Comparison of Time Series of Alluvial Groundwater Levels before and after Barrage Construction on the Lower Nakdong River

Increasing the river cross-section by barrage construction causes rises in the average river water levels and discharge rates in the rainy season. The time series patterns for groundwater levels measured at 23 riverside monitoring wells along the lower Nakdong River are compared for two cases: before and after water-filling at the Changnyeong-Haman Barrage. Monthly average groundwater levels indicate a distinct increase in groundwater levels in the upstream riverside close to the barrage. River-water level management by barrage gate control in August, during the rainy season, resulted in a 0.1 m decrease in groundwater levels, while water-filling at the barrage in December caused a 1.3 m increase in groundwater levels. The results of hierarchical cluster analysis indicate that seven groundwater monitoring wells and river water levels were in the same group before barrage construction, but that this number increased to 14 after barrage construction. Prin-cipal component analysis revealed that the explanation power of two principal components corresponding to river fluctu-ation, PC1 and PC2, was approximately 82 % before barrage construction but decreased to 45 % after construction. This finding indicates that the effect of the river level component that contributes to change in groundwater level, decrease