• Journal of Korea Water Resources Association
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• v.43 no.10
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• pp.883-891
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• 2010

More recently, there have been significant changes in the forms of channels due to runoff characteristics driven by climate changes and other alterations in basin/channel environments. Particularly, increasing local deposition in major channels is being observed nationwide. Of such phenomena, it is noteworthy that flood-plains show unidirectional growth and lowering of channels within compound channels in the form of a high-flow plain. These changes are supposed to affect management of the river ecology as well as flood control. In this study, the research on channels in Korea confirmed that the phenomenon of local deposition in those channels is actually taking place, rendering a problem to be urgently addressed. Previous studies on bed changes have been focused on low channels based on bed materials distributed over the channels. However, this research has proved that surface-layer deposition of a high-flow plain is closely related with changes in the conditions of ground surfaces and, ultimately, affects the bed of the entire channel as well. According to the intensive research on the condition of the high-flow plain of the mouth of the Han River, the silt deposited in the high-flow plain was the main cause of settlement/growth of vegetation. And this leads to landforming along with woods-forming, disturbing flood control as well as the normal river ecology.

• Journal of Korean Society of Forest Science
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• v.79 no.3
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• pp.269-277
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• 1990

In planning the disaster prevention by the erosion control facilities, it is essential to focus on the microtopography of the channel bed and the chronological process of sedimental movement in the torrential streams. For this purpose, the microtopographical change of the channel bed and the effects of the erosion control facilities in the mountain torrents were analyzed by the experimental channel and the field survey of the torrents where low-dam series had been constructed in the channel. The results of this experiment showed that the effects of construction of the low-dam series on the channel bed fixiation were the prevention of the local scouring in the experimental channel and the expansion of flow channel width and deposit space. The results are summarized as follows : 1. When the low-dam series were constructed over the whole channel bed (L'/L=1), the conning water and the sediment were seperated, simultaneously resulting in deposition of sediment and reduction of the tractive force for the running water. Therefore, the F.A. (Fluctuation area in cross-section: value was decreased to about 65% compared with that of non-work (L'/L=0). 2. The efficiencies of the low-dam series on the channel width were increased with an increment in length of working space. After the construction of low-dam series on the whole channel bed (L'/L=1), flow channel width was increased to about 1.53 times compared with that of non-work (L'/L=0). 3. It needs a deposition area to store the sediment with decrease in tractive force. The low-dam series in the experimental channel widened the deposition area about 2.10 times compared with that of non-work.

• Journal of Korea Water Resources Association
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• v.49 no.5
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• pp.391-398
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• 2016

The confluence section of rivers forms complex flow pattern due to inflow discharge variation at the mainstream and tributary. Due to complex flow characteristics, bed change and bank erosion at the local section produce lateral geomorphology changes in rivers. In this study, bankline change by bank erosion and bed change were simulated using CCHE2D of 2-dimensional numerical model for quantitative analysis of lateral changes in the confluence section of South Han River and Geumdang Stream. As a result, bankline at the left-side channel of the mainstream was largely changed in the downstream section of the confluence compared to the upstream section. Also, bank erosion in the tributary was hardly occurred and bankline at the left-side tributary and right-side main stream moved to riverside land due to decreased velocity and deposition.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.2
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• pp.103-112
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• 2011

This study aims to demonstrate the relationship between various factors and soil erosion or deposition, simulated from distributed rainfall-sediment-runoff model applications. We selected area, overland flow length, local slope as catchment representative characteristics among many important geographic factors and also used the grid-based accumulated rainfall as a representative hydro-climatic factor to assess the effect of these two different types of factors on erosion and deposition. The study catchment was divided based on the Strahler's stream order method for analysis of the relationship between area and erosion or deposition. Both erosion and deposition increased linearly as the catchment area became larger. Erosion occurred widely throughout the catchment, whereas deposition was observed at the grid-cells near the channel network with short overland flow lengths and mild slopes. In addition, the relationship results between grid-based accumulated rainfall and soil erosion or deposition showed that erosion increased gradually as rainfall amount increased, whereas deposition responded irregularly to variations in rainfall. Within the context of these results, it can be concluded that deposition is closely related with the geographic factors used in this study while erosion is significantly affected by rainfall.

