The soft ground in the southwest coastal area composed of marine clay is greatly influenced by sediment composition, particle size distribution, particle shape, adsorption ions and pore water characteristics, tide and temperature. In addition, the geotechnical properties are very complex due to stress history, change in pore water, dissolution process and gas formation. In this study, the physical and mechanical properties of the soft ground were evaluated through field tests and laboratory tests to investigate the strength increase characteristics according to consolidation on the soft ground in the southwest coast. In addition, in order to understand the consolidation behavior of soft ground such as subsidence, pore water pressure, horizontal displacement of soil by embankment load, measuring instruments such as pore water pressuremeter, settlement gauge, inclinometer and differential settlement gauge was installed, and a piezocon penetration test was carried out step by step to confirm the increase in shear strength of the ground. Through this, it was confirmed that the shear strength of the ground is increased according to the stages of filling. In addition, by evaluating the properties of consolidation behavior, strength increase and consolidation prediction by empirical methods and theories were compared to analyze the characteristics of strength increase rate and consolidation behavior in consideration of regional characteristics.
Journal of the Korean association of regional geographers
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v.13
no.4
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pp.409-421
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2007
The purpose of this paper is to consider the formation processes and depositional conditions of bars formed at the upper-stream part of Sayeon Dam since Sayeon Dam construction in 1964. Results of analyzing the shape characteristics of bars and their sediment grain size distribution are as follow: Firstly, bars are able to categorized as subaqueous bars (A, B), mid-channel bars(C, D), and tributary side-bars(E). Secondly, the outline of bars has longish along the flow path, and their height lowers more and more going towards downstream. Also the height of bar surface tend to heighten from flow path to mountain slope. However, the near part of A is comparatively higher than its distant part, A is defined as a subaqueous natural levee and back swamp. Thirdly, the average particle size of A and B become smaller toward mountain slope. In transportation style, ratio of suspended load become higher toward mountain slope. Fourthly, sorting is worse to very worse according with lake's random changable water level. Fifthly, bar A and B were formed by vertical sedimentation of sediments according as sediments transported along flow path in the subaqueous conditions were spreaded out of flow path. C and D were formed by bed load as flood level lowered. And E was formed by vertical sedimentation while stream flow stopped in tributary's mouth areas with the water level heightening.
Un-Ki Hwang;Hoon Choi;Ju-Wook Lee;Yun-Ho Park;Wonsoo Kang;Moonjin Lee
Journal of Marine Life Science
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v.8
no.1
/
pp.68-77
/
2023
In this study, we investigated the quantitative distribution of microplastics in the surface seawater at 8 points near the Taean Peninsula using fluorescence staining. The study revealed a detection range of microplastics from 0 to 360.5 particles/l, with an average of 149.7 ± 46.0 particles/l. When classifying the microplastics by size, it was found that particles smaller than 50 ㎛ were dominant, although there were differences at Site 3. Moreover, it was not possible to identify clear correlations when comparing the number of microplastics based on collection area and particle size. Various physical and chemical factors, including plastic material, dynamic ocean conditions (such as currents, wind, waves, tides), geological characteristics (topography, slope), sediment materials including coastal organisms, human activities (fishing, development, tourism), and weather conditions (floods, rainfall), affect the behavior of microplastics. Therefore, future efforts should focus on standardizing quantitative analysis methods and conducting fundamental research on microplastic monitoring, including the analysis of environmental factors.
Phenomenon of vegetation recruitment on the sand bar is drastically rising in the streams and rivers in Korea. In the 1960s prior to industrialization and urbanization, most of the streams were consisted of sands and gravels, what we call, 'White River'. Owing to dam construction, stream maintenance, etc. carried out since the '70s, the characteristic of flow duration and sediment transport have been disturbed resulting in the abundance of vegetation in the waterfront, that is, 'Green River' is under progress. This study purposed to identify the correlation among water level, water temperature, rainfall, soil moisture and soil texture out of the factors which give an effect on the vegetation recruitment on the sand bar of unregulated stream. To this purpose, this study selected the downstream of Naeseong Stream, one of sand rivers in Korea, as the river section for test and conducted the monitoring and analysis for 289 days. In addition, this study analyzed the aerial photos taken from 1970 to 2009 in order to identify the aged change in vegetation from the past to the present. The range of the tested river section was 361 m in transverse length and about 2 km in longitudinal length. According to the survey analysis, the tested river section in Naeseong Stream was a gaining river showing the higher underground-water level by 20~30 m compared to Stream water level. The difference in the underground water temperature was less than $5^{\circ}C$ by day and season and the Stream temperature did not fall to $10^{\circ}C$ and less from May when the vegetation germination begins in earnest. The impact factor on soil moisture was the underground water level in the lower layer and the rainfall in the upper layer and it was found that all the upper and lower layer were influenced by soil particle size. The soil from surface to 1 m-underground out of 6 soil moisture-measured points was sand with the $D_{50}$ size of 0.07~1.37 mm and it's assumed that the capillary height possible in the particle size would reach around 14~43 cm. On the other hand, according to the result of space analysis on the tested river section of unregulated stream for 40 years, it was found that the artificial disturbance and drought promoted the vegetation recruitment and the flooding resulted in the frequency extinction of vegetation communities. Even though the small and large scales of recruitment and extinction in vegetation have been repeated since 1970, the present vegetation area increased clearly compared to the past. It's found that the vegetation area is gradually increasing over time.
