Modeling compaction of multi-layer-aquifer system due to groundwater withdrawal

• An integrated model estimates groundwater level and subsidence near a well.
• The model was applied to aquifers with multi-well and multi-layer pumping.
• The integrated model was applied to Yunlin, Taiwan.
• Larger subsidence area is attributed to single-layer groundwater users.
• Significant local subsidence is attributed to multi-layer groundwater users.

Excessive groundwater extraction in a sedimentary environment can result in subsidence, which not only deteriorates land and agricultural resources but also endangers public infrastructure. Subsidence can be contributed by compaction in different layers. Clarifying the causes and estimating the amount of compaction remain a challenge for a multi-layer aquifer system with spatially and temporally varying pumping activities. A distributed model that comprises an analytical quasi-three-dimensional groundwater model and a one-dimensional deformation model is proposed to model the groundwater flow and deformation for a multi-layer aquifer system. Using the analytical solution, the groundwater level variation around a pumping well can be adequately modeled and then the compaction of soil layers can be calculated. Superposition allows the results to be extended to a system with multi-well and/or multi-layer pumping. The integrated model was applied to Yuanchang, in the center of the Yunlin subsidence area, Taiwan. Data of groundwater level and compaction at aquifers 2 and 3 in dry-season periods were used to explore the pumping effects on compaction. The results show that single-layer groundwater users are responsible for the large-area compaction and that significant local compaction can be attributed to multi-layer users. Constraining multi-layer pumping activities and reducing the amount of groundwater exploitation are required to mitigate the subsidence in Yunlin.