HYDROGEOLOGICAL PROPERTIES OF RIVERSIDE DEPOSITS IN THE MIDDLE AND LOWER NAKDONG RIVER BASIN

This study characterizes hydrogeological properties of fluvial deposits in the middle and lower parts of the Nakdong River. The concave and convex banks of the meandering river have their characteristic hydrogeology. Near Gumi Bridge, Waegwan Bridge, and Seongju Bridge of the middle Nakdong River, thirteen boreholes were drilled at the riverside deposits to reveal hydrogeology and geochemistry. In addition, groundwater level and river level were correlated. Two boreholes were drilled at the convex bank near the Gumi Bridge and one borehole at the concave bank. Two boreholes were completed at the concave bank and two boreholes at the convex bank of the Waegwan Bridge. In the Seongju Bridge area, four boreholes and three boreholes were installed at the concave bank and the convex bank, respectively. In the downstream area, nine wells were constructed at the concave bank in Book-Myeon bank filtration area, and seven wells at the convex bank in Daesan-Myeon bank filtration area. Drill data showed thicker sandy gravel layer at the concave bank than at the convex bank. Transmissivity was higher in the concave area than in the convex area. On the contrary, storativity was greater in the convex area than in the concave area. The ionic concentration was higher in the convex area than in the concave area. Groundwater level and stream level were correlated more highly in the concave area than in the convex area. This is explained by high hydraulic energy acting on the concave bank where the fine materials are removed and coarse materials are remained. As consequence, groundwater flows fast in the convex zone, inducing low ionic concentration due to short time for water-mineral reaction. High stream energy at the concave bank results in high correlation between groundwater level and stream level. In the convex area, fine materials deposit, leading high storativity, low transmissivity, and high ionic concentration. The correlation coefficient between groundwater and stream level is relatively low in the convex area. This study was financially supported by the Sustainable Water Resources Research Center under the 21st Century Frontier R&D Program (project no: 3-4-2), by the Fundamental Environment Survey Project by Nakdong River Water Environment Laboratory, and by the Second Stage of the BK21 Project, Ministry of Education, Korea.