• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1B
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• pp.53-57
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• 2012

This study presents a numerical model that is capable of simulating the evolution of mining pit in a stream. The numerical model is based on the quasi-steady assumption that the flow is steady with time-dependent morphological change. This hypothesis is valid due to the fact that the stream morphology changes over a long period compared with the time of flow change. Before applications, numerical experiments are carried out with two total load formulas such as Engelund and Hansen's (1967) and Ackers and White's (1973). It is found that the use of Engelund and Hansen's formula reproduces evolution of mining pit best compared with simulated profiles in Parker (2004). Then, the model is applied to two laboratory experiments in the literature. In general, the numerical model simulates properly the evolution of mining pit in laboratory open-channels. However, it is found that the model does not reproduce head-cutting, propagating upstream, and under-estimates the wave of the bed, propagating downstream, after finishing the re-fill of the mining pit.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.2
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• pp.137-153
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• 2013

In order to assess the effects of ecosystem and landscape in around spur dikes, this study had carried out monitoring on the changes of ecosystem and morphologic characteristics in around spur dikes that had been settled in bend of Youngcheon River. The study site was a short reach with length 190m, spur dikes were installed in March, 2008. Monitoring of the site had been started in May 2008 and had been completed September 2011. The results are as follow ; 1) Spur dikes that were installed for channel stabilization are performing effectively hydraulic functions at flooding time. 2) Spur dikes that were installed in water colliding front of river bend brought about sediment deposition between those and formed pools around front of those. Therefore, it was verified to create various physical characteristics in the aspect of channel topography and flow consequently. 3) The survey results that was carried out in October 2008 showed to emerge 25 species of plant, 9 species of fish and 17 species of benthic macroinvertebrates, but the survey results in October 2010 showed to emerge 74 species of plant, 12 species of fish and 19 species of benthic macroinvertebrates. In particular, plant species that emerged in 2011 increased about three times more than those in 2008.

• 한국해양학회지
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• v.26 no.4
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• pp.332-339
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• 1991

The sedimentation pattern in Namhaepo Bay, a macrotidal coastal embayment of western Korea, was investigated by means of analysing high-resolution seismic profiles, sediment samples, and tidal currents. Recent sediments up to 20 m which overlie the irregular surface of the acoustic basement. The sediments consist mainly of sandy silt and silt; the mean grain size of these sediments ranges from 4 to 5.5 phi, showing a shoreward-fining distribution pattern. This distribution pattern agrees are largely reversed during ebb, with a maximum velocity of 39 cm/sec. The calculated shear velocity of the tidal currents at sea bed ranges from 0.5 to 3.3 cm/sec during flood and from 0.7 to 2.5 cm/sec during ebb. The mean values of these velocities exceed the critical shear velocity for the silt particles. The data suggest that the tidal currents play an important role in the transportation and deposition of sediments in the bay and the surface topography of the sea floor is largely deter-mined by tidal sedimentation.

• The Journal of the Korea Contents Association
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• v.13 no.5
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• pp.485-492
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• 2013

The point sand bars of Hahoi Village on Nakdong River have undergone considerable changes including fluvial and vegetation characteristics due to flood regulation by the dams constructed upstream. In this study, the numerical fluvial/sediment and water quality model, KU-RLMS, is applied to the aquatic area near Hahoi Village (middle/upper region of the Nakdong River) for clarifying the mechanisms of changes in hydraulic and aquatic characteristics. The fixed-bed hydraulic experiment was carried out for horizontal two-dimensional numerical model. The numerical simulation reveals that flow is accelerated near the left bank of Booyongdae downstream of the Hahoi Village area. Circulatory flow pattern was observed at the right bank downstream of Hahoi Village. The simulation was in good agreement with the hydraulic/physical experiment. For the discharge of design flood, at the area of circulatory flow pattern, the superelevation of about 1.0 m at the right bank was predicted compared to the left bank of high flow velocity, which is also in good agreement with hydraulic experiment.

