• Korean Journal of Ecology and Environment
• /
• v.51 no.4
• /
• pp.253-258
• /
• 2018

Phytoplankton community was studied in relation to a typhoon at Bok-gyo Bridge area in Juam Lake, Korea. In August 31, 2000, a typhoon (Prapiroon) was passed by Juam Lake with great power enough to destroy summer stratification of Juam Lake. Destratification resulted in temporal mixing of the whole water column and changed the physical and chemical properties of water bodies, and caused the changes of the biological properties. The transparency decreased from 195 cm before the typhoon to 84 cm after the typhoon with the resuspension of the bottom sediment. In the vertical distribution of the phytoplankton population, the maximum population was measured at depth of 2 m before the typhoon. However, immediately after the typhoon, the population distributed evenly throughout the entire water layers. The carbon biomass of the phytoplankton was also highest at the depth of 2 m before the typhoon, but immediately after the typhoon, it was uniformly distributed throughout the whole water layers. The vertical profiles of the concentrations of chlorophyll a, however, did not show a significant difference before and after the typhoon. The typhoon induced destratification and restratification altered the taxa of the phytoplankton. The major dominant phytoplankton taxa before the typhoon was diatoms including Aulacoseira granulata, but the green algae overwhelmed the diatoms in cell number and biomass after the typhoon. The chlorophycean dominance was replaced by cyanophycean dominance with the heavy rain and descent of water temperture at the end of September.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.19 no.4
• /
• pp.327-333
• /
• 2013

In order to see the stratification phenomenon in the coastal area induced by oceanographic conditions of the open sea, we analyzed the CTD (Conductivity-Temperature-Depth) data taken from the oceanographic survey on February 16~28, 2013. The stratification in Jukbyun coast was stronger than those of Sokcho and Gampo coast. Jukbyun line (104 line in the Serial Oceanographic Observation of National Fisheries Research and Development Institute) showed the anticyclonic eddy in the vertical distribution of temperature. The isotherm of $10^{\circ}C$ was concaved to the depth of 200 m in the middle station (station no. 9) of the line 104. It showed above $4^{\circ}C$ in positive temperature anomaly in the depth of 100~200 m in the middle station (station no. 9) of the line 104. This positive temperature anomaly was stretched to the coastal area with shallower depth. It is suggested that the stratification in Jukbyun coast was resulted from the onshoring of the Ulleung warm eddy. The movement of warm eddy may be act as a block to migration of cold water fishes like cod.

• Journal of Korea Water Resources Association
• /
• v.43 no.10
• /
• pp.911-920
• /
• 2010

The closed water bodies, such as reservoirs and lakes, could be contaminated by an inflow of pollutants in the upstream as well as a stratification caused by seasonal natural phenomena. The vertical circulation particularly plays an important role in reduction of environmental pollutants. The factors of the vertical circulation are the temperature, wind, thermal diffusivity and sunlight. The wind is probably the most significant factor among them. Thus, it is necessary to describe the validation and application of a three-dimensional numerical model of wind-induced circulation in a thermally stratified flow. In this paper, a three-dimensional numerical model for the thermally stratified flows is presented. The model is conducted in three steps to calculate the velocity components from the momentum equations in x- and y- axis directions, the elevations from the free surface equation and the temperature from the scalar transport equation. Numerical predictions are compared with available analytical solutions for the sloshing free surface movement in a rectangular basin. The numerical results generally show a reasonable agreement with analytical solutions. And the model is applied to the circulation for the wind induced flow in a thermally stratification. Consequently, the developed model is validated by two verifications and phenomena of the internal flow.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.494-494
• /
• 2017

