• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.6
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• pp.655-662
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• 2021

This study aimed to estimate exploitable groundwater for the sustainable supply of groundwater in the Jinju region of South Gyeongsang Province. As an integrated hydrologic analysis model, SWAT-MODFLOW was used to estimate the distributed groundwater recharge in consideration of land use and soil distribution. As a result of calibration of the model, the coefficient of determination between the observed flow and the simulated flow was 0.75-0.80, which was good. The simulated groundwater recharge rate showed a spatio-temporal distribution due to heterogeneous watershed characteristics. The amount of groundwater recharge shows lower values over winter and spring, but it increases according to the pattern of precipitation in summer and autumn. The calculated average annual groundwater recharge was compared with the result using the baseflow separation method of natural flow, and the deviation of both results was small, within 3 %, confirming the validity of the estimated groundwater recharge. Exploitable groundwater is defined as the amount of recharge corresponding to low flow with 10 years of return period. Therefore, in this study, 14.2 % of the annual precipitation was found to be exploitable as a result of calculating the amount of recharge at a 10-year frequency using a statistical frequency analysis technique.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.4 no.4
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• pp.255-265
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• 1999

CTD castings and current observations are taken in June, July and October, 1997 and May and July, 1998 to investigate the effect of the Keum River dyke on the structure of physical properties and the type of the Keum River estuary. Tide and tidal current relation shows that the ebbing is longer than the flooding by 1.5 hours with the early current reversing before high tide. In the rainy season (May to July), frequent large fresh water discharge during the ebbing from the dyke changes vertical salinity difference and time variation of salinity greatly near the head of the estuary, where salinity becomes lower than 2‰ in summer fresh water flooding. Halocline developed by the fresh water discharge makes two-layer structure, of which strength and depth increase in the low tide. The relationship between tide phase and surface salinity variation shows the phase lag of 2.5 hours near the head of the estuary but the standing wave relation down the estuary. This phase lag implies that a low salinity water diluted by the fresh water discharge for 2-3 hours in the ebb period moves with tidal excursion. In the dry season, vertical salinity difference reduces significantly. We calculate stratification and circulation parameters using the observed salinity structure, surface current and fresh water discharge. The Keum River estuary shows a partially mixed type, changing the stratification parameter from the rainy to the dry season. Mean flows of observed tidal current at lower and upper layer are landward and seaward, which are consistent with the circulation of a partially mixed estuary. Based upon the estuary type and circulation we suggest that the suspended materials will move toward the upstream due to low-layer mean flow and then the Keum River estuary will be a deposit environment.

• Journal of Korea Water Resources Association
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• v.57 no.4
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• pp.289-300
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• 2024

The purpose of this study is to evaluate the applicability of the GRM (Grid based rainfall-Runoff Model) to the continuous simulation by simulating the dam inflow. The GRM was previously developed for the simulation of rainfall-runoff events but has recently been improved to enable continuous simulation. The target watersheds are Chungju dam, Andong dam, Yongdam dam, and Sumjingang dam basins, and runoff models were constructed with the spatial resolution of 500 m × 500 m. The simulation period is 21 years (2001 to 2021). The simulation results were evaluated over the 17 year period (2005 to 2021), and were divided into three data periods: total duration, wet season (June to September), and dry season (October to May), and compared with the observed daily inflow of each dam. Nash-Sutcliffe efficiency (NSE), Kling-Gupta efficiency (KGE), correlation coefficient (CC), and total volume error (VE) were used to evaluate the fitness of the simulation results. As a result of evaluating the simulated dam inflow, the observed data could be well reproduced in the total duration and wet season, and the dry season also showed good simulation results considering the uncertainty of low-flow data. As a result of the study, it was found that the continuous simulation technique of the GRM model was properly implemented and the model was sufficiently applicable to the simulation of dam inflow in this study.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.5
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• pp.779-789
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• 2016

The effective rainfall is calculated considering the soil moisture. It utilizes observed data directly in order to incorporate the soil moisture into the rainfall-runoff model, or it calculates indirectly within the model. The rainfall-runoff model, IHACRES, used in this study computes the catchment wetness index (CWI) first varying with temperature and utilize it for estimating precipitation loss. The nonlinear relationship between the CWI and the effective rainfall in the Hapcheondam watershed was derived and utilized for the long-term runoff calculation. The effects of variable and constant CWI during calibration and validation were suggested by flow regime. The results show the variable CWI is generally more effective than the constant CWI. The $R^2$ during high flow period shows relatively higher than the ones during normal or low flow period, but the difference between cases of the variable and constant CWI was insignificant. The results indicates that the high flow is relatively less sensitive to the evaporation and soil moisture associated with temperature. On the other hand, the variable CWI gives more desirable results during normal and low flow periods which means that it is crucial to incorporate evaporation and soil moisture depending on temperature into long-term continuous runoff simulation. The NSE tends to decrease during high flow period with high variability which could be natural because NSE index is largely influenced by outliers of underlying variable. Nevertheless overall NSE shows satisfactory range higher than 0.9. The utilization of variable CWI during normal and low flow period would improve the computation of long-term rainfall-runoff simulation.

