Mechanisms of Advective and Tidal Oscillatory Salt Transport in the Hypertidal Estuary: Yeomha Channel in Gyeonggi Bay

Abstract

Many estuaries have been damaged by such material movements as marine debris, suspended sediment, and pollutants. Understanding the estuarine circulation system is necessary to solve such problems. Salt transport analysis provides an insight into hydrodynamic processes about material circulation in the estuary. In this study, to understand the mechanisms of salt transport, a three-dimensional hydrodynamic model was applied in the hypertidal estuary system—Yeomha Channel in Gyeonggi Bay. The simulation period of the model was a total of 245 days (20 January to 20 September 2020), including the dry and wet seasons. The model results for the temporal variation in tide, current velocity, and salinity were validated by comparing them with the observed in-situ data. The total salt transport (FS) was calculated in three cross sections of the Yeomha Channel and was decomposed into three components (QfS0: advective salt transport; FE: steady shear dispersion; FT: tidal oscillatory salt transport). During the dry season with strong tidal forces, the total salt transport patterns were mainly dominated by QfS0. During the wet season with high river discharge, the total salt transport patterns were determined by the balance between QfS0, FE, and FT. The long-term tidal constituents (MSf and Mm) were the main mechanisms causing QfS0 with the spring–neap variation during the dry season. The tidal trapping effect, caused by a phase difference of less than 90° between tidal current and salinity, generated landward FT in the dry and wet seasons. In addition, the high river discharge during the wet season decreased the phase difference between tidal current and salinity to less than 70 °, resulting in a much stronger landward FT. This study suggests that the long-term tidal constituents and tidal trapping effect are unique characteristics that contribute to material circulation in the hypertidal estuary.

Impacts of Marine Construction on Tidal and Residual Characteristics: An Example from the Incheon Bridge

“…Overall, the salinity gradient and tidal asymmetry were spatially modified due to the construction of the IB, which could cause changes in mass transport as the opposite residual patterns between the northern and southern ends of the IB were induced. This can lead to different results from Lee, Kim, and Woo (2023), and it is necessary to apply the piers of the bridge for modeling related to mass transport.…”

“…But, there are few research results that quantitatively suggest how the residual flow pattern is changed by the construction. Lee, Kim, and Woo (2023) studied the salt transport mechanism in Gyeonggi Bay using a Finite Volume Community Ocean Model (FVCOM). However, in the aforementioned study, the grid corresponding to the IB was not applied, so it was not possible to directly evaluate the change of residual flow.…”

“…However, in the aforementioned study, the grid corresponding to the IB was not applied, so it was not possible to directly evaluate the change of residual flow. Therefore, in this study, a simulation was performed to evaluate the effect of the IB construction on the residual flow pattern by modifying the resolution of the FVCOM grid used by Lee, Kim, and Woo (2023).…”