Author(s): Shaohua Marko Hsu; Chuen-Fa Ni; Chien-Jung Liu
Linked Author(s): Shaohua Marko Hsu
Keywords: MODFLOW; Sustainable withdrawal rate; Water budgets
Abstract: Steep terrain and insufficient regulatory capacity in Taiwan have made conjunctive use of surface water and groundwater an important issue on water resource management. In order to anticipate or avoid over withdrawal of groundwater in a planned development location such as Feng-Lin area located in the upstream region of Hua-Lien River basin in eastern Taiwan, one needs to assess the impact of demanded water supply on groundwater drawdown on both spatial and temporal scales. In this study, a groundwater conceptual model for whole Hua-Lien River basin was built for better control of numerical boundaries. MODFLOW flow model associated with PEST optimization model, artificial adjustment and field data during 2001~2003 were used to calibrate and verify the distribution of hydraulic conductivity in Hua-Lien River basin. The Verified model was then employed to perform sensitivity analysis on key parameters (river leakance and recharge rates at passes of branches in Hua-Lien River basin) and assess the impact of different withdrawal rates on regional groundwater behavior. Based on different degrees of development, four different withdrawal rates including 1, 2, 3, and 4 cms were applied to Feng -Lin area and were represented by 16 distributed wells. The sensitivity analysis shows a quick response between rivers and groundwater in whole Hua-Lien River basin. By analyzing water budgets for Hua-Lien River basin and sub-regions surrounded by branches, we found that the interaction between rivers and groundwater is dominated for whole Hua-Lien River basin. However, the recharge from passes at upstream of branches is significant for sub-regions, the interaction between rivers and groundwater has relatively small amount of water exchange. With the dry year data in 2002, the results for applying different withdrawal rates in Feng -Lin area show that the sustainable withdrawal rate of groundwater in Fon-Lin area need to be less than 4 cms/day. The required discharge of Feng-Lin area now was evaluated as 3. 12 CMS which is smaller than the sustainable quantity.