| dc.description.abstract | In the complex aquifer systems of the Choushui River Alluvial Fan, Taiwan, effective groundwater management and land subsidence mitigation are crucial in the fields of geohydraulic, engineering geology, and environmental science. This study aims to clarify the impact of heterogeneous hydrogeological models on geohydrology, spanning from data to modeling. Our objectives address three primary challenges: (1) quantifying the influence of uncertainty of heterogeneous hydrogeological model on local-scale simulations of groundwater flow and land subsidence; (2) assessing the impact of borehole density on the construction and effectiveness of three-dimensional heterogeneous hydrogeological models in the basin scale; and (3) developing an uncoupled-model for groundwater and compaction that quantifies land subsidence at a basin scale. This study utilizes extensive borehole data, employing the one-dimensional (1D) continuous-lag Markov chain, the spMC package, and geostatistical methods to generate realistic hydrogeological model realizations. The Groundwater Modeling System (GMS) software, integrated with the TPROGS, MODFLOW, and SUB packages, enables simulations of transient groundwater flows and models land subsidence. These models are evaluated through Monte Carlo simulations to ascertain the variability and uncertainty of the results.
In the local scale, our findings highlight the significant impact of hydrogeological model uncertainty on the reliability of simulations for groundwater flow and land subsidence. We also explore the effects of boundary conditions on simulation outcomes, noting that assumed boundary conditions enhance the stability of groundwater flow across different models and reduce uncertainty. At the basin scale, findings highlight that higher borehole densities produce more detailed and complex hydrogeological models, enhancing the representation of geological discontinuities. Conversely, lower densities result in more continuous and uniform patterns, potentially oversimplifying subsurface complexities, yet sufficient for expansive assessments. This study emphasizes the critical role of borehole density in reducing model uncertainty and enhancing the reliability of hydrogeological model. Furthermore, an uncoupled-model for groundwater and compaction was well developed with the calibration and verification. Results from the model have demonstrated high credibility. The simulations reveal that shallow groundwater pumping significantly impacts deeper hydrogeological layer, notably along the Taiwan High-Speed Rail, contributing markedly to land subsidence. It shows that pumping activities within shallow layers account for 6% to 35% of deep compression, with variations dependent on specific hydrogeological characteristics and pumping behaviors.
In conclusion, this research provides deep insights into the dynamics affecting groundwater flow and land subsidence, emphasizing the essential roles of uncertainty of hydrogeological model, borehole density, and groundwater pumping practices in the geohydrology study. The implications of these findings are significant for groundwater management, environmental assessments, and land subsidence evaluations in regions facing severe hydrogeological and anthropogenic changes. Future research should integrate additional natural factors, such as variations in the hydrological cycle, to further refine the understanding and mitigation strategies for land subsidence and groundwater resource management. | en_US |