• Journal of Korean Society on Water Environment
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• v.33 no.1
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• pp.51-62
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• 2017

The purpose of this study is to evaluate on the applicability of Load Duration Curve (LDC) method using Maintenance of Variance Extension types 2 method and sampling data for efficient total maximum daily loads at the Nakbon-A unit watershed in Korea. The LDC method allows for characterizing water quality data such as BOD, TOC, T-N and T-P in this study at different flow regimes(or quarters). BOD usually exceeded the standard value (exceedance probability 50%) at low flow zone. On the other hand, TOC, T-N, T-P usually exceeded the standard value at dry and low flow zone. Seasonally all water quality variables usually exceeded the standard value at Q1(Jan-Mar) and Q2(Apr-Jun) zones. Improvement of effluent control from wastewater treatment plants are effective to improve BOD and T-P.

• Journal of The Geomorphological Association of Korea
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• v.24 no.1
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• pp.13-24
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• 2017

This study analyzes altitude changes of riverbed at 6 bridges in the upper and lower reaches of Yeongju Dam in Naeseong River, from 2009 to 2016 just before and after the dam construction. For 5 years from November 2010 to December 2015 when the dam was under construction, approximately 0.091m of the riverbed altitude in average more than twice before the dam construction was lowered, because of the effects of riverbed excavation for riverside maintenance in the upper reaches and transport limitation of flow and sediment by the dam in the lower reaches. Between November 2009 and December 2016 when the dam was in pre-construction and post-construction stages, respectively, the most sites in this study in the upper and lower reaches showed lowering in the riverbed altitudes. On the other hand, the riverbed around Hoeryongpo closed to the river mouth seems to be influenced by channel changes in Nakdong River rather than by the dam construction.

• Journal of Korea Water Resources Association
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• v.52 no.spc2
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• pp.777-789
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• 2019

The purpose of this study is to evaluate changes in water quality and aquatic ecosystem health by additional dam release of stream maintenance flow from multipurpose dams in Han river basin ($34,148km^2$) using SWAT (Soil and Water Assessment Tool). The period of additional release was spring (April to June) and autumn (August to October) to evaluate the changes with the data of aquatic ecosystem health survey. The amount of additional release was set proportional to the present dam release, and the maximum release amount was controlled not to exceed the officially notified stream maintenance flow from dam. The 10 percent to 50 percent additional releases showed that the stream water quality (T-N, $NH_4$, T-P, and $PO_4-P$) concentrations except $NO_3-N$ decreased in spring while increased in autumn period. Using the stream water quality results and applying with Random Forest algorithm, the grade of aquatic ecosystem health index (FAI, TDI, and BMI) was improved for both periods especially in the downstream of basin. This study showed that the additional release of stream maintenance flow was more effective in spring than autumn period for the improvement of water quality and aquatic ecosystem.

• Journal of the Korean Society of Hazard Mitigation
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• v.1 no.3 s.3
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• pp.93-102
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• 2001

In this study, the characteristics of river bed profile fluctuation are become possible to be used effectively in future estimation of Taehwa river general development plan through analysis and examination according to the effects of sediment protection weir located in the area of the estuary of Taehwa river's main channel using HEC-6 model. The flow conditions needed in analysis of the characteristics of river bed profile fluctuation refer the conditions of flow which secures 95 days in a year, flood flow, and design flood examined in the estimation of Taehwa river maintenance basic plan. First, in analysis result of river bed variation range, there is no significant variation in upstream section from Samho-gyo while there are the more active erosion and sedimentation as the more flow in downstream from Samho-gyo. Next, from the result of the capacity of sediment transfer, it is analyzed that sediment transfer capacity in the area of estuary of Taehwa river has no significant difference in before and after removal of the sediment protection weir when design flood flows while it is estimated that the more flow, the bigger sediment transfer capacity. Therefore, it is thought that the installation of a suitable hydraulic structure at the lowest point of Dong-chun tributary joins from the downstream of Taehwa river can be a good device to reduce the accumulation of sediments at the lowest point of Taehwa river considering the reduction plan of sediment inflow caused by removal of the sediment protection weir.

• Proceedings of the Korean Society of Environment and Ecology Conference
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• 2003.10a
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• pp.1-21
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• 2003

I introduce the Flexible Dam Operation (FDO) and some of sediment control techniques In dams which are implemented as trials to avoid or reduce environmental impact of dams on the downstream reaches. The FDO is a dam management method to improve river environment in the downstream reaches by means of the flushing flow, the maintenance flow and so on utilizing a vacant portion of capacity for flood control without interrupting prime flood control function during the rainy/typhoon season. It Is suggested by the guideline of the FDO that EDO should be implemented regularly after the trial for about three years. The basic conception of the FDO is described here. The example of excavation of deposited sediments in check dams and placement of sand ana gravel immediately downstream of the dams and the example of coordinated sediment flushing are described as some of sediment control techniques in dams. Now they are at the stage of experiment and trial. Therefore, it is important to increase examples and establish the technical methodology and the environmental evaluation method for them.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.10
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• pp.517-529
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• 2020

Various facilities in the river working in a complex interdependence network result in both desired and adverse effects. Among these, the weir crossing the river continuously acts in various ways, such as securing river maintenance flow and water level during dry-period, and rising flood level during rainy period. Until now, weir planning was only limited to flood mitigation management. Recently, the demand for securing river environment functions is increasing. Therefore, the necessity for an environmental flow has emerged. Nevertheless, there is no analysis and evaluation of the ecological functional aspects applying the environmental flow when planning facilities. Therefore, this study aimed to develop and systematize an assessment method that considers not only flood control but also river environment. Environmental flow was applied to the weir named Dondaet-bo and hydraulic analysis was conducted for each retention, demolition, and re-installation case. Also, this research was conducted to minimize the impact on the surrounding river facilities and flood assessments from previous perspectives were performed. The study result demonstrated a plan to reinstall the weir as a natural riffle. Through this study, it is expected that the flood control and environmental functions of rivers can be secured in combination.

