• Ocean Systems Engineering
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• v.6 no.1
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• pp.61-97
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• 2016

This is the second of two papers on the 3D numerical modeling of nearshore hydro- and morphodynamics. In Part I, the focus was on surf and swash zone hydrodynamics in the cross-shore and longshore directions. Here, we consider nearshore processes with an emphasis on the effects of oceanic forcing and beach characteristics on sediment transport in the cross- and longshore directions, as well as on foreshore bathymetry changes. The Delft3D and XBeach models were used with four turbulence closures (viz., ${\kappa}-{\varepsilon}$, ${\kappa}-L$, ATM and H-LES) to solve the 3D Navier-Stokes equations for incompressible flow as well as the beach morphology. The sediment transport module simulates both bed load and suspended load transport of non-cohesive sediments. Twenty sets of numerical experiments combining nine control parameters under a range of bed characteristics and incident wave and tidal conditions were simulated. For each case, the general morphological response in shore-normal and shore-parallel directions was presented. Numerical results showed that the ${\kappa}-{\varepsilon}$ and H-LES closure models yield similar results that are in better agreement with existing morphodynamic observations than the results of the other turbulence models. The simulations showed that wave forcing drives a sediment circulation pattern that results in bar and berm formation. However, together with wave forcing, tides modulate the predicted nearshore sediment dynamics. The combination of tides and wave action has a notable effect on longshore suspended sediment transport fluxes, relative to wave action alone. The model's ability to predict sediment transport under propagation of obliquely incident wave conditions underscores its potential for understanding the evolution of beach morphology at field scale. For example, the results of the model confirmed that the wave characteristics have a considerable effect on the cumulative erosion/deposition, cross-shore distribution of longshore sediment transport and transport rate across and along the beach face. In addition, for the same type of oceanic forcing, the beach morphology exhibits different erosive characteristics depending on grain size (e.g., foreshore profile evolution is erosive or accretive on fine or coarse sand beaches, respectively). Decreasing wave height increases the proportion of onshore to offshore fluxes, almost reaching a neutral net balance. The sediment movement increases with wave height, which is the dominant factor controlling the beach face shape.

• Proceedings of the Zoological Society Korea Conference
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• 2000.10a
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• pp.135.2-135
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• 2000

No Abstract, See Full Text

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.399-406
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• 1999

Recently, the construction of the several highway bridges in the karst area have encountered severe problems associated with cavities and sinkholes. To solve this problems, it is important to understand the distribution characteristics of cavities in the construction site on limestone area. This paper briefly describes the different types, the distribution control factors and the infill sediment types of lime-cavities in the study area, bridge site in the karst area and propose the effective method of survey design. Cavity system may be divided into two main groups, 1)'slot and cave system'and 2)'sinkhole and cave system'. And the shape, the size and the distribution pattern of cavity are controlled by three main factors - rock type, geological structure and ground water condition. Additionally, infill sediment may be considered as one of the important design factors for foundation design and divided into four types by sediment properties. There are geophysical thechnics and geologic survey and drilling test, etc. by the survey method to interpretate characteristics of cavity system, and this methods are optimally designed at the site investigation stage.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.51 no.3
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• pp.321-327
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• 2018

To classify seafloor sediments using a probabilistic neural network (PNN), the frequency-dependent characteristics of broadband acoustic scattering, which make it possible to qualitatively categorize seabed type, were collected from three different geographical areas in Korea. The echo data samples from three types of seafloor sediment were measured using a chirp sonar system operating over a frequency range of 20-220 kHz. The spectrum amplitudes for frequency responses of 35-75 kHz were fed into the PNN as input feature parameters. The PNN algorithm could successfully identify three seabed types: mud, mud/shell and concrete sediments. The percentage probabilities of the three seabed types being correctly classified were 86% for mud, 66% for mud/shell and 72% for concrete sediment.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.3 no.3
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• pp.113-125
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• 2000

