Establishment And Improvement Of Groundwater Flow-Land Subsidence Coupling Model In Tianjin Plain

Due to the complexity of regional geological settings in Tianjin plain,it will be of important to depict the relationship between the exploitation of deep groundwater and land subsidence accurately.Therefore,building the coupled model for both groundwater flow and land subsidence with a long sequence for the groundwater resources,which will be of guiding significance to the groundwater resources management and the reasonable control of ground subsidence in Tianjin plain.In view of the problems about prolonged stability and accuracy(vertical permeability change in the clay layer),this article establishes the coupled model for both groundwater flow and land subsidence with a long sequence,and by modifying the source code of MODFLOW,the article improves the part of vertical permeability as fixed value in the clay layer,which is also compared with the model modified before.The results of the study are as follows:(1)Modifying the source code of Modflow on the basis of full understanding about Sub.Using a simple model,validate the vertical permeability coefficient reached the effects,which varying with the effective stress change.(2)Successfully established a long sequences integrated numerical groundwater and subsidence model.By using contours of groundwater table,groundwater hydrograph,and land subsidence process curve graph,this numerical model has been proven to be reliable The model-based average annual exploitation is estimated to be 7.85×108m3/a,and this inversion results are more realistic and reliable,which solved an accurate estimation about the amount of groundwater exploitation.(3)By establishing groundwater flow-land subsidence coupling model with different levels of exploitation,a relationship between the county average groundwater exploitation and Settlement can be got.The results show that when mined within a certain range,ground subsidence rate is slow,when it exceeds a certain value,the ground subsidence rate increased significantly.This correlation can control the county land subsidence in Tianjin area,and provide some guidance for rational exploitation about groundwater resources.(4)When water level is lower than the record low water level,vertical permeability will decrease with the time.Through establishing 65-year forecast model,which ensures the state is under a negative balance,calculated results were compared before and after program modifications.The results show that in the modified model,the vertical permeability in the clay layer,compression and release of water and settlement are all reduced with the changing of effective stress.In serious land subsidence areas,the variation of vertical permeability coefficient has a greater impact on the region's compression and release of water and settlement.