• Journal of Korean Society of Water and Wastewater
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• 제36권4호
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• pp.239-248
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• 2022

The prediction of algal bloom is an important field of study in algal bloom management, and chlorophyll-a concentration(Chl-a) is commonly used to represent the status of algal bloom. In, recent years advanced machine learning algorithms are increasingly used for the prediction of algal bloom. In this study, XGBoost(XGB), an ensemble machine learning algorithm, was used to develop a model to predict Chl-a in a reservoir. The daily observation of water quality data and climate data was used for the training and testing of the model. In the first step of the study, the input variables were clustered into two groups(low and high value groups) based on the observed value of water temperature(TEMP), total organic carbon concentration(TOC), total nitrogen concentration(TN) and total phosphorus concentration(TP). For each of the four water quality items, two XGB models were developed using only the data in each clustered group(Model 1). The results were compared to the prediction of an XGB model developed by using the entire data before clustering(Model 2). The model performance was evaluated using three indices including root mean squared error-observation standard deviation ratio(RSR). The model performance was improved using Model 1 for TEMP, TN, TP as the RSR of each model was 0.503, 0.477 and 0.493, respectively, while the RSR of Model 2 was 0.521. On the other hand, Model 2 shows better performance than Model 1 for TOC, where the RSR was 0.532. Explainable artificial intelligence(XAI) is an ongoing field of research in machine learning study. Shapley value analysis, a novel XAI algorithm, was also used for the quantitative interpretation of the XGB model performance developed in this study.

• Korean Journal of Ecology and Environment
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• 제41권3호
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• pp.382-394
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• 2008

The objective of this study was to analyze temporal trends of water chemistry and spatial heterogeneity between the dam site (Daecheong Reservoir, S1) and the downstream (S2$\sim$S4) using water quality dataset (obtained from the Ministry of Environment, Korea) during 2000$\sim$2007. Water quality, based on eight physical and chemical parameters, varied largely depending on the years, sampling sites, and the discharge volume. Conductivity and nutrients (TN and TP) showed a decreasing trend in the downstream (S4) rather than the dam site during the monsoon. Spatial variation increased toward downstream (S4) from Daecheong Reservoir (S1). Also, BOD and COD increased toward downstream. Because of input of nutrient and pollutant nearby S1, lentic ecosystem in monsoon, BOD and COD were slightly increased. whereas relatively decreased in S4, lotic ecosystem in monsoon, by dilution effect of nutrient and pollutant by discharge from upper dam, S1. Spatial variation of SS increased toward downstream (S4) by the side of Daecheong Reservoir (S1). Based on the dataset, efficient water quality management in the point source tributary streams is required for better water quality of downstream. Monthly characteristics of DO showed the lowest value in the monsoon that tend to increase water temperature. DO was lowest in October at S1 because turbid water, input to the Daecheong Reservoir in the monsoon affect to the postmonsoon period. In contrast, water temperature increased toward summer monsoon, in spite of some differences showed between S1 and S4 environment. Overall, the characteristics of water quality in downstream region have close correlation with discharge amount of Daecheong Reservoir. Thus, those characteristics can explain that discharge control of upper dam mainly affect to the water quality variation in downstream reach.

• Journal of Korean Society of Forest Science
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• 제23권1호
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• pp.29-33
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• 1974

