• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.450-450
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• 2015

우리나라는 최근 기후변화로 인한 이상기후의 영향으로 태풍 및 국지성 집중호우의 발생빈도가 잦아지고 있으며, 이에 따른 풍수해 피해 양상 또한 과거와 비교되지 않을 만큼 대형화 되고 있다. 본 연구대상지역인 가곡천 유역은 강원도 산지로부터 발원하여 동해안으로 유입되는 산지하천 중 하나로 유로연장이 짧고 경사가 급하여 홍수기시 홍수도달시간이 매우 짧은 특징을 가지고 있어 하류부에서의 피해가 증가하고 있는 실정이다. 실제로 대상하천의 경우 2002년 태풍루사와 2003년 태풍매미 등에 의해 피해가 컸던 것으로 조사되었으며, 이러한 피해를 저감하기 위해서 정확한 유역의 유출해석이 필요하다. 따라서 본 연구에서는 가곡천 유역의 치수대책 수립을 위한 설계홍수량을 산정하기 위해 GIS 수문프로그램인 WMS(Watershed Modeling System)를 이용하여 수문해석에 필요한 수문인자들을 추출하고, WMS에 내장되어 있는 HEC-1 모형을 이용하여 유출해석을 수행하였다. 가곡천 유역에 대한 모형의 적합성 여부를 판별하기 위해 실제측정에 의해서 만들어진 수위-유량관계곡선과의 비교를 통해 모형의 적합성 여부를 검토하였다.

• Water for future
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• v.25 no.4
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• pp.87-95
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• 1992

The validity of the estimate of runoff depth and peak runoff by the basin runoff curve numbers(CN-II for AMC-II condition and CN-III for AMC-III condition) obtained from hydrologic soil-cover complexs is investigated by making use of the observed curve numbers(median curve number and optimum curve number) computed from rainfall-runoff records. For gaged basins the median curve numbers are recommended for the estimation of runoff depth and peak runoff. For ungaged basins, found is that for the estimate of runoff depth CN-III is adequate and for the peak runoff CN-II is adequate. Also investigated is the variation of curve numbers during rainfall, which is turned out to improve the estimates of both depth and peak of runoff.

• Journal of Korea Water Resources Association
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• v.53 no.3
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• pp.193-200
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• 2020

Hydrological drought is directly associated with lack of available water in rivers, reservoirs, and groundwater. It is important to analyze hydrological drought for efficient water resource management because most of rainfall is concentrated in wet seasons and water supply is highly dependent on dams and reservoirs in South Korea. Generally, a threshold level method is useful for defining hydrological droughts. However, this method causes interdependent problems between drought events which result in skewed results in further statistical analysis. Therefore, it is necessary to determine a proper threshold level to represent regional drought characteristics. In this study, applying 50~99 percentiles of daily flow-duration curve, hydrological drought events were extracted, and independence tests were conducted for 12 watersheds. The Poisson independence test showed that 87~99 percentiles were available for most stations except for Yeoju and Pyeongtaek. The generalized Pareto independence test showed that 80~90 percentiles were the most common. Mean excess plot showed that 80 ~ 90 percentiles were the most common. Therefore, the common ranges of the three independent tests were determined for each station and proper threshold levels were recommended for large river basins; 70~76 percentiles for the Han River basin, 87~91 percentiles for the Nakdong River basin, 86~98 percentiles for the Geum River basin, and 85~87 percentiles for the Youngsan and Seomjin River basin.

• 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.

• Journal of Wetlands Research
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• v.12 no.3
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• pp.99-106
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• 2010

In this study unit hydrograph and infiltration capacity curves have been determined based on rainfall-runoff data for the upper Ansung stream basin. Infiltration capacity curve also has been computed based on measurements of accumulated infiltration. Accumulated infiltration curve which has close relationship with unit hydrograph has been found in adopting the following two approach methods. In the first method the mean infiltration capacity with infiltration index method and the Kostiakov accumulation infiltration curves have been computed based on hydrological data for the GongDo gauging station of the upper Ansung stream basin. In the second method the accumulation curve has been determined through directly observed infiltration data for four points in the upper basin and has been compared with the infiltration capacity curves by three observed rainfall-runoff event.

