• Korean Journal of Ecology and Environment
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• v.46 no.1
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• pp.10-17
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• 2013

History of Instream Flow Incremental Methodology (IFIM) Following the large reservoir and water development era of the mid-twentieth century in North America, resource agencies became concerned over the loss of many miles of riverine fish and wildlife resources in the arid western United States. Consequently, several western states began issuing rules for protecting existing stream resources from future depletions caused by accelerated water development. Many assessment methods appeared during the 1960's and early 1970's. These techniques were based on hydrologic analysis of the water supply and hydraulic considerations of critical stream channel segments, coupled with empirical observations of habitat quality and an understanding of riverine fish ecology. Following enactment of the National Environmental Policy Act (NEPA) of 1970, attention was shifted from minimum flows to the evaluation of alternative designs and operations of federally funded water projects. Methods capable of quantifying the effect of incremental changes in stream flow to evaluate a series of possible alternative development schemes were needed. This need led to the development of habitat versus discharge functions developed from life stage-specific relations for selected species, that is, fish passage, spawning, and rearing habitat versus flow for trout or salmon. During the late 1970's and early 1980's, an era of small hydropower development began. Hundreds of proposed hydropower sites in the Pacific Northwest and New England regions of the United States came under intensive examination by state and federal fishery management interests. During this transition period from evaluating large federal reservoirs to evaluating license applications for small hydropower, the Instream Flow Incremental Methodology (IFIM) was developed under the guidance of the U.S. Fish and Wildlife Service (USFWS).

• Journal of Wetlands Research
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• v.24 no.1
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• pp.52-58
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• 2022

Recently, various efforts and research are being conducted to integrated management of the estuary in Nakdong River. As one of such studies, measurement of opening discharge amount for each floodgate using a three-dimensional fixed ultrasonic flow meter is being conducted, but studies on hydraulic and statistical processing procedures and techniques using actual measurement results for calculating discharge amount by opening remain at the basic level. Therefore, in this study, a data processing technique using three-dimensional fixed ultrasonic flow meter measurement data was developed, the flow coefficient was calculated based on the measured data, and the applicability of the discharge amount calculation formula development was reviewed.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.46 no.1
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• pp.59-69
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• 2013

Temporal and spatial variation in the freshwater region, created by river runoff, of a small bay, caused by the passage of typhoons was examined using a three-dimensional primitive equation model (the Princeton Ocean Model, POM). Numerical experiments were implemented focusing on temporal evolution in the freshwater region in association with typhoon tracks. The model domain covered most of the estuary around the Nakdong River, including Noksan Bay, where river water is periodically released from upstream (Noksan dam). The model showed that the extension of the freshwater region outside of the bay depended strongly on the tracks of typhoons, specifically the associated wind directions and inner flow fields that are accompanied by new clockwise eddies. The model also showed that entrainment from typhoon passage frequently creates salt wedges in the estuary, indicating that organisms in the bay are biologically and chemically influenced with variation in the freshwater region.

• Journal of Korea Water Resources Association
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• v.45 no.3
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• pp.331-347
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• 2012

The downstream of the Nam River Dam is crucial region for long-term water resource planning for Busan and Gyeongnam Province. Thus, the analysis of flow behavior and water quality is necessary for the sustainable surface water management and the control of pollutant source. In this study, the flow field and BOD transport at the downstream of Nam River Dam were analyzed by incorporating 2-D water quality model, RAM4 and 3-D water quality model, WASP with the hydrodynamic model, RAM2 and EFDC, respectively. The application of 2-D flow analysis model, RAM2 showed that velocity distributions at the five transverse sections of the meandering part closely followed the measured values by ADCP, and the flow field and overflow characteristic at the submerged weir showed satisfactory performance compared with the result of 3-D EFDC model. In addition, the BOD concentration field obtained by RAM2-RAM4 coupled modeling was in good agreement with the result by EFDC-WASP model throughout the computational domain. The hydrodynamic characteristic and water quality at the downstream reach of Nam River Dam are mainly influenced by the Dam discharge, and the water quantity is closely related to the water quality control and fishery environment at the lower part of Nakdong River. Therefore, when further quantitative analysis is necessary regarding these issues, 2-D semi-coupled modeling is recommended in terms of computational effectiveness and model application aspect.

• Journal of Korea Water Resources Association
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• v.43 no.10
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• pp.883-891
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• 2010

More recently, there have been significant changes in the forms of channels due to runoff characteristics driven by climate changes and other alterations in basin/channel environments. Particularly, increasing local deposition in major channels is being observed nationwide. Of such phenomena, it is noteworthy that flood-plains show unidirectional growth and lowering of channels within compound channels in the form of a high-flow plain. These changes are supposed to affect management of the river ecology as well as flood control. In this study, the research on channels in Korea confirmed that the phenomenon of local deposition in those channels is actually taking place, rendering a problem to be urgently addressed. Previous studies on bed changes have been focused on low channels based on bed materials distributed over the channels. However, this research has proved that surface-layer deposition of a high-flow plain is closely related with changes in the conditions of ground surfaces and, ultimately, affects the bed of the entire channel as well. According to the intensive research on the condition of the high-flow plain of the mouth of the Han River, the silt deposited in the high-flow plain was the main cause of settlement/growth of vegetation. And this leads to landforming along with woods-forming, disturbing flood control as well as the normal river ecology.

