• Proceedings of the Korean Society of Marine Engineers Conference
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• 2011.06a
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• pp.233-233
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• 2011

This study describes the characteristics of accretion and scour around artificial reefs in Korea. The survey for accretion and scour was made at a dice reef set consisting of 137 dice reefs. The volume of a dice reef unit is 8 $m^3$. The reef set was placed on the muddy sand at 21.6 m in November of 1999. Equipment used in the survey includes Side Scan Sonar, Multi Beam Echo Sounder, Sub-Bottom Profiler and water current meter. According to the results, the artificial reefs are heaped up at two to three times (4 m) the height of the dice reef. The maximum current around the artificial reefs was 81.5 cm/sec at the ebb tide and 72.7 cm/sec at the flood tide. Scour around artificial reefs occurs upstream to the flow while accretion is formed at wake zone in the downstream. The height of accretion ranges from 2.4 to 3.0 m. The crest of the accretion is formed at the distance of about 10 m from the edge of the reef. The slope of accretion is formed steeply at the vicinity of the reef which is at right angles to the direction of main current, and grows gently lower with the increased distance from the reef. Scour is continuously caused by upwelling from the reef set and by side currents that flow parallel to side of the accretion. Also, scour takes place on the deposited sediment rather than on the remaining bottom sediments. This means that, once fully formed, the depth of scour gully on both sides to the direction of main current hardly changes.

• Journal of the Korean earth science society
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• v.22 no.1
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• pp.30-39
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• 2001

To consider the distribution of the surface sediments and sedimentary processes in tidal flat after the construction of sea-walls in the semiclosed Muan Bay, the southwest coast of Korea, studies on the sediments and sedimentation rates along two transect lines from February 1999 to March 2000 were carried out. The surface sediments in the bay are classified into 5 facies on the basis of textural parameters. The gravelly sediments including the cobbles and pebbles deposited in the bay-mouth are relic sediments which are formed in nearshore and fluvial environments at the low stand of sea level. In addition, it is considered that the muddy sediments widely distributed on the tidal flat might be originated from suspended matter transported from several rivers and/or offshore. Although the sedimentation rates on the tidal flat vary with season, their estimation rates are -8.9 mm/yr on Line-GR and -48.9 mm/yr on Line-YH, respectively. The erosion-dominated processes in the tidal flat would be caused by strengthened ebb tides due to the decrease of tidal choking at Mokpogu and the migration of tidal currents at the bay-mouth. The hydrodynamical changes mentioned above are interpreted to be occurred after/before the construction of sea-dike/sea-walls in coastal zone of Mokpo.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.3 no.2
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• pp.17-29
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• 1983

The siltation of the Gun-San New Harbour is a serious problem to keep the available water depth of the basin. So, in order to make clear the behaviour of the suspended load flowing in and out of the Gun-San New Harbour obviously, the samples of the suspended load at the appropriate points were collected in the estuarine area near the Harbour and at the same time the tidal current velocities measured. Their suspended load concentrations and salinities were analyzed, and emphasis has been placed on the characteristics of the suspended load concentrations and on the relationship between the concentration and the tidal flow as well as the wave. As a result, the authors obtained the followings; 1) The main source of the suspended load in the Geum River estuarine area is transported from its upstream during floods and deposited rapidly due to the salt water, and the settled sediment is resuspended due to the tidal flow and the wave action, transported and settled again. Such a process is periodically repeated according to the tidal curve. 2) The concentrations are, in general, becoming larger with the increase of the tidal range and the wave height, and vice versa. Especially, the concentrations are relatively large in the winter season of which the wave height is larger than another seasons.

• The Korean Journal of Quaternary Research
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• v.23 no.2
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• pp.34-47
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• 2009

AMS radiocarbon dates indicated that Eurimji reservoir, located at Jecheon City, Chungbuk Province, has been formed during the late Holocene Epoch. The sedimentary sequence at bottom reveals histories in hydrology, climate conditions and past vegetation dynamics. Ages controlled sedimentological and palynological analyses on ER 3-1 Core contribute to reconstruct paleoclimate and past hydrological conditions. These analyses suggest that lower interval (307.5m~309.5m elevations) of the ER 3-1 Core was deposited in stable from 1,920 yrBP to 1,420 yrBP, but upper layer sediment above these elevations was composed of reworked sediments during the pre and post 2,000 yrBP. Pollen assemblage indicates that watershed vegetation of the Eurimji reservoir, during the period of 1,920 yrBP~1,420 yrBP, was closely comparable to modern vegetation dominated Pinus and Quercus mixed vegetation. Also, riparian including Alnus, Fraxinus and Salix were inhabited along the banks of stream, and aquatics such as Typha, Nymphaea and Persicaria flourished at shore of the reservoir. According to cultural chronicle, it infers that the Eurimji reservoir was formed from the Bronze Age to the Iron Age or the beginning of ancient society. An integrated data suggested that Quercus-Pinus-Abies mixed forest flourished under cool and dry climate conditions during 3,200 yrBP~200 yrBP.

