• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1057-1062
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• 2009

대부분의 홍수 예측모형은 도달시간 산정에 있어 지표면 흐름을 중력흐름으로 가정한다. 그러나 Woo & Brater(1961)의 실험결과 지표면 흐름의 마찰계수는 바닥정사의 함수인 것으로 나타나며 수심이 매우 얕은 흐름의 경우 조고뿐만 아니라 바닥경사에 의한 영향이 매우 큰 것으로 나타났다. 새로운 무차원수 Y는 바닥경사, 수심, 조고 및 표면장력 등을 고려하는 인자로서 중력흐름과 표면장력흐름의 각 흐름특성을 반영하기 위한 새로운 도달시간 산정식을 개발하였다. 새로운 무차원수 Y는 표면장력과 관계된 후르드수 및 웨버수의 조합으로 조고뿐만 아니라 바닥경사, 수심의 함수로 나타난다. 지표면 흐름의 마찰계수 산정시 비례상수 ${\alpha}$를 새로운 무차원수 Y의 함수로 취하여 Butler(1977)의 실험자료를 분석하였다. 중력흐름의 경우 조고만의 함수로 나타나지만 표면장력흐름은 조고뿐만 아니라 바닥경사의 영향이 매우 중요한 것으로 나타났다. 중력흐름만을 고려하여 도달시간 산정시 관측치보다 작게 산정되는 반면 표면장력흐름으로 고려하여 도달시간 산정시 관측치와 근접하게 산정되었다. 따라서 지표면 유출 흐름은 중력과 함계 표면장력의 영향이 크게 작용하는 것으로 판단된다. 분석결과와 같이 표면장력흐름 특성을 고려한 도달시간 산정식을 모형에 적용할 경우 유출모형을 통한 유출량산정의 정확도 향상에 기여할 것으로 판단된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.307-311
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• 2006

일반적으로 도달시간은 지표면 유출의 흐름상태에 의존하며, 대개 중력흐름으로 가정하여 도달시간을 산정하고 있다. 본 연구에서는 흐름상태를 중력흐름과 표면장력흐름으로 구분하고 각 흐름을 판단할 수 있는 임계치를 추정하였다. 도달시간 산정을 위해 유역경사와 지표면조고의 영향을 고려할 수 있는 무차원수를 도입하였으며, 이 임계치의 범위에 따라 중력흐름과 표면장력흐름을 구분하고 두 조건의 흐름상태에 따른 도달시간 산정식을 각각 개발하였다. 중력흐름에 의한 도달시간 산정식과 표면장력흐름에 의한 도달시간 산정식을 개발하고 검증하기 위하여 기존 외국에서 실험한 자료를 비교 분석하였다. 분석결과를 통하여 이러한 흐름특성을 고려한 도달시간 산정식을 모형에 적용할 경우 유출모형을 통한 유출량산정의 정확도 향상에 기여할 것으로 판단된다.

• Journal of Korea Water Resources Association
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• v.33 no.2
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• pp.195-205
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• 2000

Many types of factors were devised to calculate time of concentration. Singh(976) derived time of concentration of overland flow using kinematic wave theory for plane, converging, and diverging geometric configurations. The present paper investigated the time of concentration for particularly plane geometric configuration. A theoretical equation of time of concentration is derived based on the assumption of impervious overland flow as in the open channel flow. The study characterized the overland flow by many types of characteristic flow such as rough turbulent flow, smooth turbulent flow, laminar flow, and then suggested a theoretical equation on each flow condition. The present paper further considered the rainfall intensity as a main factor and devised an approximate composite equation reflecting the effect of rainfall intensity given at various return periods.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.59-63
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• 2008

The surface runoff is one of the important components for the surface water balance. However, most Land Surface Models(LSMs), coupled to climate models at a large scale for the prediction and prevention of disasters caused by climate changes, simplistically estimate surface runoff from the soil water budget. Ignoring the role of surface flow depth on the infiltration rate causes errors in both surface and subsurface flow calculations. Therefore, for the comprehensive terrestrial water and energy cycle predictions in LSMs, a conjunctive surface-subsurface flow model at a large scale is developed by coupling a 1-D diffusion wave model for surface flow with the 3-D Volume Averaged Soil-moisture Transport(VAST) model for subsurface flow. This paper describes the new conjunctive surface-subsurface flow formulation developed for improvement of the prediction of surface runoff and spatial distribution of soil water by topography, along with basic schemes related to the terrestrial hydrologic system in Common Land Model(CLM), one of the state-of-the-art LSMs.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.3
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• pp.74-80
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• 1993

Runoff simulation tests to investigate the flow mechanics of nonsuomerged overland flow in a natural grass intervening land system were condueted and a modified kinematic wave overland runoff model developed by Choi et al. (1993) was verified. Nonhomogeneity and heterogeneity of the soil, slope, local topography, infiltration, grass density, and the density and activity of the soil microhes and wild animals were the major factors affecting the flow. Streamlines were disturbed by grass stems and small concentrated flows due to the disturbed streamlines and local topography were observed a lot. Relatively larger concentrated flows were observed where bundles of grass were dominant than where individual grasses were growing. Predicted hydrographs were agreed verv well with measured hydrographs. Since the modified model considers grass density in computing flow depth and hydraulic radius, it can be better than existing kinematic wave model if it were used to route nonpoint source pollutant attenuation processes in many grass intervening land systems.