• Ocean and Polar Research
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• v.26 no.2
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• pp.255-263
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• 2004

This study was conducted to investigate the community structure and distributional pattern of meiobenthos in the deep-sea bottom of the Clarion-Clipperton Fracture Zone of the northeastern Pacific during July 2003. The samples were collected using the multiple corer at 13 stations along the transects fiom $5^{\circ}N\;to\;17^{\circ}N$. The most abundant meiobenthos was nematodes and followed by sarcomastigophorans; these two taxa comprised more than 70% of the total abundance at all stations. For size distribution analyses showed that animals which fit into the sieve mesh size of 0.063mm were abundant. The maximum density of meiobenthos was $147inds./10cm^2$ at station located in $7^{\circ}N$, and the minimum density was $6 inds./10cm^2$ at station located in $14^{\circ}N$. More than 60% of meiobenthos were distributed at surface sediment layer within 1.0cm, and the peak abundance was found at $0{\sim}0.25cm$ layer. The latitudinal distribution pattern of meiobenthos in the study area seemed to be related with the primary productivity of the surface water that is also connected to the water circulation pattern of the Pacific Ocean near the Equator, diverging at latitude of $8^{\circ}N$ and conversing at $5^{\circ}N$.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.963-966
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• 2008

본 연구에서는 최근까지 유사관측을 수행하고 있는 금강본류 하도구간의 금남$\sim$공주 지점을 대상으로 하였다. 분석을 위하여 이 지점의 총유사량 산정에 영향을 미치는 부유사량 관측 및 수위, 유량과 같은 하천 흐름 등에 관한 과거의 자료를 수집 정리 하였다. 본 연구에서 적용하고자 하는 교량의 교각에 대한 기하학적 형상은 원형, 정사각형, 정팔각형, 장방형으로 하였으며 분석 모형은 SED2D-WES 모형을 이용하여 유역에 대한 교각의 형상이 미치는 영향에 대하여 연구 하였다. 그 결과 지름이 6m, 경간장 57m인 원형교각의 경우 교각에서 약 14.3m 떨어진 곳에서 최고 유속 0.75m/s가 발생되었으며, $6{\sim}6m$의 정사각형교각의 경우 교각으로부터 약 15.8m떨어진 곳에서 0.68m/s의 최대 유속이 발생하고 $6{\sim}6m$ 정팔각형교각의 경우 교각으로부터 약 16.2m떨어진 곳에서 0.65m/s의 최대유속이 발생하고, 마지막으로 $3{\sim}6m$ 장방형교각의 경우 교각으로부터 약 21m 떨어진 구간에서 0.63m/s의 최고 유속이 발생하는 것으로 나타났다. 대상유역의 길이가 길고, 유속이 낮으므로 유출지점까지 흘러내려가는 유사량보다 하천내에 유입된 유사가 그대로 퇴적되는 경우가 많아 24시간 분석결과 하상변동량은 퇴적량과 침식량을 합하여 약 0.22%정도 변동되는 것으로 나타났으며, 교각형상에 따른 하상변동특성으로 원형교각의 경우 세굴이 일어나는 지점은 교각에서 약 16.88m떨어진 지점까지 하상변동이 일어났으며, 정사각형 교각의 경우 교각에서 약 10.96m떨어진 지점까지, 정팔각형 교각의 경우 교각에서 약 6.32m떨어진 지점까지, 장방형 교각의 경우 교각에서 약 18.23m떨어진 지점까지 하상변동이 나타남을 알 수 있었다.

