Byung Il Yoon

The Cross-sectional Mass Flux Observation at Yeomha Channel, Gyeonggi Bay at Spring Tide During Dry and Flood Season

To calculate the total mass flux that change in dry and flood season in the Yeomha Channel of Gyeonggi Bay, the 13 hour bottom tracking observation was performed from the southern extremity. The value of the total mass flux(Lagrange flux) was calculated as the sum of the Eulerian flux value and stroke drift value and the tidal residual flow was harmonically analyzed through the least-squares method. Moreover, the average during the tidal cycle is essential to calculate the mass flux and the tidal residual flow and there is the need to equate the grid of repeatedly observed data. Nevertheless, due to the great differences in the studied region, the number of vertical grid tends to change according to time and since the horizontal grid differs according to the transport speed of the ship as a characteristic of the bottom tracking observation, differences occur in the horizontal and vertical grid for each hour. Hence, the present study has vertically and horizontally normalized(sigma coordinate) to equate the grid per each hour. When compared to the z-level coordinate system, the Sigma coordinate system was evaluated to have no irrationalities in data analysis with 5% of error. As a result of the analysis, the tidal residual flow displayed the flow pattern of sagging in the both ends in the main waterway direction of dry season. During flood season, it was confirmed that the tidal residual flow was vertical 2-layer flow. As a result of the total mass flux, the ebb properties of 359 cm/s and 261 cm/s were observed during dry and flood season, respectively. The total mass flux was moving the intertidal region between Youngjong-do and Ganghwa-do.

Relation of Freshwater Discharge and Salinity Distribution on Tidal Variation around the Yeomha Channel, Han River Estuary

Salinity distribution in estuary and tidal river is presented by many parameters including tidal forcing, river discharge and geographical effect. Understanding the characteristics of salinity structure is very important in the aspect of water-quality, ecological, and engineering viewpoint. Field measurement was carried out to study the distribution of salinity structure at 2 surface stations at Yeomha channel in the Han River estuary. The results of short- and long-term salinity change according to short and long tidal variability is investigated. For analyzing the axial salinity distribution at Yeomha channel, the salinity data from NFRDI is used in this study. The relationship between freshwater discharge and salinity distribution is represented through the nonlinear regression equation. The empirical equation for salt intrusion length scale, including tide, river discharge, and topographical effect is presented. As the comparison of empirical equation and existing data collected in study area, the characteristic of salt intrusion length and salinity distribution is changed by tide, fresh water, and geographical effect.

The Regional Classification of Tidal Regime using Characteristics of Astronomical Tides, Overtides and Compound Tides in the Han River Estuary, Gyeonggi Bay

In this study, we investigate tidal wave propagation characteristics, and classify regional tidal regime using tidal form number considered distribution of astronomical tide, overtides, and compound tides in the Han River Estuary, Gyeonggi Bay. The characteristics of the tidal wave propagation in main channels show dominance of major tidal constituents (e.g., and ) contributing to the astronomical tide however, distinct increasing of shallow water (e.g., M4) and long period (e.g., MSf) components toward up-estuary. Using the characteristics of tidal form number to astronomical tide, overtides, and compound tides, the regional tidal regime could be assorted into three regions. Firstly, a dominance area of astronomical tide was presented from open sea to a front of Incheon Harbor (Yeomha channel) and to north entrance of Seokmo channel. The area between south and north entrance of Yeomha channel and Ganghaw north channel classified into zone of showing strong shallow water components. It could be separated into upper estuary, upstream the Singok underwater dam, showed dominance of shallow overtides (e.g., M4 and MS4) water and long-term compound tides (e.g., MSf) larger magnitude than astronomical tide. The shallow water components was earlier generated in lower part (south entrance) of Yeomha channel have strong bottom by effect of shallower and narrower compared with Seokmo channel. Tidal asymmetries of upper estuary cause by a development of overtides and compound tides are mainly controlled by influence of man-made structure.

Role of Baroclinic Processes on Flushing Characteristics in a Highly Stratified Estuarine System, Mobile Bay, Alabama

Flushing of an estuary quantifies the overall water exchange between the estuary and coastal ocean and is crucially important for water quality as well as biological and geochemical processes within the system. Flushing times and freshwater age in Mobile Bay were numerically calculated under realistic and various controlled forcing conditions. Their responses to external forcing were explained by the three-dimensional characteristics of general circulation in the system. The flushing time ranges from 10 to 33 days under the 25th–75th percentile river discharges, nearly half of the previous estimates based on barotropic processes only, suggesting the important contribution of baroclinic processes. Their influence, quantified as the “new ocean influx,” is on the same order of the river discharge under low to moderate river discharge conditions. The baroclinic influence increases and then decreases with increasing river discharge, aligning with the response of horizontal density gradient. By enhancing the net influx from the ocean mainly through density-driven circulation, baroclinic processes contribute to reduce flushing times. The three-dimensional circulation, which differs greatly between the wet and dry seasons, explains the temporal and spatial variations of the flushing characteristics. Wind forcing influences the three-dimensional circulation in the system with easterly and northerly winds tending to reduce the flushing time, while southerly and westerly winds the opposite.

