A study on the characteristics of groundwater in choushui river alluvial fan - Analysis of groundwater decline

The characteristics of groundwater system in Choushui River alluvial fan are explored via analysis of groundwater decline curves. The pumping influence area is thoroughly analyzed during drought periods. Choushui River alluvial fan is an important groundwater source for the western Taiwan. The fan tail area is excessive use of groundwater. However the fan top area still has water supply potential. Therefore, the groundwater resources management can be improved if the groundwater planning is considered based on the whole groundwater system. The groundwater exchange between systems is basically resulted from the artificial pumping, the rainfall recharge, and the exchanges at the boundaries. During drought periods, the rainfall recharge volume decreases. The other two mechanisms have major influences and result in net water loss of the groundwater system and the decline of groundwater level. Therefore, the decline curves during drought periods are the combination of these two mechanisms. Larger river influence results in larger groundwater level gradient and groundwater loss, which mean steeper groundwater decline curves. By contrast, mild decline curves are observed when the artificial pumping has major influence. Hence, the groundwater decline curve is an important characteristic of a groundwater system. The decline curve information is traditionally obtained using manually time-consuming processes. In this study, the Python programming language is used to develop a realtime statistical analysis model for exploring the decline curve information. The developed model provides real-time average decline slope for each observation well and the variation of the decline curves in the studied area. The fan top area is majorly influenced by rivers while the artificial pumping dominates the central and tail areas of the groundwater system. The pumping influence is clearly observed at the coastal area at Yunlin which is consistent with previous studies. This study provides a direct information to distinguish the artificial influence from the natural influence in a groundwater system. This developed can be applied to other groundwater systems.