結合HEC-RAS與MODFLOW模式評估 濁水溪沖積扇地下水位及地層下陷

Land subsidence caused by over pumping of groundwater resource has severely caused large-scale damage to the Choushui river alluvial fan of the western area in Taiwan. The center of subsidence which has gradually moved inland in recent years will affect the safety of high speed rail and that of other major engineering projects. Therefore, this study uses integrated numerical models to simulate the effect on groundwater level and land subsidence in the study area. The MODFLOW model and INTERBED model with IBS1 modulus are adopted to simulate groundwater flow and land subsidence respectively. Moreover, HEC-RAS is utilized in this study to calculate the stream water level in order to represent groundwater-river interaction in groundwater system with River package. The result shows that the mean recharge of Choushui river alluvial fan is 1.95 billion tons, and the mean surface recharge, lateral recharge and river recharge are 1.01, 0.57 and 0.36 billion tons, respectively. The discharge of Choushui river alluvial fan is 2.08 billion tons, and the maximum discharge is in aquifer two. The discharge is 0.91 billion tons. The groundwater system is still over used during the simulated period. Besides, when an integration among HEC-RAS, MODFLOW and INTERBED models with IBS1 modulus was executed, results indicated that most of the region still has the problem of subsidence in aquifer two and aquifer three on Choushui river alluvial fan. Meanwhile, the subsidence condition is slowing down gradually at the coastal area and instead moving to the inland area. The above result may apply to evaluate groundwater management and reduce the damage from the land subsidence in the study area.