• Korean Journal of Ecology and Environment
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• v.46 no.2
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• pp.215-224
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• 2013

We clarified the background for establishment of vegetation by comparing the spatial distribution maps of vegetation and substrate on a gravel bar in the Bangtae stream located on Inje-gun of Gangwon-do, the central eastern Korea. The total vegetation coverage was higher in the interior and lower in the marginal parts of the gravel bar. Spatial distribution of vegetation on the longitudinal section of the gravel bar tended to be arranged in the order of shrub, subtree, and tree dominated vegetation types from the front (upstream) toward the rear (downstream) parts. Coverage of the herbaceous plants was higher in the central and rear parts and lower in the front and right parts of the gravel bar. Vegetation height was higher in the rear part and became lowered as move toward the front part. Substrate was distributed in the order of boulder, gravel, sand, and boulder from the front toward the rear parts. Ordination of stands based on vegetation data was arranged in the order of annual plant, perennial herb, shrub, and tree dominated vegetation as move from the right to the left parts on the axis I. Species richness was higher in the order of Pinus densiflora community, Phragmites japonica community, Salix gracilistyla community, Fraxinus rhynchophylla community, annual plant dominated vegetation, and Prunus padus for. padus community based on the species rank-abundance curve. The order based on the Shannon's index was some different; diversity of Phragmites japonica community and Salix gracilistyla community, which showed higher dominance degree, were low differently from species richness. In conclusion, it was evaluated that the gravel bar newly established toward the upstream and vegetation dynamics of the gravel bar seemed to follow ecosystem mechanisms of succession. As were shown in the above results, the Bangtae stream corresponded to the upstream and thereby particle size of substrate was big. Therefore, they move by rolling and are accumulated for the upstream. Vegetation types were arranged in the order of woodland, shrub-land and grassland from the rear toward the front parts of the gravel bar and thereby reflected the formation process of the bar. However, the gravel bar is disturbed frequently by not only the running water but also the suspended sand as the dynamic space. Such disturbances cause habitat diversity and consequently led to high biodiversity.

• Proceedings of the Korea Water Resources Association Conference
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• 2002.05a
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• pp.3-16
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• 2002

This article describes some of the recent and on-going research developments of the author at Colorado State University. Advances in the field of sedimentation and river mechanics include basic research and computer modeling on several topics. Only a few selected topics are considered here: (1) analytical determination of velocity profiles, shear stress and sediment concentration profiles in smooth open channels; (2) experiments on bedload particle velocity in smooth and rough channels; (3) field measurements of sediment transport by size fractions in curved flumes. In terms of computer modeling, significant advances have been achieved in: (1) flashflood simulation with raster-based GIOS and radar precipitation data; and (2) physically-based computer modeling of sediment transport at the watershed scale with CASC2D-SED. Field applications, measurements and analysis of hydraulic geometry and sediment transport has been applied to: (1) gravel-bed transport measurements in a cobble-bed stream at Little Granite Creek, Wyoming; (2) sand and gravel transport by size fraction in the sharp meander bends of Fall River, Colorado; (3) changes in sand dune geometry and resistance to flow during major floods of the Rhine River in the Netherlands; (4) changes in hydraulic geometry of the Rio Grande downstream of Cochiti Dam, New Mexico; and (5) analysis of the influence of water temperature and the Coriolis force on flow velocity and sediment transport of the Lower Mississippi River in Louisiana. Recent developments also include two textbooks on "Erosion and Sedimentation" and "River Mechanics" by the author and state-of-the-art papers in the ASCE Journal of Hydraulic Engineering.

• Journal of the Korean Geotechnical Society
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• v.26 no.11
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• pp.5-15
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• 2010

Debris flow is defined as water mixture flow with wide range of large size soil particles such as rock, gravel and sand. Localized heavy rain, derived from abnormal weather, results in the debris flow which generally occurs in summer, especially during and after rainy season and typhoon. This study focuses on the characteristics of impact force of the debris flow with different gravels and gravel mixtures by model experiment. Based on measured experiment results, it is found that the impact force derived by debris flow is mot proportional to the amount of dry material mixture, but depends on the particle size distribution of the debris flow.

