• Journal of the Korean Society for Marine Environment & Energy
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• v.9 no.1
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• pp.36-44
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• 2006

Cohesive sediment transport in coastal region has been studied by numerical modeling. A finite element numerical model was setup to simulate hydrodynamics and sediment transport in the coastal region with complex topography. Only physical features of observed sediments has been used to determine erosion rates of bottom sediments together with the previous research results. The simulation results using the simply determined equation of erosion rates were compared with time variations of the observed SS concentration and showed good agreements. In conclusion, this method can be used to estimate transport of cohesive sediment conveniently.

• Ocean and Polar Research
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• v.25 no.spc3
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• pp.399-408
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• 2003

The behavior of Suspended Sediment Concentrations (SSC) around a silt screen in a microtidal coastal area was hydrodynamically measured. The current speed at the mid-layer about 30m downstream of the screen reduces to about half that at the same distance upstream. It was caused by the contraction of the vertical section due to the screen. Even during a relatively weak storm period the SSC increases to that of the value caused by dredging. Section-averaged SSC at the downstream of the screen is higher by about 60% than that at the upstream, suggesting that the silt screen plays an adverse effect rather than a constructive role in the reduction of SSC generated by dredging.

• Ocean and Polar Research
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• v.25 no.spc3
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• pp.409-416
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• 2003

Coastal development works generally increase the suspended sediment concentration of the ambient water, causing environmental impacts in various manners. The most active measures in three sides have been reviewed for their applicabilities in Korea. Referring to the cases in the USA, the legislation of environmental windows seems to be not proper for Environmentally Sound and Sustainable Developments (ESSD) until sufficient scientific data are obtained to address the individual issues of potential negative impacts. Feedback monitoring can be regarded as the best way for ESSD. Korea also has the basic legal system for the feedback monitoring as well as Environmental Impact Assessments (EIA). However, the frequency, period and parameter of related surveys should be improved for the true ESSD. Moreover, environmental facilities such as environmental dredgers should be widely used for mitigating environmental Impacts caused by coastal development works.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.3
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• pp.37-43
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• 2009

The objective of this study was to investigate the basic relationships between spectral reflectance and varying concentrations of sediment in surface waters. An experimental method for determining suspended sediment concentration (SSC) in the water by use of a spectroradiometer above the water surface, in visible and near-infrared (NIR) wavelengths, is applied. The main advantage of the method is the direct comparison of spectral reflectance and the SSC, but it requires an accurate knowledge of the water body and sediment. Therefore numerous spectroradiometric measurements are carried out in situ measurements, for SSC, ranging from zero to 100 percentage and two types of sediment applied in the water tank. The results indicate that the suspended sediment causes increasing spectral reflectance response in waters. We observed that spectral reflectance increases with SSC, first at the lower wavelengths (430-480 nm), then in the middle wavelengths (570-700 nm), and finally, in the NIR domain (800-820 nm); a characteristic maximum reflectance appears at 400-670 nm. Relationships between the wavelength, integral value, and the SSC were evaluated on the basis of the regression analysis. The regression curve for the relation between the wavelength, integral value, and the SSC were determined ($R^2$>0.98). Finally, the specular wavelength can be estimated to recognize the sediment and to improve SC estimation accuracy in the water.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
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• 2003.08a
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• pp.344-352
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• 2003

Sediment plumes arising from various coastal works can cause detrimental effects on the coastal ecosystem in various manners. Although the most active countermeasure against the plumes is to restrict the works to specified time periods known as environmental windows (Reine et al., 1998), silt screens have been widely used for reducing the spreading of suspended sediments (SS) generated by coastal works. (omitted)

• Journal of Environmental Science International
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• v.30 no.7
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• pp.507-517
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• 2021

In this study, the bathymetric data acquired from 2018 to 2020 and the precipitation and suspended sediment data were analyzed for changes in bathymetry owing to the discharge from the Nakdong River barrier and environmental factors, especially the torrential rain in 2020. Sediment erosion and deposition processes are repeated because of complex environmental factors such as discharge from the Nakdong River barrier and the influence of waves generated from the external sea. In the first half of the year after the dry season, bathymetric data showed relative erosion trends, whereas in the second half after the flood season, deposition trends were identified owing to the increase in sediment transport. However, the data from the second half of 2020 showed a large amount of erosion, resulting in tendencies different to those of erosion in the first half and deposition in the second half of the year. This result is judged to be influenced by the weather in the summer of 2020. The torrential rain in the summer of 2020 resulted in a higher force of erosion than that of deposition. In summary, the tendency for erosion is more significant than that of sedimentation, especially in the main channel area of the Nakdong River.

