• Journal of Korean Society on Water Environment
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• v.36 no.6
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• pp.508-520
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• 2020

Dam reservoirs have been reported to contribute significantly to global carbon emissions, but unlike natural lakes, there is considerable uncertainty in calculating carbon emissions due to the complex of emission pathways. In particular, the method of calculating carbon dioxide (CO2) net atmospheric flux (NAF) based on a simple gas exchange theory from sporadic data has limitations in explaining the spatiotemporal variations in the CO2 flux in stratified reservoirs. This study was aimed to analyze the spatial and temporal CO2 distribution and mass balance in Daecheong Reservoir, located in the mid-latitude monsoon climate zone, by applying a two-dimensional hydrodynamic and water quality model (CE-QUAL-W2). Simulation results showed that the Daecheong Reservoir is a heterotrophic system in which CO2 is supersaturated as a whole and releases CO2 to the atmosphere. Spatially, CO2 emissions were greater in the lacustrine zone than in the riverine and transition zones. In terms of time, CO2 emissions changed dynamically according to the temporal stratification structure of the reservoir and temporal variations of algae biomass. CO2 emissions were greater at night than during the day and were seasonally greatest in winter. The CO2 NAF calculated by the CE-QUAL-W2 model and the gas exchange theory showed a similar range, but there was a difference in the point of occurrence of the peak value. The findings provide useful information to improve the quantification of CO2 emissions from reservoirs. In order to reduce the uncertainty in the estimation of reservoir carbon emissions, more precise monitoring in time and space is required.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1B
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• pp.79-93
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• 2008

Water quality simulations on the Saemangeum inner reservoir have been carried out using EFDC model to understand water quality variations caused by abrupt physical changes due to closing of tidal barrier. According to hydrodynamic simulation, model reproduces not only outer regional dynamics but also inner superelevation very well. Calibration and verification of water quality models accomplished using observed data taken before closing. Also sensitivity tests regarding riverine discharges and tidal flats were done. Due to enlarging of always wet zone caused by super elevation on inner tidal flats, predicted DO decreases at that region as a result of SOD. Moreover shrink of mixing zone after closing of dike causes deteriorating of water quality showing DO as 2 mg/L during summer at Mangyeong and Dongjin estuaries, however it does not spread to middle part of the reservoir. Vertical stratification occurs after closing and shows vertical differences in DO concentration at least 6 mg/L to 7 mg/L in summer season. Most part of the reservoir is getting stratified and it leads to an oxigen deficit zone near bottom.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.840-851
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• 2010

This study analyzed data on the pore water pressure, the ground water level, the horizontal displacement and the resistivity monitoring from instrument system, which is established to evaluate the safety in reservoirs. The pore water pressure in the embankment ranged from $0.035{\sim}1.116kg/cm^2$. The seepage that piping showed, as well as the leakage from the reservoirs are acceptable for the safety management of the reservoir. The maximum horizontal displacement and direction analyzed from the measured inclinometer data gives us very effective information to evaluate the safety in reservoirs. The resistivity monitoring technique, which is obtained on the reservoir crest, is an efficient tool to detect leakage zone. The safety index(SI) was predicted by the resistivity monitoring, and was evaluated to have a safety level of 0.8-1.0 at all reservoirs. Safety evaluations of reservoir through instrument systems are effective when studying the embankment, when the results of the instrument system have been analyzed compositively.

