• The Journal of Engineering Geology
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• v.28 no.4
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• pp.661-672
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• 2018

Radon concentration was measured in a total of 5,453 groundwater samples from wells across Korea. The radon concentrations showed the values ranging from 0.1 Bq/L to 7,218.7 Bq/L, with a median of 48.8 Bq/L which is lower than those of other countries having similar geological conditions. The distribution of radon concentrations was lognormal. The median value is high in the granite areas (63.5-105.1 Bq/L) while it is low in the sedimentary rocks and Cheju volcanic area (16.0-20.3 Bq/L). When grouping the groundwater with well depth, the median radon value is high in weathering and/or upper bedrock zone (61.4 Bq/L) while it is low in alluvium and/or weathering zone (28.5 Bq/L). About 17.7% of the total samples exceeded 148 Bq/L of USEPA guideline value. The exceeding radon ratio more than 148 Bq/L in groundwater is highest in Jurassic granite area, however, the exceeding radon rates more than 300 Bq/L and 500 Bq/L are highest in CGRA area.

• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.1
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• pp.1-13
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• 2022

A weighted linear combination of seismic fragility models previously developed for cut-and-cover railway tunnels was presented and the appropriateness of the combined model was evaluated. The seismic fragility function is expressed in the form of a cumulative probability function of the lognormal distribution based on the peak ground acceleration. The model uncertainty can be reduced by combining models independently developed. Equal weight is applied to four models. The new seismic fragility function was developed for each damage level by determining the median and standard deviation, which are model metrics. Comparing fragility curves developed for other bored tunnels, cut-and-cover tunnels for high-speed railway system have a similar level of fragility. We postulated that this is due to the high seismic design standard for high-speed railway tunnel.

• Wind and Structures
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• v.37 no.3
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• pp.211-227
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• 2023

To investigate the non-Gaussian feature of fluctuating wind pressures on rectangular high-rise buildings, wind tunnel tests were conducted on scale models with side ratios ranging from 1/9~9 in an open exposure for various wind directions. The high-order statistical moments, time histories, probability density distributions, and peak factors of pressure fluctuations are analyzed. The mixed normal-Weibull distribution, Gumbel-Weibull distribution, and lognormal-Weibull distribution are adopted to fit the probability density distribution of different non-Gaussian wind pressures. Zones of Gaussian and non-Gaussian are classified for rectangular buildings with various side ratios. The results indicate that on the side wall, the non-Gaussian wind pressures are related to the distance from the leading edge. Apart from the non-Gaussianity in the separated flow regions noted by some literature, wind pressures behind the area where reattachment happens present non-Gaussian nature as well. There is a new probability density distribution type of non-Gaussian wind pressure which has both long positive and negative tail found behind the reattachment regions. The correlation coefficient of wind pressures is proved to reflect the non-Gaussianity and a new method to estimate the mean reattachment length of rectangular high-rise building side wall is proposed by evaluating the correlation coefficient. For rectangular high-rise buildings, the mean reattachment length calculated by the correlation coefficient method along the height changes in a parabolic shape. Distributions of Gaussian and non-Gaussian wind pressures vary with side ratios. It is inappropriate to estimate the extreme loads of wind pressures using a fixed peak factor. The trend of the peak factor with side ratios on different walls is given.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.160-160
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• 2023

Generally, Global Climate Models (GCM) cannot be used directly due to their inherent error arising from over or under-estimation of climate variables compared to the observed data. Several bias correction methods have been devised to solve this problem. Most of the traditional bias correction methods are one dimensional as they bias correct the climate variables separately. One such method is the Quantile Mapping method which builds a transfer function based on the statistical differences between the GCM and observed variables. Laux et al. introduced a copula-based method that bias corrects simulated climate data by employing not one but two different climate variables simultaneously and essentially extends the traditional one dimensional method into two dimensions. but it has some limitations. This study uses objective functions to address specifically, the limitations of Laux's methods on the Quantile Mapping method. The objective functions used were the observed rank correlation function, the observed moment function and the observed likelihood function. To illustrate the performance of this method, it is applied to ten GCMs for 20 stations in South Korea. The marginal distributions used were the Weibull, Gamma, Lognormal, Logistic and the Gumbel distributions. The tested copula family include most Archimedean copula families. Five performance metrics are used to evaluate the efficiency of this method, the Mean Square Error, Root Mean Square Error, Kolmogorov-Smirnov test, Percent Bias, Nash-Sutcliffe Efficiency and the Kullback Leibler Divergence. The results showed a significant improvement of Laux's method especially when maximizing the observed rank correlation function and when maximizing a combination of the observed rank correlation and observed moments functions for all GCMs in the validation period.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.328-328
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• 2023

