• International Journal of Ocean System Engineering
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• v.2 no.1
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• pp.37-49
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• 2012

An analysis of potential flooding by storm surge and wave run-up and overtopping can be used to evaluate protection afforded by the existing storm protection system. The analysis procedure can also be used to evaluate various protection alternatives for providing typhoon flood protection. To determine risk, the storm surges for both historical and hypothetical are compiled with tide conditions to represent high, slack and low water for neap, spring and mid range tides to use with the statistical procedure known as the Empirical Simulations Technique (EST). The EST uses the historic and hypothetical events to generate a large population of life-cycle databases that are used to compute mean value maximum storm surge elevation frequency relationships. The frequency-of-occurrence relationship is determined for all relevant locations along the shoreline at appropriate locations to identify the effect using the Empirical Storm Simulation (EST). To assist with understanding the process, an example is presented for a study of storm surge analysis for Freeport, Texas. This location is in the Gulf of Mexico and is subject to hurricanes and other tropical storms that approach from the Atlantic Ocean.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.981-981
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• 2012

최근 지구환경 변화에 따른 기후변화의 영향으로 자연재해의 형태는 점차 대형화, 다양화되고 있으며 극치사상의 발생 빈도가 계속해서 증가하고 있는 추세이다. 특히 도시하천의 경우 인구와 재산이 밀집해 있어 기후변화에 따른 홍수위험 및 취약성이 클 것으로 사료된다. 본 연구에서는 기후 변화에 따른 홍수위험 및 취약성 분석을 위하여 위험도 기반 불확실성을 다루는 수단으로 UQR-MCS (Upper Quartile Range-Monte Carlo Simulation)을 적용하였으며, 다양한 형태의 확률 분포로부터 특정변량(variable)의 확률분포 Quartile을 모의하였다. 또한 기후변화에 따른 도시하천의 홍수위험 및 취약성 평가를 위하여 도시하천에 적합한 홍수위험 및 취약성평가 지수(FVI: flood vulnerability index)를 산정하였으며, 홍수취약성지수는 기후변화(Climate change)와 도시화(Urbanization), 제방월류위험(Overtopping risk) 및 홍수범람 면적(Flood area) 등의 지표를 사용하였다. 각각의 지표는 엔트로피(Entropy) 기법을 적용하여 가중치를 부여하였으며, 표준화과정을 통한 일반화된 지표 값을 산정하였다. 우이천 유역의 기후변화에 따른 홍수위험 및 취약성 지표값은 KMA RCM A1B 시나리오자료를 바탕으로 추정한 미래 확률강수량과 각 인자별 재현기간에 따른 수문변량의 변화를 통하여 산정하였다. 본 연구의 결과는 향후 도시하천의 기후변화에 따른 홍수위험도분석 및 취약성 평가, 극치 수문사상에 대한 신뢰성 있는 분석과 더불어 예상치 못할 이상홍수에 대비한 하천방재 연구에 도움이 되리라 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.501-509
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• 2006

The safety of levee that depends on the river flood elevation has been regarded as very important keys to build up various flood prevention systems. However, deterministic methods for computation of water surface profile cannot reflect the effect of possible inaccuracies in the input parameters. The purpose of this study is to develop a methodology of uncertainty computation of design flood level based on steady flow analysis and Monte Carlo simulation. This study addresses the uncertainty of water surface elevation by Manning's coefficients, design discharges, river cross sections and boundary condition. Monte Carlo simulation with the variations of these parameters is performed to quantify the variations of water surface elevations in a river. The proposed model has been applied to the Kumho-river. The reliability analysis was performed within 38.5 km (95 sections) reach considered the variations of the above-mentioned parameters. Overtopping risks were evaluated by comparing the elevations of the flood condition with the those of the levees. The results show that there is a necessity which will raise the levee elevation between 1 cm and 56 cm at 7 sections. The model can be used for preparing flood risk maps, flood forecasting systems and establishing flood disaster mitigation plans as well as complement of conventional levee design.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.5
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• pp.506-513
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• 2020

Due to climate change, there is an increasing risk of complex (hybrid) disasters, comprising rising sea-levels, typhoons, and torrential rains. This study focuses on Marine City, Busan, a new residential city built on a former landfill site in Suyeong Bay, which recently suffered massive flood damage following a combination of typhoons, storm surges, and wave overtopping and run-up. Preparations for similar complex disasters in future will depend on risk impact assessment and prioritization to establish appropriate countermeasures. A framework was first developed for this study, followed by the collection of data on flood prediction and socioeconomic risk factors. Five socioeconomic risk factors were identified: (1) population density, (2) basement accommodation, (3) building density and design, (4) design of sidewalks, and (5) design of roads. For each factor, absolute criteria were determined with which to assess their level of risk, while expert surveys were consulted to weight each factor. The results were classified into four levels and the risk level was calculated according to the sea-level rise predictions for the year 2100 and a 100-year return period for storm surge and rainfall: Attention 43 %, Caution 24 %, Alert 21 %, and Danger 11 %. Finally, each level, indicated by a different color, was depicted on a complex disaster risk map.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.331-340
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• 2000

