• Journal of Wetlands Research
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• v.18 no.1
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• pp.45-57
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• 2016

Levee safety is being evaluated using one of the several failure causes including overtopping, infiltration and erosion or 1D hydraulic analysis considering physical characteristics of levee in practical engineering works. However, mentioned evaluation methods are not able to consider various failure causes of levee at the same time and to get reliable results where requires the accurate topographic information. This study proposed the flood hazard index which is able to consider several hazard factors involving overtopping, infiltration and erosion risk simultaneously. The index was generated from results of 2D hydraulic analysis reflecting accurate topographic information. The study areas are the confluences of the Nakdong River and two streams(Gamcheon and Hoecheon). Levee safety was evaluated using results based on 2D hydraulic analysis considering riverbed changes of before and after dredging work in the study area. This study will contribute to estimate the reliable safety evaluation of levee where may have hazards during extreme flood events.

• Journal of Wetlands Research
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• v.19 no.4
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• pp.542-550
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• 2017

The estimations of flow characteristics and river-bed erosion or sedimentation are very important for hydraulic structure design, floodplain management, and especially, river management. The objective of the study is therefore to estimate the change of flow characteristics and river-bed change due to a hydraulic structure construction. With 11.65 km study area of the Geum River which are located in downstream of Daecheong Dam, flow characteristics and river-bed change were estimated based on the RMA2 and SED2D model. As the result of the study, the increase of river-bed sedimentation in upstream and river-bed erosion in downstream were occurred by the construction of hydraulic structure.

• Journal of Korea Water Resources Association
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• v.47 no.4
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• pp.307-319
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• 2014

Because of the rapid rising of water related disasters due to the global warming, the extreme design criteria of levee construction for severe flood has been applied in several developed countries such as USA and Netheland. In Korea, the national river restoration projects were carried out on 4 major rivers in recent several years. The projects consisted of riverbed dredge and levee reinforcement, and new construction have caused wide change of river environment. However, concrete countermeasures for levee safety and river management have not been suggested until now. Therefore, this study assesses the levee safety of Yulji levee located in Hoechon, Nakdong Basin, where the Levee Seepage Monitoring System installed. The stability of levee is assessed based on the simulation performed by SEEP/W(2D unsaturated seepage model) and the simulated results are compared with the observed data. The effects of the flood wave and levee shape on the levee safety are investigated through several simulations.

• Journal of Korea Water Resources Association
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• v.50 no.6
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• pp.419-427
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• 2017

In mountainous rivers, the drag force acting on cobbles abundant in the riverbed surface is important in predicting behavior and response of the river. However there is little research for the drag coefficients of cobbles. This paper is to carry out the experiments for drag force of cobble and analyze the relation between the cobble shape and the drag coefficient. The effects of the shape factor on the drag coefficients $C_D$ when the long axis or the short axis of the cobbles are parallel to the direction of flow velocity were analyzed. The coefficient of drag force increased with the nominal diameter Reynolds number $R_{ep}$. The drag coefficients are greater in short axis than long axis. The coefficient of determination of the relation between $C_D$ and $R_{ep}$ is greater in long axis than short axis. This means that the drag forces acting on the irregularly-shaped cobbles depend on the axis. A change of the drag force distribution has brought about the alternative swing of cobbles. For $R_{ep}$ > 12,000, the amplitude of the swing has been increased sharply and especially was greater in short axis than long axis.

• Journal of Environmental Science International
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• v.18 no.2
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• pp.221-230
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• 2009

In this study, a river basin with a lot of measured data such as water level, flow rate, current speed, and sediment rate from the past to now was selected and geometrical shape of a pier was re-analyzed, in order to study the effects of the flow around the pier area as well as the riverbed alternation characteristics. A finite element mesh of the entire river was prepared, and via parameter revision, the section that the pier has influence on was decided, to analyze the shape of the pier using RMA-2 and SED2D-WES models. With regards to the section that the pier has influence on, analysis was done on the four pier shapes, namely circle, square, rectangle, and octagon. The results showed that the shape with the least influence around the pier around is the octagon, followed by circle, rectangle, and square, showing the different geometrical effects that the shapes have on the pier. Furthermore, it was shown that the distribution of sediment concentration had effect from about (+) 110 m of the upstream to about (-) 130 m of the downstream, from the pier installation point. Also, it was shown after analyzing drag forces for different sediment particle distributions that the shape with the greatest drag is the octagon, followed by circle, square, and rectangle.