The faunal assembalges of macrobenthos and their habitat conditions on the soft-bottoms around Dokdo(Dok Island) was investigated using a box corer and a van Veen grab in Sept. 1999 and May 2000. The sediments in the slope sites were composed of sand particles and those in Ullneung Basin were mud. The sediments in the shelf sites were in the range of fine to medium sand. The organic content of the slope sediments was in the range of 1 to 2%. The macrobenthos occurred at the slope sites represented by 15faunal groups belonging to 8 phyla, and the major faunal group was polychaetous annelids. They comprised ca. 80.6% in slope sites, and 84.8% in shelf sites. Dominant species in the slope were Exogone verugera(40.9%), Cossura longocirrata (8.4%), Tharyx sp. (6.6%), Scalibregma inflatum (4.9%), Aedicira sp. (4.7%), Aricidea ramosa (3.8%), and Sigambra tentaculata (3.7%). Dominant species in the shelf were Chone sp. (49.3%), Tharyx sp. (18.4%), Ophelina acuminata (6.7%), Chaetozone setosa (3.8%), Glycera sp. (2.6%), and Aedicira sp. (2.4%). The mean densities of macrobenthos in the slope and shelf area were $2,028\;ind./m^2$ and $456\;ind./m^2$, respectively. The trophic composition of benthic polychaete worms in the slope area was different from that in shallow shelf area: surface deposit feeding worms were most abundant in slope area whereas filter feeding worms in shelf area. According to the cluster analysis and MDS plots, the spatial distribution of macrobenthos in Dokdo slope region was related with the sediment properties such as particle size and organic content. In the case of vertical distribution of macrobenthos in slope sites, most faunas concentrated in the upper sediment layer within 2cm depth.
Kim, Jongmin;Kim, Gwang Soo;Kwon, Siyoon;Kim, Young Do
Journal of Korea Water Resources Association
/
v.56
no.12
/
pp.919-928
/
2023
Rainfall characteristics in Korea are concentrated during the summer flood season. In particular, when a large amount of turbid water flows into the dam due to the increasing trend of concentrated rainfall due to abnormal rainfall and abnormal weather conditions, prolonged turbid water phenomenon occurs due to the overturning phenomenon. Much research is being conducted on turbid water prediction to solve these problems. To predict turbid water, turbid water data from the upstream inflow is required, but spatial and temporal data resolution is currently insufficient. To improve temporal resolution, the development of the Turbidity-SS conversion equation is necessary, and to improve spatial resolution, multi-item water quality measurement instrument (YSI), Laser In-Situ Scattering and Transmissometry (LISST), and hyperspectral sensors are needed. Sensor-based measurement can improve the spatial resolution of turbid water by measuring line and surface unit data. In addition, in the case of LISST-200X, it is possible to collect data on particle size, etc., so it can be used in the Turbidity-SS conversion equation for fraction (Clay: Silt: Sand). In addition, among recent remote sensing methods, the spatial distribution of turbid water can be presented when using UAVs with higher spatial and temporal resolutions than other payloads and hyperspectral sensors with high spectral and radiometric resolutions. Therefore, in this study, the Turbidity-SS conversion equation was calculated according to the fraction through laboratory analysis using LISST-200X and YSI-EXO, and sensor-based field measurements including UAV (Matrice 600) and hyperspectral sensor (microHSI 410 SHARK) were used. Through this, the spatial distribution of turbidity and suspended sediment concentration, and the turbidity calculated using the Turbidity-SS conversion equation based on the measured suspended sediment concentration, was presented. Through this, we attempted to review the applicability of the Turbidity-SS conversion equation and understand the current status of turbid water occurrence.