• Korean Journal of Ecology and Environment
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• v.42 no.2
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• pp.221-231
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• 2009

This study was carried out to comparatively identify characteristics of turbid water influence in Imha Reservoir, Soyang Reservoir, and Daecheong Reservoir in Korea. We used 3 years dataset from 2002 to 2004 and analyzed seasonal water quality characteristics, particular parameters in association with turbidity, and light transparency to figure out the trends. All parameters to be used in the study were total phosphate (TP), total nitrogen (TN), chlorophyll-${\alpha}$ (Chl), suspended solids (SS), Secchi depth (SD), conductivity, and verticallight extinction coefficienct($K_d$), euphotic zone ($Z_{eu}$), and critical depth ($Z_p$). All parameters depend on season and watershed. Suspended solids from Soyang Reservoir were usually caused by TP, mainly related to living wastes and agricultures in upper stream. Daecheong Reservoir was influenced by organic matters related to large phytoplankton biomass in summer and inorganic suspended solids by nutrients in the winter. However, in case of Imha Reservoir, turbid water, consisted in silt and clay through heavy precipitation remained in the waterbody to decrease water transparency along with TP and caused the light limitation in winter. Overall results suggest that it was necessary to establish various management programs because the reasons occurring turbidity were varied according to the reservoir circumstances.

• Geosciences Journal
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• v.22 no.6
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• pp.1027-1039
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• 2018

Seismic attributes are often used to identify lithology and evaluate reservoir properties. However, interpretation based only on structural attributes and without knowledge of the Vp/Vs ratio can limit the ability to evaluate changes in heavy oil reservoirs. These limitations are often due to less obvious impedance differences. In order to investigate pieces of evidence of a heavy-oil shaly-sand reservoir from seismic data, besides geochemistry, we studied seismic attributes and characterized the reservoir using seismic stack data and well logging data. The study area was the Muglad rift basin in South Sudan. We conducted a seismic complex analysis to evaluate the target reservoir. To delineate the frequency responses of the different lithological units, we applied the spectral decomposition method to the target reservoir. The most unexpected result was continuous bands of strong seismic reflectors in the target reservoir, which extended across the borehole. Spectral decomposition analysis showed that the low-frequency zone of 25 Hz dominant frequency was consistent with instantaneous attributes. This approach can identify lithology, reveal frequency anomalies, and filter the stacked section into low- and high-frequency bands. The heavy-oil reservoir zones exhibited velocity attenuation and the amplitude was strongly frequency dependent.

• Journal of Environmental Science International
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• v.13 no.4
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• pp.389-401
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• 2004

Seasonal and vertical distribution of water quality were investigated from May 2001 to June 2002 in Kumoh reservoir located nearby Kumi City, Kyungpook. Kumoh reservoir that lost the role of agricultural irrigation is currently of rapid eutrophication. The vertical distribution of DO was observed clinograde with hypolimnetic anoxic zone. T-P concentrations at the surface ranged from 0.008 to 0.152 mgP/L and T-N concentrations ranged from 1.4 to 3.0 mgN/L. The vertical and seasonal variation of T-N was smaller than T-P. DOC concentrations, indicator of organic matter pollution, ranged from 2.8 to 5.4 mgC/L. Apportionment of Total-DOC (T-DOC) indicated that 14% of T-DOC was attributed to Labile-DOC(L-DOC) and the rest was due to Refractory-DOC(R-DOC). The values of TSI(Trophic State Index) ranged between 44 and 52 indicating that Kumoh reservoir is under mesotrophic condition. The results of this study indicate that Kumoh reservoir is likely to be under influence of eutrophication and thus water quality will be aggravated. Therefore, the Kumoh reservoir requires further treatment to improve water quality and a plan of the reusing water resource should be developed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2D
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• pp.335-340
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• 2006

Geology and terrain of Imha basin has a very weak characteristics to soil erosion, so much soil particles flow into Imha reservoir and bring about high density turbid water when it rains a lot. Especially, since the agricultural area of Imha basin is mainly located in river boundary, Imha reservoir has suffered from turbid water by soil erosion. Therefore, it is important to estimate the influence of soil erosion to establish efficient management of water-pollutant buffering zone for the reduction of turbid water. By applying GIS-based RUSLE model, this study can acquire 12.23% that is the ratio of soil erosion in water-pollutant buffering zone and is higher than area-ratio (9.95%) of water-pollutant buffering zone. This is why the area-ratio of agricultural district (27.24%) in water-pollutant buffering zone is higher than the area-ratio of agricultural district (14.96%) in Imha basin. Also as the result of soil erosion in sub-basin, Daegok basin shows highest soil erosion in water-pollutant buffering zone, second is Banbyeon_10 basin and last is Seosi basin.

