• Korean Journal of Agricultural Science
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• v.50 no.3
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• pp.331-347
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• 2023

The downstream submergence damages caused during the flood season in 2020, around the Yongdam-dam and five other sites, were analyzed using related dam management data. Hourly- and daily-data were collected from public national websites and to conduct various analyses, such as autocorrelation, partial-correlation, stationary test, trend test, Granger causality, Rescaled analysis, and principal statistical analysis, to find the cause of the catastrophic damages in 2020. The damage surrounding the Yongdam-dam in 2020 was confirmed to be caused by mis-management of the flood season water level. A similar pattern was found downstream of the Namgang- and Hapcheon-dams, however the damage caused via discharges from these dams in same year is uncertain. Conversely, a different pattern from that of the Yongdam-dam was seen in the areas downstream of Sumjingang- and Daecheongdams, in which the management of the flood season water level appeared appropriate and hence, the damages is assumed to have occurred via the increase in the absolute discharge amount from the dams and flood control capacity leakage of the downstream river. Because of the non-stationarity of the management data, we adapted the wavelet transform analysis to observe the behaviors of the dam management data in detail. Based on the results, an increasing trend in the discharge amount was observed from the dams after the year 2000, which may serve as a warning about similar trends in the future. Therefore, additional and continuous research on downstream safety against dam discharges is necessary.

• Korean Journal of Environment and Ecology
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• v.20 no.4
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• pp.391-399
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• 2006

The population dynamics of Zacco koreanus in the upstream and downstream of Hoengseong Lake, Korea were investigated from April to October 2005. As the result of a comparison of variations regarding the time of I koreanus populations, it was confirmed that downstream was a place to remain compared to upstream Also the b value, assessed by Length-weight relationship in upstream and downstream, were $3.21{\sim}3.35,\;and\;2.94{\sim}3.37$, respectively indicating the fish in downstream had better than upstream. Additionaly condition factor(K) of each population in upstream and downstream were $0.0292{\sim}0.0693\;and\;-0.0165{\sim}0.0499$, respectively, K value in upstream lower than downstream. On the other hand, the maximum-growth value$(L_{\infty})$ calculated by von Bertalanffy's growth model in upstream and downstream were 279.7mm and 303.9mm, respectively, indicating that the potential-growth ability of population in downstream was higher than population in upstream. Therefore, Z. koreanus population in upstream became worse based on matters of age structure, Length-weight relationship, and von Bertalanffy's growth model. These results are considered to show the change of the physical environment by the constructing of Hoengseong Dam.

• Korean Journal of Environmental Biology
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• v.33 no.2
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• pp.223-229
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• 2015

Pre-monsoon dynamics of zooplankton community were investigated in the downstream of the Gagok stream flowing into the East Sea of Korea. Monthly sampling was carried out to collect zooplankters at five sites in the stream during the period between April and July 2014. Dissolved oxygen contents exceeded $7.0mg\;L^{-1}$ all the time. Water temperature was in a range of 15.7 to $24.9^{\circ}C$ and pH 7.4 to 8.8, respectively. A total of 75 taxa consisted of 36 species of rotifers, 16 species of cladocerans, 16 species of copepods, four kinds of aquatic insects, two kinds of decapods and one nematod was occurred. One species of marine copepod and one cladoceran, and one species of brackish rotifer and one copepod distributed at the station located in the stream mouth. Zooplankton abundance showed to vary from 42 to 4202 individuals $m^{-3}$ due to the explosion of aquatic insects and Alona sp. at site 2 located in the downstream in April. Heavy rainfall during the monsoon period seems to decrease the zooplankton abundance caused by diffusion and drifting to the sea. Species diversity indices were generally high between 1.2~2.3 and were recorded to be high at the downstream throughout the study period. With the zooplankton dynamics, the influence of the input of sea waters into the stream seemed to be confined to some hundred meters of the stream mouth facing the East Sea.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.2
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• pp.260-269
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• 2000

Oil-film flow visualizations and three-dimensional flow measurements have been conducted in the downstream region of a butterfly-type valve used in air-conditioning systems, with the variation of a disk open angle. The flow visualizations in the flow symmetry plane show that there are a pair of counter-rotating separation/recirculation zones as wall as two jet-like near-wall flows. These flow disturbances are strongly depends on the disk open angle. Based on the flow visualization, a qualitative flow model is suggested in the near-field and downstream region of the valve disk. For a small disk open angle, the mean velocities and turbulent intensities have relatively small values in the near-field of the valve disk, but they do not show uniform distributions even in some downstream region. With an increment of the disk open angle, mean velocity variations and turbulent intensities are greatly increased in the immediate downstream region, but uniform distributions are quickly resumed as departing from the valve disk. The mass flow rate remains nearly constant for the disk open angles less than 30 degrees, meanwhile it strongly depends on the disk open angles between 45 and 75 degrees. The pressure loss is found to be about zero for the disk open angles less than 45 degrees, but is substantially increased for those larger than 75 degrees.

• Journal of Korean Society on Water Environment
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• v.24 no.2
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• pp.156-163
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• 2008

This study was to introduce a methodology of ecological health assessment for efficient management and to provide some diagnostic results of the survey. We evaluated ecological health assessment at five sampling locations of Sikjang Mountainous Stream using the index of biological integrity (IBI) and Qualitative Habitat Evaluation Index (QHEI) during May - October 2006. The health condition, based on the IBI model, averaged 32 and varied from 27 to 37 depending on the sampling sites. Thus, the stream health was judged as "good" to "fair" conditions. IBI values showed slight differences between upstream and downstream sites. Whereas, QHEI values varied from 75 (fair condition) to 196 (excellent condition) and QHEI at St. 4~5, indicating the downstream reach had significantly lower than the headwater site (St.1). Regression analyses also showed that QHEI values had a linear decrease from the headwater to downstream. This result indicated that habitat quality was rapidly degradated by human influence. Overall, data of IBI and QHEI suggested that the stream health was maintained well in the present but the habitat and biological quality were partially degradated in the downstream. So, the human interference should be minimized to protect the downstream environment.