This study was carried out to introduce current status and development strategy for an environmental restoration of stream side in Japan, and to consider a methodology which could be effectively applied for the environmental restoration of stream side in Korea. The strategy prospects of environmental restoration in Japan were summarized as follows : 1. When we establish the long term erosion control planning, we should make detail planning after considering of a certain block of watershed units. Because most of the disaster is caused by soil movement which was occurred by water contents. 2. Nowadays, the general torrent erosion control planning system in Japan focused on reducing the sediment such as by placement of erosion control facility and by restoration of afforestation, after calculation of several factors including expected amount of sediment, and the different amount of planned sediment and allowable sediment. 3. In the past, the goal of forest conservation and erosion control planing was to fix the amount of soil movement by construction of permanent facilities. While, the goal of forest conservation and erosion control planning in the future needs to change the techniques to a small and middle scale's soil movement which could prevent soil movement from large scale of soil disasters, but allow soil movement effectively. Also, it is considered to change erosion control dams from non passing type to passing type. 4. Restoration of stream-side ecology, erosion control for the conservation of ecology should be planned and conducted cautiously based on concepts of ecology conservation and development of environmentally sound techniques.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.519-519
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• 2023

Estuarine dams are a recent and global phenomenon. While estuarine dams can provide the benefit of improved freshwater resources, they can also alter estuarine processes. Due to the wide range of estuarine types and estuarine dam configurations, the effect of estuarine dams on estuaries is not well understood in general. To develop a systematic understanding of the effect of estuarine dam location and freshwater discharge interval on a range of estuarine types (strongly stratified, partially mixed, periodically stratified, and well-mixed), this study used a coupled hydrodynamic-sediment dynamic numerical model (COAWST) and compared flow, sediment transport, and morphological conditions in the pre- and post-dam estuaries. For each estuarine type, scenarios with dam locations at 20, 55 and 90 km from the mouth and discharge intervals of a discharge every 0.5, 3, and 7 days were investigated. The results were analyzed in terms of change in tide, river discharge, estuarine classification, and sediment flux mechanism. The estuarine dam location primarily affected the tide-dominated estuaries, and the resonance length was an important length scale affecting the tidal currents and Stokes return flow. When the location was less than the resonance length, the tidal currents and Stokes return flow were most reduced due to the loss of tidal prism, the dead-end channel, and the shift from mixed to standing tides. The discharge interval primarily affected the river-dominated estuaries, and the tidal cycle period was an important time scale. When the interval was greater than the tidal cycle period, notable seaward discharge pulses and freshwater fronts occurred. Dams located near the mouth with large discharge interval differed the most from their pre-dam condition based on the estuarine classification. Greater discharge intervals, associated with large discharge magnitudes, resulted in scour and seaward sediment flux in the river-dominated estuaries, and the dam located near the resonance length resulted in the greatest landward tidal pumping sediment flux and deposition in the tide-dominated estuaries.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.557-562
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• 2004

A surface-piercing barrier model is presented for understanding morphological development in the sheltered region and investigating the main factors causing the severe accumulation. Surface-piercing structures like vertical barriers, surface docks and floating breakwaters are recently favored from the point of view of a marine scenario since they do not in general partition the natural sea. The numerical solutions are compared with experimental data on wave profiles and morphological change rates within a rectangular harbor of a constant depth protected by surface-piercing thin breakwaters as a simplified problem. Our numerical study involves several modules: 1) wave dynamics analyzed by a plane-wave approximation, 2) suspended sediment transport combined with sediment erosion-deposition model, and 3) concurrent morphological changes. Scattering waves are solved by using a plane wave method without inclusion of evanescent modes. Evanescent modes are only considered in predicting the reflection ratio against the vertical barrier and energy losses due to vortex shedding from the lower edge of plate are taken into account. A new relationship to relate the near-bed concentration to the depth-mean concentration is presented by analyzing the vertical structure of concentration. The numerical solutions were also compared with experimental data on morphological changes within a rectangular harbor of constant water depth. Through the numerical experiments, the vortex-induced flow appears to be not ignorable in predicting the morphological changes although the immersion depth of a plate is not deep.