• Journal of Korea Water Resources Association
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• v.41 no.4
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• pp.395-404
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• 2008

It is important to understand the complex, various migration features of the alluvial channels for river engineering. In this study, the morphological changes and migration features of alluvial channels were investigated by analyzing the aerial photographs of active channels between 1972 and 2004 in Hapyeong Intake Station, Nakdong river. The lower channels were migrated from left bank to right bank and showed the features of braided channel in 2004. The instability of lower channels was increased due to the increased channel slope and width. The sinuosity of lower channels was decreased with time. As time increased, the increasing rate of lower channel and lateral migration rate were decreased. As a result of meso-scale regime analysis by using bankfull discharge, multiple row bars were developed, and suspended sediment load was governed in the flow as a sand bed channel.

• Ocean and Polar Research
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• v.35 no.4
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• pp.323-349
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• 2013

The mud shrimp Upogebia major (Upogebiidae: Decapoda: Crustacea) is a common species on muddy and sandy mud tidal flats in the west coast of Korea. They reside in Y-shaped burrows that can extend up to more than 2 meters below the sediment surface. They feed on suspended detritus carried into their burrow by the beating of their pleopods and captured by their hairy first two pairs of thoracic legs. Mud shrimp burrows provide a habitat for a variety of small organisms such as crabs, shrimps, polychaetes, and mollusks. Ovigerous females are observed from December to May. Females deposit eggs only once per breeding season. They start hatching in March and the pelagic larvae of first zoea appear in March and April, followed by benthic settlement in May. Growth over the first year is rapid, and females deposit their first eggs in the third breeding season, 31 months after their settlement. Adult shrimps live for 4~5 years. Depth of the burrow increases with body length. The deep burrows provide refuge from predators and physical stress, allowing the shrimps to survive for a long time. The mud shrimps supply oxygen-rich water to their deep burrows, and exert a great influence on the structure and metabolism of the tidal flat benthic community. However, recently this type of mud shrimp has posed a serious threat to the Korean clam industry along the west coast of Korea. The extensive burrowing shrimp populations suddenly invaded the tidal flats from 2010 where the clams (Ruditapes philippinarum) are raised. As a consequence, clam production has decreased by about 10% over the past three years in some Korean clam beds. Therefore, the objective of this study is to review the biology of this mud shrimp in order to seek solutions to control the burrowing of these shrimps.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.2
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• pp.101-108
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• 1992

A careful re-examination has been conducted on the applicability of the concept of equilibrium riverbed slope to river engineering practice and on the validity of Aki's and Mononobe's formulas that are widely used in Korea for determination of equilibrium riverbed slope. A stream in equilibrium is one in which, over a period of years, slope is naturally adjusted to provide, with available water discharge and with prevailing channel characteristics, just the velocity required for transportation of the sediment load supplied from the upstream. The equilibrium riverbed slope is the bed slope of such river. The present river engineering practice to analyze the riverbed characteristics by applying so called 'the equilibrium riverbed slope formula' to such rivers, therefore, should be avoided. Also, the validities of Aki's and Mononobe's formulas, that are presently used for determination of stable channel slope, are very dubious and should not be used in river engineering practice.

• Water for future
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• v.27 no.2
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• pp.73-83
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• 1994

The unproper development of the nearshore zone can enhance the diffusion of pollutant in the nearshore zone resulting in unbalanced sediment budget of beach which causes alteration of beach topography. Therefore, it is required to predict the effects of the envirnmental change quantitatively. In this paper, the depth-averaged and time-averaged energy balance equation is selected to acount for the wave transformation such as refraction, shoaling effect, the surf zone energy disipation, wave breaking index and bore, due to wave breaking in the shore region.(Numerical solutions are obtained by a finite difference method, ADI and Upwind. For the calculation of the wave-induced current, the unsteady nonlinear depth-averaged and time-averaged governing equation is derived based on the continuity and momentum equation for imcompressible fluid.) Numerical solutions are obtained by finite difference method considering influences of factors such as lateral mixing coefficient, bed shear stress, wave direction angle, wave steepness, wave period and bottom slope. The model is applied to the computation of wave transformation, wave-induced current and variation of mean water leel on a uniformly sloping beach.