• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.417-417
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• 2022

현재 수공 구조물 설계 시 설계강우량으로써 빈도해석과정을 통해 산정된 확률강우량을 적용하고 있다. 하지만 확률강우량의 경우 시계열 강우분포형태를 알 수 없는 문제가 존재한다. 강우의 시간분포 형태는 비점오염, 강우에 의한 수식 등 도달시간과 첨두 홍수량에 지대한 영향을 미치는 요소이다. 현재 국내에서는 Huff 4분위법이 널리 사용되고 있지만 Huff 4분위법은 기존의 강우패턴을 평균하였기 때문에 자연현상인 강우의 다양하고 복잡한 분포형태를 반영하기 어렵다는 문제를 가지고 있으며, Huff 4분위법이 갖는 한계로 정의할 수 있다. 따라서 본 연구에서는 Huff 4분위법이 갖는 한계를 보완하기 위해 설계홍수량산정지침에서 제시하고 있는 초과확률 50%의 시간분포 값을 산정하는 것에서 벗어나 한반도의 강우형태와 최근 20년간의 강우 패턴 변화를 고려한 최적 초과 확률값을 선정하였다.

• Journal of Korea Water Resources Association
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• v.42 no.5
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• pp.365-374
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• 2009

Probability plotting positions are used for the graphical display of annual maximum rainfall or flood series and the estimation of exceedance probability of those values. In addition, plotting positions allow a visual examination of the fitness of probability distribution provided by frequency analysis for a given data. Therefore, the graphical approach using plotting position has been applied to many fields of hydrology and water resources planning. In this study, the plotting position formula for the Gumbel distribution is derived by using the order statistics and the probability weight moment of the Gumbel distribution for various sample sizes. And then, the parameters of plotting position formula for the Gumbel distribution are estimated by using genetic algorithm. The appropriate plotting position formulas for the Gumbel distribution are examined by the comparison of root mean square errors and biases between theoretical reduced Gumbel variates and those calculated from derived and existing plotting position formulas. As the results, Gringorten's plotting position formula has the smaller root mean square errors and biases than any other formulas.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1765-1777
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• 2014

This study evaluated PMM (Probability Matching Method) for parameter estimation of the Z - R relation. As a first step, the sensitivity analysis was done to decide the threshold number of data pairs and the data interval for the development of a histogram. As a result, it was found that at least 1,000 number of data pairs are required to apply the PMM for the parameter estimation. This amount of data is similar to that collected for two hours. Also, the number of intervals for the histogram was found to be at least 100. Additionally, it was found that the matching the first-order moment is better than the cumulative probability, and that the data pairs comprising 30 to 100% are better for the PMM application. Finally, above findings were applied to a real rainfall event observed by the Bislsan radar and optimal parameters were estimated. The radar rain rate derived by applying these parameters was found to be well matched to the rain gauge rain rate.

• Journal of the Korean Geosynthetics Society
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• v.16 no.3
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• pp.51-62
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• 2017

For the purpose of the study, of the 76 areas subject to preliminary concentrated management on sediment disaster in the downtown area, 9 areas were selected as research areas. They were classified into three stratified rock areas (Gyeongsan City, Goheung-gun and Daegu Metropolitan City), three igneous rock areas (Daejeon City, Sejong Special Self-Governing City and Wonju City) and three metamorphic rock areas (Namyangju City, Uiwang City and Inje District) according to the characteristics of the bedrock in the research areas. As for the 9 areas, analyses were conducted based on tests required to calculate soil characteristics, a predictive model for root adhesive power, loading of trees and on-the-spot research. As for a rainfall scenario (rainfall intensity), the probability of rainfall was applied as offered by APEC Climate Center (APCC) in Busan. As for the prediction of landslide risks in the 9 areas, TRIGRS and LSMAP were applied. As a result of TRIGRIS prediction, the risk rate was recorded 30.45% in stratified rock areas, 41.03% in igneous rock areas and 45.04% in metamorphic rock areas on average. As a result of LSMAP prediction based on root cohesion and the weight of trees according to crown density, it turned out to a 1.34% risk rate in the stratified rock areas, 2.76% in the igneous rock areas and 1.64% in the metamorphic rock areas. Analysis through LSMAP was considered to be relatively local predictive rather than analysis using TRIGRS.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.38 no.3
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• pp.387-393
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• 2018

Considering the effect of climate change, a quantitative analysis of extreme drought is needed to reduce the damage from extreme droughts. Therefore, in this study, a quantitative risk analysis of extreme drought was conducted. The threshold level method was applied to define a drought event using Cheugugi rainfall data in past, gauged rainfall data in present, and climate change scenario rainfall data in future. A bivariate drought frequency analysis was performed using the copula function to simultaneously consider two major drought characteristics such as duration and severity. Based on the bivariate drought frequency curves, the risks for the past, present and future were calculated and the risks for future extreme drought were analyzed comparing with the past and present. As a result, the mean drought duration of the future was shorter than that of past and present, however, the mean drought severity was much larger. Therefore short term and severe droughts were expected to occur in the future. In addition, the analysis of the maximum drought risk indicated that the future maximum drought risk was 1.39~1.94 times and 1.33~1.81 times higher than the past and present. Finally, the risk of extreme drought over past and present maximum drought in the future was very high, ranging from 0.989 to 1.0, and the occurrence probability of extreme drought was high in the future.

