• Journal of the Korean earth science society
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• v.31 no.1
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• pp.18-35
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• 2010

Facies analysis of the Late Triassic Hajo Formation, the lowest stratigraphic unit in the Chungnam Basin, shows that the lower part is composed mainly of breccias or conglomerates; the middle part, conglomerates; and the upper part, conglomerates and sandstones. The formation consists of 13 facies, which include horizontally stratified clastsupported conglomerate, clast-supported massive breccia, matrix-supported massive breccia or conglomerate, matrixsupported graded conglomerate, massive pebbly sandstone, horizontally laminated sandstone, massive sandstone, graded sandstone, inversely graded sandstone, planar cross-bedded sandstone, trough cross-bedded sandstone, low angle crossbedded sandstone, and massive mudstone. These are grouped into 4 facies associations (FA). FA I consisted of clastsupported and matrix-supported massive breccias presumably deposited in the talus or upper fan delta environment. FA II consists of matrix-supported massive conglomerate and horizontally stratified clast-supported conglomerate of cobble size and it seems to have been deposited in the upper fan delta environment. FAIII consisted of matrix-supported massive conglomerate of pebble size, horizontally laminated sandstone and massive sandstone may have been deposited in the middle fan delta environment. FAIV consists of massive pebbly sandstone, horizontally laminated sandstone and massive sandstone and presumably was deposited in the lower fan delta environment. In general the Hajo Formation is interpreted to have been deposited at the talus/upper fan delta environment in early stage; it might have been deposited in the alternating environments of upper and middle fan delta in middle stage; and it seems to have been deposited in alternating environments of middle and lower fan delta in late stage.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.3
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• pp.205-209
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• 2016

The flowfield characteristics of a square prism having a small triangular prism at the upstream side were investigated by visualizing the flow field using PIV. The ratio of the width of the triangular prism to that of the square prism and the gap ratios between the square and triangular prisms were selected as the experimental parameters. The results are summarized as follows. The Strouhal number measured on the wake side of the square prism, which had the same characteristics as the drag reduction rate, increased, and then decreased with the gap ratio for the same width ratio. For a square prism having a small triangular prism, the stagnation regions were represented at the upstream and downstream sides of the square prism. The size of the stagnation region increased with the width ratio at the upstream side of the square prism, and decreased at the downstream side.

• Korean Journal of Environmental Agriculture
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• v.32 no.2
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• pp.148-154
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• 2013

BACKGROUND: Genetically modified(GM) trigonal cactus(Hylocereus trigonus Saff.) contained a coat protein gene of cactus virus X (CVX), which conferred resistance to the virus, phosphinothricin acetyltransferase (bar) gene, which conferred herbicide resistance, and a cauliflower mosaic virus 35S promoter (CaMV 35S). This study was conducted to evaluate the possible impact of GM trigonal cactus cultivation on the soil microbial community. METHODS AND RESULTS: Microorganisms were isolated from the rhizosphere of GM and non-GM trigonal cactus cultivation soils. The total numbers of bacteria, and actinomycete in the rhizosphere soils cultivated GM and non-GM trigonal cactus were similar to each other, and there was no significant difference. Dominant bacterial phyla in the rhizosphere soils cultivated with GM and non-GM trigonal cactus were Proteobacteria, Uncultured archaeon, and Uncultured bacterium. The denaturing gradient gel electrophoresis (DGGE) profiles show a similar patterns, significant difference was not observed in each other. DNA was isolated from soil cultivated GM and non-GM trigonal cactus, we analyzed the persistence of the inserted gene by PCR. Amplification of the inserted genes was not observed in the soil DNA, which was collected after harvest. CONCLUSION(S): This result suggests that the GM trigonal cactus cultivation does not change significantly the microbial community.

• Journal of The Geomorphological Association of Korea
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• v.18 no.2
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• pp.15-23
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• 2011

The first paper on the floodplain in Korea was published in the late 1960s. In 1970s and 1980s the study on the floodplain and delta of Korea was led by Hyuck Jae Kwon(emeritus professor at Korea University) and Hwa-Ryong Jo(emeritus professor at Kyungpook National University). Kwon established the foundation of the study and Jo analyzed the alluvial landforms microscopically. Since 1990s, the study on the floodplain and delta has entered a phase of stagnation.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.3
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• pp.243-247
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• 2015

The characteristics of the fluid force reduction of a square prism having a small triangular prism at the upstream side was investigated by measuring of lift and drag on the square prism The experimental parameters were the width ratios (H/B=0.2~0.6) of triangular prisms to the prism width and the gap ratios (G/B=0~3) between the square prism and the triangular prism. The drag reduction rate of the square prism was increased and then decreased with G/B in case of the same H/B, and was increased with H/B in case of the same G/B. The maximum drag reduction rate was represented by 78.5% at H/B=0.6 and G/B=1.5. The lift reduction rate of the square prism was hardly not affected by the width and gaps ratios, the average value was about 52.4%.

• The Korean Journal of Petroleum Geology
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• v.2 no.2 s.3
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• pp.71-81
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• 1994

Alluvial fan delta often extends into deep water, forming steep-faced delta front. Depositional features of modern steep-faced fan-delta slope and prodelta are characterized by slump scar, chute/channel, swale, lobe, splay and debris fall. These features largely originate from sediment failure or sediment-laden underflows (sediment-gravity flows) off river mouth. Sedimentary facies of equivalent ancient systems comprise sheetlike and/or wedged bodies of gravelstone and sandstones, slump-scar and -fill, chute/channel-fills, and sheetlike, lobate and slump mass on steeply-inclined fan-delta foreset and prodelta.