U-Reuk, a laureate musician in the days of King Jin-Heung, Silla Dynasty, built the Eui Rim Reservoir about 1,400 years ago. This was one of the oldest man-made reservoir. The embankment of the reservoir collapsed by the clumsy artificial drainage on August 19, 1972 when the heavy rainfall of 462 mm/day caused a dangerous overflow of the reservoir. The result of the study on the mystic ancient embankment techniques are as follows: 1. Sandy loam derived from the weathering of granite which is the most widely distributed rock type in the area, was used in the embankment. Large size logs (embankment core) of 30-50 cm in diameter were buried lengthwise along the embankment. 2. The six stocks of Pinus densiflora, 3 stocks of Quercus acutissima, 1 stock of Quercus variabilis and 1 stock of Popolus maximowiczii, altogether 11 stocks are identified. Forest types in the nearby area during the days of the reservoir construction seem to be includde a considerable number of Pinus densiflora, Quercus and Populus species. 3. The angle of repose of the earth materials is taken into account during the embankment. On top of the embankment double layers of clay (20-30 cm indepth) were spread and consolidated. Layer of litter of 20-40 cm in deep covered on the clay layer of the embankment completely, and another layer of clay was consolidated over the litter. Finally, a layer of stones of 10-30 cm in diameter and clay (yellow soil layer) toped the embankment. 4. At the lower part of the embankment clay layer was thicker and became thinner as it goes upwards. At every layer, soil was consolidated and burned. When embankment was completed, it was covered evenly with heavy clay, and finally it was topped with general soil. 5. The heavy clay layer on the inner slope of the embankment showed gray phenomena and litter remained raw humus layer. The clay layer functioned as rubber in the water, and raw humus layer prevented water from seepages. Thus, the embankment was solidly built in this way. 6. The ancient embankment techniques used soils conveyed from nearby area taking the angle of repose into account. Once embankment was completed, clay and litter layers were added to have a plasticity and to withstand the water pressure. 7. It is an excellent technique that the reservoir was constructed with least labor for maximum effects while the recent embankment techniques requires a large amount of labor.

• ALGAE
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• 제18권4호
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• pp.355-360
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• 2003

A Gram (-), rod-shaped bacterium in size of 1.6-2.8 $\times$ 0.4 μm was isolated from a eutrophic reservoir, which exhibited growth-inhibiting effect against a bluegreen alga (Anabaena cylindrica). This isolate showed positive reactions for catalase and oxidase, and optimal conditions of 35-40°C and pH 9.0. This isolate was designated AC-1 in this manuscript. In a mixed-culture of A. cylindrica and AC-1, their growth patterns were inversely correlated and the bluegreen algal vegetative cells completely disappeared within 24-36 hours. AC-1 showed similar lytic activity in natural water as in an artificial medium. The lytic activity of AC-1 was dependent on the photosynthetic activity of A. cylindrica. When observed under phase contrast microscope, the isolate lysed vegetative cells of A. cylindrica in scattered state in a liquid medium, whereas heterocysts have not been lysed.

• Proceedings of the Korea Water Resources Association Conference
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• 한국수자원학회 2008년도 학술발표회 논문집
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• pp.400-404
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• 2008

댐 군 연계운영을 위한 기존의 많은 최적화 모형은 경제성에 기반을 둔 단일 목적 함수를 가정함으로써 현실과는 동떨어진 결과를 도출하곤 하였다. 따라서 보다 현실적인 최적화 모형이 되기 위해서는 실제 운영과정을 모사할 수 있도록 적절한 초기 가중치를 부여하여 모형을 구축하고, 상충되는 목적간의 절충안으로 파레토 프런티어(Pareto-frontier)를 제시할 수 있는 다중목적 의사결정 기법이 요구된다. 본 연구의 목적은 댐 군 연계 운영을 위한 최적화 모형으로 소개된 CoMOM(Coordinated Multi-reservoir Operating Model)의 다중목적함수에 적합한 초기 가중치를 도출할 수 있는 시스템을 제안하는 것이다. 본 연구에서는 최적화 모형에 적합한 가중치를 결정함에 있어 댐의 초기저수량과 미래의 예상 유입량과 같은 수문 조건을 감안할 필요가 있음에 주목하였다. 이것은 초기저수량과 미래에 예상되는 유입량이 작을 경우 가급적 저수에 중점을 두고, 그 반대일 경우는 발전방류에 주안점을 두는 것이 바람직하다는 사실에서 추정해 볼 수 있는 가정이다. 따라서 댐의 초기 저수량 조건과 유입량 시나리오의 다양한 수문 조건별로 가장 적합한 가중치를 찾아본 후, 수문 조건을 입력요소로, 최적 가중치를 출력요소로 갖는 신경망 모형을 활용해서 수문 조건에 적합한 가중치를 예측할 수 있는 절차를 제안한다. 이 과정에서 최적 가중치를 도출하는 것이 관건이 될 수 있는데, 이를 위해 전승목 (2008)등이 제안한 DEA기반 순위결정 절차를 활용해서 최선의 파레토 최적해와 이에 대응되는 가중치를 찾아 이를 신경망 모형의 출력요소 값으로 활용하였다. 본 연구에서 제안하는 신경망 모형은 임의의 수문 상황에 대해 이에 적합한 CoMOM의 초기 가중치를 결정해 줌으로써 CoMOM과 같은 최적화 모형의 가중치 선정에 따르는 어려움을 극복하는 데 도움이 될 수 있을 것으로 기대된다.