• Journal of Wetlands Research
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• v.16 no.2
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• pp.161-171
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• 2014

Recession of hydrograph gives a significant contribution to estimation of baseflow using rainfall-runoff models and baseflow separation methods, because recession affects baseflow. This study attempted to enhance the accuracy of streamflow predictions using a Soil and Water Assessment Tool (SWAT) model and to separate baseflow from the predicted streamflow. For this, this study used two scenarios: 1) to calibrate eleven parameters using an auto-calibration tool with the alpha factor obtained from RECESS (S1); and 2) to calibrate twelve SWAT parameters including alpha factor (one of SWAT parameters) using an auto-calibration tool (S2). Then, baseflow spearation from the predicted streamflow was conducted by using Web-based Hydrograph Analysis Tool (WHAT). The results show that there is no significant difference between Nash-Sutcliffe efficiency (NSE) values of S1 and S2 for calibrations to streamflow. However, calibrations to baseflow showed that NSEs are 0.777 for S1 and 0.844 for S2, which means a significant difference. Quantitatively compared to the observed streamflow, relative errors were 20.78 % for S1 and 6.59 % for S2. Finally, this study showed the importance of recession in baseflow separated from the predicted streamflow using a rainfall-runoff model.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.17-24
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• 2018

The HEC-HMS model was applied to identify the rainfall-runoff processes for the Anseongchun basin, where the lower part of the stream has been damaged severely by tropical storms in the past. Modeling processes include incorporating with the SCS-CN model for loss, Clark's UH model for transformation, exponential recession model for baseflow, and Muskingum model for channel routing. The parameters were calibrated through an optimization technique using a trial and error method. Sensitivity analysis after calibration was performed to understand the effects of parameters, such as the time of concentration, storage coefficient, and base flow related constants. Two storm water events were simulated by the model and compared with the corresponding observations. Good accuracy in predicting the runoff volume, peak flow, and the time to peak flow was achieved using the selected methods. The results of this study can be used as a useful tool for decision makers to determine a master plan for regional flood control management.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1017-1021
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• 2009

일반적인 설계 홍수량 산정 절차는 분석하고자 하는 대상유역의 수문자료 중 홍수량 자료가 존재하지 않을 경우 강우빈도해석을 실시하고, 만약 홍수량 자료가 존재한다면 유출을 통계분석하여 홍수빈도 해석을 실시하여야 한다. 본 연구에서는 1999$^{\sim}$2008년까지 수위-유량 관측을 실시하여 유출자료를 비교적 충분히 보유하고 있는 서울시 관내 지방하천인 우이천 유역을 대상으로 수위-유량관계곡선을 작성하여 과거 호우사상을 토대로 강우-유출모형의 매개변수를 최적화하였으며, 최적화된 모형을 이용하여 기상청관할 서울지점 시간강우관측 자료를 입력 자료로 유출모의를 실시하였다. 모의된 홍수량계열과 관측유량계열을 사용하여 연최대홍수계열을 구축한 후 홍수빈도해석을 실시하였다. 분석결과 기존의 '확률강우량-단위도' 방법에 비하여 불확실성이 제거된 확률홍수량 추정치의 결과를 얻을 수 있었다.

• Proceedings of the Korea Water Resources Association Conference
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• 1992.07a
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• pp.177-186
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• 1992

한강, 낙동강, 금강, 섬진강, 영산강 등 우리나라 5대 강의 주요 지점에서의 광범위한 수문자료를 토대로 유황분석을 수행하였다. 우리나라 하천유량 자료의 신뢰도상의 한계를 감안하여, 특히 저수위시 수위-유량 관계곡선의 검토 등 본 유황분석에서 이용될 유량 자료의 검토에 세심한 배려를 하였다. 본 연구에 의하면, 우리나라의 주요 수계의 유황은 상류에 주요 다목적 댐 건설 이전과 이후에 걸쳐 크게 개선된 것으로 나타났으며, 이러한 유황 개선 효과는 홍수량의 저감 등 풍수시보다는 저수량의 증가 등 저수시에 더욱 두드러지게 나타나고 있다. 한편, 우리나라 주요 수계의 하상계수는 주요댐 건설이전의 자연상태에서는 300~500 정도이었으나, 댐 건설이후 1/2~1/3 정도 감소하여 150~300 정도로 나타났으며, 이는 댐에 의한 유황개선 효과를 단적으로 보여주는 것이다.

• Proceedings of the Korea Contents Association Conference
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• 2006.05a
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• pp.342-346
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• 2006

The method presented is also efficient and applicable in estimating the discharge in high flows that are very difficult or impossible to measure before, due to technical or theoretical reasons. The method can drastically reduce the time and cost of measurement, regardless of the irregularity in the geometrical shape. With Microwave Water Surface Velocity Meter, An entropy based method for determining the discharge in the rivers can be used to develop real-time discharge measurement system (RDMS) which can carry out the real-time inflow hydrograph.