| The Hutuo River alluvial and proluvial plain is one of the areas where the shallow groundwater is seriously over-exploited in the North China Plain.Since September 2018,the Hutuo River,as one of the pilot rivers for comprehensive treatment of groundwater over-exploitation in the North China Plain,has officially carried out groundwater recharge through river leakage.Groundwater recharged by surface river leakage is an effective way to raise groundwater levels and increase groundwater storage resources.However,there still remain some problems:firstly,if the groundwater depth of the urban area is too shallow,it will harm the safety of underground space facilities in Shijiazhuang.Secondly,the vadose zone in farmland contains chemical fertilizer and pesticide residues,and the continuous rise of groundwater level may lead to pollution diffusion and soil salinization.Therefore,controlling the regional groundwater level below the upper limits of groundwater level,and maximize the recharge of groundwater resources in the over-exploited area by river leakage,is the focus of this paper.Coupling groundwater simulation models with optimization algorithms is a common approach to solve nonlinear and multi-dimensional complex groundwater management problems.After the field investigating and data collecting in the study area,the three-dimensional unsteady groundwater flow numerical model of the Hutuo River alluvial plain was set up based on MODFLOW-USG at first.The unstructured grid was used to refine the grids along the river channel belt,to improve the simulation accuracy of the river and the groundwater balance of the study area.Secondly,the river infiltration capacity and groundwater upper-limit levels are analyzed.On this basis,the groundwater flow model and water level control optimization model were tightly coupled based on FloPy and Geatpy in Python language,and were solved by the elite genetic algorithm.Then the optimal results of 2020-2029 Hutuo River leakage to replenish groundwater are obtained.Finally,the groundwater exploitation schemes under different constraints are determined,and the influence of groundwater exploitation reduction on groundwater replenished by river is clarified.The main results and conclusions are as follows:(1)From 2010 to 2019,the total recharge and the total discharge of groundwater system in the study area were 26.26×10~8m~3/a and 36.67×10~8m~3/a,with an equilibrium difference of-10.41×10~8m~3/a,which is in a negative equilibrium state.Groundwater over-exploitation was serious,and it is urgent to reduce groundwater extraction and to replenish groundwater.(2)From 2020 to 2029,the optimal total amount of replenishment from the Hutuo River leakage to the groundwater(aquifer)is 53.6×10~8m~3,mainly concentrated in the upper reaches(R1-R3).Groundwater recharge from the river covers 17.27%of the total recharge.River leakage plays an important role in the restoration of groundwater storage resources in the over-exploited area.(3)The comprehensive treatment measures of"one increase and one decrease"formed by river replenishing groundwater and reducing groundwater exploitation have remarkable effects on stopping the decline of the groundwater level.The average groundwater level drawdown speed decreased from 0.6m/a to0.2m/a and 0.008m/a.However,with the decrease of groundwater exploitation,the optimal replenishment amount of groundwater by river leakage also decreases,which are 20.05%and 18.42%,respectively.(4)The groundwater numerical model is established using the unstructured grid subdivision method,and the optimization simulation of the leakage replenishing groundwater and water level control of the Hutuo River is based on Python.The optimal amount of groundwater replenishment by leakage in each river section can be determined according to the change of groundwater level under the interference of natural conditions and human factors.This study is of certain significance for the research on groundwater recharge in rivers and lakes. |
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