• Economic and Environmental Geology
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• v.56 no.4
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• pp.435-445
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• 2023

A delta is a depositional landform that is formed when sediment transported by a river is deposited in a relatively low-energy environment, such as a lake, sea, or a main channel. Among these, a delta formed at the confluence of rivers has a great importance in river management and research because it has a significant impact on the hydraulic and sedimentological characteristics of the river. Recently, the equilibrium state of the confluence area has been disrupted by large-scale dredging and construction of levees in the Nakdong River. However, due to the natural recovery of the river, the confluence area is returning to its pre-dredging natural state through ongoing sedimentation. The time-series data show that the confluence delta has been steadily growing since the dredging, but once it reaches a certain size, it repeats growth and retreat, and the overall size does not change significantly. In this study, we developed a model to explain the sedimentation-erosion processes in the confluence area based on the assumption that the confluence delta reaches a dynamic equilibrium. The model is based on two fundamental principles: sedimentation due to supply from the tributary and erosion due to the main channel. The erosion coefficient that represents the Nakdong River confluence areas, was obtained using data from the tributaries of the Nakdong River. Sensitivity analyses were conducted using the developed model to understand how the confluence delta responds to changes in the sediment and water discharges of the tributary and the main channel, respectively. We then used annual average discharge of the Nakdong River's tributaries to predict the dynamic equilibrium positions of the confluence deltas. Finally, we conducted a simulation experiment on the development of the Gamcheon-Nakdong River delta using recorded daily discharge. The results showed that even though it is a simple model, it accurately predicted the dynamic equilibrium positions of the confluence deltas in the Nakdong River, including the areas where the delta had not formed, and those where the delta had already formed and predicted the trend of the response of the Gamcheon-Nakdong River delta. However, the actual retreat in the Gamcheon-Nakdong River delta was not captured fully due to errors and limitations in the simplification process. The insights through this study provide basic information on the sediment supply of the Nakdong River through the confluence areas, which can be implemented as a basic model for river maintenance and management.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.55-55
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• 2019

메콩강 유역에서 가장 하류에 위치하고 있는 메콩 삼각주는 상류에 일어나는 많은 활동으로 인하여 높은 수준의 취약성을 지니고 있다. 기후 변화와 미래개발의 맥락에서 재해 위험을 평가하는 것은 기후현상/극한날씨, 취약성, 노출, 현재 위험 관리 및 적응을 충분히 고려할 필요가 있다. 홍수, 가뭄, 염수침입은 IQQQM과 IS 모델을 사용하여 분석하였다. 베트남 정부가 승인한 최신 기후변화 시나리오는 이 지역의 향후 토지이용, 물이용 및 상류에서의 수력발전 계획과 함께 모델링에 사용되었다. 홍수, 가뭄 및 염수치입 정도를 시뮬레이션 결과에 기초하여 평가하였고, 최종적으로 GIS 도구를 사용한 위험도 분석을 실시하였다. 리스크 분석 결과 저위험구역의 2모작 및 3모작 논의 면적은 6,381 ha로 떨어지고 중위험지역과 고위험구역의 2모작과 양식장 면적은 각각 약 7만 ha와 9,000 ha로 늘어나는 것으로 나타났다. 가뭄과 염도에 대한 위험 분석은 기후 변화와 해수면 상승으로 인한 위험의 심각성이 증가하는 것을 나타낸다. 분석 결과 메콩 삼각주에서는 전반적으로 향후 기후변화와 상류발전에 따른 부정적 영향으로 홍수 및 가뭄재해의 위험이 증가할 것으로 나타났다. 홍수 및 가뭄에 대한 보다 능동적이고 협력적인 관리가 향후 재난에 대비하여 지역사회의 탄력성을 유지하기 위해 필요한 것으로 나타났다.

• Journal of the Korean earth science society
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• v.26 no.5
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• pp.443-458
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• 2005

Late Quaternary deposits of the core in the western area of the Nakdong River delta consist of four sedimentary units: Unit I, II, III and IV, in ascending order, controlled by the sea-level change since the last interglacial period. Unit I unconformable overlying Cretaceous basement rocks is composed of sandy gravel and sand deposited in a fluvial channel before the first marine transgression. Unit II composed of stiff massive mud is interpreted as a shallow marine deposits formed during the last interglacial period (probably MIS 5). The development of the fissures coated with oxidized materials in the upper part of Unit II is a feature of subaerial exposure, which indicates erosional contact with the upper Unit III. Unit III is made up of soft massive mud and soft shelly massive mud deposited in a tidal flat and a inner shelf, respectively, since the Holocene transgression (about 9,000 yr BP). Unit Ⅳ consisted of soft shell bedded mud and yellowish sandy mud was deposited in the delta environments during the regression (after about 5,000 yr BP). The lower shell bedded mud was deposited in a tidal flat and the upper sandy mud was deposited in the floodplain corresponding to present site of the Nakdong River delta.

• Journal of the Korean association of regional geographers
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• v.13 no.1
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• pp.43-53
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• 2007

Rapid geomorphic changes occur in Nakdong River deltaic coast which is composed of deltaic barrier islands and tidal flats. We investigate the pattern of these rapid geomorphic changes by analyzing the distributions of sediment grain size characteristics. The distributions of sediment grain size characteristics analysis is a very efficient method to explain geomorphic changes of deltaic barrier islands. In sediments from Jinwoo Island, Sinja Island, and Doyo Island which are composed of Nakdong River deltaic coast, mean particle size increases to onshore direction and become coarser in tidal inlets. All sediments are very well sorted. Though almost sediments show little negative skewness, several sediments from tidal inlets show negative skewness. These results provide that the stronger and more regular energies affect Nakdong River deltaic coast and make fine sediments selectively move toward tidal inlets. Because of this mechanism, the recurved spits of deltaic barrier islands enlarge.