• Title, Summary, Keyword: Freshwater discharge

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Experimental Study of Freshwater Discharge and Saltwater Intrusion Control in Coastal Aquifer (해안대수층에서 담수-염수 경계면 변화에 따른 최대담수양수량과 염수침투제어에 대한 실험적 연구)

  • Suh, Seong-Kook;Oh, Chang-Moo;Kim, Won-Il;Ho, Jung-Seok
    • Journal of Korean Society of Hazard Mitigation
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    • v.10 no.5
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    • pp.159-168
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    • 2010
  • This study investigates the relationships between the maximum freshwater pumping discharge and hydraulic properties of coastal aquifer using a laboratory model. The experiment performed the fresh pumping test in various locations near the saltwedge induced by saltwater intrusion to freshwater over aquifer characteristics of hydraulic conductivity, salinity, and ground surface slope. Saltwater pumping also tested to protest saltwater intrusion to the excessively discharging freshwater well. The maximum freshwater discharges were achieved, and then the optimum saltwater discharges were measured. It is found that greater hydraulic conductivity and ground surface slope produced greater the maximum freshwater pumping discharge. Salinity gave less impact on the pumping discharge relatively. Higher freshwater discharge was found at higher hydraulic conductivity and steeper ground surface slope. The optimum saltwater discharge required 14% more pumping rate than the maximum freshwater discharge to keep saltwater intrusion to the freshwater pumping well. Pumping well located closer to salt-wedge profile promoted less freshwater pumping discharge. Therefore, pumping well location, hydraulic conductivity, ground surface slope, and salinity should be taken into account in freshwater pumping in coastal aquifer.

Phytoplankton Community and Surrounding Water Conditions in the Youngsan River Estuary: Weekly Variation in the Saltwater Zone (영산강 하구의 식물플랑크톤 군집 및 수 환경: 해수역의 주별 변동)

  • Sin, Yongsik;Yu, Haengsun
    • Ocean and Polar Research
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    • v.40 no.4
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    • pp.191-202
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    • 2018
  • In this study we conducted a weekly monitoring exercise at a fixed station in the saltwater zone during the dry season (Jan-Mar, 2013) and wet season (Jun-Aug, 2013) to understand the fluctuations in phytoplankton communities and environmental factors in the Youngsan River estuary altered by a dike constructed in the coastal area. Phytoplankton communities displayed seasonality; diatoms were dominant during the dry season whereas dinoflagellates were dominant during the wet season. T-test analysis showed that water temperature was significantly different between the seasons whereas freshwater discharge from the dike was not significantly different. This suggests that seasonal variations of phytoplankton are more likely affected by water temperature than freshwater discharge. However, a short-term fluctuation was also observed in response to freshwater discharge; freshwater species appeared during or after the discharge in the dry and wet seasons and blooms of harmful species developed after the discharge. Phytoplankton communities may be affected by changes in physical factors such as turbidity and salinity and nutrient supply resulting from freshwater discharge. Especially, the nutrient supply may directly contribute to the harmful algal blooms (HABs) composed of dinoflagellates which can adapt to low salinity after freshwater discharge.

Effect of the Freshwater Discharge on Water Quality Variation and in Haechang Bay, Korea (해창만의 수질환경변동 및 담수방류의 영향평가)

  • Lee, Dae-In;Cho, Hyeon-Seo;Lee, Moon-Ok
    • Journal of Environmental Impact Assessment
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    • v.12 no.5
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    • pp.341-348
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    • 2003
  • Seasonal characteristics of water quality and effect of the freshwater discharge during open the tide embankment in Haechang Bay were evaluated. In the freshwater, where interior of the tide embankment, COD and Chl-a exceeded about 4mg/L and $10mg/m^3$, respectively, independent of season, while in the seawater they showed high values in April and July in contrast to the other period due to input of freshwater and increase of phytoplankton, respectively. The content of seawater inorganic nitrogen maintained a relatively high level at inner part of the bay, whereas high values of inorganic phosphorus content was distributed at all over the bay. The limiting factor for algal growth was nitrogen with respect to the N/P ratio. The compass of influence by the freshwater discharge in April was quite different with water pollutants. As a result of the salinity variation with time, the freshwater extended strongly to offshore from the surface layer without mixing with depth when open the tide embankment, and reached within about one hour at a station which is 3.5km from the tide embankment. To effective water quality management of Haechang Bay, discharge rate and pollutant loads should be controlled.

