• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.1
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• pp.40-49
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• 1999

A laboratory flume experiment, using turbulence-generating acryl tank and natural sediments, was conducted to investigate the effects of salinity, concentration of suspended sediment, turbulence and clay minerals on the flocculation and settling of fine-grained suspended sediments. While experiments were run, a sequence of water samples were taken near the bottom of the tank to analyze the variations of size distribution and relative contents of clay minerals. The results of the salinity experiment indicate that median settling velocity ($W_{50}$) increases linearly with salinity. Different settling processes of suspended sediments under variable concentrations appear to be predictable, depending upon the range of the suspension concentration. At concentrations less than 200 mg/l, $W_{50}$ is rarely varied with concentration probably because of the individual--grain settling mode. In the range of 200 to 13,000 mg/l show $W_{50}$ and concentration a good relationship following an empirical formula: $W_{50}=0.45C^{0.44}$. This relationship, however, no longer holds in concentrations exceeding 13,000 mg/l; instead, a more or less reverse one is shown. This result suggests an effect of hindered settling. The turbulence effect is somewhat different from that of concentration. Turbulence accelerates the flocculation and settling susepended sediments at low concentration (200 mg/l), whereas at high concentration turbulence breaks floes down and impedes the settling. Size distribution of suspended sediments sampled near the bottom of the tank tend to be more negatively skewed and leptokurtic in turbulent conditions compared to those in static conditions. The clay mineral analysis from the sequential water samples shows that over time the content of smectite decreases most rapidly with illite remaining concentrated in suspension. This means that smectite, among other clay minerals, plays the most effective role in the flocculation of fine-grained sediment in saline water.

• 한국해양학회지
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• v.26 no.1
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• pp.38-46
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• 1991

size data of 1,044 surface sediments from Korean shelf area were compiled and reexamined. Size distribution curves of the sediments are unimodal (31% of the total number), bimodal (54%), or multimodal 915%), Size curves of the sediments and modal subpopulations of the mixed sediments show resemblance to normal curve in shape. The modal mean value shows systematic change along a direction inside the Recent mud belts of the southeastern Yellow Sea and west of Korea Strait. It was found that the areas covered by unimodal sand are minimal value areas of heavy metal and suspended sediment-concentration in the southeastern Yellow Sea and northern East China transport processes during Recent time. It was also found that the mode analysis is useful method to extract information from sediment size data.

• Journal of Ocean Engineering and Technology
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• v.19 no.4 s.65
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• pp.42-48
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• 2005

The sediment of Shihwa Lake contains an abundant quantity of cohesive sediments. The transport processes of the cohesive sediments are complex and difficult to predict, quantitatively. The cohesive sediments are the primary reason for the pollution of the environment and water quality in the coastal region. In this study, a column test has been performed. In order to quantify the settling velocities of sediment from Shihwa Lake, an experiment was conducted using a specially designed 1.8m tall settling column. A series of settling tests and physico-chemical property tests on Shihwa Lake cohesive sediments has been conducted to investigate the correlation between settling properties and their physico-chemical properties, which are represented as grain size distribution, mineralogical composition, and percentage oj organic contents. Experimental results of physico-chemical property tests show that Shihwa Lake sediments are relatively large in average grain $size(74\mu m)$ contain very small organic $material(6\%)$, and are dominantly composed of Quarts, which has relatively low cohesion. Thus, Shihwa Lake sediments might be specified as those whose settling properties are more influenced by gravity than cohesion. It is concluded that the magnitude of settling velocities of muddy sediments can be quite different, regionally, and it implies that field or laboratory experiments for settling velocity measurement should be preceded over the numerical modeling of muddy sediment transport, in order to obtain the reliable prediction results for a given specific site.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.838-845
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• 2006

Characterization of sediment in the riverbed is of importance for effective water quality management, yet have not been monitored sufficiently. This paper reports monitoring results of nutrient concentrations of sediments. Surface waters and sediments were sampled four times during rainy season at five monitoring points. Organics of overlying water were increased after high flow condition followed by decreasing tendencies. Soluble phosphorus fraction among total phosphorus was increased after high flow condition while total phosphorus was in decreasing tendencies. Monitoring result suggested that more extended monitoring scheme for flow rate, scouring velocity, and suspended material is required for analyzing relationship between water quality and sediment.

• 한국해양학회지
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• v.29 no.3
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• pp.269-277
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• 1994

Process of resuspension and accumulation well explaines the characteristics of surface sediment size distribution and suspended material in Deukryang Bay. Most of the surface sediments of the bay show asymmetric unimodal size distribution, which is found also in sediments from western part of the inner shelf mud area between Keomundo and Yokchido islands. Investigation of the size curves indicates that surface sediment in Deukryang Bay is a deposit of suspended coastal sediment transported east along southern coast of Korea. The distribution pattern of coarse sit fraction content in the surface sediment is very similar to that of computed current velocity (Lee, 1994), suggesting that fine sediment on the bed may reassumed and accumulate repeatedly due to shallow depth and strong tidal current in Deukryang Bay. The process of repeated resuspension and accumulate repeatedly due to shallow depth and strong tidal current in Deukryang Bay. The process of repeated resuspension and accumulation seems to be responsible not only to the asymmetric size distribution of the surface sediment, but also to the amount of suspended material in the bay. The difference of suspended material concentration between surface and near bottom water in summer is two times as large as that the in winter. This seems to derive from the fact that stratification of water mass prevails in summer, while total water mass is vertically mixed in winter. It was found that the most important factors to decide distribution of suspended material in Deukryang Bay are the physical properties of water mass such as current velocity and stratification, and water depth, in part with the supply of suspended sediment by rivers.

