• Korean Journal of Agricultural Science
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• v.50 no.3
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• pp.373-389
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• 2023

The downstream submergence damages caused during the flood season in 2020, around the Yongdam-dam and five other sites, were analyzed using related dam management data. Hourly- and daily-data were collected from public national websites and to conduct various analyses, such as autocorrelation, partial-correlation, stationary test, trend test, Granger causality, Rescaled analysis, and principal statistical analysis, to find the cause of the catastrophic damages in 2020. The damage surrounding the Yongdam-dam in 2020 was confirmed to be caused by mis-management of the flood season water level. A similar pattern was found downstream of the Namgang- and Hapcheon-dams, however the damage caused via discharges from these dams in same year is uncertain. Conversely, a different pattern from that of the Yongdam-dam was seen in the areas downstream of Sumjingang- and Daecheongdams, in which the management of the flood season water level appeared appropriate and hence, the damages is assumed to have occurred via the increase in the absolute discharge amount from the dams and flood control capacity leakage of the downstream river. Because of the non-stationarity of the management data, we adapted the wavelet transform analysis to observe the behaviors of the dam management data in detail. Based on the results, an increasing trend in the discharge amount was observed from the dams after the year 2000, which may serve as a warning about similar trends in the future. Therefore, additional and continuous research on downstream safety against dam discharges is necessary.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.1
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• pp.175-182
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• 2018

In this study, flood quantiles were estimated at ungauged watersheds by adjusting the flood quantiles from the design rainfall - runoff analysis (DRRA) method based on regional frequency analysis. Comparing the flood frequency analysis (FFA) and DRRA, it was found that the flood quantiles estimated by the DRRA method were overestimated by 52%. In addition, a practical method was suggested to make an flood index using natural flows to apply the regional frequency analysis (RFA) to ungauged watersheds. Considering the relationships among DRRA, FFA, and RFA, we derived an adjusting formula that can be applied to estimate flood quantiles at ungauged watersheds. We also employed Leave-One-Out Cross-Validation scheme and skill score to verify the method proposed in this study. As a result, the proposed model increased the accuracy by 23.2% compared to the existing DRRA method.

• Smart Structures and Systems
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• v.17 no.1
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• pp.149-165
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• 2016

Floods have been known to be one of the main causes of bridge collapse. Contrary to earthquakes, flood events tend to occur repeatedly and more frequently in rainfall areas; flood-induced damage and collapse account for a significant portion of disasters in many countries. Nevertheless, in contrast to extensive research on the seismic fragility analysis for civil infrastructure, relatively little attention has been devoted to the flood-related fragility. The present study proposes a novel methodology for deriving flood fragility curves for bridges. Fragility curves are generally derived by means of structural reliability analysis, and structural failure modes are defined as excessive demands of the displacement ductility of a bridge under increased water pressure resulting from debris accumulation and structural deterioration, which are known to be the primary causes of bridge failures during flood events. Since these bridge failure modes need to be analyzed through sophisticated structural analysis, flood fragility curve derivation that would require repeated finite element analyses may take a long time. To calculate the probability of flood-induced failure of bridges efficiently, in the proposed framework, the first order reliability method (FORM) is employed for reducing the required number of finite element analyses. In addition, two software packages specialized for reliability analysis and finite element analysis, FERUM (Finite Element Reliability Using MATLAB) and ABAQUS, are coupled so that they can exchange their inputs and outputs during structural reliability analysis, and a Python-based interface for FERUM and ABAQUS is newly developed to effectively coordinate the fragility analysis. The proposed framework of flood fragility analysis is applied to an actual reinforced concrete bridge in South Korea to demonstrate the detailed procedure of the approach.

• 한국방재학회:학술대회논문집
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• 2007.02a
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• pp.599-602
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• 2007

Flood damage has been increased due to abnormal climate and extreme rainfall. Especially, the increase of impervious areas and the decrease of flow travel times due to the urbanization have been caused heavy division of flood with the recent rainfall characteristics. In this study, hydrodynamics flow analysis has been needed two dimensional numerical analysis for correct stream flow interpretations on bridges as hydraulic structures in rivers. Therefore, comparative analysis has been accomplished by using HEC-RAS model and SMS-RMA2 model for one and two dimensional flow. Also, flood characteristics have been analyzed in urban stream basin.

• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.743-746
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• 2008

Recently, due to the effect of global warming and extreme rainfall, the magnitude of flood disaster and the frequency of flood is rapidly increasing. In order to mitigate the damage of human and property from this kind of meteorological phenomenon and manage water resources scientifically, effective operation of dam and reservoir is very important. In case of Andong dam which was not performed a flood control function needs to develop new types of dam safety management measure because of recent extraordinary flood by typhoons. In case of Andong dam and Imha dam, I am using HEC-5 model in order to apply reservoir simulation. In this case, complex conditions among 100-year floods , 200-year floods and PMF was used. Also, I modified the maximum outflow 3,800m3/s into 3,490m3/s and applied this modified discharge in order to secure freeboard in the downstream. In an analysis that I applied modified outflow by 100-year floods and 200-year floods to, the result showed that river didn't overflow in Andong area but some other places have relatively low freeboard. In the cases that I modified maximum outflow, results showed that freeboard of levee is larger than existed simulation. In the simulation that I applied 200-year floods and PMF to and under a condition connected with PMF, results showed overflowing the levees. Because of the difference between the frequency of dam outflow and the design flood in river, it is required to improve the existed flood plan in the downstream of Andong dam. As a result of this study, the optimal operation of reservoir systems can be proposed to mitigate the flood damage in the downstream of Andong dam and also can be used to establish the flood plans.

• Water for future
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• v.10 no.2
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• pp.113-124
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• 1977

Alone the southwesten coast of Korean peninsula, the extensive available arable acreages suited for forming are found in the development of tidal flats in the geographically curved bays with a motable tidal emplitude. It was found that the developments of these tidal flats cover an estimated area more than 276,000ha. In this paper, a flood control system by Pul's Storage Indication Method and Pul's Graphical Method at Return Periods-50 yrs, design rainfall-267mm per 48hrs and design flood-926c.m.s. and at 0.2meter control height above the High Water Ordinary Spring Tide Level (+11.0m) was studied. At the result, the flood demage in the reservoir at Return Periods-50 yrs and the tidal level at H.W.O.S.T.L. were satisfied to the below E.L. 11.20m (Flood Level in the reservoir). Well skilled flood control technique and management and control of draining sluice gate should be required for the disaster prevention from the flood and tide damage.

• Proceedings of the KSRS Conference
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• v.2
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• pp.884-887
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• 2006

This paper focuses on minimizing flood damage in the Yeongdeok basin of South Korea by establishing a flood prediction model based on a geographic information system (GIS), remote sensing, and geomorphoclimatic instantaneous unit hydrograph (GcIUH) techniques. The GIS database for flash flood prediction was created using data from digital elevation models (DEMs), soil maps, and Landsat satellite imagery. Flood prediction was based on the peak discharge calculated at the sub-basin scale using hydrogeomorphologic techniques and the threshold runoff value. Using the developed flash flood prediction model, rainfall conditions with the potential to cause flooding were determined based on the cumulative rainfall for 20 minutes, considering rainfall duration, peak discharge, and flooding in the Yeongdeok basin.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.140-148
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• 2010

The Taihu Basin is located in the east coast of China, where the threats of frequent floods have induced construction of massive, complex, hierarchical flood defense systems over the interconnected river networks. Digital modeling of flooding processes and quantitative damage assessment still remain challenging due to such complexity. The current research uses an integrated approach to meet this challenge by combining multiple types of models within a GIS platform. A new algorithm is introduced to simulate the impacts of the flood defense systems, especially the large number of polders, on floods distributions and damages.

• Journal of Environmental Science International
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• v.24 no.4
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• pp.415-424
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• 2015

As global warming has accelerated to weather in recent years, and The frequent floods are creating heavy rains and typhoons followed by considerable damage in Jeju. This study estimated design flood discharges and flood stage in Jeju, considering climate change in connection with RCP scenario, the 5th IPCC Report recently published. It also analyzed the period which might be subject to the risk of flooding in downstream of Oedo Stream. As a result, it has analyzed that there might be a risk of flooding when there were 80 years or more rainfall events in 35 years that rainfall would have increased by 10%, 69 years that 100 years or more heavy rain and rainfall would have increased by 20%, and 104 years that 100 years or more heavy rain and rainfall would have increased by 20%. It is expected that this study results of rainfall increasing trend caused by climate change will be helpful to minimize the damage of floods which will secure the future of Jeju.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.95-95
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• 2020

Urban flooding occurs in the form of internal-water inundation on roads and lowlands due to heavy rainfall. Unlike in the case of rivers, inundation in urban areas there is lacking in research on predicting and warning through measurement data. In order to analyze urban flood patterns and prevent damage, it is necessary to analyze flooding measurement data for various rainfalls. In this study, the pattern of urban flooding caused by rainfall was analyzed by utilizing the urban flooding measuring sensor, which is being test-run in the flood prone zone for urban flooding management. For analysis, 2019 rainfall data, surface water depth data, and water level data of a street inlet (storm water pipeline) were used. The analysis showed that the amount of rainfall that causes flooding in the target area was identified, and the timing of inundation varies depending on the rainfall pattern. The results of the analysis can be used as verification data for the urban inundation limit rainfall under development. In addition, by using rainfall intensity and rainfall patterns that affect the flooding, it can be used as data for establishing rainfall criteria of urban flooding and predicting that may occur in the future.