• Journal of Korea Water Resources Association
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• v.45 no.2
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• pp.151-163
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• 2012

The distribution of gravel-bed materials in mountainous river is formed by the process of deposition and transportation of sediment responding to stream power of the latest flood that is over the certain scale. The particle size of bed material was surveyed in the longitudinal points of river and detail points of a specific meandering section and used to estimate the critical velocity and stream power. Yang's critical unit stream power and Bagnold's critical stream power for gravel-bed materials increased with the distance from downstream to upstream. Dimensionless shear stress based on the designed flood discharge in Shields diagram was evaluated that the gravel-bed materials in most survey points may be transported as form of bedload. The mean diameter in the meandering section was the biggest size in first water impingement point of inflow water from upstream and the second big size in second water impingement point by reflection flow. The mean diameters were relatively the small sizes in points right after water impingement. The range of mean critical velocity was 0.77~2.60 m/s and critical unit stream power was big greatly in first water impingement point. The distribution of critical stream power, range of 7~171 $W/m^2$, was shown that variation in longitudinal section was more obvious than that of cross section and estimated that critical stream power may be affected greatly in first and second water impingement point.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.38-42
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• 2010

기후변화에 의해 집중호우의 빈도 및 강도가 증가하고 지속적인 유역개발에 따른 토지이용의 증가는 토양침식 및 토사유출로 인한 재해 및 환경문제를 야기한다. 현재 광범위하게 사용되고 있는 토양침식량 산정기법은 대부분 대상유역내의 평균 토양침식량을 산출하는 총량적 개념의 경험식이므로 호우기간동안의 유역 침식/퇴적의 시 공간적 변화양상을 모의할 수 없다는 한계를 지니고 있다. 따라서 보다 합리적인 유역규모의 강우-유사-유출 메카니즘 해석을 위해서는 집중형(lumped) 모의기법을 대체하고 다양한 기상학적/지형학적 디지털 정보를 활용할 수 있는 물리적 기반의 분포형 모형이 요구된다. 본 연구에서는 사면의 지표 및 지표하 흐름을 고려한 유출모의 모듈과 단위수류력(Unit Stream Power)이론을 기반으로 유사유출 모의모듈을 결합한 분포형 강우-유사-유출 모형을 개발하고, 용담댐 상류부의 천천유역에 적용하여 개발된 모형의 재현성 평가를 수행하였다.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.1
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• pp.117-124
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• 1991

Based on the momentum equation for the flow in a stream bend, the force per unit area which the flow exerts on the outer of a bend is directly proportional to a certain curvature coefficient, $C{\alpha}$. This coefficient is dependent on the ratio of bend radius(R) to flow width(W), as well as on the coefficient of dynamic bedload friction, $tan{\alpha}$. According to the results of the data analysis for the downstrream at the Han river, the range of R/w values is between 2.0 and 4.0. Exploring the variations of $C{\alpha}$ with R/w values a functional relationship which, for the known values of $tan{\alpha}$, shows maximum values of $C{\alpha}$ for R/w values between 2.21 and 4.42 in 1963, while in 1981 its values lied between 1.93 and 3.54.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.448-448
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• 2015

급경사면의 세류간 토양침식은 지표면과의 강우입자 충돌에 의한 튀김현상과 면상흐름에 의한 토사이송 능력의 상호작용에 의해 영향을 받는다. 강우운동에너지와 면상흐름이 세류간 토양침식 및 토사유출 발생에 있어서 상대적인 기여도에 대한 연구는 국내뿐만 아니라 전 세계적으로도 미흡하다. 본 연구에서는 강우현상을 재현할 수 있는 강우모의 실험장비와 사면 토양침식 실험을 위한 소규모 토양플롯을 제작하여 실험에 사용하였다. 강우모의에 의한 강우운동에너지는 자연강우의 운동에너지 산정식의 계산결과와 비교했을 때, 약 0.58배의 규모를 재현했다. 강우입자의 충돌을 제어하기 위한 스트립을 토양플롯에 올려놓은 경우와 커버가 없는 나지상태에서 강우모의 실험을 한 경우 사면에서 발생한 지표유출수, 지표하유출수 및 토사유출 자료를 측정하고 분석하였다. 강우강도가 증가함에 따라 지표유출량은 증가하고, 지표하유출량은 상대적으로 감소했다. 지표커버는 지표유출의 첨두유량 발생시간을 지연시켰으며, 지표유출량과 지하수량의 변화를 초래했다. 지표커버에 의해 지표유출량은 평균 1.82배 감소하지만, 토사유출량은 평균 4.93배로 상대적으로 크게 감소하였다. 단위수류력과 토사유출량과 관계를 분석한 결과 강우운동에너지는 토양입자의 튀김현상에 의한 침식을 증가시킬 뿐만 아니라 지표유출수의 유속을 증가시켜 토사이송능력을 가중시키는 것을 확인하였다.

• Journal of Korea Water Resources Association
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• v.48 no.7
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• pp.595-604
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• 2015

Interrill erosion by the rainfall is divided into a detachment of soil particles by raindrop splash when raindrops having kinetic energy strike on the surface soil and a sediment transport by sheet flow of surface runoff. Rainfall kinetic energy is widely used as an indicator expressing the potential ability to separate the soil particles from soil mass. In this study, the soil erosion experiments of rainfall simulation were operated to evaluate the effects of rainfall kinetic energy on interrill erosion as using the strip cover to control raindrop impact. The kinetic energy from rainfall simulator was 0.58 times to that of natural rainfall. Surface runoff and subsurface runoff increased and decreased respectively with increase of rainfall intensity. Surface runoff discharge from plots of non-cover was 1.82 times more than that from plots with cover. The rainfall kinetic energy influenced on the starting time of surface and subsurface runoff. Soil erosion quantity greatly varied according to existence of the surface cover that can intercept rainfall energy. Sediment yields by the interaction between raindrop splash and sheet flow increased 3.6~5.9 times and the increase rates of those decreased with rainfall intensity. As a results from analysis of relationship between stream power and sediment yields, rainfall kinetic energy increased the transport capacity according to increase of surface runoff as well as the detachment of soil particles by raindrop splash.

• Economic and Environmental Geology
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• v.50 no.2
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• pp.129-143
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• 2017

The shallow sediments in the southwestern Ulleung Basin consist of mass flow deposits such as slide/slump and debris flow deposits (DFD), caused by slope failure. These sediments are proven to be important in studying geological disaster and stability of the seafloor. In this paper, we analysised the flow accumulation and slope failure susceptibility of the Ulleung Basin on the basis of multi-beam data, collected in this area. We also studied the distribution pattern and the seismic characteristics of the DFD in the uppermost layer of the Ulleung Basin on the basis of seismic data. The slope susceptibility was calculated as the frequency ratio of each factors including slope, aspect, curvature and stream power index (SPI), which causes the slope failure. These results indicate that the slope failure is frequently to occur in the southern and western continental slope of the Ulleung Basin. The sediment flow (mass flow) caused by the slope failure converges to the north and northwest of the Ulleung Basin. According to the seismic characteristics, the uppermost layer in study area can be divided into four sedimentary unit. These sedimentary units develop from the south and southwest to the north and northwest in association with slope susceptibility and flow accumulation.