• Journal of Korea Water Resources Association
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• v.45 no.5
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• pp.431-444
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• 2012

This study investigated the differences between annual maximum series and annual maximum independent rainfall event series with relatively short and long rainfall durations. Annual maximum independent rainfall events were selected by applying various IETDs and thresholds to the hourly rainfall data in Seoul for the duration from 1961 to 2010. Annual maximum independent rainfall event series decided were then compared with the conventional annual maximum series. Summarizing the results is as follows. First, the effect of IETD and threshold was not beyond the expected level. For example, as the IETD increases, the frequencies of independent rainfall events decreased similarly in their rate for both with short and long durations. However, as the threshold increases, the frequency of those with rather long durations decreased much higher. Second, The mean rainfall intensity of the independent rainfall events was found to remain constant regardless of their duration. This indicates that the annual maximum rainfall intensity could be found in a rainfall event with longer durations. Lastly, the difference between the annual maximum rainfall series and the annual maximum independent rainfall event series with rather short rainfall durations was found significantly large, which decreases with longer durations. This result indicates that the conventional data analysis method, especially for small basins with short concentration time, could lead an unrealistic design rainfall with little possibility of occurrence.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.2
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• pp.469-478
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• 2014

The annual maximum series (AMS) is usually used to estimate hydrological quantiles in practice because it is simple to construct and straightforward to probabilistic interpretation. However, it is limited to use the AMS in Korea due to the lack of reliable observed data which leads to the overestimation of design rainfall and/or flood. Using the 40-year observations of rainfall provided by the Korea Meteorological Administration, this study constructed the AMS and non-annual exceedance series (NAES) after identifying the independent storm event, analyzed the correlation between design rainfalls estimated from the AMS and NAES, and proposed a new method of point frequency analysis to estimate design rainfalls from the small number of observations.

• Korean Journal of Hydrosciences
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• v.4
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• pp.51-63
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• 1993

This study is to verify the applicability of statistical models in predicting flood frequency at the stage gaging stations of which the flow is under natural condition in the Han River basin. The results of the study show that the statistical flood frequency models were proven to be fairly reasonable to apply in practice, and also were compared with sampling variance to calibrate the statistical efficiency of the estimators of the T year floods Q(T) by two different flood frequency models. As a result, it was showed that for return periods greater than about T = 10 years the annual exceedance series estimators of Q(T) has smaller sampling variance than the annual maximum series estimators. It was showed that for the range of return periods the partial duration series estimators of !(T) has smaller sampling variance than the annual maximum series estimate only if the POT model contains at least 2N(N : record length) items or more in order to estimate Q(T) more efficiently than the ANNMAX model.

• Journal of Wetlands Research
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• v.4 no.2
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• pp.43-56
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• 2002

About 12 rain gauge stations of Korea, annual maximum rainfall series of before and after 1980 whose durations are 1, 2, 3, 6, 12, 24, 48, 72 hours respectively were composed and statistical characteristics of those time series were calculated and probability rainfall were estimated by L-moment frequency analysis method and compared each other in order to investigate the recent quantitative rainfall variations. And also, distribution curves of each statistical variations for each duration were constructed by using Kigging method to look into spacial rainfall variation aspects. As a result, We could confirm recent rainfall increase in the South Korea. And spatial increase pattern of standard deviation and frequency rainfall appeared analogously each other. 1n the cases of comparatively short rainfall duration, we could see relatively low increase or decrease tendency in Chungchong Province, Cholla-bukdo, Cholla-namdo eastern part, Kyongsang-namdo western part area. While, variations happened great1y in seaside district of east coast, southwest seashore, Inchon area etc. In the cases of longer durations relatively low increase was showed in southern seashore such as Yeosoo area and as distance recedes from this area, showed gradually augmented tendency. The aspect of mean looks similar tendency of above except that the variation rate of almost seaside district are big in the case of shorter durations. In addition, rainfall increases of short durations which became the center of hydrologist and meteorologist are unconfirmed in this study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2B
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• pp.137-147
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• 2010

In this study, Chukwooki and modern data were compared using annual maximum rainfall event series. Annual maximum series for specified rainfall duration in modern frequency analysis can not be constructed from Chukwooki data, so the concept of independent rainfall event is introduced to compare Chukwooki and modern data. Annual maximum rainfall event is determined by applying the bivariate exponential distribution and the parameters estimated annually are selected. The results using the annual parameter show that the hydrological meaning of the parameters is related to the variation of annual total rainfall amounts. For the whole independent rainfall events, the total rainfall and the rainfall intensity of Chukwooki data are greater than those of modern data, and rainfall duration of the two periods is similar. However modern annual maximum rainfall events show different characteristics that rainfall duration is much longer, rainfall intensity is similar and the total rainfall is greater than those of Chukwooki period. The increasing trend of rainfall duration and total rainfall of the modern annual rainfall events may be regarded as the one of components of the long-term cycle.