• Economic and Environmental Geology
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• v.41 no.3
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• pp.315-326
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• 2008

Recently, the occurrence and intensity of Asian Dust have dramatically increased in Korean peninsula, resulting in severe damages to the domestic social and economic field. The most useful way to prevent the damage of Asian Dust is the restraint of the occurrence of Asian Dust itself. However, Asian dust is the one of the natural phenomena, thus there is a basic limit to manage the Asian Dust. Though it is impossible to restrain the occurrence of Asian Dust in short time at present, it is a urgent matter to minimize the damage of Asian Dust. It is necessary to construct the basic data for understanding the harmfulness of Asian Dust, and to elucidate the source area of Asian Dust in connection with the maleficence of itself. In this study, the source area of Asian Dust in spring, 2007, is investigated using the Sr-Nd isotopic ratios which is the most common method to trace the source of geological materials. The relationships of Sr-Nd isotope ratios indicate that Asian Dust was originated from Central Loess Plateau and/or Ordos desert in spring, 2007.

• Journal of the Korean association of regional geographers
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• v.22 no.1
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• pp.211-224
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• 2016

Natural lakes are estimated in variety with that's function or value depending on age environment or geographical characteristics. There are many kind of natural lakes, but the kind of natural lake is limited in rivers in korea flowing into East Sea. However, Yeonho lake in Uljin has different geographical characteristics with oxbow lake or lagoon which is common in korea's river flowing into East Sea. Therefore the purpose of this study is to analyze geographical characteristics due to the process of Yeonho's formation. Further more research for protecting wetland is needed to adequately preserve, depending on the geomorpologic process. To analyze geographical characteristics, it was essential to compare and analyze topographical map of 1918 1956 2012 and I pictured estinated line of bedrock and longitudinal section of Nam-dae cheon(Riv) Yeonho cheon(Riv). In addition, I denoted flooded areas through design flood level of Nam-dae cheon(Riv) Yeonho cheon(Riv) and analyzed particle size distribution of deposited sediment due to consider deposit environment. The results of study are as follows. In conclusion, Yeonho lake is floodbasin which was not researched at river flowing into East Sea. Through this study, my opinion is that floodbasin can be formed in the river that is steep and short. I argue that preservation methods will be seeked by geomorphologic process of floodbasin and development of downtown.

• Economic and Environmental Geology
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• v.42 no.1
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• pp.27-53
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• 2009

A 30-m-thick Middle Ordovician Jigunsan Shale exposed along the southern limb of the Backunsan (Baekunsan) Syncline, Taebacksan (Taebaeksan) basin, has been simply considered as a transgressive shale sequence onlapped the underlying Maggol platform carbonates. Results of this study, however, suggest that majority of the Jigunsan Shale be interpreted as a regressive shale sequence downlapped onto a thin (ca. 240 cm) marine stratigraphic unit consisting of organic-rich (>3 wt.% of TOC) black shales in the lower Jigunsan Shale, which was accumulated at the time of maximum regional transgression. Detailed stratigraphic analysis in conjunction with XRD, XRF, and ICP-MS as well as Rock-Eval pyrolysis allows the thin marine stratigraphic unit in the Jigunsan Shale to define a condensed section that was deposited in a distinctive euxinic zone formed due to expansion of pycnocline during the early highstand phase. As well, a number of stratigraphic horizons of distinctive character that may have sequence stratigraphic or environmental significance, such as transgressive surface, maximum flooding surface, maximum sediment starvation surface, and downlap surface, are identified in the lower Jigunsan Shale. In the future, these stratigraphic horizons will provide very useful information to make a coherent regional stratigraphic correlation of the Middle Ordovician strata and to develop a comprehensive understanding on stratigraphic response to tectonic evolution as well as basin history of the Taebacksan Basin.

