Abstract:

The land subsidence occurred in Tianjin Plain, mainly due to excessive use of groundwater resources, is characterized by affecting a wide range of area and causing serious damages, which has been a major environmental geology problem in Tianjin. In this study, firstly aquifer system in the area of study was discreted vertically into six layers based on the analysis of hydrogeological conditions of Tianjin in combination with current situation of groundwater exploitation. The groundwater was treated as three-dimensional transient flow and land subsidence model was adopted as one-dimensional consolidation/compaction model. The simulation model for both groundwater flow and land subsidence in Tianjin plain was developed by utilizing the groundwater flow simulation module-Modflow 2005 and the land subsidence simulation module-Sub package. Total area of the model domain is approximately around 1.1×10⁴ km², and the numerical model was identified using contours of groundwater table, groundwater hydrograph, and land subsidence process curve graph. The groundwater budget during the simulation period indicated that the water of vertical leakage between adjacent water-bearing units, compaction, and lateral inflow account for 41.84％, 32.15％ and 24.17％ of the groundwater recharge of deep artesian aquifers respectively. Finally, the calibrated numerical model would be used to forecast trend of land subsidence under the control of groundwater exploitation after implementation of south-north water diversion project. The result shows that the decrease or cease in groundwater exploitation will contribute to the decrease in the rate of land subsidence. Moreover, the recovery of deformation of aquifer shows heterogeneity, with slow rate in the deeper aquifer.

Key words: groundwater flow, subsidence, integrated model, Modflow2005 and Sub package