• Proceedings of the Korea Water Resources Association Conference
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• 2018.05a
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• pp.128-128
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• 2018

하구는 강이 흘러 바다로 유입되는 지역으로 강의 담수와 바다의 염수가 만나는 강의 하류에 형성되며 지형, 담수의 유입, 해수의 조석 등에 의해 염분분포가 변화 하는 특성을 가진다. 또한 하구에 형성되는 하구역은 조수 간만의 차로 인한 상하운동이 일어남으로 인해 염분 농도는 0.5~30 ‰로 매우 광범위하게 나타난다. 하구는 해수가 미치는 최대 경계인 감조역과 해수와 담수가 혼합되는 기수역이 나타나며, 하구에서의 염분의 변화는 동 식물의 생존 및 분포, 수자원 확보 및 관리, 구조물 설치 등 공학적 분야에서도 매우 중요하다. 또한, 염수쐐기와 조석의 영향으로 하구의 수층에서는 담수 및 염분분포가 지점에 따라 다르게 형성이 되기 때문에 하천 수질측정 시 염수에 의해 대표성이 결여될 수 있다. 본 연구는 바다로 유입되는 수영강을 대상으로 염분분포의 특성을 고려하여 중권역 대표지점으로서의 적합성을 판단하고자 하였다. 수영강은 부산 용천산에서 발원하여 회동수원지를 거쳐 온천천과 합류하여 남해로 유입된다. 수영강에 위치한 좌수영교와 수영교에서 조석 간만의 차가 뚜렷하게 나타날 수 있는 대조기와 소조기에 연직 염분분포를 분석하여 하천수질 측정지점의 대표성을 판단하고자 하였다. 만조에서 간조로 수위가 변화 할 때 표층의 담수층이 옅어지는 현상을 보이며 소조기 보다 대조기에서의 담수층 변화 폭이 커지며 수질측정 시 고려하여야 할 것으로 판단된다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.5
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• pp.217-227
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• 2017

The object of this study is to estimate the net volume transport and the residual flow that changed by space and time at southern part of Yeomha channel, Gyeonggi Bay. The cross-section observation was conducted at the mid-part (Line2) and the southern end (Line1) of Yeomha channel for 13 hours during neap and spring-tides, respectively. The Lagrange flux is calculated as the sum of Eulerian flux and Stokes drift, and the residual flow is calculated by using least square method. It is necessary to unify the spatial area of the observed cross-section and average time during the tidal cycle. In order to unify the cross-sectional area containing such a large vertical tidal variation, it was necessary to convert into sigma coordinate system by horizontally and vertically for every hour. The converted sigma coordinate system is estimated to be 3~5% error when compared with the z-level coordinate system which shows that there is no problem for analyzing the data. As a result, the cross-sectional residual flow shows a southward flow pattern in both spring and neap tides at Line2, and also have characteristic of the spatial residual flow fluctuation: it northwards in the main line direction and southwards at the end of both side of the waterway. It was confirmed that the residual flow characteristics at Line2 were changed by the net pressure due to the sea level difference. The analysis of the net volume transport showed that it tends to southwards at $576m^3s^{-1}$, $67m^3s^{-1}$ in each spring tide and neap tide at Line2. On the other hand, in the control Line1, it has tendency to northwards at $359m^3s^{-1}$ and $248m^3s^{-1}$. Based on the difference between the two observation lines, it is estimated that net volume transport will be out flow about $935m^3s^{-1}$ at spring tide stage and about $315m^3s^{-1}$ at neap tide stage as the intertidal zone between Yeongjong Island and Ganghwa Island. In other words, the difference of pressure gradient and Stokes drift during spring and neap tide is main causes of variation for residual current and net volume transport.