• Korean Journal of Ecology and Environment
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• v.37 no.4 s.109
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• pp.400-405
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• 2004

Since a large bank-protection works project was undertaken during winter in the middle reaches of the Chikuma, the riverbed structure was drastically altered. In order to assess the short-term impact of bank-protection works on the abundance Pattern of Stenopsyche marmorata (Trichoptera) from spring to early summer, we conducted an investigation on the capture of adults using light traps before and after construction work. The patterns of the daily capture of S. marmorata and the Namely, after construction, the daily catch of adult numbers increased only slightly during the investigation periods. This suggested that the age structure of the S. marmorata larval population had changed in the construction area. Our data suggest that bank-protection projects impact the abundance pattern of adult caddisflies in the river ecosystem.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.485-488
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• 2007

Riverbank filtration is a kind of artificial aquifer recharge for the fresh water supply. By construction of several production wells penetrating the riverbank, surface water withdrawn from the river would pass riverbed. This extracted water is well known to be cooler than surface water in summer and warmer than surface water in winter, showing more constant water temperature. This characteristic of extracted water is applied to geothermal energy utilization. Prediction of the annual temperature variation of filtrated water is the major concern in this study. In Daesan-myeon, Changwon-si, Gyeongsangnam-do, South Korea, riverbank filtration facility has been on its operation for municipal water supply and thermal energy utilization since 2006. Appropriate hydraulic and thermal properties were estimated for flow and heat transfer modeling with given pumping rate and location. With the calibrated material properties and boundary conditions, we numerically reproduced measured head and temperature variation with acceptable error range. In the numerical simulation, the change of saturation ratio and river stage caused by rainfall was calculated and the resulting variation of thermal capacity and thermal conductivity was considered. Simulated temperature profiles can be used to assess the possible efficiency of geothermal energy utilization using riverbank filtration facility. Influence of pumping rate, pumping location on the extracted water temperature will be studied.

• Journal of Environmental Science International
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• v.26 no.12
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• pp.1341-1353
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• 2017

This study aimed to identify the aquatic and riparian factors associated with the presence/absence of the Eurasian otter in the Nakdong river basin, where the species is relatively more abundant than other otter species. Environmental factors and presence records were collected. Geographical Information System technology and chi-square test were used to compare environmental gradients in aquatic and riparian factors between presence and absence sites. Aquatic habitat attributes were evaluated with natural riverside sandbars and channel crossing artificial structures, the ratio of channel width to alluvial plain width, riverbed substrate, and flow diversity. Riverbank characteristics, bank materials, man-made embankment types, and land use/land cover of inland and riverside areas were selected as riparian habitat attributes. Compared to the aquatic attributes, riparian attributes were highly significant when assessing otter presence and absence sites, suggesting that conservation of suitable riparian areas to provide maternity and resting areas for otter species is essential in the Nakdong river basin. None of the aquatic attributes examined were statistically significant when evaluating otter presence or absence. These results indicate that the presence of suitable riparian area for resting and reproduction habitats is more critical to the presence of Eurasian otter than food availability in aquatic areas. To inform implementation of effective conservation actions, broad-scale factors, such as watershed attributes, would be needed to further assess habitat conditions of the Eurasian otter.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.987-995
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• 2013

The purpose of this study is to examine the hydraulic stability of non-toxic revetment technique for eco-friendly design of the domestic river restoration. Recently, instead of the flood control function-oriented river management policy for the engineering efficiency, the improvement of the environmental performance for the ecological river restoration project is implemented. However, the inappropriate hydraulic design criteria of the new revetment technique happen to the economic losses at flood season frequently. The hydraulic stability of the riprap and the block include the banks of rivers, riverbed protection, scour protection and so on. In this study, the high speed experimental channel was developed, which has the maximum velocity of 3.5 m/s, to perform the hydraulic experiments of the block method with non-toxic glue with various conditions to find the critical velocity of the revetment block for the hydraulic stability.

• Journal of Wetlands Research
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• v.19 no.2
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• pp.181-192
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• 2017

Analysis using a numerical model is important to understand the sediment transport mechanism associated with erosion and sedimentation near weirs and other hydraulic structures within riverine systems. The local riverbed change near a hydraulic structure (Gangjeong-Goryong multi-function weir in the Nakdong river) was analyzed in order to examine the effect of hydraulic structures on local bed change. A 2D numerical model (CCHE-2D) was employed to simulate the sedimentation and erosion over a reach (25 km) including the weir. For the calibration and verification of the model, rainfall data from a real event (Typoon 'Ewiniar' in 2006) were used for flow and stage simulation. And the simulated results show a good agreement with the observed data for the whole domain. From the result, it was found that the installation and operation of the weir could aggravate bed changes by typhoon between movable weirs, and which resulted in redistribution of sediment.