• Ocean and Polar Research
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• v.32 no.4
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• pp.337-350
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• 2010

This study conducted sedimentological and geophysical surveys for 3 years (2006-2008) in southern Gyeonggi Bay, Korea to elucidate temporal changes in subaqueous dune morphology on a sand ridge trending northeast to southwest that has been excavated by marine sand mining. The sand ridge (~20 m in height, ~2 km in width and 3~4 km in length) has a steep slope on the NW side and a gentle slope on the SE side, creating an asymmetric profile. Large (10~100 m in length) and very large (>100 m in length) dunes occurring on the SE side of the ridge show a northeastward asymmetrical shape, whereas dunes on the NW side destroyed by marine sand mining display a southwestward asymmetry. The comparison between Flemming (1988)'s correlation and the height-length correlation of this study indicates that tidal current and availability of sand sediment are major controlling factors to the development and maintenance of dunes. Depth and sedimentary characteristics (grain size) are not likely to be major controlling factors, but indirectly influence dune growth by hydrological and sedimentary processes. The length and the height of dunes decrease toward the southeastern trough away from the crest of the ridge. These features result from the decrease of tidal current and sediment availability. The length and the height of dunes on the southeast side decrease gradually over time. This is a result of the interaction between tidal current and the decrease in sediment availability due to sediment extraction by marine sand mining. Marine sand mining has destroyed the dunes directly, causing irregular shapes of shorter length and lower height. The coarse fraction of suspended sediments is transported and deposited very close to the sand pit. By contrast, relatively fine sediments are transported by the tidal current and deposited over a wide range by the settling-lag effect, resulting in a decrease of sediment grain size in the area where suspended sediments are deposited. In addition, marine sand mining, decreases the height of dunes. Therefore, morphological and sedimentological characteristics of dunes around the sand pits will be significantly changed by future sand mining activities.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.39-47
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• 2020

In order to investigate current characteristics at the Gungpyung beach, which is a macrotidal flat, field measurements were carried out in the summer and winter at the intertidal and the subtidal zones. The distribution of residual current at intertidal flat was dominant in the northward direction in the summer and dominant in the northward and southwestern directions in the winter. The direction and speed of the residual current in the winter are highly correlated with the significant wave height, and the turbidity is also highly correlated with the significant wave height. Therefore, in the winter, high sediment rates are suspended by high waves, and sediments are transporting due to the residual current in the southwest direction. On the other hand, it is expected that the northward residual current is predominant due to the small wave in the summer, and sediment transport does not occur largely due to less suspended sediments. In addition, sediment transport in the southern direction is blocked by the dock, which is the artificial structure, and the erosion occurs in the south side of the dock. The erosion pattern in the macrotidal zone of Yellow sea is dominated by seasonal waves, and blocking of sediments by artificial structure is very important.

• 한국해양학회지
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• v.22 no.2
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• pp.105-118
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• 1987

A series of anchor stations were occupied along the Keum EAstuary during six different periods of tidal and fluvial regimes. The results clearly show that the formation and evolution of the turbidity maximum play an important role in the sedimentary processes in this environment. The turbidity maximum in the Keum Estuary is primarily related to the tidal range at the mouth and is caused by the resuspension of bottom sediments. In this estuary, the turbidity maximum is not a permanent feature and shows semidiurnal, fortnightly and seasonal variations. Repetition of deposition and resuspension of fine sediments occur in response to the variation in current velocity associated with semidiurnal tidal cycles. The core of turbidity maximum shifts landward or seaward accordion to the flood-ebb succession. The turbidity maximum also shows a fortnightly variation in response to the spring-neap cycles. Thus, the turbidity maximum degenerates during neap-tide and regenerates during spring-tide. The freshwater discharge is also an important factor in the formation and destruction of the turbidity maximum. The increase in freshwater discharge in rainy season can create an ebb-dominant current pattern which enhances the seaward transport of suspended sediments, resulting in the shortening of residence time of suspended materials in the estuary. Thus, under this high discharge condition, the turbidity maximum exists only during spring-tide and starts to disappear as the tidal amplitude decreases.

• Economic and Environmental Geology
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• v.27 no.1
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• pp.101-113
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• 1994

Geochemical investigations based on measurements of water parameters and sampling of stream sediments have been carried out, in the Okdongcheon stream and its tributaries in the Sangdong area of South Korea. There are two main problems occurring in the Okdongcheon stream: an acid mine drainage in the upper reaches and toxic trace metal contamination of the stream sediments mainly in the lower reaches. Acid mine water originating from coal mining was neutralized at the confluence of the Cheonpyongcheon stream whilst suspended solids due to flocculation of iron in water caused turbidity which was undesirable. Sediments in the Okdongcheon stream have been contaminated by mining activites. Iron was heavily concentrated in sediments in the upper Okdongcheon whilst toxic trace metals including Pb, Cu, Zn, Co, Cd, As and Bi were accumulated in sediments at stations draining metallic mining areas and near the tailings dam. There is now a requrement to neutralise the acid mine drainage and to use site-specific analysis of biological communities to ensure the conservation and preservation of aquatic organisms.