• Journal of the Korean Society of Environmental Restoration Technology
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• 제9권6호
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• pp.63-77
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• 2006

The research aim is to classify biotope types of rural eco-villages designed by ministry of environment and analyze landscape ecological characteristics of them. This information would provide information on eco-villages' potential and specific needs to improve landscape ecological structure of eco-villages. Two eco-villages, designated by ministry of environment, in Yoocheon-ri and Sanduk-ri were selected and the landscape ecological metrics used in this study were Area, Shannon diversity index, Shape index, Distance index. The results are as follows. 1) There were five biotope types in large-scale classification, 13 biotope types m Sanduk-ri and 9 biotope types in Yoocheon-ri in middle-scale classification, 31 biotope types in Sanduk-ri and 24 biotope types in Yoocheon-ri in small-scale classification. 2) In the case of area, artificial biotope types, such as artificial forest, agricultural irrigation canal, wet paddy, dry paddy and residential area, covered more than 80% of total area. However, natural biotope types, such as natural forest, river, reservoir, covered just more than 10% of total area. In details, an orchard (26.69%) was the dominant biotope type, followed by artificial forest (19.10%) in Sanduk-ri and the first most abundant biotope type was artificial forest (49.71%), followed by wet paddy (15.95%) in Yoocheon-ri. 3) The result of Shannon diversity index indicated that Sanduk-ri (2.158) had more heterogeneity landscape, rather than Yoocheon-ri (2.051). 4) In the case of shape index, road (13.09) had more complex and irregular shape than either agricultural irrigation canal (3.35) or artificial forest (2.46) in Sanduk-ri. Road (6.52) was also the most irregular biotope shape, followed by river (5.70) and agricultural irrigation canal (4.78) in Yoocheon-ri. 5) Mean Nearest-neighbour Distance (MND) was smallest in wet paddy and dry paddy biotope types in the two study area, suggesting that these biotope types were concentrated within these study areas. From the result, this research suggested information to protect and improve biotopes of eco-villages in the landscape ecological terms. To achieve this improvement plan, there should be strong support by ministry of environment and local governments.

• Journal of the Korean Institute of Gas
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• 제26권5호
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• pp.1-9
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• 2022

Selection of a suitable artificial lift is important in terms of efficient operation and economics for oil production. In general, process of well design includes the selection of artificial lift, but the oil recovery could be enhanced by use of hybrid system combined with two types of artificial lift method according to reservoir condition for oil production. Electric submersible pump (ESP), as a presentative artificial lift method, is a manner for supplying the pressure in the lower part of oil well by using of a multi-stage centrifugal pump with an electric energy. However, there is a disadvantage that has a limit to the application period because of mechanical defection on ESP. Accordingly, it is possible to reduce the shutdown time of production well by applying the ESP/Gas lift hybrid system, which is to switch to a gas lift when an ESP is defective. This study describes the effect of ESP/gas lift hybrid system compared with ESP method for a onshore horizontal well locating in the of Permian basin, USA. As a result of study, ESP/gas lift hybrid system could make more effective productivity than ESP method. Also, we quantitatively predicted how much economic benefit would be obtained when the hybrid system was applied in the production well.

