Application of Groundwater Modeling Systemto the Evaluation of Groundwater Resources in North China Plain

As the political and economic center of China,North China Plain is suffering from water shortage and groundwater environmental problems.In this paper,a 3D groundwater flow model is developed to evaluate groundwater.Firstly,based on the analysis of hydrogeological conditions,we built a conceptual model of this area,which divided the diluvium and alluvium vertically into three aquifers and defined their boundary conditions and parameters.The module MODFLOW in groundwater modeling software GMS(Groundwater Modeling System)is used to develop the 3D transient groundwater flow model from 2002 to 2003.The North China Plain, whose area is 13.90×104km2,was divided into 164×148 cells of 4km×4 km each with 8694 active meshes in all.The calibration is performed with trial-and-error method.By adjusting the parameters of aquifers,model structure,recharges and discharges,the flow field at the end of 2003 and the groundwater levels of 64 typical monitoring wells were simulated.Based on the groundwater balance analysis of the modeling period,the average groundwater recharge rate during 1991~2003 was evaluated as 256.68×108m3/a,in which the rate of precipitation infiltration for recharge of groundwater was 179.70×108m3/a.Considering present exploitation of groundwater and the demand for water for development need,we developed a groundwater exploitation plan and predictated the changing trend of groundwater level in the next 10 years under this plan by the model.The safe yields in each city of North China Plain were evaluated in this way.The total safe yield was 213.49×108m3/a,in which the safe yield in shallow aquifers was 191.65×108m3/a and 22.64×108m3/a in deep aquifers.In the end,the application of the model were introduced,such as planning of exploitation control under South-to-North Water Transfer,determining rational groundwater development,evaluating environmental influence of groundwater in the future,etc.