• Title/Summary/Keyword: Flood frequency

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Inference of natural flood frequency for the region affected by dams in Nam Han River (남한강 유역 댐 영향 지역의 기본홍수량 추론)

  • Kim, Nam Won;Lee, Jeong Eun;Lee, Jeongwoo
    • Journal of Korea Water Resources Association
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    • v.49 no.7
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    • pp.599-606
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    • 2016
  • The objective of this study is to estimate the unregulated flood frequency from Chungju dam to Yangpyung gauging station for the region affected by dams based on the peak discharges simulated by storage function routing model. From the flood frequency analyses, the quantiles for the unregulated flood frequency at 6 sites have similar pattern to each other, and their averaged quantile almost matched to the result from the regional flood frequency analysis. The quantile and annual mean discharge for the unregulated flood frequency for the downstream of Chungju dam show the similar behaviour to those for the upstream area. While the quantile and the annual mean discharge for the regulated flood frequency are significantly different from those for the unregulated flood frequency. In particular, the qunatile shows severe difference as the return period increases, and the annual mean discharge has a tendency to approach to the natural flood as the distance from dam increases.

Analysis of Regional Flood Damage Characteristics using Relationship between Flood Frequency and Damages (홍수피해 발생빈도-피해액 관계분석을 통한 지역별 홍수피해특성 분석)

  • Park, Tae-Sun;Choi, Min-Ha;Yeo, Chang-Geon;Lee, Seung-Oh
    • Journal of the Korean Society of Hazard Mitigation
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    • v.9 no.5
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    • pp.87-92
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    • 2009
  • It has been considered only with the concerned regional damage costs whenever the restoration and flood control measures were established in Korea. If the relationship between regional flood frequency and damages is quantitatively analyzed, more resonable and reliable countermeasure for flood protection and restoration can be proposed. Historical data ('70~'07) about flood damage in Korea were utilized and analyzed to present such relationship using the point frequency analysis. Also, the quadrant analysis was employed to divide into 4 categories: high frequency-high damage, high frequency-low damage, low frequency-high damage, and low frequency-low damage. If the results from this study were utilized well in specific cities and counties in Korea, it would be helpful to establish the countermeasures and action plans for flood protection because it was possible to compare with the relationship between flood frequency and damage of each region. And it would be the fundamental data for estimating the effect of future flood protection plan.

Study on Estimation and Application of the Fwl-D-F curves for Urban Basins (도시유역의 Fwl-D-F 곡선 산정 및 활용에 관한 연구)

  • Choi, Hyun-Il;Kim, Eung-Seok
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.11 no.7
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    • pp.2687-2692
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    • 2010
  • There have been performed many researched for flood magnitude analysis, for example, the Flood-Duration-Frequency relations in the west. Because flood water stage data are more available rather than flood amount data at flood gauge stations of Korea, this study developed Flood water level-Duration-Frequency (Fwl-D-F) curves using rainfall Intensity-Duration-Frequency(I-D-F) curves for the quantitative flood risk assessment in urban watersheds. Fwl-D-F curve is made from water level data for 18 years at Joongrayng bridge station of Joongrayng River basin in Han River drainage area. Fwl-D-F curve can estimate the occurrence frequency for a certain flood elevation, which can be used for urban flood forecasting. It is expected that the flood elevation can be estimated from the forecasted rainfall data using both Fwl-D-F and I-D-F curves.

THE STUDY OF PARAMETRIC AND NONPARAMETRIC MIXTURE DENSITY ESTIMATOR FOR FLOOD FREQUENCY ANALYSIS

  • Moon, Young-Il
    • Water Engineering Research
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    • v.1 no.1
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    • pp.49-61
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    • 2000
  • Magnitude-frequency relationships are used in the design of dams, highway bridges, culverts, water supply systems, and flood control structures. In this paper, possible techniques for analyzing flood frequency at a site are presented. A currently used approach to flood frequency analysis is based on the concept of parametric statistical inference. In this analysis, the assumption is make that the distribution function describing flood data in known. However, such an assumption is not always justified. Even though many people have shown that the nonparametric method provides a better fit to the data than the parometric method and gives more reliable flood estimates. the noparpmetric method implies a small probability in extrapolation beyond the highest observed data in the sample. Therefore, a remedy is presented in this paper by introducing an estimator which mixes parametric and nonparametric density estimate.

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Flood Frequency Analysis using SIR Algorithm (SIR 알고리즘을 이용한 홍수량 빈도해석에 관한 연구)

  • Moon, Kiho;Kyoung, Minsoo;Kim, Duckgil;Kawk, Jaewon;Kim, Hungsoo
    • Journal of Wetlands Research
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    • v.10 no.3
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    • pp.125-132
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    • 2008
  • Generally, stationary is considered as a basic assumption in frequency analysis. However, rainfall and flood discharge are changing due to the climate change and climate variability. Therefore, there is a new opinion that changing pattern of rainfall and flood discharge must be considered in frequency analysis. This study suggests the flood frequency analysis methodology using SIR algorithm which was developed from bootstrap could be used for considering climate change. Than is, SIR algorithm is selected for resampling method considering changing pattern of flood discharge and it has been used for resampling method with likelihood function. Resampled flood discharge data considering the increase of flood discharge pattern are used for parametric flood frequency analysis and this results are compared with frequency analysis results by Bootstrap and original observations. As the results, SIR algorithm shows the greatest flood discharge than other methods in all frequencies and this may reflect the increasing pattern of flood discharge due to the climate change and climate variability.