국내의 호소는 대부분이 농업용수 공급을 목적으로 설치된 인공 호소이다. 최근 이상기후 및 유역 오염원 증가로 호소의 수질오염도가 증가 추이에 있으며, 특히 하절기 외기온도 상승과 함께 녹조 대량발생, 어류 집단폐사 등 수질오염사고가 야기되고 있다. 이러한 수질오염사고는 호소의 지역적 특성으로 인한 여러 가지 원인이 있겠지만 직접적인 원인으로는 호소의 산소 고갈에 기인된다. 본 연구에서는 농업용 호소의 수온, DO, EC 등에 대한 일주기 및 계절적 동적변화를 규명하여 호소의 수질개선대책수립에 활용하고자 하였다. 연구대상 지구는 경기도 시흥시에 소재하고 있는 M 농업용 저수지이며, 2015년 6월 4일부터 9월 22일까지 수온, DO, EC을 측정할 수 있는 연속 자동측정장치를 설치하였고, 측정지점은 저수지 수심을 상(바닥층에서 1.5m 상부), 중(바닥층에서 1.0m 상부), 하(바닥층에서 0.5m 상부)로 구분하여 각각 측정하였다. 호소의 수온은 일주기로 수온성층 형성과 대류혼합이 반복되었으며, 상 하층간의 수온 차이가 평균 $1.4^{\circ}C$, 최대 $5.0^{\circ}C$의 차이를 보였다. 또한 강우가 발생한 이후에는 일시적으로 저수지 상 하 층간 수온 차이가 거의 없는 것으로 나타났는데, 이는 강우에 의한 수체의 수직혼합으로 저수지 전체의 물질순환에 영향을 미친 것으로 판단된다. 호내 DO 농도는 일(day) 주기 동안 농도변화가 크게 나타났으며, 여름철 무강우 기간에는 저수지 바닥층의 평균 DO 농도가 약 0.5mg/L로 거의 무산소 상태가 지속되는 것으로 관측되었다. DO는 기온이 낮아지거나 강수가 발생할 때 대류에 의한 수직혼합에 의해 간헐적으로 회복되다가 다시 고갈되는 현상이 반복되는 것으로 나타났다.

• 한국해양학회지
• /
• v.18 no.1
• /
• pp.43-48
• /
• 1983

Oceanic temperature inversions, with unstable stratifications, are frequently founed in the surface layer of a few tens meters in the Japan Sea and the Yellow Sea in Winter. Mechanisms responsible for the generation of temperature inversions include the followings: (1) The nat heat loss at the sea suface requires an upward transport of heat from the interior of the ocean y convection, and this convection leads to the temperature inversions. (2) The downward propagation of the annual variation of the sea surface timperature, with an exponential decrease of amplitude and a linear change of phase with depth, generates the surface inversion layer in winter. (3) The cold water cdvection by Ekman drift, of which magnitude decreases exponentially with depth, generates temperature inversions for the three possible mechanisms mentioned above.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.6B
• /
• pp.499-505
• /
• 2011

The mixing behavior of turbidity currents in a reservoir is closely related with the annual temperature change of the reservoir. In the summer, the reservoir has a well defined structure: one or two thermoclines and some layers of different densities. This density stratification inhibits vertical mixing and affects various hydrodynamic processes within the reservoir. Therefore, many reservoirs can be operated to release water of the specific quality with the selective withdrawal. In this study, the hydraulic experiments were performed to analyze the efficiency of selective withdrawal. The velocity distributions are measured with PIV in the stratified tank with the "two-tank" method. The relationship between the Richardson number and the selective withdrawal efficiency are provided using the measured velocity distributions.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2008.05a
• /
• pp.1373-1377
• /
• 2008

강우-유출에 의해 성층화된 저수지로 유입하는 하천수는 저수지 표층에 비해 낮은 수온과 높은 부유물질(SS) 농도를 가지므로 저수지 표층수보다 상대적으로 높은 밀도를 유지한다. 하천으로부터 유입한 밀도류는 유속에 의한 관성력이 두 수체의 밀도차에 의한 음의 부력보다 큰 구간까지는 저수지 표층을 따라 진행하지만, 두 힘이 같아지는 지점에서 밀도류는 더 이상 진행하지 못하고 저수지 수면 아래로 침강하며 이 과정에서 수체간의 많은 혼합이 일어난다. 따라서 홍수시 유입한 탁수의 침강점에 대한 정확한 예측은 수질관리를 위한 현장조사, 그리고 탁수거동 해석 및 최적관리대책 마련에 중요한 요소이다. 본 연구의 목적은 홍수시 대청호로 유입하는 하천 밀도류의 침강위치를 홍수규모별로 경험식과 수치모델을 통해 산정함으로써 두 방법 간의 장 단점을 비교하고, 탁수 현장조사와 최적관리를 위한 기초정보를 제공하는데 있다. 유입수의 모의조건은 그 동안 대청호에서 발생한 홍수 크기를 기준으로 9개의 등급으로 나누었으며, 저수지 성층조건은 여름철 탁수가 유입되기 전의 발달된 성층구조를 적용하였다. 유입수와 저수지 성층구조의 특성치는 밀도 Froude 수($Fr_i$)로 나타냈으며, $Fr_i$ 조건별로 침강점 위치를 저수지 단면을 삼각형태로 가정한 Hebbert et al.(1979) 경험식과 2차원 수치모델로 산정하여 그 결과를 비교하였다. 대청호로 유입한 탁수는 홍수규모에 따라 대정리 수역에서 회남수역 사이 구간에서 침강하였으며, $Fr_i$ 값이 클수록 침강점 수심이 깊어지는 경향을 보였다. 경험식으로 산정한 침강점 수심은 정상상태 조건을 가정하므로 홍수에 의한 수위변화를 고려하지 못하며, 실제의 불규칙한 하상표고를 일정한 하상경사로 가정하기 때문에 2차원 모델의 결과보다 과대산정하는 경향을 보였다. 따라서 홍수가 연속해서 발생하며 수위변화가 심한 국내 저수지 여건에서 하천 유입 밀도류의 거동을 보다 정확히 예측하기 위해서는 2차원 또는 3차원 수치모델을 적용하는 것이 타당할 것으로 판단된다.

