Présentations Colloques

The development and utilization of groundwater bring great benefits in Cangzhou, and at the same time have led to severe land subsidence, which has become an important environmental factor hindering regional sustainable development. This paper focuses on issues associated with mechanism and control measures of land subsidence in Cangzhou.**The analysis shows that multi-layer aquifer systems with deep confined aquifers and thick clay layers are the key of geological and hydrogeological conditions favorable for the development of land subsidence in this area. The land subsidence volume approximately represents the amount of water released from compression of deep aquifers and aquitards in that most land subsidence is triggered by excessive groundwater withdrawal in deep aquifer system. The ratio of the cumulative land subsidence volume to the amount of deep groundwater abstraction was estimated as 57.6% in Cangzhou. This great ratio is controlled by the local lithological structure and groundwater recharge and discharge conditions. The hydrogeological conditions in this area determine that the water released from compression of deep aquifers and aquitards may be the main source of deep groundwater abstraction, and belongs to the depletion of the storage. The hysteresis of land subsidence is also discussed and the results reveal that the time for completing the primary consolidation ranges from less than one year to tens of years. A transient 3D groundwater model was constructed with MODFLOW to analyse groundwater flow systems and to explore the optimal groundwater abstraction scenario for alleviating land subsidence. Among the four proposed abstraction scenarios, scenario S4 consists of merits of reduced abstraction and increased recharge scenarios, .and may lead to a sustainable development of groundwater resources in Cangzhou. **