• Journal of Korean Society on Water Environment
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• v.34 no.5
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• pp.470-486
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• 2018

This study is to investigate the allochthonous load and water quality of a typical river-reservoir, Paldang during spring (March ~ May) of 17 years (2001 ~ 2017). Phosphorus loading from point sources seems to have been reduced by 74 % in the 2010s. As a result, trophic state of the Paldang reservoir, eutrophic during the 2000s, has returned to the lmesotrophic state. Along with decrease in phosphorus concentration, standing crops of algae (Chl.a) decreased, and concentration of biodegradable organic material decreased to the past level. Concentration of total suspended solids has decreased, and it is due to the decrease of phytoplankton standing crops since the mid-2000s. As transparency increased, it is estimated that euphotic area increased by 22 % and euphotic capacity expanded by 27 %. In the river/transition zone of Paldang, concentration of organic matter increases slightly due to algal growth, but concentration of all water quality items decreases in the lacustrine zone. Although algal growth rate revealed positive correlation with concentration of phosphorus, it was insignificant. Algal growth appeared to be dependent on renewal of phosphorus by flow, than either flow rate or phosphorus concentration. The empirical model including inflow phytoplankton concentration fit well with observed values, and indicates the Paldang reservoir is greatly influenced by allochthonous loads.

• Journal of Korean Society on Water Environment
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• v.28 no.1
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• pp.26-37
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• 2012

Multi-dimensional hydrodynamic and water quality models are widely used to simulate the physical and biogeochemical processes in the surface water systems such as reservoirs and estuaries. Most of the models have adopted the Eulerian grid modeling framework, mainly because it can reasonably simulate physical dynamics and chemical species concentrations throughout the entire model domain. Determining the optimum grid cell size is important when using the Eulerian grid-based three-dimensional water quality models because the characteristics of species are assumed uniform in each of the grid cells and chemical species are represented by concentration (mass per volume). The objective of this study was to examine the effect of grid-size of a three dimensional hydrodynamic and water quality model (EFDC) on hydrodynamics and mass transport in the Saemangeum Reservoir. Three grid resolutions, respectively representing coarse (CG), medium (MG), and fine (FG) grid cell sizes, were used for a sensitivity analysis. The simulation results of numerical tracer showed that the grid resolution affects on the flow path, mass transport, and mixing zone of upstream inflow, and results in a bias of temporal and spatial distribution of the tracer. With the CG, in particular, the model overestimates diffusion in the mixing zone, and fails to identify the gradient of concentrations between the inflow and the ambient water.

• Journal of Korea Water Resources Association
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• v.40 no.8
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• pp.601-615
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• 2007

A selective withdrawal method has been widely used to control the quality of water released from a stratified reservoir and to improve downstream ecosystem habitats. Recently, several existing reservoir withdrawal facilities have been modified to accommodate multi-level water intake capabilities in order to adapt the impact of long-term discharge of high turbidity flow. The purpose of this study was to assess the effect of selective withdrawal method on the control of downstream turbidity and its impact on water quality in Daecheong Reservoir. A laterally integrated two-dimensional hydrodynamic and eutrophication model, which was calibrated and validated in the previous studies, was applied to simulate the temporal variations of outflow turbidity with various hypothetical selective withdrawal scenarios. In addition, their impacts on the algal growth as well as water quality constituents were analyzed in three different spatial domains of the reservoir The results showed that the costly selective withdrawal method would provide very limited benefits for downstream turbidity control during two years of consecutive simulations for 2004-2005. In particular, an excessive withdrawal from the epilimnion zone for supplying upper layer clean water resulted in movement of turbidity plume that contained high phosphorus concentrations upward photic zone, and in turn increased algal growth in the lacustrine zone.