• Journal of Wetlands Research
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• v.22 no.3
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• pp.217-224
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• 2020

Waterlogging and unintended lake formation become the main problem in some parts of the world. Starting from 1989, the waterlogging problem was observed in the farmland of the Jarso community of Konso Woreda adjacent to the Segen River in Ethiopia. Therefore, the objectives are determining the extent and causes of unintended lake formation using GIS/RS in addition to a preliminary field survey to mitigate the problem. The analysis of satellite images revealed that over the years invasion of the irrigable land by unwanted water had increased, as, in 1989, the size of the wetland area was about 8 Km²; in 2000 the size of the un-intended lake was only 8.23 ㎢. Alarmingly the size of the lake increased to 19.68 Km² in 2014. Silting up of Weir and changing the flow of River Segen and Human Intervention and changing the natural flow of River Yanda were the main causes of this unwanted prolonged water-logging. The ecological and social environment has been degrading as the people of the waterlogged area have been experiencing some settlement and losing their land. Another problem encountered was flooding from River Barka and invasion of the farmland. Sediment control best management practices (BMPs) i.e, Removal of sediment, providing sandbags and well-scheduled maintenance; Changing the junction point of Yanda and Segen River were suggested for the long-term and short term possible remedial measures. Gabion retaining wall on the bank of the Segen River to the face of Barka River was suggested to protect the farmland from flooding.

• Journal of Korea Multimedia Society
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• v.21 no.12
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• pp.1431-1438
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• 2018

In this paper, we proposed a river water level detection and tracking of the river or dams based on image processing system. In past, most of the water level detection system used various water sensors. Those water sensors works perfectly but have many drawbacks such as high cost and harsh weather. Water level monitoring system helps in forecasting early river disasters and maintenance of the water body area. However, the early river disaster warning system introduces many conflicting requirements. Surveillance camera based water level detection system depends on either the area of interest from the water body or on optical flow algorithm. This proposed system is focused on water scaling area of a river or dam to detect water level. After the detection of scale area from water body, the proposed algorithm will immediately focus on the digits available on that area. Using the numbers on the scale, water level of the river is predicted. This proposed system is successfully tested on different water bodies to detect the water level area and predicted the water level.

• Journal of Environmental Science International
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• v.22 no.5
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• pp.571-580
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• 2013

In this study, compared with the result of water surface elevation and water velocity on the establishment of river maintenance basic plan and result of HEC-GeoRAS based GIS, and after use the result of water surface elevation and velocity were observed in the Han stream on Jeju island, analysis 2 dimensional stream flow. the lateral hydraulic characteristics and curved channel of the stream were analyzed by applying SMS-RMA2 a 2 dimensional model. The results of the analysis using HEC-RAS model and HEC-GeoRAS model indicated that the distribution ranges of water surface elevation and water velocity were similar, but the water surface elevation by section showed a difference of 0.7~2.18 EL.m and 0.63~1.16 EL.m respectively, and water velocity also showed differences of maximum 1.58m/sec and 2.67m/sec. SMS-RMA2 analysis was done with the sphere of Muifa the typhoon as a boundary condition, and as a result, water velocity distribution was found to be 1.19 through 3.91 m/sec, and the difference of lateral water velocity in No. 97 through 99 the curved channel of the stream was analyzed to be 1.59 through 2.36 m/sec. In conclusion it is anticipated that the flow analysis of 2 dimension model of stream can reflect the hydraulic characteristics of the stream curved channel or width and shape, and can be applied effectively in the establishment of river maintenance basic plan or management and designing of stream.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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• pp.383-394
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• 2013

A sedimentation basin is used to remove suspended sediments which can cause abrasive and erosive wear on hydraulic turbines of hydropower plants. This sediment erosion not only decreases efficiency of the turbine but also increases maintenance costs. In this study, the three-dimensional numerical simulations were carried out on the overseas hydropower project. The simulations of flow and suspended sediment concentration were obtained using FLOW-3D computational fluid dynamics code. The simulations provide removal efficiency of a sedimentation basin based on particle sizes. The influence of baffles on the flow field and the removal efficiency of suspended sediments in the sedimentation basin has been investigated. This paper also provides the numerical simulations for sediment-induced density currents that may occur in the sedimentation basin. The simulation results indicate that the formation of density currents decreases the removal efficiency. When a baffle is installed in the sedimentation basin, the baffle provides intensive settling zones resulting in increasing the sediments settling. Thus the enhanced removal efficiency can be achieved by installing the baffle inside the sedimentation basin.