• Journal of Korea Water Resources Association
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• v.54 no.8
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• pp.629-641
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• 2021

In this study, a two-dimensional numerical model (Nays2DH) was applied to analyze the process of morphological changes in the river channel bed depending on the changes in the amount of flooding after fully opening the Sejong weir, which was constructed upstream of the Geum River. For this, numerical simulations were performed by assuming the flow conditions, such as a non-uniform flow (NF), unsteady flows (single flood event, SF), and a continuous flood event (CF). Here, in the cases of the SF and CF, the normalized hydrograph was calculated from real flood events, and then the hydrograph was reconfigured by the peak flow discharge according to the scenario, and then it was employed as the flow discharge at the upstream boundary condition. In this study, to quantitatively evaluate the morphological changes, we analyzed the time changes in the bed deformation the bed relief index (BRI), and we compared the aerial photographs of the study area and the numerical simulation results. As simulation results of the NF, when the steady flow discharge increases, the ratio of lower width to depth decreases and the speed of bar migration increases. The BRI initially increases, but the amount of change decreased with time. In addition, when the steady flow discharge increases, the BRI increased. In the case of SF, the speed of bar migration decreased with the change of the flow discharge. In terms of the morphological response to the peak flood discharge, the time lag also indicated. In other words, in the SF, the change of channel bed indicates a phase lag with respect to the hydraulic condition. In the result of numerical simulation of CF, the speed of bar migration depending on the peak flood discharges decreased exponentially despite the repeated flood occurrences. In addition, as in the result of SF, the phase lag indicated, and the speed of bar migration decreased exponentially. The BRI increased with time changes, but the rate of increase in the BRI was modest despite the continuous peak flooding. Through this study, the morphological changes based on the hydrological characteristics of the river were analyzed numerically, and the methodology suggested that a quantitative prediction for the river bed change according to the flow characteristic can be applied to the field.

• Geophysics and Geophysical Exploration
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• v.26 no.1
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• pp.18-30
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• 2023

Submarine mud volcanos are topographic features that resemble volcanoes, and are formed due to eruptions of fluidized or gasified sediment material. They have gained attention as a source of subsurface heat, sediment, or hydrocarbons supplied to the surface. In the continental slope of the Canadian Beaufort Sea, mud volcano exists at various water depths. The MV420, is an active mud volcano erupting at a water depth of 420 meters, and it has been the subject of extensive study. The Korea Polar Research Institute(KOPRI) collected high-resolution seismic data and heat flow data around the caldera of the mud volcano. By analyzing the multi-channel seismic data, we confirmed the reverse-polarity reflector assumed by a gas hydrate-related bottom simulating reflector(BSR). To further elucidate the relationship between the BSR and gas hydrates, as well as the thermal structure of the mud volcano, a numerical geothermal model was developed based on the steady-state heat equation. Using this model, we estimated the base of the gas hydrate stability zone and found that the BSR depth estimated by multi-channel seismic data and the bottom of the gas hydrate stability zone were in good agreement., This suggests the presence of gas hydrates, and it was determined that the depth of the gas hydrate was likely up to 50 m, depending on the distance from the mud conduit. Thus, this depth estimate slightly differs from previous studies.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.26 no.5
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• pp.327-334
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• 2014

This study aims to estimate settling velocity ($W_s$) for cohesive sediments from water bodies (Incheon Coast, Kulpo Stream and Han River) mainly connected to the Kyeongin Ara-waterway through the laboratory settling experiments. Results of settling tests for these sediments show that $W_s$ values for sediments are quite different each other: $W_s$ values of Kulpo Stream sediments (0.01 < $W_s$ < 3.07 mm/s) are quite similar with those of Han River sediments (0.01 < $W_s$ < 2.97 mm/s) over the whole range of suspension concentration C (0.1 < C < 90 g/ L), while they are quite different with those for Incheon Coast sediments (0.01 < $W_s$ <0.92 mm/s). Qualitative analyses on test results for physico- chemical properties of sediments and waters with respect to settling velocities show that these differences in settling velocities are mainly due to the salinity difference in the water.

• Journal of the Korean association of regional geographers
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• v.9 no.2
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• pp.203-216
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• 2003

The process of constructing coastal digital elevation model(DEM), for the 3 dimensional analysis, is composed by abstracting land layers for land elevation and water depth, reprojecting UTM, relocating geographical grid, and interpolating works. The geomorphic set of shallow sea, including tidal current, tidal zone deposition, and water depth distribution, was analyzed by eye search of Landsat TM image, masking of land zone, band combination and regression analysis. Some horizontal differences, between combined DEM and surveyed data of shallow sea, was corrected for analysis. Analyzed geomorphic elements are stream channel, alluvial fan, coastal terrace, tidal current. and shallow sea bank. Results of analysis present that transported fluvial materials influence tidal sedimentation, especially from Gahwacheon river, for the role of artificial draining flooding waters from Jinyang Reservoir, almost in the summer season. In the coastal area with less tidal current, more fine materials are deposited. The influence of currental deposition are higher on small pockets with west coast of well developed terraces. The lower skirt of alluvial fans developed into the tidal zone of shallow sea. Small pocket type bays are closed by coastal current, and less influenced from tidal deposition. The bank of Jinju Bay are developed originally from submerging of remnant erosional mountain ranges, and play on the role of trapping fine materials.

