play a particularly significant role in the vast karst mountainous regions.In China,research on large karst springs has a long history with remarkable achievements,but it is predominantly concentrated in northern regions.However,studies on large karst springs in southern regions still remain insufficient and require deeper and broader investigation.In recent years,due to the frequent occurrence of extreme weather events and the intensified human engineering activities in southern karst areas,large karst springs have been faced with ecological and environmental challenges.Therefore,it is urgent to conduct scientific and targeted analyses of the hydrological processes of karst springs in south China under multifactorial disturbances. The eastern part of Yunnan is widely recognized as one of the most prominent and typical regions for environmental issues related to large karst springs in south China's karst area.This study focuses on the Xiaolunan large karst spring in southeastern Yunnan.Persistent drought in the region,combined with tunnel dewatering within the spring area,has disrupted the discharge dynamics of the Xiaolunan karst spring,causing abnormal fluctuations.Based on hydrogeological investigations and regional hydrochemical and isotopic tests,this study identified the genetic characteristics of the spring,its recharge sources,and hydraulic connections with the tunnel project.Using synchronous monitoring data of precipitation,spring discharge,and tunnel borehole water levels,we analyzed their variation trends and correlations.Finally,a hierarchical groundwater flow system for the spring area was constructed to enhance understanding of the hydrological processes in large karst springs. The primary findings of this study are as follows:(1)The recharge area of the Xiaolunan large karst spring is located within the Honghe River Basin.During groundwater runoff,the water transitions from phreatic to confined conditions and eventually rises and discharges as a spring due to fault obstruction.After surfacing,the spring water flows downhill into the Pearl River Basin's water system.Therefore,the Xiaolunan large karst spring is a fault-controlled uplifted spring with cross-basin recharge.The hydrogen and oxygen isotopes of the spring closely align with the atmospheric precipitation line,indicating that its recharge originates from atmospheric precipitation.Hydrochemical ion signatures show that tunnel construction drainage has impacted the hydrological processes of the large karst spring. (2)Precipitation in the spring area exhibits marked seasonality under the influence of the plateau monsoon climate.The borehole water level generally shows a downward trend,primarily caused by continuous dewatering from tunnel construction.Over a two-year period,under the combined influence of precipitation changes and tunnel disturbances,the discharge of the large karst spring remained stable.The time-series curves were categorized into two types:asymmetric sharp peaks characterized by steep rises and falls,and relatively gentle,wave-like undulations.The exhibited a weak correlation with precipitation,with a lag time of 1 to 2 months during certain periods. (3)Multiple crustal uplifts since the Neotectonic Movement have caused spatial shifts in the erosional datum within the spring area,which have sequentially evolved into the present-day local and regional flow systems.The impacts of tunnel construction have created an intermediate flow system within a specific part of the spring area.The combined synergistic effects of the intrinsic properties of the regional flow system and the local flow system maintain the dynamic balance of large karst spring discharge across different hydrological periods,while also reducing the spring's sensitivity to precipitation events.The intermediate flow system induces groundwater capture and pressure relief in the karst aquifer,directly leading to a reduction in discharge from the large karst spring. Continuous drainage of static groundwater reserves from the aquifer by the tunnel will cause the drawdown cone to expand progressively,increasingly threatening spring discharge.To protect the water resources of the large karst spring,it is recommended that the tunnel construction strictly implement water sealing and discharge limitations.Grouting and sealing of excavated sections should be promptly carried out,with particular focus on outer lining gaps and sections containing concentrated runoff channels,to minimize groundwater extraction.During the tunnel's operational period,borehole water levels and spring discharge should be continuously monitored,and their recovery dynamics should be consistently tracked.