Changes in Phytoplankton Community Structure by Freshwater Input in the Cheonsu Bay, Korea (담수 유입에 따른 천수만 해역의 식물플랑크톤 군집 변화)

  • Lee, Seung-Min;Chang, Soo-Jung;Heo, Seung
    • Journal of Environmental Science International
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    • v.28 no.11
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    • pp.1005-1017
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    • 2019
  • Environmental factors and changes in phytoplankton community structure before (August 5, 2017), during (August 18 and 25) and after (August 30 and September 15) freshwater input were analyzed to investigate the effects of freshwater input from Ganwol and Bunam lakes located in the upper part of Cheonsu Bay. Due to the large amount of freshwater input in the Cheonsu Bay, the surface salinity of the bay decreased by more than 8 psu, and the thermocline existing in the bay during August weakened. In addition, hypoxic phenomena occurred temporarily in the bay as the low oxygen water mass from the freshwater lakes flowed into the bay, and chemical oxygen demand, nutrients, and N/P increased with freshwater inflow. The density of phytoplankton during the freshwater inflow increased owing to their input from the freshwater lakes. Diatom species (Eucampia zodiacus) dominated the phytoplankton community in the bay before freshwater input; nanoflagellates, chlorophyta, cyanobacteria, and diatoms (Pseudonitzschia delicatissima, Chateocceros spp.) entered during freshwater input; and after freshwater inflow ended, diatoms (Chateocceros spp.) again became predominant indicating a return to previous conditions. The amount of phytoplankton standing crops increased sharply due to the inflow of freshwater species into the bay on the second day of discharge compared to before freshwater input; pre-discharge conditions were restored at most stations except at some sites close to the Bunam Lake three days after discharge. Therefore, the large amount of freshwater flowing into the bay affects not only the geochemical circulation in the bay but also the phytoplankton community structure. In particular, the high concentration of nutrients in the freshwater lake affect the marine ecosystem of the bay during August.

DETECTION OF GROUNDWATER DISCHARGE POINTS IN COASTAL REGIONS AROUND MT. CHOKAISAN, JAPAN BY USING LANDSAT ETM+ DATA

  • Kageyama, Yoichi;Shibata, Chieko;Nishida, Makoto
    • Proceedings of the KSRS Conference
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    • pp.57-60
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    • 2008
  • The flow of freshwater into the sea, termed as submarine groundwater discharge, is a key factor for understanding the hydrological cycle in both the sea and land regions. The numerous positions from which freshwater gushes out or its quantity impedes the understanding of its properties. Therefore, this study detects groundwater discharge points arising due to the difference in freshwater and seawater by using the multispectral Landsat ETM+ signals. A case study in coastal regions around Mt. Chokaisan, Japan is performed. This study comprises three procedures: (1) computer simulation of the flow of submarine groundwater discharge in the study area, (2) performance of preliminary experiment on the band properties of the Landsat ETM+, (3) detection of the difference in water properties by using the Landsat multispectral bands. Our experimental results obtained by the Landsat ETM+ are in considerable agreement with the realities in the study area.

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Effect of Freshwater Discharge on the Nakdong River Estuary: Mooring Observations of Water Temperature and Salinity (낙동강 하구의 담수 방류와 표층 수온 및 염분 반응 : 계류형 센서 연속관측 결과)

  • Kim, Sangil;Youn, Seok-Hyun
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.25 no.1
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    • pp.89-95
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    • 2019
  • Mooring observations of water temperature and salinity were conducted to investigate the effects of freshwater discharge patterns on the mouth of Nakdong River from April 2017 to March 2018. More than $500-1000m^3\;s^{-1}\;d^{-1}$ of freshwater was frequently discharged into the estuary throughout the rainy season, but less than $200m^3\;s^{-1}\;d^{-1}$ was discharged through the normal season. Sluice gates of the estuarine barrage operated depending on the tide level during spring tide, but they were constantly open during neap tide. Water temperature and salinity fluctuated regularly with intermittent discharges of freshwater, whereas they were stable while freshwater discharge was continuous. Mean salinity was 29 during the study period. Salinity exceeded the mean value in the normal season and rapidly recovered after a temporary reduction. In contrast, water with salinity below the mean value prevailed in the estuary for three months over the rainy season. These results indicate that water temperature and salinity were affected by the amount of freshwater discharge, as well as the frequency of discharge on a large scale and the time over which the freshwater discharge continued.

