Relative contribution of dam construction and land reclamation to geomorphological change in the Nakdong Estuary

Throughout human history, the Nakdong River Estuary (NRE) of Korea has been developed for various human purposes. Two estuarine dams were built in 1934 and 1987, respectively, to ensure freshwater storage by preventing saltwater intrusion. About 17 km² of tidal flats were reclaimed to generate land for agriculture and industry from 1927 to 2009. These anthropogenic developments altered the regime of hydrodynamics and sediment transport, which enhanced sedimentation by up to 6 cm/year in the Nakdong estuary. This study aims to determine the relative importance of human alterations to the increased sedimentation by using the ROMS (Regional Ocean Modeling System) routines for sediment transport. Four model simulations were carried out: 1) dam construction, 2) tidal flat reclamation, 3) both dam construction and reclamation, 4) pristine estuary. The model results were then analyzed to evaluate effects of different Anthropocene developments on overall deposition and erosion. The dam construction significantly changed the hydrodynamics by enhancing the variation of discharge between flood and dry seasons. This variation of discharge caused the environment to be river dominant during the flood season, resulting in high deposition in east Nakdong region. The reclamation of tidal flats reduced the accommodation space for sediment. As a result, the sedimentation rate increased compared to the pre-development, pristine environment.