• Journal of the Korean association of regional geographers
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• 제13권2호
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• pp.187-200
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• 2007

This study look into the 3 stages which is distinguished by the usage of human in Man-Kyeong river. 'A nature based usage stage' is acknowledge the river itself and used only the tributary and built reservoir in a small scale from ancient to 1910s. 'A human based usage stage' is built the large scale reservoir at upper stream area and make the artificial waterway from 1920s. And the main stream is remodeled to protect the flood and get the agricultural land. 'A human and nature integration stage' is the main stream has a role not only the spill way but also clean water for inhabitants does together with river. The role and meaning of river is given newly. The development of technique and increase the need of the human is required the change in the role and meaning of river. The river is natural existence as it is, but the meaning and role is given by the human. Also it accompanied the change of the landscape in neighbor region. The natural river is controled the human life in the past, but it changed to social existence which is given the role and meaning by the human now.

• Journal of the Korean Institute of Gas
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• 제22권6호
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• pp.90-103
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• 2018

This paper presents the development of two ANN models which can predict an optimum production rate by controlling choke size in oil well, and gas injection rate in gas-lift well. The input data was solution gas-oil ratio, water cut, reservoir pressure, and choke size or gas injection rate. The output data was wellhead pressure and production rate. Firstly, a range of each parameters was decided by conducting sensitive analysis of input data for onshore oil well. In addition, 1,715 sets training data for choke size decision model and 1,225 sets for gas injection rate decision model were generated by nodal analysis. From the results of comparing between the nodal analysis and the ANN on the same reservoir system showed that the correlation factors were very high(>0.99). Mean absolute error of wellhead pressure and oil production rate was 0.55%, 1.05% with the choke size model, respectively. And the gas injection rate model showed the errors of 1.23%, 2.67%. It was found that the developed models had been highly accurate.

• Korean Journal of Environmental Biology
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• 제30권1호
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• pp.15-25
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• 2012

From April to November 2009, we performed field investigation to survey the characteristics of fish fauna and fish community structure inhabited in Yongdam reservoir in the upper Geumgang, which is changed into flat-water zone from flow-water zone by blocking the continuity by the gigantic submerged weir built in the upstream of Geumgang. 15 species belonging to 8 families were collected from natural habitat (St. 1) where its natural characteristics is well preserved, and 11 species were korean endemic fish species. 24 species belonging to 10 families were collected at the down region of Yongdam dam (St. 3), which might be affected by the change of water environment due to the dam, and 11 species were korean endemic fish species. On the other hand, 20 species belonging to 7 families were collected inside Yongdam reservoir (St. 2) which is changed into flat-water zone from flow-water zone by the dam reservoir, and 6 species were korean endemic fish species. In the dam reservoir, due to Yongdam dam built in the upper Geumgang, the original flow-water zone fish such as $Acheilognathus$ $koreensis$, $Pseudopungtungia$ $nigra$, $Coreoleuciscus$ $splendidus$, and $Gobiobotia$ $macrocephala$ were disappeared, and instead, the kinds of fish habitating in the flat-water zone tend to increase rapidly, such as $Carassius$ $auratus$, $Opsarichthys$ $uncirostris$ $amurensis$, $Hemiculter$ $eigenmanni$, $Zacco$ $platypus$, and $Lepomis$ $macrochirus$. Relative abundance of the insective fish was 66.7% at St. 1, 40.0% at St. 2, and 54.2% at St. 3. In order to preserve endemic fish species and aquatic ecosystem, it is desirable to minimize the artificial installation in the upper river, such as a large scale dam which can affect the habitat and if inevitable, it is required to prepare preservation measures when building facilities.