Study on Variability of Residual Current and Salinity Structure According to River Discharge at the Yeoungsan River Estuary, South Korea

The Yeoungsan River Estuary (YRE) made change of estuarine circulation environment at not only control of inflow of freshwater but also decreasing tide speed under construction of estuary bank. The estuarine circulation in the estuary made change rapidly at discharge of the estuary bank. We investigated variation of salinity and residual current in study area during freshwater discharge and non-discharge period. To determine effect of artificial freshwater discharge on the spatial and temporal variability of the residual current and salinity distribution, current and density profile data were analyzed in partially stratified YRE. The current and density data, obtained from two cross-sectional transects, was conducted during freshwater discharge and non-freshwater discharge. We observed flow rate and salt during 13 h with 1 h interval to investigate changes of marine environment. The residual current structure is complex, such as multi-layer, during non-freshwater discharge because tides and wind effects combined with topography influences. Strong freshwater discharge is influences to vertical mixing at the surface layer,however freshwater is not effected at the bottom layer. These distinction of freshwater effect causes the salinity gradient and strongly stratification. Freshwateris toward to open-sea through surface layer during freshwater discharge period. In other words, the distinction of residual current and the stratification are controlled according to whether artificial freshwater discharge or not.