Influence on Water Resource System of Feitsui Reservoir if Inter-Basin Water Transport from Nanshi River

Taipei Water Department serves the Greater Taipei Area with water resources that approximately 99% come from the Xindian River (Nanshi River, and Feitsui Reservoir releasing water), and has been considered water-sufficient. During the 2020-2021 drought event, the inter-basin water transport from Nanshi River to Shimen Reservoir had been planned and assessed by the Taiwan government. However, this engineering plan aroused intense social concern, and thus its environmental impact assessment for the plan was withdrawn. Nevertheless, the risks of water shortage and drought remain in Taiwan, and similar plans may reappear again in the future. Since stream flow from the Nanshi River catchment provides approximately 70% of the raw water supplied to purification plants, inter-basin water transport may increase the stress on the Greater Taipei Area. To quantify the impact of water transport, we built a system dynamic model (SDM) and simulated the operation of Feitsui Reservoir and the water resource system with the historical inflow of the Feitsui Reservoir. The inter-basin transported water was assumed as a ratio (0 to 20% was used) of the historical flow rate of the Nanshi River. Two scenarios were considered: (1) transporting year-round, and (2) transporting only during winter. We also simulated the water level of the Shimen Reservoir using an SDM constructed in our previous study. The simulation results indicate that “transporting only during winter” does not remarkably aggravate the water stress on the water supply system that belongs to the Feitsui Reservoir, nor does it noticeably raise the water level of the Shimen Reservoir. “Transporting yearround” noticeably increases the water level of the Shimen Reservoir during drought events, while this measure results in decreases in the Feitsui Reservoir’s water level and increases in the water stress of Feitsui Reservoir. Nonetheless, the score of water stress risk usually increases inconsiderably, except during the severe drought event in 2020.