• International Journal of Railway
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• v.6 no.2
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• pp.53-58
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• 2013

In this study, cyclic triaxial tests were carried out with the coarse granular materials used in Korean railway infrastructure (reinforced trackbed, gravel of transition zone, upper subgrade of railway) and Young's modulus for the target materials in small strain level were suggested. And the result of elastic modulus suggested in this study is expected to be effectively applied to dynamic analysis of the railway embankment structure using similar material, since the grain size distributions and unit weight of the material tested in this study are specified in Korean Railway Design Criteria.

• Journal of Environmental Science International
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• v.8 no.6
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• pp.677-684
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• 1999

To investigate size distribution and metallic elements of surface sediments in Hampyong Bay, the southwestern coast of Korea, sedimentological and geochemical studies on surface sediments are carried out. The surface sediments of Hampyong Bay are classified into gravel, muddy sandy gravel, gravelly muddy sand, gravelly sandy mud, mud facies in accordance with areal characteristics. The coarse sediments are distributed on the subtidal zone along the main tidal channel and southeast intertidal flat of Hampyong Bay. On the other hand, the fine sediments are dominated in northeast and west intertidal flat of Hampyong Bay. Most metallic elements except for Ba in the sediments are closely interrelated with fine sediments and mutually with each element. Ba is maybe related with sandy sediments and inversely related with carbonate contents. Normalized by Al content, the sediment do not show any remarkable metal enrichments influenced by resonable artificial or environmental factors.

• Asian Journal of Turfgrass Science
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• v.13 no.4
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• pp.181-190
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• 1999

This study was carried out to survey green system, area, green slope, green turfgrass variety, green section, and particle size of green construction materials, and to investigate and evaluate the characteristics of Design and Construction in Korean golf course green for improving the quality of Korean golf course into that of the international golf course held international tournament. The results were as follows. 1. The greens of 129 Korean golf courses consisted of 2(two) green system and 1(one) green system. 2(two) green system was 50.8%, 1(one) green system was 40.7%, and 1+2 green system was 8.5% of them. 2. In 48 Korean golf courses, the green area of 2(two) green system was mostly 400~$600\m^2$(56.5%) and the green area of 1(one) green system was mostly 600~$800\m^2$(47.8%). In 48 Korean golf courses, 1.5~3% green slope appeared the highest frequency(50.0%) and the next was 3~5%(29.4%). 3. Penncross variety was the highest frequency(71.2%). The next was mixed variety (Penncross+Crenshaw, Penn A-1, Pennlinks, or Penneagle/SR 1020+SR 1019) and the frequency of mixed variety was 7.6%. 4. In 48 Korean golf courses, 70~80cm total thickness of green appeared the highest frequency(36.1%), 10~20cm thickness of green mixed sandy layer appeared the highest frequency(43.6%), and 10~20cm thickness of green coarse sandy layer appeared the highest frequency(55.6%). 0~10cm thickness of green gravel layer appeared the highest frequency(67.6%), 20~30cm thickness of green drain layer appeared the highest frequency(52.8%), and 20~30cm width of green drain layer appeared the highest frequency(44.4%). Below 1mm sand diameter used in green mixed sandy layer appeared the highest frequency(46.2%), below 2mm or over 2mm sand diameter used in green coarse sandy layer appeared the highest frequency(31.4%). 20~40mm coarse gravel diameter used in green gravel layer appeared the highest frequency(43.2%) and 0~20mm fine gravel diameter used in green gravel layer appeared the highest frequency(65.8%). 20~40mm gravel diameter used in green drain layer appeared the highest frequency(64.1%).

• Journal of Korea Water Resources Association
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• v.42 no.8
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• pp.619-629
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• 2009

The objective of this study is to estimate bed-resistance in gravel-bed rivers using the equivalent roughness height($k_s$). We calculated the friction factor(f) with the measured data from 8 domestic gravel-bed rivers and investigated the size distributions of the bed materials. The averaged $k_s$ in each cross-section, which is determined under the hypothesis that the vertical velocity distribution follows the logarithmic law, is compared with the reach $k_s$ which is calculated with the cumulative grain diameter distribution curve of bed materials. Moreover, the applicability of existing formulae, such as Strickler type equations, is examined by comparing with Manning's n value converted from the $k_s$. According to the results, the reach $k_s$ proves to be a good indicator of representative characteristic of bed materials in a reach, and the Manning's n based on the reach $k_s$ is appropriate for practical estimation of the bed-resistance, for RMS errors between calculated and measured Manning's n is less than 0.003. The correlation between the $k_s$ and specified bed-material size($D_i$) is very low, so it is difficult to select a proper one among the existing empirical equations.