표준강수지수(Standardized Precipitation Index, SPI)는 강수량 변동의 정도를 표준화하여 나타낸 지수로, 가뭄 평가에 적용되고 있다. 일반적으로 SPI를 산정할 때는 월 단위의 시간 척도를 적용하며, 장기간의 가뭄에 대해 평가한다. 그러나 시간 척도가 길어질수록 가뭄 발생 후 가뭄을 감지하는 데 걸리는 시간이 더 길어지기 때문에 대처가 더욱 어려워진다. 또한, 기후변화로 인해 가뭄 빈도가 증가하고, 그 정도가 더욱 심화되면서 일 단위의 적용이 필요해지고 있다. 본 연구는 한반도 남부지역을 대상으로 일 단위의 SPI 적용을 위한 최소 시간 척도를 조사하였다. 대상 지역을 강원권, 수도권, 부울경, 대경권, 호남권, 충청권의 총 6개 지역으로 분리하여, 각 지역별, 계절별 최소 시간 척도를 조사하였다. SPI 산정을 위해 후보 분포형으로 Gumbel, Gamma, GEV, Loglogistic, Lognormal, Weibull을 적용하였으며, 시간 척도는 5일부터 365일까지 총 10개로 설정하였다. 본 연구에선 크게 적합도 검정과 정규성 검정으로 진행하였다. 적합도 검정에서는 Chi-square test를 적용하였으며, 이때 일 단위의 짧은 시간 척도를 적용할 경우 누가 강수 시계열의 값이 0으로, 0값이 시계열에 포함되면 SPI의 정확도가 떨어지는 문제가 발생하는데, 이를 보완하기 위해 누가 강수 시계열의 0값을 고려하였다. 마지막으로 각 후보 분포형을 적용하여 산정된 SPI가 표준정규분포에 합당한지를 검증하기 위해 Anderson-Darling test를 수행하였다. 결과적으로 대부분의 지역에서는 봄과 여름의 경우 최소 15일 정도의 시간 척도까지는 적용할 수 있을 것으로 판단되며, 겨울의 경우는 최소 30일 정도의 시간 척도를 적용해야 함을 확인하였다. 지역별로 차이가 크진 않지만, 이러한 연구 결과를 참고하여 각 지역별로 더 나은 가뭄 대책을 마련할 수 있을 것으로 기대된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.384-384
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• 2020

