• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.1
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• pp.13-23
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• 2008

In coastal region, eutrophication, Do deficit and red tide are frequently occurred by influx of fresh water. When the fresh water containing pollutants is discharged into the sea, the surrounding water is contaminated by dispersion of freshwater flowing into coastal waters. The prediction and analysis about the dispersion process of the discharged fresh water should be conducted. A modeling system using GUI was developed to simulate hydrodynamic flow and fresh water dispersion in coastal waters and to analyze the results efficiently. The modeling module of the system includes a tide model using a finite element method and a fresh water dispersion model using a particle-tracking method. This system was applied to predict the tidal currents and fresh water dispersion in Mokpo coastal zone. To verify accuracy of the hydrodynamic model, the simulation results were compared with observed sea level and time variations of tidal currents showing a good agreement. The fresh water dispersion was verified with observed salinity distribution. The dispersion model also was verified with analytic solutions with advection-diffusion problems in 1-dimensional and 2-dimensional simple domain. The system is operated on GUI environment, to ease the model handling such as inputting data and displaying results. Therefore, anyone can use the system conveniently and observe easily and accurately the simulation results by using graphic functions included in the system. This system can be used widely to decrease the environmental disaster induced by inflow of fresh water into coastal waters.

• Journal of Korea Water Resources Association
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• v.47 no.11
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• pp.1087-1094
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• 2014

Saltwater pumping method can be used to mitigate saltwater intrusion in coastal aquifers. However, the saltwater pumping well may discharge large freshwater along with saltwater, thereby wasting precious resources. A double negative barrier was proposed: an inland well to capture freshwater and a saltwater well near the coastline to pump saltwater. A previous study anaylzed effects of double negative barriers in dispersion-dominated coastal aquifers and determined the critical pumping rate at the saltwater well which minimized the saltwater ratio at the freshwater well. However, the study resulted in 1~15% of saltwater ratios, which were too high, for example, for drinking water standards. This study analyzed cases that were considered in the previous study, but for advection-dominated cases, and found that freshwater with sufficiently low saltwater ratios could be developed at the freshwater well. In addition, for optimal groundwater management of a watershed not only the minimum saltwater ratio at the freshwater well but also the least freshwater wasted at the saltwater well must be pursued.

• Korean Journal of Hydrosciences
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• v.7
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• pp.1-8
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• 1996

The location and the shape of a freshwater transition zone in a coastal aquifer are affected by many hydraulic variables. To data most works to determine the effects of these variables are limited to qualitative comparison of transiton zones. In this work characteristics of transition zones are analyzed quantitatively. The investigation is limited to a steady-state transition zones. Three dimensionless variables are defined to represent characteristics of steady-state transition zones. They are maximum introsion length, thickness, and degree of stratification. Effects of principal hydraulic variables (velocity and dispersivity) on these characteristics are studied using a numerical model. Dimensional analysis is used to systematically analyze entire model results. Effects of velocity and dispersivity are seem clearly. From this study, increase in velocity is found to cause shrinkage of transition zones. This observation contradicts claims by some that, because dispersion is proportional to velocity, increase in velocity would cause expansion of transition zones.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2000.10a
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• pp.371-377
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• 2000

Environmental impact on a land reclamation project, Hwaong tidal barrier was studied using the dispersion and advection model to predict the influence of polluted water discharged from freshwater reservior. The simulation results show that the distribution of concentration by influence of polluted water discharged during a tidal cycle appeared to be extinguished at atmost all points after two tidal cycle. Peak concentration near the sluice gate is found out to be higher during the spring tide than neap tide. Equi-concentration contour line appeared to distributed a longer according to line of sea dike in spring tide than neap tide. The reasons is because influence by currents of northwest direction is a stronger, compared to spring tide and neap tide in the flood tide.

• Water for future
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• v.28 no.2
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• pp.137-143
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• 1995

The location and the shape of freshwater-saltwater transition zones in coastal aquifers are affected by many hydraulic variables. To date most work to determine the effects of these variables are limited to qualitative comparison of transition zones. In this work characteristics of transition zones (maximum intrusion length, thickness, and degree of stratification) are quantified, and effects of principal hydraulic variables(velocity and dispersivity) on these characteristics are studied using a numerical model. Dimensional analysis is used to assemble entire model results. Effects of velocity and dispersivity are seen clearly. From this study, increase in velocity is found to cause shrinkage of transition zones. This observation contradicts claims by some that, because dispersion is proportional to velocity, increase in velocity would cause expansion of transition zones.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1189-1192
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• 2005

Due to their slow degradation properties, hydrophobic organic contaminants in estuarine sediment have been a concern for risks to human health and aquatic organisms. Studies of fate and transport of these contaminants in estuaries are further complicated by the fact that hydrodynamics and sediment transport processes in these regions are complex, involving processes with various temporal and spatial scales. In order to simulate and quantify long-term attenuation of Polycyclic Aromatic Hydrocarbons (PAH) in the Elizabeth River, VA, we develop a modeling approach, which employs the U.S. Environmental Protection Agency's water quality model, WASP, and encompasses key physical and chemical processes that govern long-term fate and transport of PAHs in the river. In this box-model configuration, freshwater inflows mix with ocean saline water and tidally averaged dispersion coefficients are obtained by calibration using measured salinity data. Sediment core field data is used to estimate the net deposition/erosion rate, treating only either the gross resuspension or deposition rate as the calibration parameter. Once calibrated, the model simulates fate and transport PAHs following the loading input to the river in 1967, nearly 4 decades ago. Sediment PAH concentrations are simulated over 1967-2022 and model results for Year 2002 are compared with field data measured at various locations of the river during that year. Sediment concentrations for Year 2012 and 2022 are also projected for various remedial actions. Since all the model parameters are based on empirical field data, model predictions should reflect responses based on the assumptions that have been governing the fate and sediment transport for the past decades.