Temporal Variability of Velocity Structure according to Artificial Discharge in Yeoungsan Lake

ABSTRACT Song, J.I.; Kim, J.W.; Yoon, B.I., and Woo, S.-B., 2017. Temporal variability of velocity structure according to artificial discharge in Yeoungsan Lake. In: Lee, J.L.; Griffiths, T.; Lotan, A.; Suh, K.-S., and Lee, J. (eds.), The 2nd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 79, pp. 274–278. Coconut Creek (Florida), ISSN 0749-0208. An estuary dyke makes a closed environment in an artificial lake such as Yeoungsan Lake, thereby restricting material circulation. Because the artificial discharge serves as an external force with dominant effects on the internal material circulation of the lake, the effects of this discharge need to be investigated. This study analyzed the water temperature and velocity data for Yeoungsan Lake to identify the change in water temperature due to the discharge and the mechanism of the two-layer velocity structure found after the discharge. During the discharge, the downstream velocity and water temperature of the bottom layer of Yeoungsan Lake rapidly increased. After the discharge, a two-layer velocity structure repeatedly appeared, with flows in the downstream direction at the surface layer and upstream direction at the bottom layer. The water temperature, which rapidly increased at the bottom layer during the discharge, rapidly decreased after the water was completely discharged. Consequently, the water temperature after the discharge remained higher than that before the discharge. The inflow of water mass from the upstream area during the discharge led to a spatial density difference and generated the two-layer velocity structure after the discharge. The vertical mixing due to this two-layer velocity structure after the discharge increased the water temperature at the bottom layer and decreased stratification.

Study of the Residual Flow and Salinity during the Spring and Neap Tides at the Seokmo Channel, South Korea

ABSTRACT Yoon, B.I.; Choi, N.Y.; Gu, B.H.; Kim, J.W.; Song, J.I.; Lim, C.W.; Kim, M.S., and Woo, S.B., 2016. Study of the residual flow and salinity during the spring and neap tides at the Seokmo channels, South Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1422 - 1426. Coconut Creek (Florida), ISSN 0749-0208. The Seokmo (SM) channel of Gyeonggi Bay, located in the South Korea, exhibits unique and complex estuarine circulation characteristics. This study analyzed the salinity observations, and the cross-sectional variations in the residual current and strengths of stratification by tidal current, along two cross-channels transects, during the 13-hour periods of the spring and neap tides, respectively. The cross-sectional averaged residual velocity, at the northern entrance of the SM channel, showed a seaward directional flow of 0.05 m/s during the neap tide, and 0.21 m/s during spring tide. At the southern entrance, the residual current showed two-layer circulation with a landward flow in the bottom layer, and a seaward flow in the surface layer. The spatial characteristics of the landward residual current, at the southern entrance are different for the eastern and western sides of the channel, depending on the spring and neap tidal cycles. The variation in the location of the observed landward residual current, caused by the changes in spring and neap tidal cycles, and the correlation between this variation and the stratification, were analyzed using the Richardson number. At the northern and southern end of the SM channel, a landward residual current appeared in the location that Richardson number was large. These results suggested that the cross-sectional residual current pattern, at the SM channel, changes depending on freshwater and topographical influences, and is sensitive to tidal changes, such as changes in the spring and neap tidal cycles.

Spatial and Temporal Variability of Residual Volume Transport according to Artificial Freshwater Discharge in Yeoungsan River Estuary, South Korea

ABSTRACT Song, J.I.; Kim, J.W.; Yoon, B.I., and Woo, S.B., 2016. Spatial and temporal variability of residual volume transport according to artificial freshwater discharge in Yeoungsan river estuary, South Korea. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 153–157. Coconut Creek (Florida), ISSN 0749-0208. To determine the effect of artificial freshwater discharge on the spatial and temporal variability of residual current and residual volume transport, current and density profile data have been analyzed in the Yeoungsan River estuary (YRE), South Korea. Current and density data were obtained from three transects during no freshwater discharge and during freshwater discharge. The residual current structure is complex (e.g., vertically multi-layer) during no freshwater discharge, due to the combined influence of tides, wind, and topography. In contrast, strong freshwater discharge influences vertical mixing at the surface layer and no mixing at the bottom layer. This mixing characteristic causes a salinity gradient with depth and significant stratification. The direction of residual volume transport is flood-direction during no freshwater discharge and ebb-direction during freshwater discharge. Residual volume transport and stratification are shown to be dependent on artificial freshwater discharge in the YRE.