Change in sediment fl ux mechanisms under estuarine dam construction and reclamation in the altered Nakdong estuary,Korea

초록

The Nakdong Estuary (NRE) of Korea has been developed for variouspurposes over the last century. Estuarine dams were constructed tosecure freshwater and to prevent saltwater intrusion in 1934 and 1987,while about 17 km 2 of tidal fl ats were reclaimed to provide agriculturaland industrial land. These human alterations changed the regime ofhydrodynamic, intensifying the sedimentation rate up to 6 cm/year inthe Nakdong Esutary. This study aims to evaluate how the sedimenttransport mechanisms change by estuarine dam and reclamation and todetermine the relative contribution of these anthropogenic alterationsto the morphologic change of the Nakdong estuary. COAWST modelsimulation was performed over four scenarios (1) present condition withestuarine dams and reclamation, 2) no dams, 3) no reclamation, 4) nodams and reclamation. The sediment transport mechanisms wereevaluated via a sediment fl ux decomposition (Burchard et al., 2018). Thedam construction reduced the current velocity, resulting in a decreasedSSC, increased residence time of SSC, and increased sedimentation ratein the estuary. Reclamation didn’t signifi cantly change the currentvelocity from the current condition but caused an increase in SSC due todecreased accommodation space. In the main channel, the meansediment fl ux was dominantly seaward for all scenarios during adischarge period. During non-discharge periods, the seaward meansediment fl ux was dominant for scenarios 1) and 3), while the seawardtidal pumping and landward estuarine circulation contributed to theover all seaward mean fl ux for scenarios 1) and 3). The sediment fl uxmagnitude was always higher for scenarios 2) and 4), indicating that dam construction caused more signifi cant change to the sedimenttransport and morphologic change in the Nakdong estuary. This studyaids to understand the changes in sediment transport due to humandevelopment especially for micro-tidal Anthropocene estuaries.