Analysis Of Groundwater Dynamic Characteristics And Prediction Of Well Closure Effect In A Karst Mountainous Area In Southeast Shanxi Province

Gaoping City is situated in the southeastern part of Shanxi Province,where surface water resources are scarce,and the development and utilization of water resources primarily rely on groundwater.Since the 1980s,extensive coal mining has resulted in the depletion of pore and fissure water in multiple areas,compounded by the lack of major storage projects,making it challenging to harness rainfall runoff.This has intensified the dependence on deep groundwater extraction,leading to overexploitation of groundwater resources.In December2020,the Ministry of Water Resources issued a notice titled"Regarding the Suspension of New Water Extraction Permits in Water-Overloaded Areas of the Yellow River Basin"to promote a shift from inefficient and extensive water usage to a more efficient and sustainable approach.The objective is to strengthen the rigid constraints on water resources,implement strategies where land and production are determined by water availability,and accelerate the ecological conservation and high-quality development of the Yellow River Basin.As a result,the groundwater overexploitation control plan has been implemented in Gaoping City.This article analyzes the regional natural geography,engineering geology,and hydrogeological conditions.It combines long-term monitoring data on groundwater dynamics with a combined approach of correlation analysis and numerical simulation.Taking the year 2020 as the baseline,the dynamic changes in groundwater levels in Gaoping City before and after the implementation of the"well closure and production restriction"plan are analyzed and studied.The following research findings have been achieved:(1)Based on extensive monitoring data of groundwater level dynamics and in conjunction with precipitation and extraction data,a comparative analysis utilizing mathematical statistical methods was conducted to examine the relationship between the burial depth of groundwater in representative monitoring wells and the quantities of precipitation and extraction.Pearson correlation analysis was performed to assess the correlation between the dependent variable(water level burial depth)and the independent variables(precipitation and extraction quantities).The findings indicate the following:During the period of 2014 to 2020,there was a significant negative linear correlation between the burial depth of pore and fissure groundwater and precipitation in Gaoping City,while no significant correlation was observed with extraction quantities,the reason is that the actual extraction quantity is less than the recoverable quantity,and the extraction of pore and fracture water has not reached the conditions for significant water level changes.Over the same period,the average water level in the karst region of Gaoping City exhibited an overall fluctuating downward trend,showing no apparent response to precipitation and extraction quantities.Within the karst water overexploitation area from 2014 to 2020,there was a significant positive linear correlation between the burial depth of karst groundwater and extraction quantities.Given that the average burial depth of karst water exceeded 250 meters,there was no significant linear correlation between water level burial depth and precipitation,thus establishing extraction quantity as the primary factor influencing karst water levels.(2)Based on the hydrogeological profile map and geological borehole data of Gaoping City,the hydrogeological conditions,aquifer stratigraphy,and boundary conditions of the study area were synthesized.Subsequently,a conceptual hydrogeological model and a mathematical model for groundwater flow were established,followed by numerical simulations using the finite difference method.The model was validated and verified using field measurements from six observation wells within the study area,namely Ducun,Haozhuang,Kangying,Majiagou,Diyuan Company,and Yuancun No.9.The absolute errors between the observed values and simulated values of water level measurements were 0.1m,0.03m,1.63m,0.88m,0.04m,and 0.87m,respectively.Moreover,more than 80%of the observation wells exhibited absolute errors in water level measurements and simulated values of less than 1m.This indicates a strong fit of the model,as the calculated flow field closely resembled the morphology of the observed flow field.Consequently,the model can be utilized for subsequent predictions of groundwater resources.(3)Employing Geographic Information Systems(GIS),the model’s computational results were discretized,and the"equilibrium extraction method"was utilized to calculate the exploitable volume and extraction coefficients of karst water in various townships and districts of Gaoping City in 2014.The pan-Kriging interpolation method was employed to analyze the spatial distribution of groundwater table elevations in 2015 and 2020,thereby determining the locations and extent of groundwater drawdown cones.By integrating the existing"shut-in drill pipe pressure"plan,the dynamic changes in water levels,flow fields,and groundwater drawdown cones within the overexploitation area were forecasted.The findings reveal that the impacted area of drawdown cones caused by pumping within the overexploitation zone expanded from 11.14km~2 in 2015 to 19.79km~2 in 2020,with an average annual increase of 1.73km~2.Subsequent to the implementation of the remediation plan,the minimum closing water level of the drawdown cones within the overexploitation area rose from 565m in 2021 to 585m in 2024.Moreover,the groundwater flow velocity decreased from 3.83m/day in 2021 to 1.92m/day in 2024,signifying an effective restoration of karst groundwater levels and flow velocities.Consequently,the overexploitation of groundwater within the affected area was significantly alleviated,highlighting the noteworthy effectiveness of the overexploitation management measures.