• Journal of Korea Water Resources Association
• /
• v.46 no.11
• /
• pp.1115-1128
• /
• 2013

The purpose of this study is to evaluate the suspended solids and eutrophication processes relationships in Chungju lake using CE-QUAL-W2, two-dimensional (2D) longitudinal/vertical hydrodynamic and water quality model. For water quality modeling, the lake segmentation was configured as 7 branches system according to their shape and tributary distribution. The model was calibrated (2010) and validated (2008) using 2 years of field data of water temperature, suspended solids (SS), total nitrogen (TN), total phosphorus (TP) and algae (Chl-a). The water temperature began to increase in depth from April and the stratification occurred at about 10 m early July heavy rain. The high SS concentration of the interflow density currents entering from the watershed was well simulated especially for July 2008 heavy rainfall event. The simulated concentration range of TN and TP was acceptable, but the errors might occur form the poor reflection for sedimentation velocity of nitrogen component and adsorption-sediment of phosphorus in model. The concentration of Chl-a was simulated well with the algal growth patterns in summer of 2010 and 2008, but the error of under estimation may come from the use of width-averaged velocity and concentration, not considering the actual to one side inclination by wind effect.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.26 no.1
• /
• pp.65-74
• /
• 2020

The purpose of this study was to investigate the physical characteristics of marine environment, and to predict the probability of the occurrence of hypoxia in the Dangdong bay. We predicted hypoxia using the logistic regression model analysis by observing the water temperature, salinity, and dissolved oxygen concentration. The analysis showed that the Brunt-Väisälä frequency which was shallow than the deep bay entrance, was higher inside the bay due to a lesser amount of fresh water inflow from the inner side of the bay, and density stratification was formed. The Richardson number, and Brunt-Väisälä frequency were very high occasionally from June to September; however, after September 2, the stratification had a tendency to decrease. Analysis of dissolved oxygen, water temperature, and salinity data observed in Dangdong bay showed that the dissolved oxygen concentration in the bottom layer was mostly affected by the temperature difference (dt) between the surface layer and bottom layer. Meanwhile, when the depth difference (dz) was set as a fixed variable, the probability of the occurrence of hypoxia varied with respect to the difference in water temperature. The depth difference (dz) was calculated to be 5 m, 10 m, 15 m, 20 m, and the difference in water temperature (dt) was found to be greater than 70 % at 8℃, 7℃, 5℃, and 3℃. This indicated that the larger the difference in depth in the bay, the smaller is the temperature difference required for the generation of hypoxia. In particular, the place in the bay, where the water depth dif erence was approximately 20 m, was found to generate hypoxia.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.23 no.6
• /
• pp.442-450
• /
• 2011

A three dimensional random walk particle tracking method is applied to the Saemangeum area in order to find stepwise environmental changes according to long term construction. Flow regime around Mangyeong, Dongjin and Geum river estuary changed greatly due to dike construction. It is distinctive that reduction of Byeonsan area's flow field and stagnant change in the northern part of the inner reservoir. Similar characteristics are found through the tidal excursion analysis. By analysis of the vertical mixing structures according to density stratification based on temperature and salinity variation, a salt wedge and very strong stratification arises in the inner part of the reservoir after final closure, while it has been well mixed or partially mixed estuary during construction. Shrinking of horizontal dispersion and vertical mixing capability may cause adverse effect on water quality not only inner part but also outer region of the Saemangeum reservoir.