• Korean Journal of Ecology and Environment
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• v.53 no.4
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• pp.331-335
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• 2020

The red swamp crawfish (Procambarus clarkii) is native to northeastern Mexico and south-central United States. But the species has been introduced to other parts of the world, and cause ecological problems including habitat destruction and competition with indigenous species. In this study, we identified the distribution of P. clarkii in the freshwater system in Korea. P. clarkii were collected in the field sampling and it is assumed that they have settled in major domestic water systems of Korea including six points in the Yeongsangang River, five points in the Mangyeonggang River, two points in the Seomjingang River, and one point in the Geumgang River. In particular, more than 20 individuals were found in Seobongri, Wanjugun and Mosanri, Hampyeonggun, which are believed to form a relatively large population. Considering high mobility and environmental adaptability of the species, the possibility of their dispersal to other water systems is very high. Therefore, continuous monitoring and assessment of their distribution and potential spread are required and effective management to remove them policy is needed to prevent damage in the Korean ecosystem.

• Journal of the Korean Society for Marine Environment & Energy
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• v.3 no.4
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• pp.37-55
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• 2000

Two-dimensional numerical experiments and field surveys have been conducted to clarify some environmental variations in the flow and sedimentation in the adjacent seas after the construction of a tidal embankment. Velocities of flow and water levels in the bay decreased after the construction of the barrage. When the freshwater was instantly released into the bay, the conditions of flow were unaltered, with the exception of a minor variation in velocities and tidal levels around the sluices at the ebb flow. The computational results showed that freshwater released at the low water reached the outside of the bay and then returned to the inside with the tidal currents at the high water. The front sea regions of the embankment had a variety of sedimentary phases such as a clayish silt, a silty clay and a sandy clayish silt. However, a clayish silt was prevalent in the middle of the bay. On the other hand, the skewness, which reflects the behaviour of sediments, was $\{pm}0.1$ at the front regions of the embankment while it was more than ±0.3 in the middle of the bay. Analytical results of drilling samples acquired from the front of the sluice gates showed that the lower part of the sediments consists of very fine silty or clayish grains. The upper surface layer consisted of shellfish, such as oyster or barnacle with a thickness of 40～50 cm. Therefore, it seemed that the lower part of the sediments would have been one of intertidal zones prior to the embankment construction while the upper shellfish layer would have been debris of shellfish farms formed in the adjacent seas after the construction of the embankment. This shows the difference of sedimentary phases reflected the influence of a tidal embankment construction.

• Journal of Korea Water Resources Association
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• v.32 no.5
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• pp.547-555
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• 1999

The economical manufacturing process of fluorescent sediments (FS) which makes use of the understanding of coastal sediment path has been suggested with respect to the Lagrangian viewpoint. First, the fluorescent liquids were made by the mixing of the fluorescent materials, acetone, and xylene. Second, the sediments collected in Gamami beach were desalinized by the freshwater washing, dried indoors to protect the fine-sediment scattering, and classified by the sieve analysis. Finally, the FS which have seven different colors were manufactured by the mixing of fluorescent liquids and prepared sediments. The FS were used to figure out the major sediment supply routes of the intake channel in the YoungKwang nuclear power plant. From the field experiments, it was shown that the sediments were suspended and dispersed by the strong seasonal NW wind and the tide, and the sediments in suspension were flowing into the intake channel due to very strong suction speed. All the FS injected in stations were detected in the channel sampling points, thus we concluded that the sediments in suspension and dispersion were flowing into the intake channel from all directions in adjacent coastal zone.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.63-75
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• 2013

The Inner Port Phase 2 area of the Pyeongtaek-Dangjin Port is enclosed by a total of three permeable sea-walls, and the disposal site to the east of the Inner Port Phase 2 is also enclosed by two permeable sea-walls. The maximum tidal range measured in the Inner Port Phase 2 and in the disposal site in May 2010 is 4.70 and 2.32 m, respectively. It reaches up to 54 and 27%, respectively of 8.74 m measured simultaneously in the exterior. Regression formulas between the difference of hydraulic head and the rate of interior water volume change, are induced. A three-dimensional numerical hydrodynamic model for the Asan Bay is constructed incorporating a module to compute water discharge through the permeable sea-walls at each computation time step by employing the formulas. Hydrodynamics for the period from 13th to 27th May, 2010 is simulated by driving forces of real-time reconstructed tide with major five constituents($M_2$, $S_2$, $K_1$, $O_1$ and $N_2$) and freshwater discharges from Asan, Sapkyo, Namyang and Seokmoon Sea dikes. The skill scores of modeled mean high waters, mean sea levels and mean low waters are excellent to be 96 to 100% in the interior of permeable sea-walls. Compared with the results of simulation to obstruct the flow through the permeable sea-walls, the maximum current speed increases by 0.05 to 0.10 m/s along the main channel and by 0.1 to 0.2 m/s locally in the exterior of the Outer Sea-wall of Inner Port. The maximum bottom shear stress is also intensified by 0.1 to 0.4 $N/m^2$ in the main channel and by more than 0.4 $N/m^2$ locally around the arched Outer Sea-wall. The module developed to compute the flow through impermeable seawalls can be practically applied to simulate and predict the advection and dispersion of materials, the erosion or deposion of sediments, and the local scouring around coastal structures where large-scale permeable sea-walls are maintained.