• Journal of the Korean Society of Marine Environment & Safety
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• v.12 no.4 s.27
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• pp.301-306
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• 2006

In order to estimate the characteristics of water movements around artificial upwelling structure, current measurements were carried out along lines E-W and S-N on May 4th(neap tide} and May 30th(spring tide), 2006. In the study area, southeastward flow was dominant during the field observations, and the pattern of water movement in the upper layer above 30m depth was different from that in the lower layer below 30m depth Vertical flow(w-component} around the artificial structure area and western area was shown to be upward flow, but downward flow occurred in the southern, northern and eastern parts at the neap tide. At the spring tide, the ebb current along E-W line showed upwelling flow in the eastern part and western area and showed upwelling flow near the artificial structure area and downwelling flow far away that one. At the spring tide, upward flow was dominant along S-N line during the flood current Volume transport by upward flow was higher than that by downward flow. Volume transport by upward flow during ebb of neap tide was greater than during flood current of neap tide, but was reverse at the spring tide.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.31 no.2
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• pp.127-141
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• 1995

The distribution of water mass in Deukryang Bay was investigated using observational data obtained on July 12 (spring tide) and 19 (neap tide) in 1994. In characteristics of water mass at the bay the area is divided into three ones by a vertical attenuation coefficient k and a stratification parameter, log sub (10) (H/U super (3)), was H is depth, and U mean velocity in the bay. The contour of k=0.6 has a similar distribution to the isobath of 10m depth in spring tide, and of 5m depth in neap tide, respectively. This indicates that the water mass in the area between the isobath of 5m and 10m depth is changed by tidal periods. The stratification parameter corresponding to k=0.6 was 2.1~2.2. In the shallow water of 5m depth the characteristics of water mass was distributed in temperature of 25.5~31.$0^{\circ}C$ and salinity of 32.8~33.8PSU(Practical Salinity Unit), the temperature was high and the salinity distributed widely. In the deep water of 10m depth it was the temperature of 22.0~29.5$^{\circ}C$ and the salinity of 33.0~33.6PSU, the temperature was low and the salinity distributed narrowly. In the middle depth water of 5m to 10m depth, the temperature of 22.0~30.$0^{\circ}C$ and the salinity of 32.8~33.5PSU, its values showed the middle between the values of the deep area and the values of the shallow area.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.478-478
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• 2022

섬진강은 하굿둑이 없는 열린 하구로서 하구로부터 약 21km까지 조석의 영향을 받아 강물의 염도가 시간에 따라 변하는 환경이다. 오랫동안 섬진강 하구는 다양한 원인으로부터 바다화로 대표되는 염하구 문제가 지역 현안 사항으로 제기되어 왔다. 상류에서의 용수사용 증가로 인한 하천 유하량 감소 또한 그 원인들 중 하나로 판단됨에 따라 실제 하구까지 내려오는 하천유량과 바다로부터 유입되는 해수를 구분하여 정량화하는 연구가 필요한 사안이다. 본 연구의 목적은 섬진강 수계 하구에서의 다양한 생태환경을 보전하기 위한 적정 염분유지가 요구됨에 따라 섬진강하구 염분계측기(섬진강대교)를 설치하여 염분농도를 관측하고 하천유량, 하천취수 및 해양조위에 따른 염분농도 변화를 모의하여 하천유량과 염분과의 관계를 제시하고자 하였다. 본 연구에서는 EFDC(Environmental Fluid Dynamics Code) 수치모델을 이용하여 상류로는 구례군(송정리) 수위관측소부터 하류로는 여수해만 및 문의리까지의 구역을 설정하고 광양조위, 하동수위 및 고정식 염분 계측기 관측염분농도 자료를 이용하여 수치모델링의 재현성을 검증하였다. 검증 결과, 결정계수(R²)는 0.87(하동수위), 0.93(광양조위), 0.56(섬진강대교 염도)를 나타냈다. 모델 검보정 후 하천유량에 따른 염분변화 실험을 실시하여 염분농도 거동을 분석하였다. 모델 결과, 섬진강하구에서의 염분거동은 소조기때 염분체류 현상으로 인해 대조기 거동과는 큰 차이를 나타냈다. 따라서, 모델링 결과를 이용한 유량-염분 조견표는 각각 대조기와 소조기로 구분하여 산정하였다. 대조기때는 송정유량이 10톤/초의 평균갈수량이 흐를 경우 다압에서의 취수량이 2.52톤/초 ~ 4.63/초로 증가할수록 18.8psu ~ 19.9psu로 증가하였다. 소조기의 경우는 25.5psu ~ 25.7psu로 대조기와 비교하여 크게 증가됨을 나타냈다. 본 연구의 결과는 객관적인 생태환경 보전을 위한 적정염분농도 범위가 도출된다면 이를 유지하기 위한 필요유량과 필요유량을 확보하기 위한 장단기적인 대책수립이 가능할 것으로 기대된다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.116-126
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• 1999

