• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.60-68
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• 2006

High-frequency bistatic scattering measurements from a corrugated surface were made in an acoustic water tank. First the azimuthal scattering pattern was measured from an artificially corrugated surface which has varying impedance. The corrugated surface was installed both transverse to the direction of incident wave and longitudinal to the direction of incident wave. The angle between the corrugated surface and the direction of the incident wave was about $45^{\circ}$. Second, the scattering strengths were measured from the flat sediment and the corrugated sediment. A critical angle of about $37^{\circ}$ was calculated in the acoustic water tank. The measurements were made at three fixed grazing angles: $33^{\circ}$ (lower than critical angle), $37^{\circ}$ (critical angle), and $41^{\circ}$ (higher than critical angle). The scattering angle and the grazing angle are equal in each measurement. Frequencies were from 50 kHz to 100 kHz with an increment of 1 kHz. The corrugated sediment was made transverse to the direction of the incident wave. The first measurement indicates that the scattering patterns depend on the relations between the corrugated surface and the direction of the incident wave. In the second measurement, the data measured from the flat sediment were compared to the APL-UW model and to the NRL model. The NRL model's output shows more favorable comparisons than the APL-UW model. In case of the corrugated sediment, the model and the measured data are different because the models used an isotropic wave spectrum of sediment roughness in the scattering calculations. The isotropic wave spectrum consists of $w_2$ and ${\gamma}_2$. These constants derived from sediment names or bulk size. The model which used the constants didn't consider the effect of a corrugated surface. In order to consider a corrugated surface, the constants were varied in the APL-UW model.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2011년도 학술발표회
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• pp.17-17
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• 2011

As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. As a method of countermeasure to bed degradation and armoring phenomena of bed material in the downstream area of dam reservoirs, sediment augmentation (replenished sediment) has been carried out in many Japanese rivers. In general, bed of the replenished sediment site is composed of rocks, because the site is located in the downstream area of the dams and sediment supply is very small. Bed deformation process has been researched by many researchers. However, most of them can treat movable bed only and cannot be applied to the bed deformation process of sediment on rocks. If the friction angle between the sediment and the bed surface is assumed to be the same as the friction angle between the sediment and the sediment, sediment transport rate must be smaller without sediment deposition layer on the rocks. As a result, the reproduced bed geometry is affected very well. In this study, non-equilibrium transport process of non-cohesive sediment on rigid bed is introduced into the horizontal two dimensional bed deformation model and the model is applied to the erosion process of replenished sediment on rock in the Nakagawa, Japan. Here, the Japanese largest scale sediment augmentation has been performed in the Nakagawa. The results show that the amounts of the eroded sediment and the remained sediment reproduced by the developed numerical model are $56300m^3$ and $26800m^3$, respectively. On the other hand, the amounts of the eroded sediment and the remained sediment measured in the field after the floods are $56600m^3$ and $26500m^3$, respectively. The difference between the model and field data is very small. Furthermore, the bed geometry of the replenished sediment after the floods reproduced by the developed model has a good agreement with the measured bed geometry after the floods. These results indicate that the developed model is able to simulate the erosion process of replenished sediment on rocks very well. Furthermore, the erosion speed of the replenished sediment during the decreasing process of the water discharge is faster than that during the increasing process of the water discharge. The replenished sediment is eroded well, when the top of the replenished sediment is covered by the water. In general, water surface level is kept to be high during the decreasing process of the discharge during floods, because water surface level at the downstream end is high. Hence, it is considered that the high water surface level during the decreasing process of the water discharge affects on the fast erosion of the replenished sediment.

• 한국조경학회지
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• 제26권4호
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• pp.59-69
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• 1999

This study examines the existing theories related to detention basin and embodies the calculation process of sediment basin. It investigated the scale of sediment basin by actual measurement at Buju Mountain, Mokpo city which causes the environmental problems like erosion and outflow of sediment due to the excessive development, finds the problems of existing sediment basin by applying and analyzing the physical factors which affect the execution of sediment basin using GIS as the method establishing the scale of sediment basin embodied in this study and then suggests the oteimum scale. Comparing the surface area of the existing sediment basin and of the required one, all of the surface areas of the existing sediment basins were smaller than those of the required one. Therefore, it can be expected that the trap efficient of sediment will be declined. The required one. Therefore, it can be expected that the trap efficient of sediment will be declined. The required minimum depth was fully satisfied, but it is analyzed that the volume of sediment basin will affect the neighboring environment because it can not accomodate the inflow discharge volume except sediment basin C. It is consistent with the actual situation which causes a serious environmental problem due to the overflow of sediment basin during the heavy storm event except sediment basin C and also it verifies the validity of calculation process of establishing optimum sediment basin suggested in this study.

• 한국환경과학회지
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• 제12권10호
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• pp.1121-1129
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• 2003

We report the distributions of Sb and As in the surface sediment of the Yellow Sea and the coastal areas of Korea. The mean concentrations of Sb and As range from 0.68 ppm to 1.01 ppm and from 7.4 ppm to 15.8 ppm, respectively, and show relatively the high concentrations at the coast of Weolseong in the East Sea for Sb and at the coast of Gadeok Island in the South Sea far As. This may be due to the anthropogenic input of these elements via river and atmosphere from industry complex and agriculture regions around the study areas. Because of the difference of clay to silt proportion, the correlation between silt plus clay contents and Sb, As in the coastal surface sediment of Korea is not shown, the concentrations of Sb and As vary widely for the sample in which the silt plus clay contents are the same. Therefore, we suggest that the distribution patterns of Sb and As in surface sediment of the Yellow Sea and the coastal areas of Korea are mainly controlled by the anthropogenic inputs and the sediment characteristics. On the other hand, the Sb concentrations are lower than those of the lowest effect level which is the standard of judgment for contamination, while the As concentrations are higher than those of the lowest effect level. This implies that the surface sediments of the Yellow Sea and the coastal areas of Korea are considerably contaminated for As.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2007년도 학술발표회 논문집
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• pp.157-161
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• 2007

