• Journal of Korea Water Resources Association
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• v.49 no.9
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• pp.731-740
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• 2016

This study conducts the hydrological component analysis from 2010 to 2015 at the water curtain cultivation area in Cheongwon-gu, Cheongju-si and investigates the monthly based groundwater recharge variation. It is found that the rates of evaportranspiration, surface runoff and groundwater recharge were varied according to the total annual precipitation and their correlations were also changed annually. Annual recharge rates for annual precipitation ranged from 8.3% to 19%, and their coefficient of determination ranged from 0.39 to 0.94. Especially in 2015, when the severe drought came upon this area, the lack of groundwater recharge made groundwater level decrease consistently. Thus, it is thought that the special method of estimating exploitable groundwater in water curtain cultivation site is to be introduced.

• Magazine of the Korean Society of Agricultural Engineers
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• v.21 no.4
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• pp.108-117
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• 1979

In order to obtain the basic data for design of water structures which can be contributed to the planning of water use. Best fitted distribution function and the equations for the probable minimum flow were derived to the annual minimum flow of five subwatersheds along Geum River basin. The result were analyzed and summarized as follows. 1. Type III extremal distribution was considered as a best fit one among some other distributions such as exponential and two parameter lognormal distribution by $x^2$-goodness of fit test. 2. The minimum flow are analyzed by Type III extremal distribution which contains a shape parameter $\lambda$, a location parameter ${\beta}$ and a minimum drought $\gamma$. If a minimum drought $\gamma=0$, equations for the probable minimum flow, $D_T$, were derived as $D_T={\beta}e^{\lambda}1^{y'}$, with two parameters and as $D_T=\gamma+(\^{\beta}-\gamma)e^{{\lambda}y'}$ with three parameters in case of a minimum drought ${\gamma}>0$ respectively. 3. Probable minimum flow following the return periods for each stations were also obtained by above mentioned equations. Frequency curves for each station are drawn in the text. 4. Mathematical equation with three parameters is more suitable one than that of two parameters if much difference exist between the maximum and the minimum value among observed data.

• Proceedings of the Korea Water Resources Association Conference
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• 1992.07a
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• pp.411-418
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• 1992

The purpose of this study is to develop dynamic-stochastic models that can forecast the inflow into reservoir during low/drought periods and flood periods. For the formulation of the models, the discrete transfer function is utilized to construct the deterministic characteristics, and the ARIMA model is utilized to construct the stochastic characteristics of residuals. The stochastic variations and structures of time series on hydrological data are examined by employing the auto/cross covariance function and auto/cross correlation function. Also, general modeling processes and forecasting method are used the model building methods of Box and Jenkins. For the verifications and applications of the developed models, the Chungju multi-purpose reservoir which is located in the South Han river systems is selected. Input data required are the current and past reservoir inflow and Yungchun water levels. In order to transform the water level at Yungchon into streamflows, the water level-streamflows rating curves at low/drought periods and flood periods are estimated. The models are calibrated with the flood periods of 1988 and 1989 and hourly data for 1990 flood are analyzed. Also, for the low/drought periods, daily data of 1988 and 1989 are calibrated, and daily data for 1989 are analyzed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2245-2254
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• 2013

A vulnerability index was developed for drought by using trend analysis and Delphi method. Twelve indicators were selected based on three groups, i.e., hydrological, meteorological, and humanistic groups. Data were collected from Nakdong river watershed. Three trend tests, i.e., Mann-Kendall, Hotelling-Pabst, and Sen's trend tests, were performed for standardizing the indicators and Delphi method was used to estimate the weights for individual indicators. The drought vulnerability index was calculated for seven regions in the Nakdong watershed and Hapcheon turned out to be the most vulnerable region among the study regions. The drought vulnerability index developed in this study can be applied to other regions in Korea for establishing national water resources management plan.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.152-152
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• 2020

가뭄은 장기간에 걸쳐 광범위하게 발생하는 특징으로 인해 자연재해뿐만 아니라 사회·경제적으로도 큰 피해를 야기한다. 즉, 가뭄으로 인한 댐의 용수 공급 부족은 공업·농업뿐만 아니라 국민들의 생활에도 상당한 피해를 미친다. 하지만, 가뭄으로 인한 지역의 피해정도는 해당 지역의 특성 또는 가뭄에 대한 지역의 대처 능력에 따라 매우 상이하게 나타난다. 따라서, 가뭄에 의한 피해를 저감시키고 안전한 용수공급이 이루어질 수 있도록 지역의 특성 및 용수 공급 체계를 고려한 위험 정도를 분석하는 것이 필요하며, 사람들과 직접적인 연관성이 높은 물수급 관련 인자들을 고려하여 가뭄의 잠재적 영향 및 피해정도를 파악할 수 있는 가뭄 위험도 평가가 수행되어야 한다. 그러나 용수공급 및 수요 현황을 반영한 가뭄 노출성 및 취약성 평가는 아직 부족한 실정이며, 각 인자에 대한 가중치를 산정하는데 설문조사 또는 단순평균방법이 많이 이용되고 있다. 본 연구에서는 용수공급 체계 및 지역적 특성을 고려하고 객관적인 가중치 산정방안이 적용된 확률·통계적 가뭄 위험도를 평가방법을 제시하였다. 먼저, 용수공급 실패 사상의 발생 확률이 적용된 결합가뭄관리지수(Joint Drought Management Index, JDMI)를 통해 가뭄노출성지수(Drought Hazard Index, DHI)를 산정하고, 각 인자에 대한 영향정도를 객관적으로 판단할 수 있는 가우스 혼합 모델을 활용하여 가뭄취약성지수(Drought Vulnerability Index, DVI)를 산정하였다. 이 두 지수를 결합하여 가뭄위험도지수(Drought Risk Index, DRI)를 계산하고 위험도 평가를 수행하였다. 충청지역에 적용한 결과, DHI는 용수공급 실패 사상의 발생확률이 큰 보령시가 가장 높게 나타났으며, DVI는 농업적 요소의 가중치가 크게 산정됨에 따라 청주시가 가장 높게 산정되었다. DHI와 DVI가 결합된 DRI의 경우는 청주시가 가장 위험한 것으로 나타났다. 따라서, DRI가 가장 높은 청주시는 충정 지역의 가뭄 위험 경감을 위한 대응 수립시 우선적으로 고려되어야 한다.