• 한국해양학회지
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• v.22 no.1
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• pp.25-33
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• 1987

The transport and fate of fine-grained, cohesive sediments in an estuary were investigated numerically. A numerical model of sediment entrainment, deposition, and transport has been developed by incorporating recent results of laboratory and field investigations. The time-dependent flow fields produced by fiver inflow and semi-diurnal tides, were calculated, and the corresponding distributions of suspended-sediment concentrations were obtained. The time-changes of sediment bed condition due to entrainment and deposition were obtained. The entrained sediments contribute initially to high sediment concentrations in the estuary basin. As the time passes, the suspended-sediment concentrations were much reduced by the seaward transport due to residual currents. The erosional and dipositional areas were appeared to be strongly dependent on the current-velocity fields and sediment properties of the estuary.

• Magazine of the Korean Society of Agricultural Engineers
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• v.44 no.4
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• pp.62-74
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• 2002

The purpose of this study is to find the variation of sedimentation patterns before Saemangeum reclamation. Residual flow before Saemangeum reclamation was calculated diagnostically from the observed water temperature and salinity data in May 1992 by the Marine Development Institute of Kunsan National University and wind data which were obtained from spring 1969 through winter 1977 by the Gunsan Meteorological Observatory. Three dimensional movements of injected particles due to currents, turbulence and sinking velocity are tracked by the Euler-Lagrange method. Calculated sedimentation patterns of riverine materials are highly similar to the observed ones. When suspended sediments with the size of soil grain of 60 ${\mu}m$ are injected from the Mangyeong River, their dispersion range of sediment is about 25km for 24 hours after the injection, while about 35km for 72 hours after the injection. When suspended sediments with the size of soil grain of 200 ${\mu}m$ are injected, their dispersion range of sediment is about 18km for 24 hours after the injection, while about 21km for 72 hours after the injection.

• Journal of Korean Society on Water Environment
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• v.23 no.2
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• pp.287-293
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• 2007

Heavy metal contamination and biological toxicity of mine drainages and sediments in abandoned mines were studied. Mine drainages had pH at a range of 2.94~7.86, and contained heavy metals at a toxic level. For coal mines, toxicity of mine drainage to Daphnia magna was attributable to acidic pH. In addition to the low pH, suspended heavy metals such as Zn and Cu contributed to toxicity of mine drainages at abandoned metalliferous mines. All mine sediments studied in this work showed biological toxicity to Chironomus riparius, having mortality at a range of 15~60%. However, its relationship with physicochemical properties including heavy metal content of the sediments was not statistically explained. Exceptionally clay ($< 2{\mu}m$ particle) content was negatively correlated with the biological toxicity for sediment samples collected at the same abandoned mines.

• Journal of Wetlands Research
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• v.8 no.3
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• pp.67-77
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• 2006

Sedimentological investigations on surface and suspended sediments were performed in Masan Bay of the South Sea in order to reveal recent changes in depositional environments concerning anthropogenic influence. Surface sediments had been classified as 3 sediment facies: mud, slightly gravelly mud, and gravelly mud. In general, mud facies with more than 60% of silt is predominant and slightly gravelly mud facies occurs at the watercourse of bay's central area. The silt-dominant mud faices appears to be predominant before and after dredging. Temperature and salinity changes during one tidal cycle for each season suggest that water columns were stratified without vertical mixing regardless of the season due to weak intensity of tide from the effect of geographical features. The effect of freshwater discharge from the land seems to be insignificant. The strongest current was observed during ebb tide in spring and autumn while observed during flood tide in summer and winter. Net sediment flux (fs) and net suspended sediment transport (Qs) for suspended sediment were determined by remaining drift developed here. Net suspended sediment transport loads were seaward with $62.02{\times}10^3kgm^{-1}$, $31.84{\times}10^3kgm^{-1}$ in spring and fall, respectively, and landward with $18.23{\times}10^3kgm^{-1}$, $3.22{\times}10^3kgm^{-1}$ in summer and winter, respectively.

• Structural Engineering and Mechanics
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• v.63 no.4
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• pp.567-574
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• 2017

Sedimentation tanks are essential structures to filter the suspended sediments in the inlet flow which are constructed at the inlet of the basins forked from rivers and irrigation canals. The larger the constructed tank, the better the sedimentation process is conducted. However, the construction and dredging costs increase. In this regard, improving the performance and sedimentation efficiency seem necessary by alternative methods. One of these effective methods is using baffle plates. Most of the studies carried out in this field are on the use of these baffles in the primary and secondary sedimentation tanks. Hence, this study is carrier out with the objective of increasing the retention efficiency in the irrigation sedimentation tanks using baffles. To reach this goal, the experiments were carried out in a flume with length 8 meters, width 0.3 meters, and height 0.5 meters, considering a sedimentation tanks with a length of 3 meters, in three different inlet concentration, three flow rates and three Froude numbers. The baffles were mounted at the bottom of the tank and the effects of the angle, height and position in the tanks were investigated. The results showed that on average, employing the baffles increased the sedimentation efficiency 5 to 6% and the highest value was obtained for angle 60 with respect to the flow direction. According to the results of this study, the most favorable height and position of these baffles were obtained to be in 40% of the depth of the flow and 50% of the length of the sedimentation tank, respectively. Also, by increasing the number of baffles, the sedimentation efficiency decreased. Regarding the sedimentation regions in this case, more than 80% of the settled sediments were observed in the middle of the tank measured from the inlet.