Impacts of agricultural groundwater use in shallow aquifer on land subsidence: a case study in Chou-shui River alluvial fan

Abstract

Land subsidence is the result caused by the inappropriate management of water and land resources in Taiwan Continuous compaction of deep stratum in Chou-shui River alluvial fan has reached up to 50% of the total subsidence Agricultural pumping has been recognized as the major groundwater use in Changhua and Yunlin counties However the question on whether the agricultural pumping from the shallow aquifer to cause the compaction of deep stratum is still under debate We first characterize the hydrogeology to identify the connectivity of aquifers Then numerical modeling is performed for the groundwater flow and soil compaction using COMSOL The result shows that agricultural pumping in shallow aquifer did affect the groundwater level of aquifer at different depth Agricultural groundwater pumping and groundwater level are negatively correlated with average coefficient in F1 F2 F3 and F4 are -0 404 -0 380 -0 303 and -0 271 respectively The results also show that the average of correlation coefficient of agricultural groundwater pumping and land subsidence at (a) shallow (b) deep aquifer are 0 458 and 0 322 respectively It indicates that the shallow pumping will influence the aquifer system not only at shallow aquifer but also at that of deeper aquifer The result of numerical modelling shows that when the ratio of discharge of shallow aquifer to deep aquifer is 1:1 2:1 3:1 and 3 65:1 (CEPD 2011) the proportions of deformation in the deep aquifer due to agricultural pumping at shallow aquifer are 25 9% 41 1% 51 2% and 56 1% respectively Although pumping in shallow aquifer does not directly pump deep aquifer water moves through leaky aquitard to reach upper aquifer and causes the compaction of the deep aquifer

Date of Award	2019
Original language	English
Supervisor	Kuo-Chin Hsu (Supervisor)