갈수량은 연간 355번째에 해당하는 일유량으로 연중 10일은 유지할 수 있는 유량을 의미한다. 갈수량은 하천유지유량을 결정하고 다목적댐의 이수안전도를 평가하는 기준으로 활용되는 지표로 활용되고 있으나 현재 기준으로는 과거사상에 초점을 맞추어 산정되고 있다. 본 연구에서는 기후변화에 따른 수문사상의 변화로 인한 미래 극한사상에 대비한 평가기준 마련을 위하여 CMIP5의 GCM 자료를 활용한 한강수계의 소양강댐의 실제증발산량을 추정하고, 이를 고려한 갈수량을 전망하고자 한다. 실제증발산의 경우 관측자료가 부재하므로 증발산 보완관계 가설 기반의 간접계산을 통해 추정하였으며, 잠재증발산량은 FAO Penman-Monteith 공식, 습윤증발산량은 Priestley-Taylor공식을 활용하여 산정하였다. 기준기간(1974-2000년) GCM 자료의 보정은 강우 및 증발산에 대하여 정상성 분위사상법을 적용하였으며, 우리나라의 홍수기 특성을 반영하기 위하여 홍수기(6~9월) 및 비홍수기(10~5월)로 구분하였다. 소양강댐 유역에 대한 연단위 원시 GCM의 경우, 연단위 강우와 실제증발산 각각 -20.0%, +17.3%의 오차율을 보였으나, 지역오차보정 후 각각 -1.2%, -0.2%로 개선되었다. 전망기간(2011-2100년)에 대해서는 비정상성 분위사상법을 적용하였으며, 지역오차보정 과정을 거친 강우 및 실제증발산 자료는 장기유출모형의 입력자료로 활용되었다. 실제증발산을 고려한 유출량을 산정하기 위해 IHACRES 모형을 활용하였으며, 갈수량은 모형으로부터 산정된 유출 시계열에 대한 lognormal 분포의 누적확률밀도함수의 3%에 해당하는 값으로 결정하였다. 전망결과는 근미래(Near future, 2011~2040년), 중미래(Midcentury future, 2041~2070년), 먼미래(Distance future, 2071~2100년)로 나누어 제시하였으며, 미래구간별 추세를 반영한 증감율을 제시하였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.317-317
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• 2020

수재해는 수자원 인프라의 부족 및 관리 미흡 등 많은 요인들이 있지만 강우의 유무와 크기가 가장 원초적인 요인들 중 하나이다. 정확한 강우량 추정 및 강우발생시간 예측은 수재해로 인한 피해를 예방하고 빠르게 대처할 수 있다. 그러나 강우예측에는 많은 불확실성을 내포하고 있기 때문에 이러한 불확실성을 이해하고 줄여 나가는 것이 필요하다. 최근 컴퓨터의 성능의 발전에 비례해 강우 예측 자료들도 점진적으로 발전을 거듭하고 있다. 이를 강우-유출 모형에 적용시 유출량 예측의 정확성 또한 비례하여 한층 더 발전할 수 있을 것이다. 하지만 신뢰성이 낮은 입력자료를 대상으로 하는 유출해석 모형은 많은 불확실성을 내포할 것이다. 따라서 본 연구에서는 위천 유역에 대해 LENS(Limited area ENsemble prediction System) 강우앙상블 예측자료의 적용성을 검토하고 그리드 기반 강우 유출 모델 GRM(Grid based Rainfall-runoff Model) 에 적용하여 유출예측의 불확실성을 평가하고자 하였다. 또한 강우예측 및 유출예측은 수 많은 매개변수를 포함하며 최종적인 예측은 더 큰 불확실한 범위로 산출될 수 있다. 이에 따라 본 연구에서는 Python3 기반 코딩으로 LENS 자료 구축 및 GRM 모형의 매개변수 보정을 각 2000회 씩에 걸쳐 총 2회 실시하여 수문학적, 지형학적 인자에 따른 불확실성 범위를 보정하고자 하였다. 매개변수의 보정은 비정형우도(Informal likelihood) NSE, 정형우도(Formal likelihood) Lognormal(Log-likelihood function)의 우도에 따른 행위모델을 산정하여 보정하였다. 따라서 본 연구에서는 선행연구들을 참고한 정형, 비정형 우도의 임계치를 이용한 불확실성해석에 적용하였으며 이는 사용자의 행위모델선정 임계치 범위 선정으로 인한 불확실성을 줄여나감에 기여할 수 있을것으로 사료된다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.5D
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• pp.497-504
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• 2010

In this paper, the author presents a reliability estimation technique to analyze the effects of traffic loads on pavement mean life based on the national highway database of Suwon and Uijeongbu region from 1999 to 2008. The estimation of the mean life, its standard deviation and reliability for pavement sections are calculated by using an appropriate distribution, Lognormal distribution, based on reliability theory. Furthermore, the probability paper method and Maximum likelihood estimation are both used to estimate parameters. The author found that mean life of newly constructed sections and over-layed sections is about 6.5 to 7.9 years and 7.3 to 9.1 years, respectively. The author also ascertained that the results of cumulative failure probability for pavement life between the proposed methods and observed data are similar. Such an assessment methodology and measures based on reliability theory can provide useful information for maintenance plans in pavement management systems as long as additional life data on pavement sections are accumulated.