This study aims to develop a methodology of real time forecasting of mundation risk based on DAMBRK model and Kalman filter. The model is based on implicit, nonlinear finite difference approximatIons of the one-dimensional dynamic wave equations. The stochastic estimator uses on extended Kalman filter to provide optimal updating estimates. These are accomplished by combining the predictions of the determurustic model with real time observauons modified by the Kalman filter gain ractor. Inundation risks are also estimated by applying Monte Carlo simulation to consider the variability in cross section geometry and Manning's roughness coefficient. The model calibrated by applying to the floods ot South Han River on September, 1990 and August, 1995. The Kalman tilter model indicates that significant improvement compared to deteriministic analysis in flood routing predictions in the river. Overtopping risk of levee is also presented by comparing levee height with simulated flood level. level.

• Journal of Korea Water Resources Association
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• v.50 no.4
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• pp.277-288
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• 2017

A probabilistic risk analysis of levee system estimates the overall level of flood risk associated with the levee system, according to a series of possible flood scenarios. It requires the uncertainty analysis of all the risk components, including hydrological, hydraulic and geotechnical parts computed by employing MCMC (Markov Chain Monte Carlo), MCS (Monte Carlo Simulation) and FOSM (First-Order Second Moment), presents a joint probability combined each probability. The methodology was applied to a 12.5 km reach from upstream to downstream of the Gangjeong-Goryeong weir, including 6 levee reaches, in Nakdong river. Overtopping risks were estimated by computing flood stage corresponding to 100/200 year high quantile (97.5%) design flood causing levee overflow. Geotechnical risks were evaluated by considering seepage, slope stability, and rapid drawdown along the levee reach without overflow. A probability-based compound risk will contribute to rising effect of safety and economic aspects for levee design, then expect to use the index for riverside structure design in the future.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.448-452
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• 2011

기존의 하천개수사업 치수경제성분석에서는 홍수피해경감편익 산정시 계획홍수위 이하의 홍수에 대해서 제방이 완벽히 방어한다는 가정 하에 제방으로 인한 피해경감액을 편익으로 산정하고 있다. 그러나 전통적 빈도해석 방법 및 수리수문 모형에 내재된 매개변수 불확실성으로 인하여 특정 하천구간에서 산정된 계획빈도 이하의 홍수위가 제방고에 해당하는 임계사상을 초과할 수도, 반대로 계획빈도 이상의 홍수위가 임계사상을 초과하지 않을 가능성도 있다. 이러한 불확실성은 수공구조물의 붕괴에 대한 잠재성을 가진 중요한 요인으로도 작용한다. 본 연구는 이러한 잠재적 위험도를 제방 월류위험도로 정의하고 이를 Bayesian MCMC에 의해 산정하는 방법을 제시하였다. 제시된 방법론은 4대강살리기사업 전 후에 대해 적용하였으며, 계획홍수위 저하에 따른 잠재적 홍수위험 감소 효과를 정량적으로 나타낼 수 있었다. 월류 위험도는 빈도별 홍수피해액의 피해발생 확률로서도 적용될 수 있으며, 이는 물리적 침수구역 설정의 어려움에 따른 홍수피해액 과다산정 문제 해결의 대안으로서도 의미가 있다.

• Journal of the Korean Society of Hazard Mitigation
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• v.10 no.5
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• pp.125-133
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• 2010

In general, curved bends raises a risk of overtopping due to floods and also threatens a bank safety due to a local flow concentration. This study aims to test the applicability of CCHE2D model for experimental flumes with two different types of bends and then investigate flow characteristics in the sharply-curved bend of a natural channel. The results demonstrated that the percent error of water level was within 4.9% for experimental flume applications and the simulated spatial distribution of velocity matched the observed results very closely. The calibrated model based on the experimental flumes was also applied to analyze the flow characteristics in natural channel bends of the Daeyu reach, located in a downstream of the Youngdam Dam. The results showed that in upstream, the simulated water level by the CCHED was observed at 1.5 m higher than the 1-D numerical model (HEC-RAS) result since the HEC-RAS could not represent the bend geometry effect on streamflow. However, the calculated results by several empirical formula support that the CCHE2D is suitable for the super elevation simulation as well as flood stage and velocity in a natural channel bend.

• Journal of the Korean Association of Geographic Information Studies
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• v.12 no.3
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• pp.88-100
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• 2009

An inundation analysis was performed on Hwapocheon, one of the tributaries of Nakdong River, which was inundated by heavy rain in August, 2002 with overtopping and levee break. The results of the developed model, 2D diffusion wave inundation analysis model, was compared with inundation trace map as well as inundation depth in terms of time and maximum inundated area calculated from FLUMEN model for the assessment of model applicability. The results from the developed model showed high fitness of 88.61% in comparison with observed data. Also maximum inundated area and spatial distribution of inundation zone were also found to be consistent with the results of FLUMEN model. Therefore, inundation zone and maximum inundation area calculated over a period of time by adopting 2D diffusion wave inundation analysis model can be used as a database for identifying high risk areas of inundation and establishing flood damage reduction measures.