Study On Influence Of Compressed Water Release Of Aquifer System On Groundwater Cycle Parameters And Water Supply Capacity

Deep groundwater(confined water)in North China Plain has been seriously overexploited for a long time,resulting in depletion of groundwater resources,loss of aquifer water supply capacity and large-scale land subsidence,which directly threatens the water security,food security and safety of major engineering facilities in the area.A large part of deep groundwater exploitation comes from the pressure release of weak permeable stratum,which is non-elastic deformation and can not be restored.Therefore,the pressure release of weak permeable stratum is a permanent loss of groundwater resources.Meanwhile,the change of hydrogeological parameters of aquifer system is accompanied by land subsidence.The occurrence of soil compression deformation will make the porosity of soil layer decrease continuously,and the permeability coefficient and water release coefficient decrease accordingly.The compression index and water release coefficient of soil layer at different depths in different periods are different.Therefore,it is of great significance to clarify the coupling relationship between deep groundwater exploitation and land subsidence,to explore the changing trend of key hydrogeological parameters,and to identify the changes of deep groundwater reserves and water supply capacity for the scientific management,development and protection of groundwater resources in North China Plain,and to alleviate the geological environment problems related to groundwater overexploitation.Based on the effective stress principle and the compressive water release principle of aquifer system,a one-dimensional non-linear compressive water release model for the variation of water release coefficient and permeability coefficient of aquifer system is constructed by mathematical means.Cangzhou,a typical subsidence area of North China Plain,is taken as the research object.With the exploitation of deep groundwater,land subsidence begins to occur and confined water head drops continuously.The variation of hydrogeological parameters and the variation of groundwater supply capacity and reserves are simulated.The influence on the sustainable utilization of groundwater resources is analyzed.The main contents and achievements of this paper are as follows:(1)The non-linear variation of hydrogeological parameters and the loss of water supply capacity caused by land subsidence are explored.The variation of confined water head and the exploitation of deep groundwater in Cangzhou subsidence center are used as input conditions respectively to simulate the variation of relevant hydrogeological parameters.The simulation results show that the inelastic water release coefficient of Cangzhou subsidence center decreases by 39%and the maximum can be reduced by 77%.The loss of the inelastic water release coefficient of the whole Cangzhou area is 0.005?0.032,resulting in an average decrease of 220 million m3 in the deep groundwater that can be exploited for every 1 meter of confined water level in Cangzhou area.(2)The permanent consumption of deep groundwater resources caused by land subsidence caused by overexploitation of groundwater is explored.The simulation results show that the proportion of inelastic water release from weak permeable strata in the subsidence center of Cangzhou is reduced from 76%to 35%of the total production,and the cumulative inelastic water release accounts for 54%of the total production.According to the cumulative groundwater exploitation in Cangzhou area,the permanent consumption of groundwater resources in Cangzhou area is estimated to be 9.41 billion m3,which is also the loss of groundwater reservoir capacity,equivalent to the loss of two Miyun reservoirs.(3)The influence of overflow recharge on deep groundwater exploitation and groundwater circulation is discussed.With the continuous decline of confined water level,the compressive water release of aquifer system decreases gradually,while the contribution of overflow recharge to the exploitation of deep groundwater increases gradually,which alleviates the crisis of reducing the compressive water release capacity of aquifer system and slows down the decline rate of confined water level,but may cause the consequences of shallow salt water and pollution downward movement.(4)The influences of hydrogeological parameters,water supply capacity and deep groundwater reserves on groundwater resources management and utilization in Cangzhou are analyzed.On the one hand,the dynamic changes of hydrogeological parameters change the conditions and environment of groundwater circulation,on the other hand,the use of fixed parameters will affect the reliability of groundwater simulation calculation.The decrease of water supply capacity and deep groundwater reserves will affect the groundwater security in Cangzhou area.