• Journal of The Geomorphological Association of Korea
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• v.20 no.4
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• pp.51-70
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• 2013

The characteristics of deposits formed by the Daejon-cheon and Soobuk-cheon, dissecting the mountains such as Byungpung Mt. and Samin Mt. in western part of Damyang county, Jeonmam province. Results from field survey and bore hole logging by KIGAM are used in interpreting depositional environment, in this study. By the result of deposits near of the channels Daejon-cheon and Soobuk-cheon, and main channel of Youngsan River, the depth of sediment layers in this area is 4~7m, far thinner than formerly estimated. Weathered material of local rocks forms the base of the sedimentary layers. It can be assumed that the location channel of the Youngsan river has been stable ever since the start of the sedimentary events. Sediment particles of tributaries are angular than those of Youngsan River. Particles are larger and sorting is poor. It is interpreted as mount flash flood deposits. Main sources of sediments at the valley bottom or deposition dominated area are the terrace deposits or slope deposits over the gentle foot-slope or front of surrounding mountains. Some particles show polygonal cracking on the surface originated from the strong chemical weathering, while most of these has high angularity. It means various geomorphic processes operate to produce and transport the particles in this area.Isolated hills within the sedimentary plains are made with weathered materials of local bedrock. In the case of foot-slope of the hills, thin sedimentary layers are found. So it can be concluded that surface features of deposition zone of the Daejon-cheon and Soobuk-cheon is formed by the filling of lower part of the valley and its feature partly controlled by the relief of the weathering front.

• Journal of Korea Water Resources Association
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• v.43 no.11
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• pp.995-1009
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• 2010

Accelerated soil erosion due to extreme climate change, such as increased rainfall intensity, and human-induced environmental changes, is a widely recognized problem. Existing soil erosion models are generally based on the gross erosion concept to compute annual upland soil loss in tons per acre per year. However, such models are not suitable for event-based simulations of erosion and deposition in time and space. Recent advances in computer geographic information system (GIS) technologies have allowed hydrologists to develop physically based models, and the trend in erosion prediction is towards process-based models, instead of conceptually lumped models. This study aims to propose an effective and robust distributed rainfall-sediment yield-runoff model consisting of basic element modules: a rainfall-runoff module based on the kinematic wave method for subsurface and surface flow, and a runoff-sediment yield-runoff model based on the unit stream power method. The model was tested on the Cheoncheon catchment, upstream of the Yongdam dam using hydrological data for three extreme flood events due to typhoons. The model provided acceptable simulation results with respect to both discharge and sediment discharge even though the simulated sedigraphs were underestimated, compared to observations. The spatial distribution of erosion and deposition demonstrated that eroded sediment loads were deposited in the cells along the channel network, which have a short overland flow length and a gentle local slope while the erosion rate increased as rainfall became larger. Additionally, spatially heterogeneous rainfall intensity, dependant on Thiessen polygons, led to spatially-distinct erosion and deposition patterns.

• Ocean and Polar Research
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• v.28 no.4
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• pp.361-368
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• 2006

The Saemangeum tidal flat with an area of approxirnately $233km^2$ is one of the biggest estuarine tidal flats on the west coast of Korea. Because of its location in the estuary of Mangyeong and Dongjin Rivers, the tidal flat receives large amount of sediments. A 33-km long sea dyke, enclosing a coastal zone of $401km^2$, was constructed to reclaim tidal flat in the Saemangeum area. The dyke construction radically changes the local tidal current regime and estuarine circulation. These have an effect on sedimentary environments in the tidal flat. On the tidal flats of the study area net deposition occurred, but net erosion occurred near tidal channel in 2004. The comparison of topography and surface sediments in summer 2004 with those in summer 1988 before the dyke construction showed that elevation increased with maximum 80cm and mean grain sizes were fining at Gwanghwal tidal flats. Sedimentary facies of two cores from Gwanghwal tidal flat revealed homogeneous layers in the upper part suggesting rapid deposition after the dyke construction. The sedimentation rate in Gwanghwal tidal flat(GW 6) using $^{210}Pb$ analysis was about 5.4cm/yr which is well matched with the sedimentation pattern revealed by change in topography.

• Ocean and Polar Research
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• v.26 no.3
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• pp.385-400
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• 2004