• Journal of the Korean earth science society
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• v.41 no.1
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• pp.19-30
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• 2020

To understand the impact of typhoons on Gamji gravel beach Taejongdae in Busan, we carried out beach profiling using a VRS-GPS system and a Drone photogrammetry for the typhoons 'Kong-rey' invaded in October 2018 and 'Danas' in July 2019. In addition, grain sizes are analyzed to investigate the overall distribution pattern of gravels on the beach, and the beach topography is surveyed periodically to confirm the recovery rate of the beach. Grain-size analysis reveals that mean gravel sizes, in general, become finer from -6.2Φ to -5.4Φ towards the east in the seashore line direction. Variation in mean sizes is obviously observed in the cross-shore direction. Gravels in the swash zone are relatively fine about -4.5Φ in size and equant in shape, whereas the coarse and oblate gravels ranged from -5Φ to -6Φ are found in the berm. Gamji gravel beach particularly has two lines of berms: a lower berm situated facing beach and an upper berm about 10 m landward. After the typhoon Kong-rey passed by, about 1.4 m of severe erosion in upper berm occurred, and the berm eventually disappeared. On the backshore of the upper berm about 50 cm of erosion took place so that the elevation became lower. However, tangible erosion was not observed in the lower berm. When typhoon Danas hit, rated as mild storm, both upper and lower berm were eroded out. However, about 50 cm of deposition occurred only in the backshore. Only three days later, the new lower berm was formed, meaning that sedimentation rate must be high. This result indicates that Gamji gravel beach is recovered very fast from erosion caused by the typhoons when it is under the fair-weather condition even though beach morphology changes dramatically in a short period of time. Gravel beach is estimated to be or evaluated very resilient to typhoon erosion.

• Korean Journal of Environment and Ecology
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• v.32 no.6
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• pp.591-602
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• 2018

Clithon retropictus has been designated as an endangered wildlife Class II due to its high value as a biological indicator species capable of judging environmental quality such as salinity, water flow, and ground conditions. However, basic research on its physiological and ecological characteristics is still lacking. As such, this study intended to examine the impact of environmental conditions such as salinity and soil particle size on the size and density of Clithon retropictus at the Yeoncho river estuary. The investigation of the salinity, which is a key variable that affects the distribution of organisms in the estuary, showed that Clithon retropictus could grow at a salinity ranging from 0#x2030; (freshwater) to 25‰ (brackish water). The coarse gravel (19-75mm) tended to increase nearer the upper stream (under the Yeoncho weir), while the proportion of particles smaller than sand (less than 19mm) increased toward the downstream. The population and the size of the individuals decreased rapidly in the downstream where water stagnated near the Yeoncho weir, and the salt water joined. The results indicated that Clithon retropictus had a high tolerance to salinity, but the adaptability was weaker toward the extremes since the population, and the size tended to decrease as the salinity increased. The correlation analysis revealed that both salinity and soil particle size affected the population and individual size. The correlation between the individual size and salinity was -0.242 (P <0.01), indicating that the size decreased with increasing salinity. The correlation between individual size and coarse gravel having a particle size of 19mm or more was 0.420 (P <0.01), indicating that the size increased with increasing the particle size.

• Journal of The Geomorphological Association of Korea
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• v.20 no.3
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• pp.1-14
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• 2013

This study aims to investigate the formation and sedimentary environment including formative period, grain composition and climate change from loess-paleosol sequence deposited on a gravel bed of river terrace in the Jincheon Basin, Chungbuk Province. The Jincheon section consists downward of a surface layer, loess-paleosol sequence, transitional layer I, transitional layer II and gravel bed. It can be suggested from the OSL age dating that the sequence was deposited during MIS 6 to 4. The sequence can be divided into four horizons based on the variation in the magnetic susceptibility values. Grain size analysis reveals that the sequence indicates similar properties of grain size to loess deposits in Korea and especially, the Y values in the sequence are lower than those in the loess and paleosol horizons in the Chinese Loess Plateau and similar to those in the Red Clay in the Chinese Loess Plateau and Xiashu loess in the lower reaches of the Yangtze River. These Y values in the sequence can be attributed to the remote source and/or experience of intensive weathering process after deposition in the Korean Peninsula.