• Journal of Korea Water Resources Association
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• v.47 no.7
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• pp.599-614
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• 2014

In this study, two dimensional finite volume model was parallelized to improve computing time, which has been developed to be able to apply for the mixed meshes of triangle and quadrilateral. MPI scheme which is free from limitation of the number of cores was applied, and non-blocking point-to-point communication was used for fluxes and time steps calculation domain. The developed model is applied to analyze dam break in a L-shaped experimental channel with $90^{\circ}$ bend and Malpasset dam breach event to calibrate the consistency between parallelized model and existing model and examine the speed-up and efficiency of computing time. Computational speed-up about the size of the input data was considered by simulating 4 cases classified by the number of meshes, Consequently, the simulation results reached a satisfactory accuracy compared to measured data and the results from existing model, and achieved more than 3 times benefit of computational speed-up against computing time of existing model. Simulation results of 3 cases classified by the size of input data lead us to the conclusion that it is important to use proper size of input data and the number of process in order to minimize the communication overhead.

• Journal of Korea Water Resources Association
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• v.49 no.6
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• pp.459-467
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• 2016

LISFLOOD-FP model in which channel flows are resolved separately from the floodplain flows using either a kinematic or diffusive wave approximation has been used to analyze flooding behavior on the lower Mankyung River influenced by backwater. A calibration and validation process was applied using the previous flood events to assess the model performance. Sensitivity analysis was conducted for main calibrated parameters, such as Manning roughness coefficient and downstream boundary condition. Also, we examined the effect of warm-up for the initial conditions. The results show that the computed hydrograph is in good agreement with measured data on the study reach, even though it was a hydrologic kinematic wave model. The sensitive analysis show that the difference between the computed results may be greater depending on the used calibrated parameters and that the sufficient calibration/validation process against various flood events is necessary. If the flood inundation simulation is performed using the validated model, it is expected to be able to contribute about river planning and policy decision-making for flood damage reduction.

• Korean Journal of Ichthyology
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• v.11 no.1
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• pp.62-71
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• 1999

The seasonal distribution of Maurolicus muelleri eggs and larvae were determined using samples collected from the Korea Strait and the southern part of the East Sea in May and November, 1992, August, 1993, and January, 1994. The eggs were most abundant in summer and the larvae in spring, while, their abundance was low in winter. The eggs were mainly found from in all season around sea of the front area of latitude $35{\sim}36^{\circ}N$ and the West Channel of the Korea Strait found the middle or bottom water lower than $15^{\circ}C$. The seasonal distribution of the eggs in the western Korea Strait varied according to the structure of the bottom cold water of the Korea Strait. The M. muelleri larvae in different stage were most abundant in the front area of latitude $35{\sim}36^{\circ}N$. The spawning and hatching area of the M. muelleri was considered to be the front area located in the shelf break, and some eggs can be transported into the Korea Strait by westward cold bottom current in summer. The Korea Strait would be the southern margin of the distribution of Maurolicus muelleri eggs and larvae of the East Sea.

• Journal of Korea Water Resources Association
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• v.36 no.3 s.134
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• pp.507-520
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• 2003

A V-shaped riffle is an artificial hydraulic structure haying two wings from the streamside with a narrow opening in between. It is usually made of crushed stones or large boulders. It limits channel width and accelerates the flow through the constricted section causing a local scour just downstream. The V-shaped riffle provides with a unique aquatic habitat by forming a pool and sandbars around the pool edge, increasing local morphologic, hydraulic and sedimentological diversity. This study investigates experimentally the scour characteristics of the V-shaped riffle in the sandbed stream and proposes a predictive equation for the scour. Total 45 cases of experiments were conducted to examine the effect of hydraulic factors and configuration of V-shaped riffle on the geometry of scour holes. From the comparison of the experimental results of this study with the predictive equation of spur dike by Breusers and Raudkivi(1991), it is found that their predictive equation of spur dike underestimates the maximum scour depth downstream of the V-shaped riffle. h new predictive equation for the maximum scour depth was developed using the non-dimensional hydraulic and geometrical variables. The parameters used in the proposed equations were determined using the experimental data. The analysis reveals that the scour depth is dependent dominantly on the Froude number at the opening of the V-shaped riffle, while the angle of riffle and the opening width also affect the scour depth. The proposed equation for the scour of V-shaped riffle well agrees with the experimental data. It can be used for estimating the scour of the V-shaped riffle in sandbed streams.

