SEDIMENTARY PROCESSES OF BARRIER-LAGOON SYSTEM IN THE NAKDONG RIVER ESTUARY, SOUTH KOREA

Abstract

The Nakdong River estuary on the southeastern coast of Korean Peninsula is an enclosed type with two large estuarine dams that were constructed in 1934 and between 1983 and 1987. The estuary has been characterized as barrier-lagoon system with various subenvironments and microtidal with a mean tidal range of 1.07 m. The sedimentary analyses, monitoring short-term sedimentation rates and suspended sediments were investigated to understand characteristics of depositional environments in barrier-lagoon system of the Nakdong River Estuary. The surface sediments generally showed sand sediment was dominated in the seaward side of barrier islands and muddy sand sediment was dominated on the lagoon. In comparison of surface sediment distributions in the summer 2015 and 2016, sandy sediments expanded to the north of lagoon from the barrier islands. The short-term sedimentation rates from May 2015 to May 2016 were obtained that the deposition was dominated on the tidal flat between mainland and Jinudo and Sinjado with the net deposition rate of 10.09 mm/year and 12.38 mm/year, respectively. The erosion was dominated on the tidal flats at Eulsukdo, located on the east side of the system, with an annual erosion rate of -13.15 mm/year. Two 12.5-hours anchoring surveys at inlets were revealed that net suspended sediments were transported to the open sea during a tidal cycle in summer 2015 and 2016. The sedimentary processes of the anthropogenically altered barrier-lagoon system in Nakdong estuary showed that sediments transported into the lagoon through inlets during flood condition and moved to westward and deposited sediments on the tidal flat and channels near dams in low energy environments (Figure 1). In the east side of the system, sediments flowed out the sea with discharge from Nakdong Dam during ebb condition.