As a result of recent climate change, the dry and wet seasons in Taiwan have become clearly distinguishable.
Although the duration of rainfall has decreased during the wet season, the intensity of the rainfall has increased during this period. The dry season has low rainfall. Because of the inconsistency in the duration and spatial distribution of rainfall and the difficulty in retaining water on steep slopes and where the velocity of the flow is great, Taiwan currently has plentiful rainfall but lacks water resources. Taiwan’s main water resources include surface water and groundwater. Since groundwater is less affected by evapotranspiration and man-made pollution, it is more stable water resource than other sources, although it only contributes to 20% of all usable water in Taiwan. This study uses a river recession analysis for the Jhuoshuei River Basin to analyze the basin’s baseflow coefficient (a) and the characteristic
drainage time scale (K). A water-balance conceptual model is used in this study. This uses low flow recession to
determine the changes in long-term groundwater storage during periods when there is no rainfall, without taking into account the effect of evaporation. The results show that the Zhoushui River Basin’s typical drainage duration constant is between 82 and 189 days, with an average of 118 ± 51 days. The analysis of changes in groundwater storage shows that except for the Zhangyun Bridge Station, which exhibits a decrease of 0.566mm/y, all gauge stations in the Jhuoshuei River Basin show increased storage. The findings of this study will serve as a reference for the future management and allocation of water resources.
Key Words: Low flow analysis, discharge, groundwater storage.