• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1039-1049
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• 2015

The inflow estimation at large multipurpose dam reservoir is carried out by considering the water balance among the discharge, the storage change during unit time interval obtained from the observed water level near dam structure and area-volume curve. This method can be ideal for level pool reservoir but include potential errors when the inflow is influenced by the water level slope due to backwater effects from upstream flood inflows and strong wind induced by typhoon. In addition, the other uncertainties arisen from the storage reduction due to sedimentation after the dam construction and water level noise due to mechanical vibration transmitted from the electric power generator. These uncertainties impedes the accurate hydraulic inflow measurement requiring exquisite hydrometric data arrangement for reservoir waterbody. In this study, the distributed hydrologic model using UBC-3P boundary setting was applied and its feasibility was evaluated. Finally, the modeling performance has been verified since the calculated determination coefficient has been in between 0.96 to 0.99 after comparing with observed peak inflow and total inflow at Namgang dam reservoir.

• Korean Journal of Agricultural Science
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• v.36 no.1
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• pp.99-109
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• 2009

This study was performed to evaluate the effect of increasing instream flow at Nonsancheon stream of Nonsan city by securing water storages in upstream reservoirs; Ge-ryong, Gyoung-cheon, Dae-dun, and Tab-jeong. The paralleled and cascaded upstream reservoir operations for 8 storage securing scenarios were considered to simulate daily streamflows at Nonsan station. Using Tab-jeong reservoir water storage, the DAWAST model's parameters were determined, and the verified result showed Nash-Schcliffe's coefficient of 0.666. Instream flows were analyzed to supply maximum $59.85Mm^3$ on an annually average from upstream reservoir storage securing scenarios. The storage securing set of 2 m heightened Ge-ryong, 5 m Dae-dun, and 1 m Tab-jeong showed that the additional secured water storages were $17.132Mm^3$ and instream flow at Nonsan station was increased to $2.183m^3/s$, 2 times of present condition.

• Journal of Soil and Groundwater Environment
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• v.8 no.1
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• pp.48-56
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• 2003

A geophysical conductivity logging technique has been adopted to determine hydraulic constants using a simplified physical model that depicts the borehole condition. An experiment has been made by monitoring the conductivity change within the model hole using borehole environment water and incoming-outgoing water of different salinity, under the state of constant flow rate by maintaining balance between inflow and outflow. Conductivity variation features were observed that depended on flow rate, salinity contrasts between fluid within the hole and incoming-outgoing fluid, and density contrasts between fluid conductivity within the hole and incoming fluid. The results of the experiment show the uniform change of fluid conductivity within the hole with time, a fairly good correlation between the flow rate and the conductivity change rate. The geophysical conductivity logging technique can be an efficient tool for determining hydraulic constants if the model equation is verified by henceforward experiments.

• Journal of Korea Water Resources Association
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• v.49 no.3
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• pp.227-239
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• 2016

This study is to estimate Surface Energy Balance Algorithm for Land (SEBAL) daily spatial evapotranspiration (ET) comparing with eddy covariance flux tower ET in Seolmacheon mixed forest (SMK) and Cheongmicheon rice paddy (CFK). The SEBAL input data of Albedo, Land Surface Temperature (LST), Normalized Difference Vegetation Index (NDVI) from Terra MODIS products and the meteorological data of wind speed, and solar radiation were prepared for 2 years (2012-2013). For the annual average flux tower ET of 302.8 mm in SMK and 482.0 mm in CFK, the SEBAL ETs were 183.3 mm and 371.5 mm respectively. The determination coefficients ($R^2$) of SEBAL ET versus flux tower ET for total periods were 0.54 in SMK and 0.79 in CFK respectively. The main reason of SEBAL ET underestimation for both sites was from the determination of hot pixel and cold pixel of the day and affected to the overestimation of sensible heat flux.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.4
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• pp.1389-1400
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• 2013

