• Journal of Korea Water Resources Association
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• v.48 no.3
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• pp.169-183
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• 2015

As a basic work for river restoration, analysis on fluvial geomorphological characteristics is made using past and present data to understand close-to-nature geomorphic status. The Miho and the Naesung Rivers are targets of this study. Fluvial geomorphic variables including valley-floor width, sinuosity, bankfull width, channel gradient, bed material size, bankfull discharge and unit stream power are evaluated with dominant processes. Though common sand-bed rivers with similar catchment area, the Miho and the Naesung Rivers are different in terms of valley-floor width, channel shape variables and dominant processes related with longitudinal location. In addition, analyses on interrelationship among the geomorphological variables are carried. Bankfull width is shown to be proportional to bankfull discharge, as is in a rough agreement with the previous studies. Relationship of bankfull discharge and channel gradient shows meandering and braiding are prevalent in the Miho River, whereas the most of the sub-reaches of the Naesung River fall to braiding. Relationship of channel gradient with width-depth ratio indicates dune-ripple processes are dominant in the Miho River, while the Naesung River shows longitudinal diversity from braiding in the downstream sub-reaches to riffle-pool and plane-bed along the upper ones. Analyses based on the past data on a river in a close-to-nature status are thought to be rather reasonable in comparison with those on the same river in a engineered condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.6
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• pp.1753-1764
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• 2014

Numerical flow simulation models in the riverine environments have been widely utilized for analyzing flow dynamics in various degrees in researches and practical applications. However, most of the simulated results have been validated based on the data from indoor experimental models or very limited in-situ measurements. Therefore, it has been required to more accurately validate the performance of the numerical models in terms of the detailed field observations. In particular, it was also hard to validate the performances of the existing numerical models in the real meandered river channels that encompass more sophisticated flow and geometric structures. Recently, advancements of the modern flow measuring instrumentations such as acoustic Doppler current profilers (ADCPs) enabled us to efficiently acquire the detailed flow field in the broad range of river channels, thus that it became to be possible to accurately validate any numerical models with the field observations. In this study, based on the detailed flow measurements in a actual meandered river channel using ADCP, we validated FaSTMECH model in iRIC in terms of water surface elevation, which is relatively new but began to get highlighted in the research areas. As the validation site, a meandering channel in River Experiment Center of KICT was chosen, which has 6.5 m of width, 0.38m of flow depth, 1.54 m3/s of flow discharge, 0.61 m/s of mean flow velocity, and 1.2 of sinuosity. As results, whereas the FaSTMECH precisely simulated water surface elevation, simulated velocity field in the bend did not match well with ADCP dataset.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.469-479
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• 2006

In order to investigate characteristics of the primary flow and the secondary currents in meandering channels, the laboratory experiments were conducted in S-curved channels with angle of bend, $150^{\circ}$, and sinuosity of 1.52. The experimental conditions was decided varying average depth and velocity. Under these experimental conditions, spatial variations of the secondary currents in multiple bends were observed. The experimental results revealed that the distribution of primary flow in straight section is symmetric without respect to the experimental condition and the maximum velocity line of the primary flow occurs along the shortest path in experimental channel, supporting the result of previous works. The secondary currents in second bend became more developed than those in first bend. Particularly, the outer bank cell developed distinctively and the secondary current intensity was low at the straight section and high at the bends, periodically. Also, the secondary current intensity at the bends was as twice to three times as that at the straight section, and has its maximum value at the second bend. The turbulent flow characteristics of meandering channel was investigated with turbulent intensity of the primary flow and Reynolds shear stress. It was observed that the turbulent intensity is increasing when the velocity deviation of the primary flow is large whereas Reynolds shear stress increases when both the velocity deviation of the primary flow and the secondary current are large.

• Ecology and Resilient Infrastructure
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• v.8 no.4
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• pp.179-193
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• 2021

This study examines the use of satellite images for river classification and determination of stream reach, which is the first priority in the river environment assessment system. In the river environment assessment system used in South Korea, it is proposed to set a stream reach by using 10 or 25 times the width of the river based on the result of river classification. First, river classification for the main stream section of Cheongmi stream was performed using various river-related data. The maximum likelihood method was applied for land cover classification. In this study, Sentinel-2 satellite imagery, which is an open data technology with a resolution of 10 m, was used. A total of four satellite images from 2018 was used to consider various flow conditions: February 2 (daily discharge = 2.39 m³/s), May 23 (daily discharge = 15.51 m³/s), June 2 (daily discharge = 3.88 m³/s), and July 7 (daily discharge = 33.61 m³/s). The river widths were estimated from the result of land cover classification to determine stream reach. The results of the assessment reach classification were evaluated using indicators of stream physical environments, including pool diversity, channel sinuosity, and river crossing shape and structure. It is concluded that appropriate flow conditions need to be considered when using satellite images to set up assessment segments for the river environment assessment system.