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      • KCI등재

        Modeling of water flow and heat transport in the vadose zone: Numerical demonstration of variability of local groundwater recharge in response to monsoon rainfall in Korea

        구민호,김용제 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.2

        The rainfall of Korea in the summer monsoon period occupies more than 50% of the annual precipitation in most areas, and thus groundwater recharge to shallow aquifers is dominantly controlled by the amount and the pattern of monsoon precipitation. This paper presents two numerical models that demonstrate linear relationships between precipitation and recharge. First, a simple heat transport model employing a lumped parameter approach is presented for estimating two lumped parameters related to water flux and thermal diffusivity in the vadose zone. The model determines the parameters by a simple optimization process that minimizes the root-mean-square error between simulated and measured temperatures. The model is applied to 22-year time series data of soil temperatures measured at a synoptic station of Korea. The impact of monsoon precipitation on the thermal regime is clearly reflected in the simulated results by illustrating a linear relationship between precipitation and the water flux in the vadose zone. Secondly, an infiltration model is presented for analyzing variability of precipitation recharge in relation to the monsoon rainfall. The model simulates the unsaturated flow from time series data of precipitation and pan evaporation, assuming immediate removal of surface ponding, a linear relationship between the evaporation rate and the soil water content, and a static water table. Numerical simulations were performed for three soil textural groups by using 20-year meteorological data. The results demonstrate that the annual recharge is linearly proportional to the annual precipitation with varying degrees of the correlation coefficient depending on soil types. Sensitivity analyses show that the uncertainties in evaporation-related model parameters significantly affect the model results with controlling tradeoff between recharge and evaporation estimates.

      • KCI등재

        Estimating apparent thermal diffusivity using temperature time series: A comparison of temperature data measured in KMA boreholes and NGMN wells

        구민호,송윤호 한국지질과학협의회 2008 Geosciences Journal Vol.12 No.3

        Two different time series data sets, shallow ground temperatures of 58 synoptic stations of the Korea Meteorological Administration (KMA) and groundwater temperatures of 67 wells of the National Groundwater Monitoring Network (NGMN), were analyzed to estimate the apparent thermal diffusivity by using the analytical solution of the one-dimensional heat conduction equation. The KMA temperature data measured at 1-5 m depths illustrated values of the phase delay and the amplitude decay coincident with their theoretical relationship, indicating that the conductive heat transport should prevail over the nonconductive processes. On the contrary, some of the estimates from temperatures at a depth of 0.5 m were away from the theoretical values. It is most likely that the deviation would be caused by the effects of latent heat associated with freezing and thawing of the near ground surface. In contrast to KMA data, results obtained from the NGMN data highly deviated from the theoretical ones, and thereafter yielded unacceptably high values of thermal diffusivities as compared to the representative values of soils and rocks. Implication of the discrepancy between two data sets was discussed in conjunction with perturbation of the conductive heat transport by free convection of water and air occurring in large diameter wells as well as the convective heat transport by groundwater flow.

      • KCI등재

        가우시안 프로세스 회귀분석을 이용한 지하수 수질자료의 해석

        구민호,박은규,정진아,이헌민,김효건,권미진,김용성,남성우,고준영,최정훈,김덕근,조시범,Koo, Min-Ho,Park, Eungyu,Jeong, Jina,Lee, Heonmin,Kim, Hyo Geon,Kwon, Mijin,Kim, Yongsung,Nam, Sungwoo,Ko, Jun Young,Choi, Jung Hoon,Kim, Deog-Geun,Jo, 한국지하수토양환경학회 2016 지하수토양환경 Vol.21 No.6

        Gaussian process regression (GPR) is proposed as a tool of long-term groundwater quality predictions. The major advantage of GPR is that both prediction and the prediction related uncertainty are provided simultaneously. To demonstrate the applicability of the proposed tool, GPR and a conventional non-parametric trend analysis tool are comparatively applied to synthetic examples. From the application, it has been found that GPR shows better performance compared to the conventional method, especially when the groundwater quality data shows typical non-linear trend. The GPR model is further employed to the long-term groundwater quality predictions based on the data from two domestically operated groundwater monitoring stations. From the applications, it has been shown that the model can make reasonable predictions for the majority of the linear trend cases with a few exceptions of severely non-Gaussian data. Furthermore, for the data shows non-linear trend, GPR with mean of second order equation is successfully applied.

      • KCI등재

        표준강수지수(SPI)를 이용한 가뭄에 대한 지표수와 지하수 반응 비교

        구민호,김원겸,송성호,Koo, Min-Ho,Kim, Wonkyeom,Song, Sung-Ho 한국지하수토양환경학회 2022 지하수토양환경 Vol.27 No.5

        A correlation analysis was performed to investigate differences in the response of surface water and groundwater to drought using the Standardized Precipitation Index (SPI). Water level data of 20 agricultural reservoirs, 4 dams, 2 rivers, and 8 groundwater observation wells were used for the analysis. SPI was calculated using precipitation data measured at a nearby meteorological station. The water storage of reservoirs and dams decreased significantly as they responded sensitively to the drought from 2014 to 2016, showing high correlation with SPI of the relatively long accumulation period (AP). The responses of rivers varied greatly depending on the presence of an upstream dam. The water level in rivers connected to an upstream dam was predominantly influenced by the dam discharge, resulting in very weak correlation with SPI. On the contrary, the rivers without dam exhibited a sharp water level rise in response to precipitation, showing higher correlation with SPI of a short-term AP. Unlike dams and reservoirs, the responses of groundwater levels to precipitation were very short-lived, and they did not show high correlation with SPI during the long-term drought. In drought years, the rise of groundwater level in the rainy season was small, and the lowered water level in the dry season did not proceed any further and was maintained at almost the same as that of other normal years. Conclusively, it is confirmed that groundwater is likely to persist longer than surface water even in the long-term drought years.