This study developed an operating rule curve (ORC) for multipurpose water supply (irrigation and environmental water) in heightened agricultural reservoir. Among the 20 reservoirs in improvement project of agricultural reservoir dam heightening, the 4 representative reservoirs (Ungyang, Gungchon, Yongam and Unam) were selected for the study according to the analysis of statistical characteristics. Available environmental water supply amounts during irrigation and non-irrigation periods, which is the range from release restricted water level to high water level were estimated by water balance analysis using reservoir operation model. Reliability, resiliency and vulnerability criteria for water system performance were used to assess the multiple water supply capacity. The ORC was presented as the percentile rank for the daily reservoir water level from the results of reservoir operation using the past couple of decades weather data. The water levels for each percentile were divided into 3 buffer sections representing drought (5~25%), normal (25~75%), and flood (75~95%) year to operate the heightened agricultural reservoir with ORC.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.3
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• pp.63-73
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• 2013

The objectives of this study were to develop a hydrologic simulation model to estimate surface drainage for irrigation districts consisting of paddy and protected cultivation, and to evaluate the applicability of the developed model. The model consists of three sub-models; agricultural supply, paddy block drainage, and protected cultivation runoff. The model simulates daily total drainage as the sum of paddy field drainage, irrigation canal drainage, and protected cultivation runoff at the outlets of the irrigation districts. The agricultural supply sub-model was formulated considering crop water requirement for growing seasons and agricultural water management loss. Agricultural supply was calculated for use as input data for the paddy block sub-model. The paddy block drainage sub-model simulates paddy field drainage based on water balance, and irrigation canal drainage as a fraction of agricultural supply. Protected cultivation runoff is calculated based on NRCS (Natural Resources Conservation Service) curve number method. The Idong reservoir irrigation district was selected for surface drainage monitoring and model verification. The parameters of model were calibrated using a trial and error technique, and validated with the measured data from the study site. The model can be a useful tool to estimate surface drainage for irrigated districts consisting of paddy and protected cultivation.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.385-385
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• 2011

유역 스케일의 실제 증발산량을 산정하는 대표적인 방법으로 관측 강우량과 유출량의 관계로부터 증발산량을 간접적으로 추정하는 물수지(water balance)법, 증발력과 토양수분량의 변화량 (soil moisture accounting)을 고려한 유역 수문모델링을 이용하는 방법, 잠재 증발산량과 실제 증발산량간 보완관계식(complementary relationship)을 이용하는 방법 등이 있다. 물수지법은 관측치를 기반으로 한다는 점에서 신뢰도가 높다고 할 수 있으나, 기본적으로 유역 저류량의 변화를 무시하기 때문에 연 단위와 같이 긴 시간 스케일에 적용 가능하고 작은 시간 스케일에는 적용성이 떨어진다. 유역 수문모델링을 이용하는 방법은 기상, 토양 및 식물 조건을 모두 고려하는 방법으로 유역의 불균질성을 반영할 수 있고 일 단위 등의 비교적 작은 시간 스케일에 대해서도 증발산량을 산정할 수 있는 장점이 있으나, 수많은 입력자료가 필요하며 간접적인 추정 방식이기 때문에 모형의 정확한 검증과 상당한 숙련도가 뒷받침되어야 한다. 잠재 증발산량과 실제 증발산량간 보완관계식을 이용하는 방법은 토양이나 식물 등의 지표면 조건에 대한 정보를 필요로 하지 않으며 단지 기상자료만을 이용하는 방법으로 적용하기 쉽다는 장점이 있으나 잠재 및 실제 증발산량간의 보완피드벡 매카니즘이 존재한다는 가정이 수반되어 있어 적용시 이를 입증해야 하는 어려움이 있다. 이 처럼 각기 장단점을 가진 여러 방법으로 증발산량을 산정하고 있지만, 각 방법 간의 연결고리를 맺는 연구는 심도 있게 수행되지 못하고 있다. 따라서 본 연구에서는 상기 언급한 증발산량 산정 방법 중 보완관계식을 이용하는 방법과 유역수문모형에 의한 방법 간의 연관성을 평가하고자 하였으며, 이를 위해 충주댐 상류유역에 대해서 SWAT-K에 의한 증발산량 모의치가 보완관계식을 따르는 지에 대해 고찰하였다. 모의기간동안 계산된 잠재 및 실제 증발산량을 습윤지수(humidity index)에 따라 함께 도시해본 결과, 연 단위의 경우에는 건조할수록 잠재 증발산량은 점차 커지고 실제 증발산량은 작아지는 것으로 나타나 보완관계가 성립하였고, 월 단위 경우에는 강우에 비해서 비교적 증발산량이 큰 5, 6월에 가장 명확한 관계가 보여 늦은 봄과 초여름에 보완적 관계가 뚜렷하게 발생하는 반면에 동절기에는 보완관계가 성립하지 않는 것으로 나타나는 등 분석 단위기간별로 보완관계의 성립여부를 판별할 수 있었다.