Nutrients were investigated for surface water, bottom sediment and ground water in a rural watershed from January 2006 to March 2007. The concentrations of TN and $NO_3-N$ in ground water were higher than those in surface water due to fertilization on cabbage upland neighboring a river during March to August, but lower than those in surface water during September to February. However, the concentrations TP and $PO_4-P$ in ground water were lower than those in surface water. The concentrations of TP and $PO_4-P$ in surface water was lower than those in bottom sediment. The TP concentration in the bottom greatly decreased during rainy season. due to flush sediment of bottom, and then gradually increased.

• 한국물환경학회지
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• 제26권1호
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• pp.125-132
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• 2010

Characterization of sediment quality is important for the proper management of surface water quality, yet sediment has not been monitored sufficiently. In this study, fecal indicator microorganism concentrations of sediments in the Geum River Basin were monitored. Sampling was carried out at one paddy field, one lakeshore and five monitoring stations in the lower reach of the Geum River Basin. Surface waters and sediments were sampled four times during rainy season. Total coliform concentrations of sediments were 12 times higher in average to those of surface waters while E. coli concentrations of sediments were six times higher. No correlation found between indicator microorganism concentration between surface waters and sediments.

• Journal of Forest and Environmental Science
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• 제29권4호
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• pp.314-323
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• 2013

To examine surface erosion and sediment export patterns on a hillslope, which was devastated by a shallow landslide and which was slowly revegetating by natural plant species, we surveyed variations in surface erosion depth on the upper-, middle- and lower-section of the hillslope, and subsequent sediment yield from the whole hillslope. The result showed that, with the passing of year, surface erosion on the devastated hillslope was regulated by higher rainfall intensity due to the supply-limitation of exportable sediment, and its variation range decreased. In addition, surface erosion on the upper-section with steep slope was regulated by higher rainfall intensity, which might result in raindrop erosion, compared to it on the lower-section with relatively gentle slope. Besides, the sediment yield from the devastated hillslope had nonlinear relationship with surface erosion depth on the hillslope because sediments on the hillslope are exported downwards while repeating their cycle of transport and redistribution. Our findings suggest the establishment of management strategy to prevent sediment-related disasters occurred during torrential rainfall events, which was based on the continuous field investigation on the hillslope devastated by landslides.

• 한국농공학회논문집
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• 제53권6호
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• pp.129-136
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• 2011

To measure effects of surface cover on runoff and sediment discharge reduction using rainfall simulator, four(5 m${\times}$30 m scale) plot experiments were conducted in this study. Surface covers made with straw mat, Polyacrylamide (PAM), chaff, and sawdust were simulated 4 times under 31.1~44.4 mm/hr rainfall intensities. Compared with results from control plot, the time of runoff generation is delayed and outflow volume decreased with surface cover. Effects on runoff reduction of straw mat, PAM, sawdust and chaff ranged 4.7~81.5 % and runoff rate reduced by 6.5~76.1 % respectively, when compared with those from control plot. The percentage of decrease in sediment discharge were 99.7~99.8 % from straw mat+sawdust+PAM plots, 85.9~95.6 % from straw mat+PAM plots, and 98.5~99.4 % from straw mat+chaff+PAM plots. The runoff, sediment discharge, and SS concentration reduction efficiencies of the cover materials were outstanding when compared to control plot. It was analyzed that reduction of runoff and sediment discharge were mainly contributed by decrease in rainfall energy impact and flow velocity and increase of infiltration due to the surface cover materials. The results could be used as a base for the development of best management practices (BMPs) to reduce runoff, sediment discharge from sloping field.

• Environmental Engineering Research
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• 제15권1호
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• pp.41-48
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• 2010

This paper describes the influence of nutrient salts eluted from the bottom of a closed water area where polluted sediment has been deposited by inflowing river water. The elution pattern was monitored at our experimental facility. Both the sediment pore water and water above the bottom were sampled using a dialyzer sampler (peeper). The pore water of the eutrophicated sediment contained a large amount of nutrient salts, and the effect of elution was confined to a limited area of the bottom surface. The nutrient concentration of the sediment pore water was closely related to both the water temperature and dissolved oxygen (DO) concentration. The eluted nutrients from the sediment provided a source for phytoplankton and algae growth. This experimental data indicated that the water quality of the surface was not directly connected to the eluted nutrient salts, while it was indirectly affected by the total ecosystem, including all the organisms within an area and their environment.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2015년도 춘계학술대회
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• pp.179-180
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• 2015

The variety of organic and inorganic pollutants are introduced to coastal sediment and making highly contaminated due to rapid development of industralization and economic development. Numerous contaminants are release into marine sediment and it significantly affect marine aquatic environment. In the present study stated the optimize the biostimulant ball (BSB) in coastal sedimentand stabilse the heavy metals present in the sediment. The effective variables like BSB size, distance and month variables on Cu stabilization was determined by using Response surface methodology(RSM). The analysis of variance (ANOVA) and coefficient determination (R2) of Cu reduction 0.9610 and maximum stabilisation was obtained in 3cm ball size and 5.5cm distance and 4 month interval time. This result revealed that the BSB in effective for Cu reduction in coastal sediment.