Water Quality Behavior by the Sluice Gate Operation of Freshwater Lake (배수갑문 방류시점 및 방류량에 따른 담수호의 수질변화)

  • 김선주;김성준;김필식;이창형
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.45 no.1
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    • pp.91-101
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    • 2003
  • Boryeong Seadike located at southwestern seashore of Korean peninsula completed in 1997. Sluice gate operation can be an important factor to maintain lake water quality and reduce retaining time of pollutants within lake. The lake water quality simulation model, WASPS was adopted and tested to find out proper gate operation timing and discharge amount. From the simulation of sluice gate operation, the results showed that the later the time of discharge for loosing 1 day successively to 6 days, the better the quality of water. Discharge amount showed relatively minor changes of water quality. This means that pollutants flowed into lake from watershed do not have enough time to mix up with deep water when the gate opened at early time. About 3 days delay of discharge caused the dilution effect to stabilize the lake water quality in case of Boryeong freshwater lake.

The numerical simulation on variation of phytoplankton maximum region in the estuary of Nakdong river -I. The state of variation of phytoplankton maximum region- (낙동강 하구해역의 식물플랑크톤 극대역 변동에 관한 수직시뮬레이션 -I. 식물플랑크톤 극대역 변동 현황-)

  • 이대인
    • Journal of Environmental Science International
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    • v.9 no.5
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    • pp.369-374
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    • 2000
  • The estuary of Nakdong river is very influenced by the freshwater contained nutrients and organic materials. The response results of these influences are eutrophication and red tide outbreak in this region. Concentration of chlorophyll a was 0.78~62.55$\mu\textrm{g}$/L in February 1.20~21.29$\mu\textrm{g}$/L in April 1.88~188.35$\mu\textrm{g}$/L in June and 0.78~11.21$\mu\textrm{g}$/L in August respectively. The decrease of chlorophyll a is considered that residence time is shorten by increase of freshwater discharge and unfavorable growth condition of phytoplankton is created by diffusion of low salinity and increase of turbidity. The phytoplankton maximum region located inner side of this estuary during winter season whereas it was moved to outer side when mean discharge of the Nakdong risver was increased, Therefore the variation of phytoplankton maximum region was affected by input discharge from the Nakdong river basin.

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Effect of the Freshwater Discharge on Seawater and Sediment Environment in a Coastal Area in Goheung County, South Korea

  • Nguyen, Hoang Lam;Jang, Min-Seok;Cho, Hyeon-Seo
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.20 no.3
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    • pp.270-276
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    • 2014
  • Seasonal characteristics of water and sediment qualities and potential effects of the freshwater discharge from a small tide embankment interior in a coastal area in Goheung county were investigated from May to September in 2012. Chemical oxygen demand values (COD) were mostly higher than 2 mg/L in summer ebb tide, which exceed the standard value of water quality criteria II of acceptable level for aquaculture activities. Nitrogen and phosphorus were found as the limiting nutrients for algae growth in summer and fall and in spring, respectively. Nitrogen was the limiting nutrient for diatom growth in the whole studied period. The sudden high values of COD, ammonia, dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP) were found in water sample collected from station 5 which located in front of the tide embankment sluice gate during spring ebb tide. The freshwater discharge form the tide embankment interior maybe affected the survey areas during a short time interval. Mean values of eutrophication index of the surveyed coastal region in spring, summer and fall were all bigger than 1. Water quality was mostly considered at level II which acceptable for aquaculture activities. Sediment quality in this study was generally in the range of standard for fisheries environment.

A Study of Transient Estuarine Circulation in the Chunsu Bay, Yellow Sea: Impact of Freshwater Discharge by Artificial Dikes

  • Jeong, Kwang-Young;Ro, Young Jae;Kang, Tae Soon;Choi, Yang Ho;Kim, Changsin;Kim, Baek Jin
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.26 no.3
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    • pp.242-253
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    • 2020
  • This study examined the ef ects of freshwater discharge by artificial dikes from the Kanwol and Bunam lakes on the dynamics in the Chunsu Bay, Yellow Sea, Korea, during the summer season based on three-dimensional numerical modeling experiments. Model performances were evaluated in terms of skill scores for tidal elevation, velocity, temperature, and salinity and these scores mostly exceeded 90 %. The variability in residual currents before and after the freshwater discharge was examined. The large amount of lake water discharge through artificial dikes may result in a dramatically changed density field in the Chunsu Bay, leading to an estuarine circulation system. The density-driven current formed as a result of the freshwater inflow through the artificial dikes (Kanwol/Bunam) caused a partial change in the tidal circulation and a change in the scale and location of paired residual eddies. The stratification formed by strengthened static stability following the freshwater discharge led to a dramatic increase in the Richardson number and lasted for a few weeks. The strong stratification suppressed the vertical flux and inhibited surface aerated water mixing with bottom water. This phenomenon would have direct and indirect impacts on the marine environment such as hypoxia/anoxia formation at the bottom.