Unraveling the heterogeneous hydrogeological characteristics in the Choushui River alluvial fan, Taiwan, through observations from the multi-layer compaction monitoring wells

Abstract

An extensive monitoring dataset gathered from 35 multi-layer compaction monitoring wells (MLCWs), 83 groundwater level monitoring wells, and four extensometers were used in this study to comprehend the susceptibility of geological materials to land subsidence at the Choushui River alluvial fan due to the contrasting subsidence trends observed in the Yunlin (south) and Changhua (north) areas of the alluvial fan in central Taiwan. The precision of MLCW is approximately 0.5–2.5 mm based on the time series analysis. We proposed an alternative classification method that uses the alignment of seasonal fluctuation patterns observed through MLCWs, highlighting the compaction properties of subsurface strata. The resultant vertical and horizontal sensitivity models uncover the distinct inherent material properties and their response to groundwater extraction between the Yunlin and Changhua regions. The Yunlin region exhibits extensive land subsidence, mirroring a ‘big sponge’ due to its high porosity and low permeability. In contrast, the subsidence in the Changhua region is more localized, resulting from stratigraphic distinctions. This comprehensive analysis not only provides insights into the complex mechanisms driving land subsidence but also suggests innovative strategies for its mitigation, emphasizing the importance of nuanced understanding and tailored approaches in addressing this critical issue in Taiwan and similar settings worldwide.