• Journal of Korean Society on Water Environment
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• v.39 no.5
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• pp.396-412
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• 2023

Species from the mayfly genus Ephemera (Order Ephemeroptera) was assessed for their physical microhabitat suitability (namely E. strigata, E. separigata, and E. orientalis-sachalinensis). Probability distribution models (Exponential, Normal, Lognormal, Logistic, Weibull, Gamma, Beta, and Gumbel) based on the data collected from 23,957 sampling units of 6,787 sites in Korea from 2010 to 2021 were used. Mode and standard deviation calculated from the best-fitting models to species distribution along a water depth gradient were 265 cm and 159 cm in E. orientalis-sachalinensis; 10 cm and 83 cm in E. strigata; 20 cm and 15 cm in E. separigata, respectively. The current velocity gradient was 22 cm/s and 40 cm/s in E. orientalis-sachalinensis; 60 cm/s and 53 cm/s in E. strigata; 82 cm/s and 25 cm/s in E. separigata, respectively. The mean diameter (phi scale) of substrate grains were -3.6 and 2.2 in E. orientalis-sachalinensis; -7.4 and 1.5 in E. strigata; -5.8 and 0.9 in E. separigata, respectively. Habitat suitability range of E. orientalis-sachalinensis was estimated to be 161~369 cm (water depth), 5~44 cm/s (current velocity), -5.2~-2.0 (mean diameter); 3~34 cm (water depth), 36~94 cm/s (current velocity), -8.1~-6.3 (mean diameter) for E. strigata; 12~32 cm (water depth), 63~96 cm/s (current velocity), -6.3~-5.2 (mean diameter) for E. separigata. In relative comparison, E. orientalis-sachalinensis was estimated to be rheophobic, eurybathophilic, and eurypsephophilic; E. strigata to be euryrheophilic, bathophobic, and lithophilic; E. separigata to be stenomesorheophilic, stenobathophobic, stenolithophilic.

• Journal of Korea Soil Environment Society
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• v.2 no.2
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• pp.81-94
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• 1997

In many solute transport studies, either flux or resident concentration has been used. Choice of the concentration mode was dependent on the monitoring device in solute displacement experiments. It has been accepted that no priority exists in the selection of concentration mode in the study of solute transport. It would be questionable, however, to accept the equivalency in the solute transport parameters between flux and resident concentrations in structured soils exhibiting preferential movement of solute. In this study, we investigate how they differ in the monitored breakthrough curves (BTCs) and transport parameters for a given boundary and flow condition by performing solute displacement experiments on a number of undisturbed soil columns. Both flux and resident concentrations have been simultaneously obtained by monitoring the effluent and resistance of the horizontally-positioned TDR probes. Two different solute transport models namely, convection-dispersion equation (CDE) and convective lognormal transfer function (CLT) models, were fitted to the observed breakthrough data in order to quantify the difference between two concentration modes. The study reveals that soil columns having relatively high flux densities exhibited great differences in the degree of peak concentration and travel time of peak between flux and resident concentrations. The peak concentration in flux mode was several times higher than that in resident one. Accordingly, the estimated parameters of flux mode differed greatly from those of resident mode and the difference was more pronounced in CDE than CLT model. Especially in CDE model, the parameters of flux mode were much higher than those of resident mode. This was mainly due to the bypassing of solute through soil macropores and failure of the equilibrium CDE model to adequate description of solute transport in studied soils. In the domain of the relationship between the ratio of hydrodynamic dispersion to molecular diffusion and the peclet number, both concentrations fall on a zone of predominant mechanical dispersion. However, it appears that more molecular diffusion contributes to the solute spreading in the matrix region than the macropore region due to the nonliearity present in the pore water velocity and dispersion coefficient relationship.