• 한국농공학회:학술대회논문집
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• 한국농공학회 2000년도 학술발표회 발표논문집
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• pp.365-370
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• 2000

Sea dike construction for the tidal flat reclamation works in estuary and coast may change the characteristics of tidal motion and wave conditions in the region. In turn, a new hydraulic condition provides the impacts on sediment transport pattern and forms a new morphological environment. Also, morphological changes during the closure works of sea dike are closely related with a safy of sea dike. Therefore, the prediction of morphological changes is required secure the safe closure work and the economic design of sea dikes. To investigate morphological changes due to sea dike construction, hydrodynamic changes of tides and waves have to be evaluated, then sediment transport and sea bottom changes are computed. Mathematical modelling is required for representation of interrelation of tidal motion, wave and sediment transport. In this study, numerical model MORSYS is applied to compute the hydrodynamics and morphological changes around the closure gap for Saemankuem dike. This model allows a flexible integration of the module for waves, currents, sediment transport and bottom changes.

• Ocean Science Journal
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• 제41권3호
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• pp.139-148
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• 2006

The distribution of the taxonomical composition and the density of meiobenthos depending on the sediment type has been studied in bottom sediments of Nha Trang Bay. The maximal population density and the taxonomical diversity were observed in the silted coarse and heterogeneous sand ($1031.4{\pm}419.7\;ind.\;10\;cm^{-2}$), whereas the minimal level of density and diversity ($588.1{\pm}152.5\;ind.\;10cm^{-2}$) was in the coarse and heterogeneous sand with shell debris and corals. The correlation between the median diameter of sediment particles and population density of meiobenthos has been revealed (r=0.82, p<0.05). In bottom sediments of Nha Trang Bay, twenty six taxonomic groups of meiobenthos were observed. Nematodes dominated in all sediment types. Representatives of four orders, twenty eight families and ninety seven genera of marine nematodes were identified. The vertical distribution of meiobenthos in different sediment types was considered. A sediment column (10 cm height) was sectioned by five 2 cm portions. In the last layer (8-10 cm) the most number of meiobenthic groups was found in sandy sediments. In the lower layers of silt sediments, only nematodes were found.

• 한국물환경학회지
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• 제27권4호
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• pp.542-550
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• 2011

Changes of suspended sediment concentration in the Seomjin river estuary located in south sea of the Korea peninsula were investigated during the spring tide in autumn (i.e. 25 hours in October) 2000 and winter (i.e. 25 hours in February) 2001. The changes of temperature and salinity during the spring tide in October 2000 showed larger variations than the those in February 2001. During the spring tide in October 2000, currents at bottom layer were observed to be stronger than during the spring tide in February 2001, showing that both of the two periods had ebb currents-predominant tide asymmetries. The suspended sediment concentrations in October 2000 were larger than the those in February 2001. At the time of the maximum of tide currents or after about one hour of the maximum during the autumn months, the suspended sediment turbidity was observed to be maximum. Another observation station at Hadong upstream from the Seomjin river estuary showed about one hour delay in tide phase, Thereby, the suspended sediment concentration showed high turbidity after two hours at bottom and three hours at surface layer, in particular, in October 2000. This results can be explained by the facts that river discharge increased significantly after the summer rainy season, causing also increase of erosion processes by strong current velocity at bottom layer.

• 한국음향학회지
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• 제22권1호
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• pp.78-87
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• 2003

고주파 (126-㎑) 음향 신호를 이용하여 퇴적층의 구성 매질 및 표면 형태에 따른 산란 신호 변화를 측정하였다. 퇴적층은 구성 매질에 따라 사니질 (sandy mud), 사질 (sand), 자갈 (gravel)의 세가지 경우와 이를 혼합한 경우로 하였으며, 표층 연흔 (ripple) 형태에 따라 연흔과 음파 진행방향이 직각을 이루는 경우 및 평행한 경우를 모의하였다. 평면입사각 변화 및 연흔 구성 형태에 따른 후방산란 강도는 평면입사각에 비례하여 증가하였으며, 연흔 형성 방향과 음파 진행 방향이 이루는 각이 작을수록 삼차원적인 측방산란이 강하게 나타났다. 연흔과 음파가 이루는 각이 증가할수록 후방산란은 증가하였으며, 지음향적 요소 외에도 연흔 형성과 방향에 음파 산란이 강하게 의존함을 알 수 있었다.

• 환경위생공학
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• 제14권3호
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• pp.71-79
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• 1999

The Hg, Cd, Cu, Mn, and Zn in bottom sediments of han river and their tributaries were analyzed to evaluate the seasonal variations of heavy metals. Leaching tests were also performed for estimation of availability of heavy metal retention in sediments. Sediments of Anyang stream showed the highest concentration of heavy metal in the sediment samples. Heavy metal concentration was heavily depended upon the heavy metal source of tributaries of han river and particle distribution. Clay and silt had higher concentration of heavy metals than very fine san and fine sand due to difference of retention capability of heavy metal. The highest concentration of heavy metal was observed in bottom sediments irrespective of sites investigated. Heavy metals and ignition loss showed positive relations, and higher relationships with p-value <0.01 were observed between copper and lead. copper and zinc, and depended on the pH condition of leaching test, and leachated fraction increased with decrease of the pH.