In this paper, we have studied the seasonal vanatIons of near-field dilutions of wastewater discharged from the submerged mutiport-diffuser in Masan Bay. Seasonal changes of temperature and salinity, and tidal currents were measured at 16 stations in Masan Bay. Based on the observed ambient field data, the seasonal changes of near-field dilutions due to ambient current and density fields were calculated by CORMIX model. Because of the shallow ambient water depth of 15 m, the density profiles are isopycnal in autumn and winter seasons, in which the dilution factors were the highest, 168 with the strong spring-tidal current and 110-120 with the weak neap-tidal current. As the season changes from spring to summer, the dilution factors are considerably reduced by the factor of 2 as the thermocline is getting deepened up to Sm in depth in summer. In the case of a weak ambient current, the dilution factor in summer was reduced to 1/4 of the dilution in winter. However, with strong ambient current the difference between summer and winter dilutions becomes relatively small by 30%. The results indicate that the seasonal variation of near-field dilution is very large up to 4 times with a weak neap-tidal current, but its variations become small under a strong ambient current of spring tide in MasanBay.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.257-268
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• 2012

The EFDC model with find grid resolution system connecting the Gyeong-Gi bay and Han River estuary was constructed to study on spring-neap variability of net volume transport at each channel of the Han River estuary. The simulation time of numerical model is 124 days from May to August, 2009 with freshwater discharge at Han, Imjin and Yeseong River. The calibration and verification of model results was confirmed using harmonic components of water level and tidal current. The net volume transport was calculated during 30 days with normal freshwater conditions at Seokmo channel and Yeomha channel around Ganghwado. The ebbing net volume transport of 44% and 56% is drained into Gyeong-Gi bay through Yeomha and Seokmo channel, respectively. The ebbing net volume transport nearby Seodo at Yeomha channel convergence flooding net volume transport at Incheon harbor, and drain (westward direction) through channel of tidal flat between Ganghwado and Yeongjongdo to the Gyeong-Gi bay. The averaged net volume transport during 4 tidal cycles was compared to variation of spring-neap periods of the Yeomha channel. The convergence position is moved up- and down-ward according to spring-neap variability. The movement of the convergence zone is appeared because 1) increasing of discharged rate tidal flat channel between Ganghwado and Yeongjongdo at the spring period, 2) The growth of barotropic forcing with downward direction at the spring tide, and 3) The strength of the baroclinic pressure gradient is greater than spring with mixing processes.

• 한국해양학회지
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• v.22 no.2
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• pp.105-118
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• 1987

A series of anchor stations were occupied along the Keum EAstuary during six different periods of tidal and fluvial regimes. The results clearly show that the formation and evolution of the turbidity maximum play an important role in the sedimentary processes in this environment. The turbidity maximum in the Keum Estuary is primarily related to the tidal range at the mouth and is caused by the resuspension of bottom sediments. In this estuary, the turbidity maximum is not a permanent feature and shows semidiurnal, fortnightly and seasonal variations. Repetition of deposition and resuspension of fine sediments occur in response to the variation in current velocity associated with semidiurnal tidal cycles. The core of turbidity maximum shifts landward or seaward accordion to the flood-ebb succession. The turbidity maximum also shows a fortnightly variation in response to the spring-neap cycles. Thus, the turbidity maximum degenerates during neap-tide and regenerates during spring-tide. The freshwater discharge is also an important factor in the formation and destruction of the turbidity maximum. The increase in freshwater discharge in rainy season can create an ebb-dominant current pattern which enhances the seaward transport of suspended sediments, resulting in the shortening of residence time of suspended materials in the estuary. Thus, under this high discharge condition, the turbidity maximum exists only during spring-tide and starts to disappear as the tidal amplitude decreases.