• Journal of the Korean Geotechnical Society
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• v.33 no.5
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• pp.5-13
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• 2017

The sand layer deposited in clay is called a sand seam, which is formed by inflow of sands due to river flooding or slope failure in the middle of sinking and sediment of clay. When the sand seam exists in clay layer, the drainage direction changes from one way to both ways, and the time of consolidation may be reduced. However, it is not clearly proved due to lack of studies of sand seam and currently is not reflected in the design of soft soil improvement. As a fundamental study about sand seam, the oedometer tests and constant rate of strain tests with Rowe cell were conducted on clay specimens with sand seam. For tests, a frozen method was specially designed for making the sand seam. It was concluded that the test results showed the sand seam affects the coefficient of consolidation of clay. If the thickness of sand seam exceeds 0.05 times of specimen height, the sand seam works as drainage layer of pore water horizontally as well as vertically, and consequently the consolidation is accelerated.

• Journal of The Geomorphological Association of Korea
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• v.23 no.1
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• pp.17-33
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• 2016

Samples from newly exposed outcrop of sedimentary layers forming Jeongdongjin coastal terrace in Gangreung area are collected and analyzed to find the sedimentary environment. The site are located at the gentle hillslope of the terrace surface area. The height of the outcrop is about 8m and the altitude of it's highest part is 68~73m MSL. The lowest part of this out crop is the partly consolidated sand layer with gravel veneer within it. It is found that this part is not in-situ weathered sand stone through the OSL method. This sand layer is overlain by the gravel layer with sand matrix. The shapes of the gravels from this part are mainly 'platy', 'elongated', and 'bladed' by the index of Sneed and Folk(1958). In addition, mean roundness is not so high. It is sceptical to regard this part as marine sediments which are continuously exposed to erosional processes. The boundary between the lowest sand layer and gravel layer showing the abrupt change in forming material without any mixture or transitional zone, so gravels are seemed to deposited after some degree of consolidation of the lowest sand layer. In addition, the hight of the boundary between layers are changed by the place, so the surface of the partly consolidated sand layer is not flat and has irregularity on topography when it buried by gravels. Main part of this out crop is the poorly sorted coarse gravel(22.4mm) with sand matrix($1.36{\phi}$) layer with at least 2m thick covering the relatively fine gravels discussed above. Over 20% of particles have 'very platy', 'very elongated' and 'very bladed' shape and only less than 5% of particles have 'compact' shape, So this particles are also very hard to be regard as marine gravels which are abraded by marine processes. It can be concluded that this gravel layer formed by fluvial processes rather than coastal processes base on the form of the clast and sedimentary structure. The gravel layer is covered by fine($3{\sim}4{\phi}$) material layers of psudo-gleization which showing inter-bedding of red and white layers. Chemical composition of matrix and other fine materials should be analyzed in further studies. It is attempted to fine the burial ages of the sediment using OSL method, but failed by the saturation. So it can be assumed that these sediments have be buried over 120ka.

• Economic and Environmental Geology
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• v.55 no.3
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• pp.295-307
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• 2022

We studied the Cretaceous Jeonggaksan Formation to determine depositional processes of pyroclastic density currents entering into the lacustrine environments. This formation is composed largely of sandstone-mudstone couplets and (tuffaceous) normally graded sandstones deposited in lacustrine environments, interbedded with two pyroclastic beds: welded massive lapilli tuff and normally graded lapilli tuff. The welded massive lapilli tuff (10 m thick) is composed of poorly sorted, structureless lapilli supported by a welded ash matrix. The normally graded lapilli tuff (4 m thick) is characterized by moderately to well sorted natures and multiple normally graded divisions in the lower part of the bed with internal boundaries. The contrasting depositional features between these lapilli tuff are suggestive of different physical characteristics and depositional processes of pyroclastic density currents in the lake. Overall poorly sorted and massive natures of the thick, welded massive lapilli tuff are interpreted to have been formed by rapid settling of pyroclastic sediments from highly concentrated and sustained pyroclastic density currents. In this case, the pyroclastic density currents were able to displace lake water from shoreline and the pyrolclastic density currents preserved their own heat except for frontal parts of the currents. As a result, welded textures can be formed despite entrance of pyroclastic density currents into the lake. The internal boundaries of the normally graded lapilli tuff reflect unsteady natures of the pyroclastic density currents at the time of the deposition and the pyroclastic density currents can not provide sufficient pressure to displace lake water. As a consequence, the pyroclastic density currents transformed into water-saturated turbidity currents, forming relatively well sorted, normally graded lapilli tuff.