      • KCI등재

        지하수위 변동법에 의한 함양량 산정: 하천-대수층 상호작용의 영향

        구민호,김태근,김성수,정성래,강인옥,이찬진,김용철,Koo, Min-Ho,Kim, Tae-Keun,Kim, Sung-Soo,Chung, Sung-Rae,Kang, In-Oak,Lee, Chan-Jin,Kim, Yongcheol 한국지하수토양환경학회 2013 지하수토양환경 Vol.18 No.5

        The water-table fluctuation (WTF) method has been often used for estimating groundwater recharge by analysis of waterlevel measurements in observation wells. An important assumption inherent in the method is that the water level rise is solely caused by precipitation recharge. For the observation wells located near a stream, however, the water-level can be highly affected by the stream level fluctuations as well as precipitation recharge. Therefore, in applying the WTF method, there should be consideration regarding the effect of stream-aquifer interactions. Analysis of water-level hydrographs from the National Groundwater Monitoring Wells of Korea showed that they could be classified into three different types depending on their responses to either precipitation recharge or stream level fluctuations. A simple groundwater flow model was used to analyze the errors of the WTF method, which were associated with stream-aquifer interactions. Not surprisingly, the model showed that the WTF method could greatly overestimate recharge, when it was used for the observation wells of which the water-level was affected by streams. Therefore, in Korea, where most groundwater hydrographs are acquired from wells nearby a stream, more caution is demanded in applying the WTF method.

      • KCI등재

        국내 지면온도의 시공간적 변화 분석

        구민호,송윤호,이준학,Koo Min-Ho,Song Yoon-Ho,Lee Jun-Hak 대한자원환경지질학회 2006 자원환경지질 Vol.39 No.3

        58개 기상관측소에서 최근 22년간(1981-2002) 측정된 기상 자료를 이용하여 국내의 기온(SAT) 및 지면온도(GST)의 시공간적 변동 경향을 분석하였다. 먼저 관측 자료로부터 각 관측소의 평균기온(MSAT)과 평균지면온도(MGST)를 계산하였으며, 다중선형회귀분석을 통해 MSAT와 MGST를 예측할 수 있는 회귀식을 산정하였다. 회귀모형의 회귀변수는 관측소의 위도 및 고도이다. 회귀모형의 추정치와 실제 관측값의 결정계수($R^2$)는 각각 0,92와 0.94로 나타나 모형의 예측 정확성이 매우 높은 것으로 분석되었다. MGST는 지열펌프 시스템 설계의 주요 입력 변수이므로 최근 지열에너지자원 활용 분야에서 매우 중요하게 다루어지는 변수이다. 따라서 제시된 회귀모형은 신뢰할만한 관측 자료가 없는 지역에서 MGST를 추정하는데 매우 유용하게 이용될 수 있을 것으로 예상된다. SAT 자료에 대한 선헝회귀분석을 통해 지구온난화 및 도시화에 기인한 기온 상승의 장기 추세 변동성을 탐색하였다. 1개 관측소를 제외한 57개 관측소에서 $0.005{\sim}0.088^{\circ}C/yr$ 범위의 기온증가율을 가지는 추세 변동이 확인되었다. 또한 GST에 영향을 미치는 기상요소로서 일사량, 지구복사, 강수량 및 적설량 자료를 분석하였다. GST는 주로 SAT 및 일사량에 의하여 결정되지만 강수 및 증발에 의한 토양의 열용량 변화, 적설에 의한 대기와 지표면 차단, 지구복사에 영향을 줄 수 있는 대기의 조건 변화 등이 복합적인 변동 요인으로 작용하는 것으로 나타났다. Recent 22-year (1981-2002) meteorological data of 58 Korea Meteorological Adminstration (KMA) station were analyzed to investigate spatial and temporal variation of surface air temperature (SAT) and ground surface temperature (GST) in Korea. Based on the KMA data, multiple linear regression (MLR) models, having two regression variables of latitude and altitude, were presented to predict mean surface air temperature (MSAT) and mean ground surface temperature (MGST). Both models showed a high accuracy of prediction with $R^2$ values of 0.92 and 0.94, respectively. The prediction of MGST is particularly important in the areas of geothermal energy utilization, since it is a critical parameter of input for designing the ground source heat pump system. Thus, due to a good performance of the MGST regression model, it is expected that the model can be a useful tool for preliminary evaluation of MGST in the area of interest with no reliable data. By a simple linear regression, temporal variation of SAT was analyzed to examine long-term increase of SAT due to the global warming and the urbanization effect. All of the KMA stations except one showed an increasing trend of SAT with a range between 0.005 and $0.088^{\circ}C/yr$ and a mean of $0.043^{\circ}C/yr$. In terms of meteorological factors controlling variation of GST, the effects of solar radiation, terrestrial radiation, precipitation, and snow cover were also discussed based on quantitative and qualitative analysis of the meteorological data.

      • KCI등재후보

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