• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.232-241
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• 2012

The seasonal changes in phytoplankton species composition, standing crops, dominant species, species diversity and physico-chemical characteristics in the Unmun dam were studied, from August, 2009 to April, 2010. The phytoplanktons of a total of 121 taxa were identified, the composition of phytoplankton community was characterized by a green algae and diatoms, and the quantity composition of standing crops was dominated by diatoms and dinophyceae. The diatoms Aulacoseria granulata and blue-green alga Anabaena planktonica in Summer, Peridinium voltzii in Autumn and Asterionella formosa in Winter to Spring were, especially, prominent. The seasonal changes of the biomass varied from 578 cells $mL^{-1}$ to 12,938 cells $mL^{-1}$, and the maximum algal density was observed in April, Asterionells formosa contributed to 88% of the total cell numbers. The species diversity and richness were highest during autumn, and dominance index was highest in the spring season.

• Korean Journal of Ecology and Environment
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• v.33 no.3 s.91
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• pp.311-318
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• 2000

The purpose of this study was to determine the optimum water intaking depth for water treatment plant based on the changes of phytoplankton distributions in Unmun reservoir. Sampling was carried around of intaking tower near the Dam site at monthly intervals from February to Ocotber in 1998. Total 79 phytoplankton taxa were observed and they were classified into 4 varieties, 75 species within 51 genera. Diatoms were mainly dominated from February to July. However Rhodomonas sp. was a dominant species in August, and Microcystis ichthyblabe in September and October. Cell density of 122,800 cells/mL in October was the highest, and 415 cells/mL in May was the lowest. The pattern of vertical distribution was similar until May; however, the cell density in the epilimnion was much higher than it in the hypolimnion during the periods with the high water temperature over $20^{\circ}C$ since June. The water depths showing over 5,000 cells/mL ranged from the surface to 9m in June, surface to 6m in September, and on the only surface in October. Based on water temperature and phytoplankton vertical distribution, the depth of 6m appeared to be the optimum intaking depth far water treatment plant: 75.4 to 98.0% of phytoplankton cell densities could be avoided and the temperature over $18.3^{\circ}C$ was preserved to prevent cold water damage for rice growth at the water depth during cyanobacterial blooming period in Unmun reservoir.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.165-177
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• 2003

The purpose of this paper is to analyze the behavior and to study the safety evaluation of the Unmun Dam located in Cheongdo-Gun of GyeongBuk Province, Korea. For this purpose, soil analyses including boring data, geophysical surveys were conducted. In this paper, especially many geophysical methods were adopted to configure out the subsurface situation of dam. Applied geophysical methods were: 1) electric resistivity survey, 2) high frequency magnetotelluric (HFMT) survey, 3) ground penetrating radar (GPR) survey, 4) seismic refraction survey, 5) seismic cross-hole tomography survey, and 6) high frequency impedance (ZHF) survey. Each of geophysical surveys were analyzed and joint analyses between geophysical surveys were also performed to deduce the more reliable subsurface information of Dam by using the features and characteristics of each geophysical survey. Since many defects, such as gravel and weathered rock blocks in the dam core, and lots of amounts of leakage, by boring analyses were found, reinforcement by compaction grouting system (CGS) has been conducted in some range of dam. Some geophysical data and data of geotechnical gauges were also used to confirm the effects of reinforcement. Electric resistivity, EM, GPR, ZHF, seismic refraction and seismic tomography surveys show that left side of dam is weak, which means the possibility of existence of gravel, rock block, water and cavities in the core of dam. This result coincides with the boring data. Especially, electric survey after reinforcement shows that even the right side of the dam has been deformed by the strong pressure during the reinforcement itself. As a conclusion, some problems in the dam found. Especially, the dam near spillway shows the high possibility of leakage. It should be pointed out that only the left side of he dam has not a leakage problem. As a whole, the dam has problems of weakness, because of unsatisfactory construction. It is strongly recommended that highly intensive monitoring is required.

• Journal of the Korean Geophysical Society
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• v.6 no.3
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• pp.189-207
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• 2003

The purpose of this paper is to analyze the behavior and to study the safety evaluation of the Unmun Dam located in Cheongdo-Gun of GyeongBuk Province, Korea. For this purpose, soil analyses including boring data, geophysical surveys and monitoring the buried geotechnical gauges, such as pore-pressure gauge, earth-pressure gauge, displacement gauge, multi-layer settlement gauge, leakage flow-meter, were conducted. In addition to these data, numerical analyses of behavior of dam were performed to predict and to compare the data which were obtained from the above methods. Since many defects, such as gravel and weathered rock blocks in the dam core, and lots of amounts of leakage, by boring analyses were found, reinforcement by compaction grouting system (CGS) has been conducted in some range of dam. Some geotechnical gauge data were also used to confirm the effects of reinforcement. Analyses of monitoring the data of geotechnical gauges buried in the dam, such as pore-pressure gauge, earth-pressure gauge, displacement gauge, multi-layer settlement gauge, and leakage flow-meter shows the load transfer of dam and the possibility of hydraulic fracturing. As a conclusion, some problems in the dam found. Especially, the dam near spillway shows the high possibility of leakage. It should be pointed out that only the left side of he dam has not a leakage problem. As a whole, the dam has problems of weakness, because of unsatisfactory construction. It is strongly recommended that highly intensive monitoring is required.

• Journal of Korea Water Resources Association
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• v.56 no.1
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• pp.11-21
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• 2023

This study suggests the drought resilience index as S-day as a means of preparing for the recent extreme drought, allowing for the actual operational identification of each drought countermeasure's priority as well as the vulnerability of water resource facilities to drought. Although each dam's drought measures are unique in this case, the representative examples include adjusting the water supply, linking the functioning of various facilities, and considering emergency capacity. Here, 15 multipurpose dams and water supply dams in Korea were inspected. Under the return period of 20-year drought, most of dams showed stable by adjusting the water supply overall. The measures, however, did not seem to be able to resist a multi-year drought lasting more than two years. Besides, Hoengseong and Anodong-Imha Dam only lasted a year under the 100-year drought return period with other measures. Without the deployment of drought mitigation strategies, it is expected that the Hoengseong Dam, Andong-Imha Dam, Gunwi Dam, Unmun Dam, Daecheong Dam, and Juam Dam would not be able to meet the all water demand for a year under the 20-year drought condition. The ideal capacity for each drought measure was then suggested. Additionally, by increasing or decreasing the current supply contract by 10% in order to account for demand changes resulting from socio-economic instability, the drought response capacity of all 15 dams was re-evaluated. By lowering the supply contract amount by 10%, it was possible to endure a severe drought.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.41-51
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• 2012

Sometimes, there exist many alternatives for doing a SOC project. However, the limitation of the fund requires the determination of investment priority for the alternatives. This may be performed according to the degree of importance of individual alternatives. Especially, the river improvement project at the downstream of dams has complex and various values and this characteristics make it difficult decision-maker to do reasonable determination. This study aims to determine an investment priority of 33 alternatives in the river improvement project at the downstream of dams using PROMETHEE method which has advantages in determining the priority. In this study, we determined evaluation criteria and attributes by considering the functions and objectives of the river improvement project at the downstream of dams. The eigenvector method in AHP was used to estimate the relative importance of evaluation criterion. Based on the estimation, we determined investment priority of 33 alternatives by PROMETHEE method and the priority of alternatives was derived in the order of Juam regulation dam, Unmun dam, Yongdam dam and so on. The results of this study could provide a reasonable standard to the decision-maker for the determination of investment priority of alternatives.