The concentrations of 16 priority PAHs (US EPA standard) were analyzed in the surface sediments obtained from 23 sampling sites near Kwangyang Bay in Korea. There was a local variability in the total PAHs ranged from 0.01 to 171.39 mg/kg, with a mean value of $8.13{\pm}24.8mg/kg$. The major pollution sources of PAHs near Kwanyang Bay were Taeindo, Sueo stream and Wallae stream, whose concentrations were 114.81, 38.37 mg/kg and 19.05 mg/kg, respectively. It showed that PAHs concentrations were increased with the decrease of particle size and with the increase of organic carbon contents in three fractioned sediments. From the analysis of PAHs source using LMW/HMW, Phe/Ant, and Fla/Pyr, pyrolysis by-products were mostly showed in Kwangyang Bay and some place showed the mixure of pyrolysis by-products, and crude oil by-products. Besides, the toxic effects assessment on benthic ecosystem for three major pollution sources showed that the PAHs concentration of Taindo which was mainly accumulated with carcinogenic PAHs exceeds ERM value and the PAHs of Sueo and Wallae streams are the degree of ERL value.
This study presents a numerical model for simulating turbidity currents using the ULTIMATE scheme. For this, the layer-averaged model is used. The model is applied to laboratory experiments, where the flume is composed of sloping and flat parts, and the characteristics of propagating turbidity currents are investigated. Due to the universal limiter of the ULTIMATE scheme, the frontal part of the turbidity currents at a sharp gradient without numerical oscillations is computed. Simulated turbidity currents propagate super-critically to the end of the flume, and internal hydraulic jumps occur at the break-in-slope after being affected by the downstream boundary. It is found that the hydraulic jumps are computed without numerical oscillations if Courant number is less than 1. In addition, factors that affect propagation velocity of turbidity currents is studied. The particle size less than $9{\mu}m$ does not affect propagation velocity but the buoyancy flux affects clearly. Finally, it is found that the numerical model computes the bed elevation change due to turbidity currents properly. Specifically, a discontinuity in the bed elevation, arisen from the hydraulic jumps and resulting difference in sediment entrainment, is observed.
Kim, Do-Hwan;Lee, Doo-Jin;Hwang, Jin-Su;Choi, Doo-Yong
Journal of Korean Society of Environmental Engineers
/
v.35
no.5
/
pp.312-320
/
2013
Particulates in drinking water distribution system (DWDS) are mostly influenced by internal corrosion of metal pipes and sediment in pipelines due to the solution of this effect is limited. The particle size, component and properties of compounds for particulates in distributed water are different and the difference of these characteristics will be occurred by the kind of facilities, pipe condition, external factors and supply system etc. In this study, conducting the investigation of water quality in DWDS researches with particulates in the water. Monitoring sites were each water supply reservoir and the end of water supply area in DWDS. To collect particulate material at each sampling site, $47{\phi}$ glass microfiber filter type GF/C was performed using a filtration. Substances that the effect of the turbidity in the water according to particulate suspended solids and inorganic materials is due to the increasing particulates in the end of DWDS were increased. The result of compounds analysis by using X-ray diffraction (XRD) were Goethite (${\alpha}$-FeOOH), Magnetite ($Fe_3O_4$) in the end of DWDS and Quartz ($SiO_2$), Yeelimite ($Ca_4Al_6O_{12}SO_4$) at the effluent of waterworks and reservoirs. There were differences the compounds and sediments in the releasing or remaining water distribution facilities.
The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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v.2
no.1
/
pp.31-41
/
1997
This study was carried out to investigate the composition and the distribution of the benthic community in the coastal area of Inchon seasonally from May 1994 to February 1995, and to estimate the environmental factors that effect the temporal and the spatial changes of benthic species composition. In the present study, 231 species were collected with the average density of 455 ind./$m^2$. The dominant species were Heteromastus sp., Sternaspis scutata, Chaetozone setosa, Mediomastus sp., Glycinde sp., Glycera sp. and Nephtys oligobranchia, which are in the polychaete group; abundance of these species showed seasonal and spatial variations. The study area was divided into 4 regions by cluster analysis such as outside area of Palmido (I), main channel region and adjacent are of Shihwa sea wall (II), north-eastern area of Youngjongdo (III), and the Inchon harbor and the mouth area of Sorae harbor (IV). The particle size of sediment which generally influences the distribution of the benthic community, the differences of the concentration of heavy metals, and of the dissolved oxygen, the increase of the proportion of polychaetes and molluscs, the absence of the crustacean phoxocephalids, and the increase of the abundance of pollution indicator species, indicated that the environment of the areas have been degrading gradually from Group I to Group IV.
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