• Journal of Korea Water Resources Association
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• v.45 no.9
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• pp.887-900
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• 2012

Drought is a non-negligible disaster of nature and it is mainly caused by rainfall shortage for a long time though there are many definitions of drought. 'Standard Precipitation Index' (SPI) that is widely used to express the level of meteorological drought intensity has a limit of not being able to consider the hydrological changes such as rainfall and evapotranspiration caused by climate change, because it does not consider the temperature-related variables other than the precipitation. Recently, however, 'Standardized Precipitation Evapotranspiration Index' (SPEI), a drought index of new concept which is similar to SPI but can reflect the effect of temperature variability as well as the rainfall change caused by climate variation, was developed. In this study, the changes of drought occurrence in South Korea were analyzed by applying SPEI for meteorological data (1973~2011) of 60 climate observatories under Korea Meteorological Administration (KMA). As the result of application, both of SPI and SPEI showed the trend of deepening drought in spring and winter and mitigating drought in summer for the entire nation, with SPI showing greater drought intensity than SPI. Also, SPI and SPEI with 12 months of duration showed that severe droughts with low frequency of around 6 years are generally being repeated.

• Journal of Korea Water Resources Association
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• v.54 no.12
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• pp.1295-1304
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• 2021

For the efficient use and management of water resources, a reliable rainfall-runoff analysis is necessary. Still, continuous hydrological data and rainfall-runoff data are insufficient to secure through measurements and models. In particular, as part of the reasonable improvement of a rainfall-runoff model in the case of an ungauged watershed, regionalization is being used to transfer the parameters necessary for the model application to the ungauged watershed. In this study, the GR4J model was selected, and the SCEM-UA method was used to optimize parameters. The rainfall-runoff model for the analysis of the correlation between watershed characteristics and parameters obtained through the model was regionalized by the Copula function, and rainfall-runoff analysis with the regionalized parameters was performed on the ungauged watershed. In the process, the intermediate state variables of the rainfall-runoff model were extracted, and the correlation analysis between water level and the ground water level was investigated. Furthermore, in the process of rainfall-runoff analysis, the Standardized State variable Drought Index (SSDI) was calculated by calculating and indexing the state variables of the GR4J model. and the calculated SSDI was compared with the standardized Precipitation index (SPI), and the hydrological suitability evaluation of the drought index was performed to confirm the possibility of drought monitoring and application in the ungauged watershed.

• The Journal of Engineering Geology
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• v.30 no.3
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• pp.253-268
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• 2020

In this study, recharge rates are estimated using SWAT-K (a distributed hydrological model). The validity of the estimated recharge rates were evaluated by employing the baseflow separation method based on observed hydrological data. The exploitable groundwater is typically determined as the 10-year drought frequency recharge rate that is calculated by average recharge ratio multiplied by 10-year drought frequency precipitation. In practice, however, recharge rates typically decrease in line with precipitation; therefore, exploitable groundwater could be overestimated when average recharge rates are used without considering precipitation. To resolve this overestimation, exploitable groundwater was calculated by re-estimating recharge rates that consider precipitation intensity. By applying this method to the Uiwang, Gwacheon, and Seongnam sub-basins, the exploitable groundwater decreased by 55.5~77.6%, compared with recharge rates obtained using the existing method.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.203-215
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• 2021

In the present study, hydrologic data and topographical data from 2010 to 2019 were collected from three gauging stations placed in the watershed of Naeseong stream to determine changes and rates of changes in rainfall, water level & mean velocity, and water level & discharge, together with changes in rates of erosion and deposition at cross-sections of the river. Besides, effects of regulated and non-regulated rivers according to the presence of artificial regulation of flow rate of the river via artificial structure located at Seo stream (Yeongju si (Wolhogyo) station), the tributary free from construction of dams, were compared and analyzed. Results of analyses conducted in the present study revealed vegetational establishment and landforming due to increasing area of vegetational sandbar evolved in the flood plain (intermediate- or high- water level) by the drought sustained from 2013 to 2015. Continuous erosion of river bed was appeared because of narrowed flow area with low water level and increased velocity and tractive force on river bed.

• Journal of Korea Water Resources Association
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• v.50 no.11
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• pp.745-758
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• 2017

The copula-based models have been successfully applied to hydrological modeling including drought frequency analysis and time series modeling. However, uncertainty estimation associated with the parameters of these model is not often properly addressed. In these context, the main purposes of this study are to develop the Bayesian inference scheme for bivariate copula functions. The main applications considered are two-fold: First, this study developed and tested an approach to copula model parameter estimation within a Bayesian framework for drought frequency analysis. The proposed modeling scheme was shown to correctly estimate model parameters and detect the underlying dependence structure of the assumed copula functions in the synthetic dataset. The model was then used to estimate the joint return period of the recent 2013~2015 drought events in the Han River watershed. The joint return period of the drought duration and drought severity was above 100 years for many of stations. The results obtained in the validation process showed that the proposed model could effectively reproduce the underlying distribution of observed extreme rainfalls as well as explicitly account for parameter uncertainty in the bivariate drought frequency analysis.