| In order to meet the water consumption for economic and social development of Zhecheng County,the groundwater abstraction showed a noticeable increase.As a result geological environment issues such as in some areas of Zhecheng County groundwater resource have been overexploited for a long period of time;groundwater table witnessed a considerable decline and therefore a depression cone with significant area formed;the deterioration on groundwater hydrochemical quality;the downward movement of brackish aquifer as well as the interruption of surface runoff.On the basis of identifying the geological and hydrogeological settings of the study area,the hydrogeological conceptual model and corresponding mathematical model were established and using numerical methods to evaluate the groundwater resource.These can provide a basis for the sustainable utilization and scientific management of groundwater resources in Zhecheng County hence it has important scientific and practical significance.The research results of this study are summarized as follows:1)The three-dimensional visualization model which wad build on the basis of the generalization of lithology was employed to analyze the geological and hydrogeological conditions.According to the analysis,the geological formation of the study area was vertically classified as follow:shallow aquifer group,first weak permeable layer,intermediate aquifer group(brackish water aquifer group),second weak permeable layer,deep aquifer group,and bottom water barrier.The structure characteristics and spatial distribution pattern of each layer were described.To the brackish water aquifer group,the spatial pattern,recharge,flow,discharge,and the hydraulic interaction with neighbor aquifers,and the recharge-discharge pattern under different abstraction scheme were described in detail.These could provide instruction for constructing numerical model and reasonable exploration of groundwater.2)Hydrogeological conceptual model and its numerical model were established,then numerical method was employed to solve the numerical model.Trial-correction method was used to identify and verify the numerical model and quantitative statistical method and qualitative graphic method were employed to evaluate the model accuracy.During the simulation period(January 2016?December 2016 identification period,January 2017?December 2017 verification period),the process fitting line of measured groundwater table was consistent with the process fitting line of simulated water table very well with error was less than 0.5m.Moreover,the characteristics of the measured flow field and the simulated flow field were highly similar.The total recharge was 89 million m~3 and the total discharge was 88.8 million m~3,therefore the equilibrium difference is 0.2 million m~3.The hydrogeological parameters and the water balance calculation results were confident comparing to the reality and the numerical model meets the accuracy requirements,hence the model was highly reliable.3)The numerical model which had been identified and verified was used to predict the flow field after 10 years of operation(December 2027)under the two mining schemes in the study area and to evaluate the groundwater resources.The results were summarized as fellow:(1)The first mining scheme is set to take the 2017 mining volume as the mining volume during the forecast period.The second mining scheme is set to increase the shallow groundwater extraction by 10%,and the deep groundwater extraction layout is to add 6 new deep mining wells(the extraction is about 3.65 million m~3/a),and close the wells in Xuyuan Water Source(the exploitation is about 1.86 million m~3/a).(2)The groundwater recharge was 42.04 million m~3/a in 2016,and 53.76 million m~3/a in 2017 respectively.(3)The allowable groundwater withdrawal in the shallow aquifer was the exploitation volume stabilized at the restricted water table of 39.12m,it is about 31.86million m~3/a?Under the first mining scheme,the abstract amount was 28.54 million m~3/a,which was less than the exploitable amount of shallow groundwater.Therefore,the shallow groundwater system could have an exploitation potential of about 3.32million m~3/a.However,there was no exploitation potential under the second mining scheme,the groundwater extraction is about 31.39 million m~3/a,which is basically in balance with the allowable groundwater exploitation.(4)According to the replenishment and discharge relationship of the numerical simulation model,the allowable groundwater withdrawal of deep aquifer group was determined by the mean recharge of groundwater,which was about 11.65 million m~3/a.The deep groundwater extraction was 12.05 million m~3/a under the first mining scheme and 13.84 million m~3/a under the second mining scheme respectively,both of which are greater than the allowable exploitation.Consequently,modifying the mining layout and reducing the abstraction were all needed in order to alleviate the downward trend of water table and to avoid the expansion of deep confined depression cone.Reasonable mining layout and reasonable groundwater extraction obtained in this study can help alleviate the decline of groundwater table and the expansion of the depression cone of groundwater table,which have practical significance for the sustainable utilization and scientific management of groundwater resources in Zhecheng County. |
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