• The Journal of the Acoustical Society of Korea
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• 제13권2E호
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• pp.76-82
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• 1994

천해 해저 퇴적물의 특성은 수 미터 깊이에서도 변할 수 있다. 퇴적층에서의 음속 뿐만 아니라 감쇠계수도 퇴적물의 성분과 특성 자체에 의해서 결정되므로 감쇠계수는 퇴적층 깊이에 따라 가변적이라고 여기는 것이 합리적이다. 본 연구에서는 포물선 방정식 기법을 도입한 음향모델을 이용하여 퇴적층 종파 감쇠계수의 변화가 100-805 Hz 대역 음파의 전파에 미치는 영향을 고찰하였다. 대상 해역은 해저면이 사질로 구성되어 있고, 수심과 최적층의 깊이는 각각 40 m, 10m이다. 감쇠계수가 퇴적층 깊이에 따라 일정하게 또는 가변적으로 가정함에 따라 음파의 전파손실은 15 km 거리에서 10dB 까지 차이가 발생한다. 모델에 의하여 계산된 전파손실은 감쇠계수를 퇴적층 깊이에 따라 변하게 할 경우 실측된 전파손실과 잘 일치한다.

• 한국음향학회지
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• 제29권4호
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• pp.223-228
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• 2010

남해 진해만에서 주파수 17-40 KHz를 이용하여 수평 입사각 $82^{\circ}$에 대한 고주파 해저면 반사손실을 측정하였다. 측정된 해저면 반사손실은 주파수에 따라서 주기적인 변동성을 보였으며 이러한 특성은 이층 구조의 해저면을 가정한 레일리 반사 계수 모델을 사용하여 예측한 결과와 비교 분석되었다. 이층 구조 반사 계수 모델은 수층, 상부퇴적층, 그리고 하부 퇴적층으로 구분되며 총 9개의 입력 인자 (수층의 음속과 밀도, 상부 퇴적층의 음속, 밀도, 감쇠계수, 두께, 하부 퇴적층의 음속, 밀도, 감쇠계수)가 사용된다. 하부 퇴적층의 지음향 인자들은 코어로부터 측정된 평균 입도 크기로부터 유추되었으며 상부층의 음속, 밀도, 감쇠계수와 두께는 몬테카를로 방법을 이용하여 역추정되었다. 지음향 인자들의 민감도 조사로부터 다층구조 해저면에서 나타나는 반사계수의 종속성은 상부 퇴적층의 두께에 가장 민감하게 반응함을 확인하였다.

• 한국수산과학회지
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• 제36권3호
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• pp.290-297
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• 2003

To describe vertical distribution of dinoflagellate cysts in bottom sediments from Gwangyang Bay, three short-core sediment samples were collected with a gravity core sampler on 24 August 2001: St. 1 core (27.5 cm) in the northeastern part of the bay, St. 14 core (30.5 cm) in the southwestern part, and St. 16 core (25.9 cm) near Yeosu Sound. Total cyst densities generally decreased from the top of the sediment samples through the bottom. The highest cyst densities were observed at 2-3 cm in St. 1 core, 4-5 cm in St. 14 core, and 0-1 cm in St. 16 core respectavely. Living cysts were observed till the bottom of the sediment samples. The increase of heterotrophic dinoflagellate cyst proportion may indicate that the eutrophication process was recently escalated in the study area.

• 한국물환경학회지
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• 제25권6호
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• pp.935-942
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• 2009

During period of the rainy season of spring tide Aug. 2005, the suspended sediment transport rate from Seomjin River increased ten times as high as neap tide of low river discharge. During ebb tide of high terrestrial input, the grain size of suspended particles of both surface and bottom layer of the water column, showed a uni-modal distribution with a dominant peak at coarse fraction, which suggests a characteristic development of floc-sized particles of low mean effective density. On the contrary, the particles supplied toward upstream of Seomjin river from Gwangyang Bay during flood tide showed a bi-modal distribution with a secondary peak at finer fraction, possibly due to the resuspension and the deflocculation associated with the increased shear velocity at near bottom. Break-up of large flocs is also suggested by the increased mean effective density. However, settling velocity was lower during flood tide because of smaller grain size. Thus, net deposition of suspended sediment is expected at within Gwangyang Bay instead of upstream of Seomjin River, even though suspended sediment transport rate at near bottom water was three times higher than that at surface water during flood tide.

• The Journal of the Acoustical Society of Korea
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• 제25권2E호
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• pp.60-68
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• 2006

High-frequency bistatic scattering measurements from a corrugated surface were made in an acoustic water tank. First the azimuthal scattering pattern was measured from an artificially corrugated surface which has varying impedance. The corrugated surface was installed both transverse to the direction of incident wave and longitudinal to the direction of incident wave. The angle between the corrugated surface and the direction of the incident wave was about $45^{\circ}$. Second, the scattering strengths were measured from the flat sediment and the corrugated sediment. A critical angle of about $37^{\circ}$ was calculated in the acoustic water tank. The measurements were made at three fixed grazing angles: $33^{\circ}$ (lower than critical angle), $37^{\circ}$ (critical angle), and $41^{\circ}$ (higher than critical angle). The scattering angle and the grazing angle are equal in each measurement. Frequencies were from 50 kHz to 100 kHz with an increment of 1 kHz. The corrugated sediment was made transverse to the direction of the incident wave. The first measurement indicates that the scattering patterns depend on the relations between the corrugated surface and the direction of the incident wave. In the second measurement, the data measured from the flat sediment were compared to the APL-UW model and to the NRL model. The NRL model's output shows more favorable comparisons than the APL-UW model. In case of the corrugated sediment, the model and the measured data are different because the models used an isotropic wave spectrum of sediment roughness in the scattering calculations. The isotropic wave spectrum consists of $w_2$ and ${\gamma}_2$. These constants derived from sediment names or bulk size. The model which used the constants didn't consider the effect of a corrugated surface. In order to consider a corrugated surface, the constants were varied in the APL-UW model.