Modeling and Quantifying Deep Subsurface Compression Induced by Shallow Pumping Through a Stochastic Approach

Groundwater over-pumping from aquifer system is the primary driver of land subsidence in alluvial plains, causing serious impacts on engineering geology and/or environment, typically shallow aquifers within 300 m. However, in the Choushui River Alluvial Fan of Taiwan, subsidence rates reaching 20 mm per year have been recorded at depths greater than 300 m, indicating deep compression. This observation highlights the importance of evaluating not only the responses of shallow aquifers but also the contribution of deep compression to total subsidence. In this study, a stochastic heterogeneous hydrogeological model (HHM) is developed using 468 geological borehole data to assess and quantify the influence of shallow groundwater pumping on deep compression. The model simulates transient groundwater flow and compaction and is calibrated and validated using monitoring data from 2018 to 2021. Simulation outcomes indicate that shallow pumping accounts approximately 1.265 billion m3 annually. This contributes 6-35% of deep compression along the Taiwan High-Speed Rail corridor, with spatial variability governed by hydrogeological structure and pumping area. The HHM successfully captures depth-dependent groundwater flow and subsidence behavior. Future work will extend the model to scenario-based predictions to support high-speed rail safety and promote sustainable groundwater resource management.