• Water for future
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• v.25 no.2
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• pp.89-97
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• 1992

This study is to verify the applicability of statistical models for predicting flood frequency at the stage gaging stations selected by considering whether the flow is natural condition in the Han River basin. From the result of verification, this statistical flood frequency models showed that is fairly reasonable to apply in practice, and also were compared with sampling variance to calibrate the statistical dfficiency of the estimate of the T year flood Q(T) by two different flood frequency models. As a result, it was showed that for return periods greater than about T=10 years the annual exceedence series estimate of Q(T) has smaller sampling variance than the annual maximum series estimate. It was showed that for the range of return periods the partial duration series estimate of Q(T) has smaller sampling varianed than the annual maximum series estimate only if the POT model contains at least 2N(N:record length)items or more in order to estimate Q(T) more efficiently than the ANNMAX model.

• Magazine of the Korean Society of Agricultural Engineers
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• v.28 no.3
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• pp.69-78
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• 1986

This studies were established to find out the characteristics of frequency distributiom for the number of occurrence and magnitude, probable flood flows according to the return periods, design floods, and design frequency factors for the studying basins in relation to the risk levels which can be correlated with design return period and the life of structure in the non-annual exceedance series. Eight watersheds along Han, Geum, Nak Dong and Seom Jin river basin were selected as studying basins. The results were analyzed and summarized as follows. 1. Poisson distribution and Exponential distribution were tested as a good fitted distributions for the number of occurrence and magnitude for exceedance event, respectively,at selected watersheds along Han, Geum, Nak Dong and Seom Jin river basin. 2.Formulas for the probable flood flows and probable flood flows according to the return periods were derivated for the exponential distribution at the selected watersheds along Han, Geum, Nak Dong, and Seom Jin river basin. 3.Analysis for the risk of failure was connected return period with design life of structure in the non-annual exceedance series. 4.Empirical formulas for the design frequency factors were derivated from under the condition of the return periods identify with the life of structure in relation to the different risk levels in the non-annual exceedance series. 5.Design freguency factors were appeared to be increased in proportion to the return periods while those are in inverse proportion to the levels of the risk of failure. Numerical values for the design frequency factors for the non-annual exceedance series ware appeared generally higher than those of annual maximum series already published by the first report. 6. Design floods according to the different risk levels could be derivated by using of formulas of the design frequency factors for all studying watersheds in the nor-annual exceedance series.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.2249-2253
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• 2008

본 연구에서는 지점빈도분석과 지역빈도분석을 이용하여 확률홍수량을 산정 하였다. 지점빈도 분석은 Annual Maximum Series(AMS) 및 Partial Duration Series(PDS)를 이용하여 자료를 추출하고 각 자료에 적합한 확률분포를 이용하여 확률홍수량을 산정하였다. 그러나 AMS를 이용한 확률홍수량의 산정은 표본의 개수가 부족하면 이에 따른 변동성(variability)이 커지게 되는 단점이 존재하며, PDS를 사용하면 임계값(threshold)에 따른 주관적 영향이 결과에 반영되는 단점이 존재하는 것으로 알려져 있다. 따라서 본 연구에서는 PDS를 사용하는 경우의 단점을 해결하기 위해 연 1.7회의 발생횟수를 갖는 자료를 추출하고 몬테카를로 모의시험을 통하여 주관적 영향을 제거하였다. 또한 두 가지 방법에 의해 산정된 확률홍수량의 비교검토를 위해 지역빈도분석을 수행하였다. 유역의 면적과 일평균강우량으로부터 확률홍수량을 산정할 수 있는 것으로 알려진 Bayesian-Generalized Least Square(B-GLS) 방법을 이용하여 확률홍수량을 산정하였다. 최종적으로 안양천 유역의 13개 소유역에 대한 세 가지 방법에 의해 산정된 확률홍수량을 비교 검토한 결과, 특정한 방법이 항상 우수하다는 결론은 얻을 수 없었으나 각 유역별로 AMS가 가장 크고 B-GLS가 가장 작은 확률홍수량을 갖는 경향을 나타내었다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.515-524
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• 2008

An estimation of reliable probability precipitation is one of the most important processes for reasonable hydrologic structure design. A probability precipitation has been calculated by frequency analysis using annual maximum rainfall series on the each duration among the observed rainfall data. Annual maximum rainfall series have abstracted on hourly rainfall data or daily rainfall data. So, there is necessary to proper conversion factor between the fixed and sliding durations. Therefore, in this study, conversion factors on the each duration between fixed and sliding durations have calculated using minutely data compared to hourly and daily data of 37 stations observed by Meteorological Administration in Korea. Also, regression equations were computed by regression analysis of conversion factors on the each duration. Consequently, conversion factors were used basis data for calculations of stable probability precipitation.

• 한국방재학회:학술대회논문집
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• 2009.02b
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• pp.153.2-153.2
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• 2009