• Journal of the Korean Association of Geographic Information Studies
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• v.11 no.1
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• pp.20-30
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• 2008

This study is to analyse the hydrological behavior of agricultural reservoir using SWAT model. For the upsteam watershed of Gongdo water level gauge station in Anseongcheon watershed, the streamflows at 2 reservoir (Gosam and Geumgwang) locations and Gongdo station were simulated with reservoir inclusion and exclusion. The daily water surface area and storage have been calculated considering the stage-storage curve function of the reservoir. Afterwards, the reservoir operation module in SWAT was modified from original module in SWAT for daily reservoir discharge simulated by water balance equation. Model validation results were Nash-Sutcliffe model efficiency coefficients value of 0.55, root mean square error value of 2.33 mm/day. On the other hand, the simulation results of two reservoir exclusion were Nash-Sutcliffe model efficiency coefficients value of 0.37, root mean square error value of 2.91 mm/day. The difference of Nash-Sutcliffe model efficiency coefficients between the simulation results of two reservoir inclusion and exclusion at Gongdo station was 0.18. This is caused by the storage and release operation of agricultural reservoirs for the runoff occurred at 2 reservoir watersheds.

• Journal of the Korean Association of Geographic Information Studies
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• v.18 no.1
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• pp.156-169
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• 2015

This study was to evaluate the RCP climate change impact on hydrological components in the Imha-Dam watershed using SWAT(Soil and Water Assessment Tool) Model. The model was calibrated for six year(2002~2007) and validated for six year(2008~2013) using daily observed streamflow data at three watershed stations. The overall simulation results for the total released volume at this point appear reasonable by showing that coefficient of determination($R^2$) were 0.70~0.85 and Nash-Sutcliffe model efficiency(NSE) were 0.67-0.82 for streamflow, respectively. For future hydrologic evaluation, the HadGEM3-RA climate data by scenarios of Representative Concentration Pathway(RCP) 4.5 and 8.5 of the Korea Meteorological Administration were adopted. The biased future data were corrected using 34 years(1980~2013, baseline period) of weather data. Precipitation and temperature showed increase of 10.8% and 4.9%, respectively based on the baseline data. The impacts of future climate change on the evapotranspiration, soil moisture, surface runoff, lateral flow, return flow and streamflow showed changes of +11.2%, +1.9%, +10.0%, +12.1%, +18.2%, and +11.2%, respectively.

• Journal of Korea Water Resources Association
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• v.46 no.12
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• pp.1141-1155
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• 2013

A number of studies have been performed to analyze climate change impacts of water resources system. In this study, a coordinated dam operation is compared with an existing operation strategy for coping with projected future runoff scenarios. GCMs (Global Circulation Models) and the LARS-WG downscaling method was used to project future climate scenarios. The water balance model called abcd was employed to estimate future runoff scenarios. The existing dam operation comes from the national dam construction guideline, which is called the "level-operation method." The alternative coordinated dam operation are constructed as a linear programming using New York City rule for refill and drawdown seasons. The results of annual total inflow in future is projected to decrease to 72.81% for Andong dam basin and 65.65% for Imha dam basin. As a result of applying future runoff scenarios into the dam operation model, the reliability of coordinated dam operation, 62.22%, is higher than the reliability of single dam operation, 46.55%. Especially, the difference gets larger as the reliability is low because of lack of water. Therefore, the coordinated operation in the Andong & Imha dams are identified as more appropriate alternative than the existing single operation to respond to water-level change caused by climate change.