• The Journal of the Acoustical Society of Korea
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• v.22 no.4E
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• pp.167-175
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• 2003

Shear wave velocity was measured and grain size analysis was conducted on two core samples obtained in unconsolidated marine sediments of the western continental margin, the East Sea. A pulse transmission technique based on the Hamilton frame was used to measure shear wave velocity. Duomorph ceramic bender transducer-receiver elements were used to generate and detect shear waves in sediment samples. Time delay was calculated by changing the sample length from the transducer-receiver element. Time delay is 43.18 μs and shear wave velocity (22.49 m/s) is calculated from the slope of regression line. Shear wave velocities of station 1 and 2 range from 8.9 to 19.0 m/s and from 8.8 to 22 mis, respectively. Shear wave velocities with depth in both cores are qualitatively in agreement with the compared model〔1〕, although the absolute value is different. The sediment type of two core samples is mud (mean grain size, 8-9Φ). Shear wave velocity generally increases with sediment depth, which is suggesting normally consolidated sediments. The complicated variation of velocity anisotropy with depth at station 2 is probably responsible for sediment disturbance by possible gas effect.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.4
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• pp.121-131
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• 2013

This study focused on the sediment reduction effects of VFS (vegetative filter strip) systems for the general characteristics of uplands in Korea. General conditions of upland fields were investigated through national scales of annual agricultural statistics. 7-15 % of slope with loam soil was the dominant types of uplands, and the hydrologic soil group feature usually belong to Type B. The common sizes of uplands were bigger than 0.1 ha and less than 0.2 ha, and 86.2 % of them account for less than 1.0 ha. With this information, 0.1 ha, 0.5 ha, and 1.0 ha of uplands with various shapes and 7-15 % of slopes were considered for the VFS system simulations. 20 mm, 40 mm, and 100 mm of daily precipitation were applied. As a result, the trapping efficiencies of VFS systems were obtained 37.4~100 % for 7 % slope and 18.1~98.0 % for 15 % slope of the less than 1.0ha of uplands. As rainfall increased, sediment loads also increased with slope and slope length increase. Also as size and slope of uplands and slope length increased with VFS length decrease, the trapping efficiency decreased for the same amount of rainfall. The optimum lengths of VFS systems for the givien upland conditions were suggested based on the modelling results with condition of VFS length less than 20 % of upland areas.

• 한국해양학회지
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• v.30 no.3
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• pp.147-162
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• 1995

The circulation due to tidal current and river discharge, and the associated suspended suspended sediment transport in macrotidal Keum Estuary, were studied through a series of field measurements of tidal currents and suspended sediment concentration at three anchored stations from 1990 through 1992. From the measurements, the following results were obtained. At the seaward entrance of the estuary, the veritical profiles of the ebb and flood currents were almost symmetric. At the southern channel the flood current was dominant in the whole water column, but in the northern channel the ebb current was dominant in the surface and bottom layers and the flood current was dominant in the intermediate layer. The maximum velocity of the tidal current in the southern channel was 174 cm/s during flood tide in the intermediate layer. The maximum velocity, 148 cm/s in the northern channel also appeared during flood tide in the intermediate layer. However, in the surface and bottom layers, the maximum velocities were 110.6 cm/s during ebb tide and 92.1 cm/s during flood tide, respectively. The type of the Keum Estuary can be categorized to 'Type 3' of Hansen and Rattray's scheme. The water column of the estuary during the flood tide becomes stratified, and after high water the ebb current reduces the density difference and the water column becomes turbulent. The lower layer of the water column is generally turbulent. The largest sediment flux 20.61 ton/s was found in the southern channel during flood current in the lowest river discharge (May, 1991), while the smallest flux, 0.65 ton/s in the northern channel in the lowest tidal range (July, 1992). The stronger bottom shear velocity for the present study area seems to erode the bottom sediments during the flood tide, and the relatively long duration of the ebb tide to transport the suspended sediments. Under normal river discharge conditions, the suspended sediments are transported mainly through the southern channel. However, under high river discharge condition the suspended sediment transport is dominant through the northern channel.