• The Journal of Korean Society for Radiation Therapy
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• v.24 no.1
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• pp.1-10
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• 2012

Purpose: To evaluate dose distribution differences when the dose rates are randomly changed in intensity-modulated radiation therapy using a dynamic multileafcollimator. Materials and Methods: Two IMRT treatment plans including small-field and large-field plans were made using a commercial treatment planning system (Eclipse, Varian, Palo Alto, CA). Each plan had three sub-plans according to various dose rates of 100, 400, and 600 MU/min. A chamber array (2D-Array Seven729, PTW-Freiburg) was positioned between solid water phantom slabs to give measurement depth of 5 cm and backscattering depth of 5 cm. Beam deliveries were performed on the array detector using a 6 MV beam of a linear accelerator (Clinac 21EX, Varian, Palo Alto, CA) equipped with 120-leaf MLC (Millenium 120, Varian). At first, the beam was delivered with same dose rates as planned to obtain reference values. After the standard measurements, dose rates were then changed as follows: 1) for plans with 100 MU/min, dose rate was varied to 200, 300, 400, 500 and 600 MU/min, 2) for plans with 400 MU/min, dose rate was varied to 100, 200, 300, 500 and 600 MU/min, 3) for plans with 600 MU/min, dose rate was varied to 100, 200, 300, 400 and 500 MU/min. Finally, using an analysis software (Verisoft 3.1, PTW-Freiburg), the dose difference and distribution between the reference and dose-rate-varied measurements was evaluated. Results: For the small field plan, the local dose differences were -0.8, -1.1, -1.3, -1.5, and -1.6% for the dose rate of 200, 300, 400, 500, 600 MU/min, respectively (for 100 MU/min reference), +0.9, +0.3, +0.1, -0.2, and -0.2% for the dose rate of 100, 200, 300, 500, 600 MU/min, respectively (for 400 MU/min reference) and +1.4, +0.8, +0.5, +0.3, and +0.2% for the dose rate of 100, 200, 300, 400, 500 MU/min, respectively (for 600 MU/min reference). On the other hand, for the large field plan, the pass-rate differences were -1.3, -1.6, -1.8, -2.0, and -2.4% for the dose rate of 200, 300, 400, 500, 600 MU/min, respectively (for 100 MU/min reference), +2.0, +1.8, +0.5, -1.2, and -1.6% for the dose rate of 100, 200, 300, 500, 600 MU/min, respectively (for 400 MU/min reference) and +1.5, +1.9, +1.7, +1.9, and +1.2% for the dose rate of 100, 200, 300, 400, 500 MU/min, respectively (for 600 MU/min reference). In short, the dose difference of dose-rate variation was measured to the -2.4~+2.0%. Conclusion: Using the Varian linear accelerator with 120 MLC, the IMRT dose distribution is differed a little <(${\pm}3%$) even though the dose-rate is changed.

• Journal of the Korean Society for Marine Environment & Energy
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• v.11 no.2
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• pp.70-77
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• 2008

In this study, to establish countermeasure from marine casualties as a basic study fur long-term prediction of topographical change around Jinudo in the Nakdong river estuary, spatio-temporal topographical change monitoring was carried out. Also, in order to estimate the deposition variations concerning SS (Suspended Solid) flux which moved at St.S1 during neap and spring tide, respectively. From the topographical monitoring, it was found that the annual mean ground level and deposition rate were 141 mm and 0.36 mm/day and all parts except the northern part of Jinudo had the active topographical changes and a tendency to annually deposit. From vertical distribution of SS net fluxes, $SS_{LH}$ (latitudinal SS net flux) during spring tide overall flows average 28 $kg/m^2/hr$ (eastward), and $SS_{LV}$ (longitudinal SS net flux) flows average 11.1 $kg/m^2/hr$ (northward). And, $SS_{LH}$ overall flows average 4.8 $kg/m^2/hr$ (eastward), and $SS_{LV}$ flows average 1.5 $kg/m^2/hr$ (northward) during neap tide similar with spring tide. The depth averaged values of the latitudinal and longitudinal SS net fluxes during spring tide were approximately 6 times higher than those during neap tide. As result of, it was considered that topographical change of southern part of Jinudo was affected by resuspension of bottom sediments due to strong current in bottom layer during flood flow.