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

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 (F-S) was calculated in three cross sections of the Yeomha Channel and was decomposed into three components (Q(f)S(0): advective salt transport; F-E: steady shear dispersion; F-T: tidal oscillatory salt transport). During the dry season with strong tidal forces, the total salt transport patterns were mainly dominated by Q(f)S(0). During the wet season with high river discharge, the total salt transport patterns were determined by the balance between Q(f)S(0), F-E, and F-T. The long-term tidal constituents (MSf and M-m) were the main mechanisms causing Q(f)S(0) with the spring-neap variation during the dry season. The tidal trapping effect, caused by a phase difference of less than 90 degrees between tidal current and salinity, generated landward F-T 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 degrees, resulting in a much stronger landward F-T. 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.

Automated summary

Many estuaries are damaged by material movements such as marine debris, suspended sediment, and pollutants. Understanding the estuarine circulation system is crucial for addressing these issues. This study applies a three-dimensional hydrodynamic model in the Yeomha Channel to investigate salt transport mechanisms. The model results are validated by comparing them with in-situ data, and the study identifies the dominant factors for salt transport patterns in different seasons. Long-term tidal constituents and tidal trapping effect are found to be unique characteristics contributing to material circulation in hypertidal estuaries.