• Journal of Korea Water Resources Association
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• v.52 no.9
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• pp.627-635
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• 2019

In Korea, snow damage has been happened in the region with no snowfalls in history. Also, casual damage was caused by heavy snow. Therefore, policy about the Natural Disaster Reduction Comprehensive Plan has been changed to include the mitigation measures of snow damage. However, since heavy snow damage was not frequent, studies on snowfall have not been conducted in different points. The characteristics of snow data commonly are not same to the rainfall data. For example, some parts of the southern coastal areas are snowless during the year, so there is often no values or zero values among the annual maximum daily snow accumulation. The characteristics of this type of data is similar to the censored data. Indeed, Busan observation sites have more than 36% of no data or zero data. Despite of the different characteristics, the frequency analysis for snow data has been implemented according to the procedures for rainfall data. The frequency analysis could be implemented in both way to include the zero data or exclude the zero data. The fitness of both results would not be high enough to represent the real data shape. Therefore, in this study, a methodology for selecting a probability density function was suggested considering the characteristics of snow data in Korea. A method to select probability density function using conditional joint probability distribution was proposed. As a result, fitness from the proposed method was higher than the conventional methods. This shows that the conventional methods (includes 0 or excludes 0) overestimated snow depth. The results of this study can affect the design standards of buildings and also contribute to the establishment of measures to reduce snow damage.

• Journal of Korea Water Resources Association
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• v.40 no.2 s.175
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• pp.159-170
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• 2007

This study evaluated the parameters of Clark unit hydrograph (UH) estimated using the rainfall-runoff measurements and evaluated their variability. This also includes the quantification of basin and meteorological factors using probability density functions, selection of storm events with mean affecting factors, and derivation of average parameters of the Clark UH from storm events selected. Summarizing the results from this procedure are as follows. (1) It is not easy to avoid much uncertainty on the decision of runoff characteristics (that is, the concentration time and storage coefficient) even with some rainfall-runoff events are available. (2) As the distribution function of concentration time is very skewed, a simple arithmetic mean may lead a biased estimate. That is, the arithmetic mean based on the normal distribution can not be representative anymore. The mode may well be the representative in this case. On the other hand, the storage coefficient shows a symmetric distribution function, so the arithmetic mean may be used use for its representative. For the basin in this study, the concentration time in this study is estimated to be about 7 hours, and the storage coefficient about 22 hours.

• Journal of Korea Water Resources Association
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• v.43 no.1
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• pp.15-24
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• 2010

Regional frequency analysis is often used to overcome the limitation of point frequency analysis to estimate probability rainfall depths. However, point frequency analysis is still used in drought analyses. This study proposed a practical method to categorize the homogeneous regions of drought characteristics for the analyses of regional characteristics of droughts in Korea. Using rainfall data from 58 observation stations managed by the Korea Meteorological Administration, this study calculated drought attributes, i.e., mean drought indices for various durations using the Standardized Precipitation Index (SPI) and drought severities expressed by durations, depth, and intensity. The drought attributes provided useful information for categorizing stations into the hydrological homogeneous regions. This study introduced a cluster analysis with K-means techniques to group observation stations. The cluster analysis grouped observation stations into 6 regions in Korea. The data in the hydrological homogeneous region would be used in spatial analysis of drought characteristics and drought regional frequency analysis.

• Journal of Korea Water Resources Association
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• v.36 no.6
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• pp.961-969
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• 2003

Formulation of quasi-dynamic wetness index was derived to predict the spatial and temporal distribution of the soil moisture. The algorithm of dynamic wetness index was developed through introducing the convolution integral with the rainfall input. The spatial and temporal behaviors of the wetness index of the Sulmachun Watershed was calculated using the digital elevation model(DEM) and the rainfall data for two years. The spatial distribution of the dynamic wetness index shows most dispersive feature of flow generation among the three assumptions of steady, quasi-dynamic and dynamic. The statistical distribution of the quasi-dynamic wetness index and the dynamic wetness index approximate to the steady state wetness index as the time step is increased. The dynamic wetness index shows mixed distribution of the normalized probability density function.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.1068-1074
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• 2006

For receiving water quality protection a control systems of urban drainage for CSOs reduction is needed. Examples in combined sewer systems include downstream storage facilities that detain runoff during periods of high flow and allow the detained water to be conveyed by an interceptor sewer to a centralized treatment plant during periods of low flow. The design of such facilities as storm-water detention storage is highly dependant on the temporal variability of storage capacity available as well as the infiltration capacity of soil and recovery of depression storage. For the continuous long-term analysis of urban drainage system this study used analytical probabilistic model based on derived probability distribution theory. As an alternative to the modeling of urban drainage system for planning or screening level analysis of runoff control alternatives, this model has evolved that offers much ease and flexibility in terms of computation while considering long-term meteorology. This study presented rainfall and runoff characteristics of the subject area using analytical probabilistic model. Runoff characteristics manifested the unique characteristics of the subject area with the infiltration capacity of soil and recovery of depression storage and was examined appropriately by sensitivity analysis. This study presented the average annual CSOs, number of CSOs and event mean CSOs for the decision of storage volume.