Groundwater modeling and the analysis of improvement scenarios in the adjacent areas of Taiwan high speed rail in Yunlin County

In order to clarify the influence of groundwater pumping of Taiwan Water Corporation (TWC) in Yunlin area and the adjacent areas of Taiwan High Speed Rail (THSR), the MODFLOW software is used to develop a groundwater numerical model for Jhoushuei River Alluvial Fan. The verified model is applied to evaluate the recovery quantity of groundwater level under different scenarios. Maintaining the pumping situation is defined as the control scenario (scenario 0) for the comparison with others. Closing all pumping wells of TWC is defined as scenario A. The stop of groundwater pumping according to "The exactly strategy and execution project for the solution of the long-term subsidence problem in Yunlin and Changhua Counties" is defined as scenario B. Considering the surface water and groundwater resources conjunction under different situations is defined as scenario C. The results show that the largest recovery quantity of groundwater level is not in the adjacent areas of THSR in scenario A. In scenario B, the recovery quantity of groundwater level is less than those of other scenarios due to a small quantity of stop of groundwater pumping. The recovery quantities of groundwater level in the third and fourth aquifers are larger than those in the first and second aquifers in scenario C. The recovery quantities of groundwater level in the adjacent areas of THSR are larger than those in the whole area of Yunlin County under the scenarios of water resources conjunction (scenarios B and C). It shows the fact that the conjunction of water resources can reach the target of reducing subsidence in the adjacent areas of THSR. Comparing scenarios A and C, the recovery quantity of groundwater level is the largest in the year when the pumping stop and then becomes stable in five years. Therefore, the earlier the pumping stops the larger the recovery quantity is obtained. The study results can be used in arranging the close of pumping wells for managing future water resources in Yunlin County.