Application Of Multi-scale Model Based On MODFLOW-LGR In Karst Water Source Simulation

Karst groundwater is an important component of groundwater resources.The quality of karst groundwater in Beijing is excel ent and it is one of the important sources of water supply in the capital.Large-scale models are often unable to accurately reflect local hydrogeological conditions and the regime of groundwater flow.And the size of the model grid also has some influence on the calculation results.Therefore,it is one of the hotspots in the research field of karst groundwater simulation to establish a more precise multi-scale model of karst groundwater.The groundwater system of overlapping uplift karst in Daxing is selected as the research area in this article,and is simulated based on a program named MODFLOW-LGR which using the GHOSTNODE coupling method.In this paper,the application effect and the rationality of the multiple-scale model will be analyzed.The multiple-scale model in this article is based on the uplift karst water flow numerical model built by someone before.The regions for centralized water supply in Niantan,Donggaodi and Longwangzhuang are selected as the encrypted range.The conceptual model of water source encryption model is built.The local encryption model of karst water system in water source area is established with 153 stress periods.Partial encryption model cost more hours and take up more storage space than Unencrypted model,due to the number of grids.At the water level of the shal ow aquifer,the results calculated by the local encryption model and the unencrypted model are not much different;but In the water level of deep aquifers,the absolute difference between the two models increases with the increase of simulation time.Besides,in terms of the calculated equilibrium term,most results of the local encryption model is greater than that of the unencrypted model.In terms of the flow rate of the main mining layer,the encryption model is not much different from the unencrypted model,while in terms of GHOST-NODE boundary,the two models differ greatly.Combined with the result of model calculation,calculation principle and data processing method,the result of partial encryption model is better,and the result is more accurate and reasonable than that of unencrypted model.In this paper,the local encryption prediction model in Donggaodi and Longwangzhuang water supply areas under extreme conditions is established and compared with the unencrypted prediction model.According to the results of the model,the greater the pumping amount is,the more obvious the encryption effect will be.The water level of Donggaodi’s encryption area can be basically restored to the premining level after 2 months;But in Longwangzhuang’s encryption area,the water level recovered very slowly,and the water level dropped sharply,and the aquifer storage loss was large.In Longwangzhuang’s encryption area,increasing mining would strengthen lateral recharge from quaternary system in region to the encryption area and the vertical flow from quaternary groundwater system to bedrock aquifers in the encryption area;compared with the Donggaodi’s encryption area,the quaternary groundwater system has less influence on the bedrock aquifers in the Longwangzhuang’s encryption area.