THE ROLES OF HYDROGEOLOGY AND DRIVING FORCES ON SUBSIDENCE OF CHOUSHUI RIVER ALLUVIAL FAN, TAIWAN

Choushui River alluvial fan is the most serious subsidence area in Taiwan. The subsidence has appeared since 1970 with a total deformation more than 2.5 m due to developments of aquiculture, agriculture and domestic water use. The public concern has been raised on the safety of the high-speed railway passing this area. However the reason for the subsidence is not clear due to the complicated hydrogeology, multiple groundwater users and unregulated groundwater use. We simulate the groundwater flow and subsidence in this area using provided hydrogeological information using COMSOL. Mass groundwater use in shallow aquifer for agriculture and deep aquifer pumping of aquiculture are modeled. The results show that hydrogeology plays a vital role on the spreading of subsidence. For the existence of permeable aquitard, both shallow and deep groundwater extraction cause the whole-depth soil deformation. The result provides the essential information for the groundwater management in Choushui River alluvial fan.