• Water for future
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• v.27 no.4
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• pp.69-84
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• 1994

The aim of this paper is suggest how to control the real time reservoir operation for the optimal operation of reservoir during the draught and the rainy season. The realease and the storage lead to the achievement or the deviation losses, higher or lower than the target level. Considering this deviation as one of the losses, putting the penalty on the losses, the way of optimal reservoir operation is discussed in order to minimize the penalty losses. This study draw the deviation losses' curve depending on the operation objectie for the Daechung Dam, and apply the optimal operation to the Dam by the linear programing technique, using the slope of the deviation curve as the losses coefficience for the objective function. Conclusively, in this paper I can combine the opposing subjects -the release and the storage- as one objective function by the deviation curve, and also show how to decide the criterion relate to the real time reservoir operation by analysing to what extent and how easily the objectives can be achieved, subject to the inflows.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.238-238
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• 2011

복단면 하도는 홍수소통을 위한 상부 하도와 생태계 서식처 강화와 유사이송능력 개선, 경제적인 유지유량의 확보 등을 도모하는 자연적인 저수로 하도로 구성된다. 그러므로 갈수기와 홍수기의 유량차가 큰 하천에서, 복단면 하도는 하천 공학, 환경 생태 관점에서 다양한 이점을 제공한다. 그러나 복단면 하도에서의 흐름저항, 조도계수, 통수능, 수위-유량관계, 횡방향 유속분포, 그리고 하상전단응력 분포는 단단면 하도와 상이하며, 중요한 차이점은 주수로부와 홍수터부 사이의 유속차로 인하여 발생하는 활발한 운동량 교환에 의해 추가적인 전단층이 생성되는 점이다. 주수로와 홍수터 사이에서 발생된 경계전단력(Apparent Shear Force, ASF)은 하천의 전반적인 통수능을 감소시켜 홍수의 하도내 저류효과를 증가시킬 수도 있다. 또한 주수로 및 홍수터가 분담할 수 있는 유량은 경계전단력에 민감하기 때문에, 홍수터에 수목 식재, 구조물 설치 등을 계획할 경우 정량적인 항력저항의 산정을 위하여 매우 중요하다. 현재까지 복단면에서 발생하는 경계전단응력을 추정하는 다양한 방법들이 개발되었으며, 각각의 방법으로 부터 경계전단력을 정량적으로 예측할 수 있다. 그러나 대부분의 방법이 실험에 근거한 경험적 방법이므로 각 식의 개발에 사용된 자료에만 적합할 수 있는 한계가 있으며, 균일한 수로의 기하학적 변수(전단면과 주수로의 하폭비, 홍수터와 주수로의 수심비, 홍수터와 주수로의 조도비, 주수로의 하폭대 수심비 등)에 의한 식으로 구성되어 수치모형에서 직접 활용하기에는 한계가 있다. 따라서 본 연구에서는 복단면 경계전단력 산정을 위하여 개발된 다양한 연구결과들을 비교 검토하고, 기존문헌 또는 웹상에서 가용한 수리실험 자료들을 이용하여 각 방법에서 계산된 유량과 실측 유량을 비교함으로써 각 방법이 지닌 한계를 분석하였다. 본 연구에서 검토된 5가지 방법은 Knight and Demetriou (1983)(이하 KD), Wormleaton and Merret (1990)(이하 WM), Cristodoulou (1992), Bousmar and Zech(1999) (이하 BZ) 그리고 Moreta and Martin-Vide (2010)(이하 MM)이다. BZ 방법을 제외하고 나머지 방법들은 전체 유량의 비교에서 5% 이내의 오차를 나타내었다. 그러나 나머지 4가지 방법 중 주수로부 유속의 비교에 있어서는 소규모 수로 실험자료만 이용한 KD 방법이 5% 이상의 오차를 나타내어 정확도가 떨어지는 것으로 나타났다. 따라서 비교적 단순한 형태의 Cristodoulou (1992) 방법이 적용하고자 하는 수로의 규모와 무관하게 복단면 유량예측에 적합할 것으로 판단된다.

• 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.

• Journal of the Korean GEO-environmental Society
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• v.17 no.6
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• pp.33-41
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• 2016

This study attempted to investigate drain capacity and vegetation potential of made-planting soil via finite element simulations. Engineering drain capacity of made-planting soil can be evaluated by an analysis of unsaturated soils. In a perspective for vegetation landscape, it is necessary to check whether the minimum amount of water in the made-planting soil can be supplied for the survival of plants. Herein, 1-m high soil column covered by made-planting soil were numerically simulated. Numerical results showed that how the coefficient of permeability of saturated soil and soil-water characteristics of unsaturated soil are considered significantly influences the drain capacity of soils. Variation in the volumetric water content within the Least Limiting Water Range (LLWR) provides us with information on whether the soil can contain a sufficient amount of water for the plants to survive the drought.

• Journal of Korea Water Resources Association
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• v.43 no.4
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• pp.325-336
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• 2010

This study presents the alteration of flow regime by effects of dams and water use in the Geum River Basin. The surface water use rate and the Impounded Runoff (IR) index were examined to assess the pressure indicators of the flow alteration. We applied the flow duration curve, flow regime coefficient, flood and low-flow frequency analysis as well as Range of Variability Approach (RVA) to investigate the quantitative changes in natural flow regimes. The results indicate that the high flow decreased and low flow increased respectively compared to the natural flow regimes at eight gauging stations. The Geum river is regulated by 139 dams and reservoirs storing 24% of the annual mean discharge and has high surface water use rate of 36%. These indicators are main pressure factors to alter flow regimes.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.263-277
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• 2024

The availability of groundwater in the Yeoncheon area, South Korea, was estimated using the distributed hydrological model SWAT-K to calculate recharge rates based on land use and soil distribution. Model calibration and validation results were consistent between observed and simulated streamflows, with coefficients of determination of 0.75~0.97. Calculated groundwater recharge rates varied temporospatially, with lower rates in winter and spring than in summer. Estimated recharge rates were compared with the baseflow index of natural streamflow to assess the validity of estimated recharge amounts. Groundwater development potential was determined by calculating the recharge amount for a 10-year period by statistical frequency analysis, confirming it to be 11.5% of annual precipitation.