• Water Engineering Research
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• v.3 no.1
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• pp.45-55
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• 2002

The Szentgotthard Flood Protection Project is located in the southeasters part of Austria, very close to the Hungarian border and to the Hungarian town of Szentgotthard situated near the Junction of the rivers Lafnitz and Raab. During heavy rainstorms, this area has always been liable to severe floodings, affecting the town itself and upstream reaches, where major industrial and commercial development is planned. In order to solve these problems, several solutions have been developed by means of a series of model tests performed at the hydraulic laboratory of the Technical University of Graz, Austria. The model was constructed to scales 1:75 (lengths) and 1:25 (heights). This trebled scale allowed greater accuracy in the measurement of discharge depths. The results from the model tests have led to the following proposals: - Construction of a flood relief trough with an inflow section 3.5 km upstream of the junction of the rivers Lafnitz and Raab. - Use of a former river bed for the flood relief trough. - Design of a lowered embankment crest section to pass one-third of the maximum flood flow of the river Lafnitz. - Connection of the flood relief trough to the Lahnbach stream, a tributary of the river Raab.

• 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 Wetlands Research
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• v.17 no.4
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• pp.380-390
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• 2015

In this study, the major 38 tributaries in Nakdong River were monitored for flow rate and water quality in order to understand the characteristics of the watershed and to find improvement plan. The flow rate and water quality for each target tributary were evaluated based on the monitoring data in 2013~2014 using a statistical package SPSS-22.0. In addition, the tributary grouping method was conducted using a $BOD_5$ concentration/flowrate and TP concentration/flowrate monitoring data. The average values of $BOD_5$, $COD_{Mn}$, TP and TOC concentrations in Gumicheon, Gyeonghocheon, Jincheoncheon, Gisegokcheon, Yonghacheon and Yonghocheon located at Nakdong Waegwan and Nakdong Goryung watershed were high and in the grade of III or IV (5~8 mg/L). The Pearson correlation coefficients of TOC with $BOD_5$, $COD_{Mn}$, and TP were greater (r=0.8, p<0.01) than those of the other water quality parameters (12 species). The tributaries with high values of water quality parameters ($BOD_5$ > 3.0 mg/L, TP > 0.1 mg/L) and flowrate (Q > $0.1m^3/sec$) were selected for improving water quality according to the stream grouping method. Five tributaries (Gumicheon, Gisegokcheon, Yonghacheon, Yeongsancheon, Mijeoncheon and Yonghocheon) were classified as Group I, which require polices and plans for water quality improvement.

• Journal of Korean Society on Water Environment
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• v.36 no.5
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• pp.392-404
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• 2020

The focus of this study was to quantify the thermal stratification and analyze the relationship between the stratification structure and the tributaries to understand flow variations in the Paldang Reservoir. The vertical distribution of the temperature and density gradients, and the depth and thickness of the thermocline were quantitatively calculated using a lake physics tool (rLakeAnalyzer) and high-frequency monitoring data. Based on a density gradient of 0.2 kg/㎥/m, the thermocline was formed from mid-May to early-September 2019 and the other periods were weakly stratified or mixed. The thickness of the thermocline was developed until 4.7 m and the depth of the thermocline was formed at a depth of 3 - 6 m at the front of the Paldang Reservoir. During the formation of the thermocline, the Namhangang and Gyeongancheon tributaries with relatively high water temperature (low-density) flowed into the upper layer of the reservoir, and the Bukhangang tributary with low water temperature (high-density) mainly affected the lower layer of the reservoir. This is because the density currents were formed due to the difference in the water temperature of the tributaries. The findings of this study may be used for constructing high-frequency monitoring and quantitative data analyses of reservoirs.

• Journal of Korea Water Resources Association
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• v.56 no.12
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• pp.871-881
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• 2023

This study investigates the geomorphic changes and Bed Relief Index of the river downstream of the Yeongju Dam by Nays2DH, a two-dimensional numerical model, in order to grasp the dynamics of the downstream river while applying various flow patterns such as pulse discharge. It shows that the geomorphic and the bed elevations changes are the largest under the condition of the normalized pulse discharge. The total change in the riverbed is 29.88 m for uniform flow, 27.46 m for normalized hydrograph, 29.63 m for pulse flow and 31.87 m for pulse flow with normalized hydrograph which result in the largest variation in scour and deposition. The Bed Relief Index (BRI) increases with time under conditions of uniform flow, pulse flow and pulse flow with normalized hydrograph. However, BRI increased rapidly until 30 hrs after the peak flow (14 hrs), but decreased from 56 hrs under the condition of normalized hydrograph. Therefore, the condition of normalized hydrograph gives greater dynamics than the condition of a single flood or constant flow, and the dynamics increase downstream than upstream, resulting in an effect on improving the environment of the river downstream of the dam.