The Lago Sofia Conglomerate encased in the 2km thick hemipelagic mudstones and thinbedded turbidites of the Cretaceous Cerro Toro Formation, southern Chile, is a deposit of a gigantic submarine channel developed along a foredeep trough. It is hundreds of meters thick kilometers wide, and extends for more than 120km from north to south, representing one of the largest ancient submarine channels in the world. The channel deposits consist of four major facies, including stratified conglomerates (Facies A), massive or graded conglomerates (Facies B), normally graded conglomerates with intraformational megaclasts (Facies C), and thick-bedded massive sandstones (Facies D). Conglomerates of Facies A and B show laterally inclined stratification, foreset stratification, and hollow-fill structures, reminiscent of terrestrial fluvial deposits and are suggestive of highly competent gravelly turbidity currents. Facies C conglomerates are interpreted as deposits of composite or multiphase debris flows associated with preceding hyperconcentrated flows. Facies D sandstones indicate rapidly dissipating, sand-rich turbidity currents. The Lago Sofia Conglomerate occurs as isolated channel-fill bodies in the northern part of the study area, generally less than 100m thick, composed mainly of Facies C conglomerates and intercalated between much thicker fine-grained deposits. Paleocurrent data indicate sediment transport to the east and southeast. They are interpreted to represent tributaries of a larger submarine channel system, which joined to form a trunk channel to the south. The conglomerate in the southern part is more than 300 m thick, composed of subequal proportions of Facies A, B, and C conglomerates, and overlain by hundreds of m-thick turbidite sandstones (Facies D) with scarce intervening fine-grained deposits. It is interpreted as vertically stacked and interconnected channel bodies formed by a trunk channel confined along the axis of the foredeep trough. The channel bodies in the southern part are classified into 5 architectural elements on the basis of large-scale bed geometry and sedimentary facies: (1) stacked sheets, indicative of bedload deposition by turbidity currents and typical of broad gravel bars in terrestrial gravelly braided rivers, (2) laterally-inclined strata, suggestive of lateral accretion with respect to paleocurrent direction and related to spiral flows in curved channel segments around bars, (3) foreset strata, interpreted as the deposits of targe gravel dunes that have migrated downstream under quasi-steady turbidity currents, (4) hollow fills, which are filling thalwegs, minor channels, and local scours, and (5) mass-flow deposits of Facies C. The stacked sheets, laterally inclined strata, and hollow fills are laterally transitional to one another, reflecting juxtaposed geomorphic units of deep-sea channel systems. It is noticeable that the channel bodies in the southern part are of feet stacked toward the east, indicating eastward migration of the channel thalwegs. The laterally inclined strata also dip dominantly to the east. These features suggest that the trunk channel of the Lago Sofia submarine channel system gradually migrated eastward. The eastward channel migration is Interpreted to be due to tectonic forcing imposed by the subduction of an oceanic plate beneath the Andean Cordillera just to the west of the Lago Sofia submarine channel.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.2
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• pp.137-153
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• 2013

In order to assess the effects of ecosystem and landscape in around spur dikes, this study had carried out monitoring on the changes of ecosystem and morphologic characteristics in around spur dikes that had been settled in bend of Youngcheon River. The study site was a short reach with length 190m, spur dikes were installed in March, 2008. Monitoring of the site had been started in May 2008 and had been completed September 2011. The results are as follow ; 1) Spur dikes that were installed for channel stabilization are performing effectively hydraulic functions at flooding time. 2) Spur dikes that were installed in water colliding front of river bend brought about sediment deposition between those and formed pools around front of those. Therefore, it was verified to create various physical characteristics in the aspect of channel topography and flow consequently. 3) The survey results that was carried out in October 2008 showed to emerge 25 species of plant, 9 species of fish and 17 species of benthic macroinvertebrates, but the survey results in October 2010 showed to emerge 74 species of plant, 12 species of fish and 19 species of benthic macroinvertebrates. In particular, plant species that emerged in 2011 increased about three times more than those in 2008.

• Fisheries and Aquatic Sciences
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• v.13 no.2
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• pp.167-181
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• 2010

To predict changes in the marine environment of the Beolgyo Stream Estuary in Jeonnam Province, South Korea, where cohesive tidal flats cover a broad area and a large bridge is under construction, this study conducted numerical simulations involving tidal flow and cohesive sediment transport. A wetting and drying (WAD) technique for tidal flats from the Princeton Ocean Model (POM) was applied to a large-scale-grid hydrodynamic module capable of evaluating the flow resistance of structures. Derivation of the eddy viscosity coefficient for wakes created by structures was accomplished through the explicit use of shear velocity and Chezy's average velocity. Furthermore, various field observations, including of tide, tidal flow, suspended sediment concentrations, bottom sediments, and water depth, were performed to verify the model and obtain input data for it. In particular, geologic parameters related to the evaluation of settling velocity and critical shear stresses for erosion and deposition were observed, and numerical tests for the representation of suspended sediment concentrations were performed to determine proper values for the empirical coefficients in the sediment transport module. According to the simulation results, the velocity variation was particularly prominent around the piers in the tidal channel. Erosion occurred mainly along the tidal channels near the piers, where bridge structures reduced the flow cross section, creating strong flow. In contrast, in the rear area of the structure, where the flow was relatively weak due to the formation of eddies, deposition and moderated erosion were predicted. In estuaries and coastal waters, changes in the flow environment caused by artificial structures can produce changes in the sedimentary environment, which in turn can affect the local marine ecosystem. The numerical model proposed in this study will enable systematic prediction of changes to flow and sedimentary environments caused by the construction of artificial structures.