• Journal of Environmental Science International
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• v.17 no.11
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• pp.1295-1305
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• 2008

This study aims at the analyze of unsteady downstream flow due to dam failure along dam failure scenario and applied to Yeoncheon Dam which was collapsed August 1st 1999, using HEC-RAS simulation model. The boundary conditions of this unsteady flow simulation are that dam failure arrival time could be at 02:45 a.m. August 1st 1999 and failure duration time could be also 30 minutes. Downstream 19.5 km from dam site was simulated for unsteady flow analysis in terms of dam failure and non-failure cases. For the parameter calibration, observed data of Jeonkok station were used and roughness coefficient was applied to simulation model. The result of the peak discharge difference was 2,696 to $1,745\;m^3/sec$ along the downstream between dam failure and non-failure and also peak elevation of water level showed meanly 0.6m difference. Those results of these studies show that dam failure scenarios for the unknown failure time and duration were rational because most results were coincident with observed records. And also those results and procedure could suggest how and when dam failure occurs and downstream unsteady flow analyzes.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.3
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• pp.95-105
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• 2018

Understanding the composition of the dam inflow can improve the efficiency of dam operation considering the seasonal characteristics. Hydrograph analysis is one of the methods to identify the characteristics of dam inflow. In addition, baseflow separation on the dam inflow can be affected by anthropogenic influences depending on dam locations. In this regard, the objectives of this study are 1) to analyze yearly and monthly baseflow contribution to the dam inflow and 2) to compare the baseflow contribution to the inflow in dams located upstream and downstream of the watershed. The result shows that the estimated baseflow index was smaller in the upstream dams compared to the downstream dams. Discharge from the upstream water infrastructure including dams and reservoirs can be a part of inflow into the downstream water infrastructure. Based on this scenario, the discharge regulated from the upstream dam could lead to overestimation of baseflow contribution to inflow into the downstream dam. We expect that the results from this study elucidate the role and function of dams and hence, contribute to the efficient operation of dams located in the upstream and the downstream of the watershed.

• Journal of Korean Society on Water Environment
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• v.34 no.2
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• pp.202-209
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• 2018

The purpose of this study was to analyze the correlation between the effluent of a sewage treatment plant (STP) and the adjacent stream located downstream of the STP in Nakdong River. Flow and water quality data, such as BOD, COD, SS, T-N, and T-P data, for 12 STPs and adjacent downstream monitoring stations in the main stream and tributaries of Nakdong River were collected from 2012 to 2015. As a result of correlation analysis between river flow and water quality at the river water quality measurement point, COD, SS, and T-P were correlated positively with the river flow rate at 6, 8, and 6 points, respectively. As a result of analyzing the water quality of sewage treatment plant effluents and downstream streams, BOD and COD were correlated at 2 and 3 points, respectively. T-N showed a positive correlation at 9 points, and 7 of them had a strong positive correlation, indicating that sewage treatment effluent had a large effect on downstream streams. In this study, we found that the correlation between the river flow rate and the water quality factors (COD, SS, TP) was high at river water measurement points, and the sewage treatment plant effluent was correlated with the T-N value of adjacent streams.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.933-943
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• 2001

Using a semi-circled blunt body model, the geometrical effects of injection hole on the turbine blade leading edge film cooling are investigated. The film cooling characteristics of two shaped holes (laterally- and streamwise-diffused holes) and three cylindrical holes with different lateral injection angles, 30°, 45°, 60°, respectively, are compared with those of cylindrical hole with no lateral injection angle experimentally and numerically. Kidney vortices, which decrease the adiabatic film cooling effectiveness, appear on downstream of the cylindrical hole with no lateral injection angle. At downstream of the two shaped holes have better film cooling characteristics than the cylindrical one. Instead of kidney vortices, single vortex appears on downstream of injection holes with lateral injection angle. The adiabatic film cooling effectiveness is symmetrically distributed along the lateral direction downstream of the cylindrical hole with no lateral injection angle. But, at downstream of the cylindrical holes with lateral injection angle, the distribution of adiabatic film cooling effectiveness in the lateral direction shows asymmetric nature and high adiabatic film cooling effectiveness regions are more widely distributed than those of the cylindrical hole with no lateral injection angle. As the blowing ratio increases, also, the effects of hole shapes and injection angles increase.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.423-425
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• 2001

The Proper Orthogonal Decomposition (POD) technique was applied to investigate the effects of Reynolds number and the characteristics of the organized motions or coherent structures as a function of downstream position from x/D=2 to 6 in a turbulent axisymmetric shear layer at Reynolds numbers of 78,400, 117,600, and 156,800. Data were collected simultaneously using the 138 hot-wire probe used by Citriniti and George (2000). The POD was then applied to a double Fourier transform in time and azimuthal direction of the double velocity correlation tensor. The lowest azimuthal mode for all POD modes, which dominated the dynamics at x=D = 3 in the previous experiments, dies off rapidly downstream. This is consistent with a trend toward homogeneity in the downstream evolution, and suggests that some residual value may control the growth rate of the far jet. On the other hand, for the higher azimuthal modes, the peak shifts to lower mode numbers and actually increases with downstream distance. These mixing layer data, normalized by similarity variables for the mixing layer, collapse at all downstream positions and are nearly independent of Reynolds numbers.