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A study on the Flood Frequency Analyzed in Consideration of Low Outliers. (Low Outliers를 고려한 홍수빈도분석에 관한 연구)

  • 이순혁;홍성표;박명근
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.4
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    • pp.62-70
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    • 1988
  • This study was conducted to solve the problems for the unsuitable parameters and the uncertainty of design flood can be appeared by low outliers were inclined to the lower part from the trend of the balance of the data. Derivation of reasonable design flood was attempted finally by modification of low outliers with analysis of flood frequency by means of Log Pearson Type Ill distribution. Three subwatersheds were selected as studying basins with the annual maximum series including low outliers along Geum River basin. The results through this study were analyzed and summarized as follows. 1. Log Pearson Type In distribution was confirmed as a reasonable one by X$^2$ goodness of fit test at Gong Ju, Gyu Am, og Cheon watershed along Geum River basin. 2. Probable flood flows for each watershed were derivated by flood frequency curve with outliers. 3. Weighted skew coefficient for each watershed was calculated for the evaluation of freq- uency factor which is needed for the modification of low outlier. 4. It was confirrned that adjusted frequency curve has a lower tendency than that of deletion of low outlier in common at all watersheds. 5. Final probable flood flows were derivated by modification with evaluation of modified basic statistics for three watersheds. 6. In comparison with a frequency curve with modification and one with outlier, The former has a higher probable flood flow within three years of return periods than that of the latter, and vice versa over three years of return periods.

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Comparative Study of Flow Profiles & Discharge due to Rainfall Frequency Analysis (강우빈도 해석을 통한 하천 수리$\cdot$수문량 비교 연구)

  • Seo Kyu Woo;Lee In Rock;Won Chang Hee;Shim Bong Joo
    • Proceedings of the Korea Water Resources Association Conference
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    • 2005.05b
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    • pp.1533-1537
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    • 2005
  • The recent rainfall has happened to exceed the design rainfall after 1990 often, due to the characteristic of the rain to be changed. So, it is failing the ability safety of flood defense equipments to exist. This study analyzed the rainfall of Busan in 2003 since 1961 through the FARD2002(Frequency Analysis of Rainfall Duration). The result is equal to the thing which the design rainfall increased a little since 1991. The change of design rainfall created the result to be a flood discharge increase. This study investigated about the impact to influence on the river bank according to the change of flood discharge, the rainfall pattern change as well. This study used the program of HEC-RAS with HEC-HMS and calculated flood discharge with flood level of river. The result is equal to the thing which the computation became a flood level which exceed 50year(River design criteria-Korea water resources association 2002) criteria with 30year(River establishment criteria-Ministry of construction & transportation 1993), because of an area of impermeability increased of model basin.

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Evaluation of Flood Severity Using Bivariate Gumbel Mixed Model (이변량 Gumbel 혼합모형을 이용한 홍수심도 평가)

  • Lee, Jeong-Ho;Chung, Gun-Hui;Kim, Tae-Woong
    • Journal of Korea Water Resources Association
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    • v.42 no.9
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    • pp.725-736
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    • 2009
  • A flood event can be defined by three characteristics; peak discharge, total flood volume, and flood duration, which are correlated each other. However, a conventional flood frequency analysis for the hydrological plan, design, and operation has focused on evaluating only the amount of peak discharge. The interpretation of this univariate flood frequency analysis has a limitation in describing the complex probability behavior of flood events. This study proposed a bivariate flood frequency analysis using a Gumbel mixed model for the flood evaluation. A time series of annual flood events was extracted from observations of inflow to the Soyang River Dam and the Daechung Dam, respectively. The joint probability distribution and return period were derived from the relationship between the amount of peak discharge and the total volume of flood runoff. The applicability of the Gumbel mixed model was tested by comparing the return periods acquired from the proposed bivariate analysis and the conventional univariate analysis.

Estimation of Design Discharge Considering Nonstationarity for River Restoration in the Mokgamcheon (목감천 복원설계를 위한 비정상성을 고려한 설계홍수량의 산정)

  • Lee, Kil Seong;Oh, Jin-Ho;Park, Kidoo;Sung, Jang-Hyun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.33 no.4
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    • pp.1361-1375
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    • 2013
  • The design flow considering nonstationarity is estimated to determine the design flood related to hydraulic structure quantitatively based on the design process for stream restoration in the Mokgamcheon watershed proposed by Lee et al. (2011). The purpose of this research is to suggest new ways that the design flood was calculated considering nonstationarity at the Mokgamcheon watershed. Storm-unit hydrograph method to calculate design flood and direct frequency analysis were applied and nonstationarity was considered for the frequency analysis through extRemes toolkit developed at NCAR (National Center for Atmospheric Research). Although the method of direct flood frequency analysis due to dealing with flowrates directly has a more reliable than strom-unit hydrograph method, as a result, the method of direct flood frequency analysis underestimated the design flood than strom-unit hydrograph method due to the characteristics of the flow data. Therefore, the flood of storm-unit hydrograph method (100 years frequency) was determined as the design flood in the Mokgamcheon watershed.

Estimation of Flood Quantile in Ungauged Watersheds for Flood Damage Analysis Based on Flood Index of Natural Flow (미계측 유역의 홍수피해분석을 위한 자연유량의 홍수지표 기반 확률홍수량 산정)

  • Chae, Byung Seok;Choi, Si Jung;Ahn, Jae Hyun;Kim, Tae-Woong
    • 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.