Study On Resilient Groundwater Extraction Options In Zhongmu County Under Drought Situation

Due to the increasing conflict between water supply and demand,groundwater has become the main source of water to alleviate this conflict,especially in drought conditions,groundwater has become a strategic resource that is difficult to replace.However,with the influence of human activities such as groundwater mining,construction of surface water projects and global climate change,the groundwater system has undergone great changes,triggering a series of ecological and environmental geological problems.In response to the problems caused by unreasonable groundwater development and utilization,the implementation of dual control management of groundwater quantity and level and the development of a resilient groundwater exploitation plan are the urgent needs of current groundwater management.This study identified the critical point of regional groundwater resource system state under the premise of meeting resource function,ecological function and geoenvironmental function,established groundwater flow system alternative model,constructed groundwater regulation and control model,proposed a resilient groundwater exploitation scheme under drought situation,and provided theoretical basis for groundwater resource development,utilization and protection.In order to meet different mining requirements under different drought scenarios,the lower critical water level in Zhongmu County was divided into three scenarios: medium drought,severe drought and exceptional drought,corresponding to precipitation guarantee rates of 75%,90% and 97%,respectively.Based on the topography and hydrogeological conditions of Zhongmu County,the study area was divided into five calculation partitions.The upper critical water level depth of each partition in Zhongmu County was determined using the capillary water rise height method.The water balance method was used to determine the lower critical water table depth of each subzone in Zhongmu County under three guaranteed rates.The water level variation method was used to determine the resilient extraction volume under the three guaranteed rates for each partition in Zhongmu County.Visual MODFLOW was selected to establish the numerical groundwater flow model,and the alternative model of the numerical groundwater flow model was established using the dual response surface method.The results showed that the average relative errors of the mean values of water table depth reduction between the numerical groundwater flow model and the alternative model under medium drought,severe drought and exceptional drought conditions were 0.010%,1.697% and 0.005%,respectively,and the average relative errors of the remaining standard deviations of water table depth reduction were 0.001%,3.314% and 0.018%,respectively.The relative errors of mean and residual standard deviation are less than ±5%,and the established dual response surface model can replace the numerical model of groundwater flow for the prediction of the mean value of regional water level drop depth caused by mining volume.A groundwater regulation model was constructed using Lingo software with the minimum water deficit as the objective function and water demand,water supply and critical water level as constraints.The groundwater and Yellow River water regulation water supply quantities of five sub-districts in Zhongmu County were simulated and calculated under different drought scenarios in the base year,2025 and 2035,respectively.The results showed that the flexible groundwater extraction scheme proposed can meet most of the water demand for irrigation and fishery although there is an imbalance between supply and demand in a few years.