• Water for future
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• v.25 no.1
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• pp.101-110
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• 1992

In this paper for simulating spatially and temporally varied moving storm in a watershed a distributed model was developed. The model is conducted by two major flow simulations which overland flow simulation and channel network flow simulation. Two dimensional continuity equation and momentum equation of kinematic approximation are used in the overland flow simulation. On the other hand, in the channel networks simulation two types of governing equations which are one dimensional continuity and momentum equations between two adjacent sections in a channel, and continuity and energy equations at a channel junction are applied. The finite element formulations were used in the overland flow simulation and the implicit finite difference formulations were used in the channel network simulation. The finite element formulations for the overland flow are analyzed by the Gauss elimination method and the finite difference formulations for the channel network flow are analyzed by the double sweep method having advantages of computational speed and reduced computer storages. Several recurrent coefficient equations for channel network simulation are suggested in the paper.

• Magazine of the Korean Society of Agricultural Engineers
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• v.35 no.2
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• pp.57-64
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• 1993

A modified kinematic wave model of the overland flow in vegetated filter strips was developed. The model can predict both flow depth and hydraulic radius of the flow. Existing models can predict only mean flow depth. By using the hydraulic radius, erosion, deposition and flow's transport capacity can be more rationally computed. Spacing hydraulic radius was used to compute flow's hydraulic radius. Numerical solution of the model was accomplished by using both a second-order nonlinear scheme and a linear solution scheme. The nonlinear portion of the model ensures convergence and the linear portion of the model provides rapid computations. This second-order nonlinear scheme minimizes numerical computation errors that may be caused by linearization of a nonlinear model. This model can also be applied to golf courses, parks, no-till fields to route runoff and production and attenuation of many nonpoint source pollutants.

• Proceedings of the Korea Air Pollution Research Association Conference
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• 2000.11a
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• pp.173-175
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• 2000

도시기상의 원인으로는 지표면 상태의 변화, 인공구조물과 인공열 방출을 들 수 있으며 그 외 오염물질 또한 하나의 원인이다. 도시의 낮은 함수률의 지표면 증가는 증발산 영역을 감소시켜 결과적으로 잠열방출을 감소시키고 현열을 증가시킨다(Tapper, et. al., 1981). 또한 도시의 배수시설은 유입된 강수의 흐름을 시골보다 짧은 기간 머무르게 하여 도시에서 낮은 절대 습도를 가지게 한다. (중략)

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.3
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• pp.23-27
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• 2008

The new conjunctive surface-subsurface flow model at a large scale was developed by using a 1-D Diffusion Wave (DW) model for surface flow interacting with the 3-D Volume Averaged Soil-moisture Transport (VAST) model for subsurface flow for the comprehensive terrestrial water and energy predictions in Land Surface Models (LSMs). A selection of numerical implementation schemes is employed for each flow component. The 3-D VAST model is implemented using a time splitting scheme applying an explicit method for lateral flow after a fully implicit method for vertical flow. The 1-D DW model is then solved by MacCormack finite difference scheme. This new conjunctive flow model is substituted for the existing 1-D hydrologic scheme in Common Land Model (CLM), one of the state-of-the-art LSMs. The new conjunctive flow model coupled to CLM is tested for a study domain around the Ohio Valley. The simulation results show that the interaction between surface flow and subsurface flow associated with the flow routing scheme matches the runoff prediction with the observations more closely in the new coupled CLM simulations. This improved terrestrial hydrologic module will be coupled to the Climate extension of the next-generation Weather Research and Forecasting (CWRF) model for advanced regional, continental, and global hydroclimatological studies and the prevention of disasters caused by climate changes.

• Water for future
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• v.26 no.1
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• pp.81-91
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• 1993

In this paper, a moving storm in the real watershed was simulated using a distributed model. Macks Creek Experimental Watershed in Idaho, USA was selected as a target watershed and the moving storm of August 23, 1965, which continued from 3:30 P.M. to 5:30 P.M., was utilized. The rainfall intensity of the moving storm in the watershed was temporally varied and the storm was continuously moved from one place to the other place in a watershed. Furthermore, runoff parameters, which are soil types, vegetative cover percentages, overland plane slopes, channel bed slopes and so on, are spatially varied. The model developed in the previous paper was utilized as a distributed model for simulating the moving storm. In the model, runoff in a watershed was simulated as two parts which are overland flow and channel flow parts. The good agreement was obtained between a simulated hydrograph using a distributed model and an observed hydrograph. Also, the conservations of mass are well indicated between upstream and downstream at channel junctions.