• Korean Journal of Remote Sensing
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• v.29 no.1
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• pp.11-20
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• 2013

Space-borne Synthetic Aperture Radar(SAR) has been one of the most effective tools for monitoring quantitative oceanographic physical parameters. The Doppler information recorded in single-channel SAR raw data can be useful in estimating moving velocity of water mass in ocean. The Doppler shift is caused by the relative motion between SAR sensor and the water mass of ocean surface. Thus, the moving velocity can be extracted by measuring the Doppler anomaly between extracted Doppler centroid and predicted Doppler centroid. The predicted Doppler centroid, defined as the Doppler centroid assuming that the target is not moving, is calculated based on the geometric parameters of a satellite, such as the satellite's orbit, look angle, and attitude with regard to the rotating Earth. While the estimated Doppler shift, corresponding to the actual Doppler centroid in the situation of real SAR data acquisition, can be extracted directly from raw SAR signal data, which usually calculated by applying the Average Cross Correlation Coefficient(ACCC). The moving velocity was further refined to obtain ocean surface current by subtracting the phase velocity of Bragg-resonant capillary waves. These methods were applied to Envisat ASAR raw data acquired in the East Sea, and the extracted ocean surface currents were compared with the current measured by HF-radar.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.1393-1397
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• 2005

홍수유출을 저감시키기 위해서 유역의 저류기능을 강화시킬 수 있는 댐 건설은 이수적인 측면에서 안정적인 용수공급을 보장해주는 수단으로 겸용되어 왔으며, 특히 다목적댐이 건설되면서 하도의 첨두홍수유출량을 줄이는데 크게 기여해 왔다. 하지만 그로 인해 물의 흐름이 막히는 정체수역이 증가하고 있으며, 생활오수, 산업폐수의 발생은 정체수역에서의 영양염류 부하량을 증가시켜 부영양화를 초래하고 있다. 수생식물은 태양빛을 받아 광합성 작용을 하여 수중에서 성장하면서 수중의 유$\cdot$무기물질을 영양소로 섭취함으로써 수질을 정화시키는 작용을 하게 된다. 영양염류 부하량이 큰 정체수역의 오염된 물은 식물의 성장활동에 의해서 어느 정도 정화시킬 수 있으며, 이와 같이 수중에 식물을 식재하기 위해서는 식물이 하상에 쉽게 그리고 지속적으로 성장하고 번식활동을 할 수 있는 여건이 필요하다. 따라서 본 연구에서는 Mattress/Filter를 정체수역에 설치함으로써 이러한 식물의 성장과 번식을 도와줄 수 있는 환경조건을 제안하였다. 연구결과, Mattress에 식재한 갈대, 줄 및 애기부들의 피도는 $60-80\%$ 정도로 나타났다. 각 Mattress의 식물군집에는 초기 식재한 식물의 우점도가 가장 높았으나 갈대와 줄 군락의 경우 다른 종이 많이 출현하는 것으로 나타났다. 갈대 군락에서는 갈대가 크게 우점하였으나 그 외에 돌피, 하늘지기, 여뀌바늘 등이 우점하는 것으로 나타났다. 또한 줄 군락에서는 역시 줄이 크게 우점하였으나 방동사니, 돌피, 조개풀 등이 출현하였다. 애기부들 군락에서는 애기부들외에 세모고랭이와 미국가막사리 두가지 종만 출현한 것으로 나타났다. 갈대와 줄 군락의 출현 종수는 각각 7과 11이었으며, 다양도지수가 1.67, 2.18로 식물다양성이 크게 증가한 것으로 나타났다. 수질은 BOD 10mg/L, TN 15mg/L, TP 2.0mg/L이하로 이를 유등천 상류부에 공급할 경우 유등천의 수질은 BOD 6.7mg/L, TN 9.80mg/L, TP 0.90mg/L를 나타낼 것으로 예측된다. 고도처리시설의 도입 후 금강 합류점에서 갑천의 예측 BOD는 7.4mg/L로 현재 9.0mg/L에 비하여 개선되지만 이는 금강수계 오염총량 관리계획의 시$\cdot$도 경계지점 목표수질인 5.9mg/L를 만족시키지 못하므로, 이를 만족시키기 위해서는 방류수 BOD 7.2mg/L이하로 처리해야 할 것으로 판단된다.which support only concepts or image features.방하는 것이 선계기준에 적합한 것으로 나타났다. 밸브 개폐에 따른 수압 변화를 모의한 결과 밸브 개폐도를 적절히 유지하여 필요수량의 확보 및 누수방지대책에 활용할 수 있을 것으로 판단된다.8R(mm)(r^2=0.84)$로 지수적으로 증가하는 경향을 나타내었다. 유거수량은 토성별로 양토를 1.0으로 기준할 때 사양토가 0.86으로 가장 작았고, 식양토 1.09, 식토 1.15로 평가되어 침투수에 비해 토성별 차이가 크게 나타났다. 이는 토성이 세립질일 수록 유거수의 저항이 작기 때문으로 생각된다. 경사에 따라서는 경사도가 증가할수록 증가하였으며 $10\% 경사일 때를 기준으로 $Ro(mm)=Ro_{10}{\times}0.797{\times}e^{-0.021s(\%)}$로 나타났다.천성 승모판 폐쇄 부전등을 초래하는 심각한 선천성 심질환이다. 그러나 진단 즉시 직접 좌관상동맥-대동맥 이식술로 수술적 교정을 해줌으로써 좋은 성적을 기대할 수 있음을 보여주었다.특히 교사들이 중요하게 인식하는 해방적 행동에 대한 목표를 강조하여 적용할 필요가 있음을 시사하고