Threshold of Groundwater Over-exploitation and Conservation-restoration in Tianjin Land Subsidence Area

The land subsidence in Tianjin has been wide coverage,high degree and great danger,which mainly caused by water shortage and groundwater over-exploitation.In order to prevent the development of land subsidence,the main measures include strict controlling of over-exploitation and conservation-restoration of groundwater aquifers system.The article is based on characteristics of the groundwater flow system and the development of land subsidence,comprehensive analysis of threshold of groundwater over-exploitation and conservation-restoration,the land subsidence area in Tianjin has been over-exploitation as a whole firstly,the studies of whether over-exploitation only in a area may result in some mistake,such as small on big and so on.It has been recommended that evaluating over-exploitation of groundwater resources by hydrological geological unit as a unit.Furthermore,the groundwater table has been required grate recovery upon the critical level,which as threshold of effective conservation-restoration of groundwater resource.