• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.2
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• pp.76-93
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• 2013

The hydrodynamics in the Youngsan River Estuary has changed due to coastal developments such as the estuary dam and two tidal barriers. As the freshwater discharge is artificially controlled, the circulation pattern is different from those of natural estuaries and the river-born sediment supply is restricted. 3D numerical modeling system EFDC was applied to investigate the sediment transport pattern and budget in summer with river floods. The real-time driving forces and the fluvial sediment discharges from the watershed modeling were assigned for the simulation period. The size classes of sand, silt and clay were adopted based on the grain-size distribution of bottom sediments. The modeling results were calibrated and validated with the observed tides, tidal currents and suspended sediment concentrations. The suspended sediments are transported to the offshore at surface layer, whereas upstream toward the dam at mid- and bottom layers in August 2011. The characteristic estuarine circulation induced by the freshwater discharge from the dam, causes the deposition of silt-sized sediments on the whole and the sustained suspension of clay-sized sediments.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.1
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• pp.65-72
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• 1995

This paper describes the applications of the SCS TR-20 hydrologic model for simula- tion of hourly inflow rates from sixty-six ungaged tributaries and subareas between the Naju station and the estuarin dam at the Yongsan River Basin. The model was tested for the ungaged conditions with fifteen storm events at Naju station. Hourly simulated run- off data were compared with the observed, and the results showed less correlationships between the two data than those from TANK model. The coefficients of correlation ranged from 0.74 to 0.87. The curve numbers and time of concentration were defined from topographic dta for each of sixty-six tributaries for the estuarine dam and used for TR-20 applications. The results were within an acceptable range of errors in simulating the inflow fluctuations for the flood forecasting at the estuarine dam.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.21 no.3
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• pp.91-102
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• 2016

The spatio-temporal variations of the dissolved methane concentration were investigated and the methane budget was estimated in the Nakdong Estuary in January, September, and November of 2014. Dissolved methane showed seasonal variation (21~874 nM) with high concentration in summer due to enhanced temperature and fresh water discharge. Decreasing trends of dissolved methane from the river to the estuary were consistent in all seasons showing the main source of the estuarine methane is river discharge. However, the decreasing trends were modified seasonally due to the local sources such as organic-rich sediments in intertidal zone or near the estuarine barrage. Dissolved methane concentration in the Nakdong Estuary was high, compared to other estuaries probably due to the well developed wetland in Nakdong-river system and stagnation effect from barrages and dams. Dominant sink for the Nakdong estuarine methane was outflux into the atmosphere. Relatively long residence time (produced by barrier island and estuarine dam) in the estuary might provide the enough time for the outgassing.

• Journal of Soil and Groundwater Environment
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• v.18 no.3
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• pp.11-22
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• 2013

SEAWAT, a linked modeling program of Visual MODFLOW was used to analyze the change in groundwater levels and salinity related groundwater dam construction in Cheongsan island, Wando-Gun, Jeollanam-Do. The steady-state model results show the groundwater flow and salinity distribution of the studied area. The groundwater flows from north-west and south-east highlands into the river, located in the middle part of the basin, and is eventually discharged to the ocean. Part of the sea water infiltrates into the river; and through the estuary's alluvium aquifer, the sea water intrusion takes place spreading to about 830 m from the ocean. The transient model results show that after the groundwater dam construction, groundwater levels will rise to a maximum of 2.0 m upstream, and the groundwater storage will increase 21,000 after 10 years. Meanwhile 31% of the total area affected by sea water intrusion will decrease. To conclude, the groundwater dam is a very useful method for a secure water resource in preparation for drought and water shortages in the island regions.

• Korean Journal of Ecology and Environment
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• v.40 no.2
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• pp.273-284
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• 2007

The spatial and temporal zooplankton dynamics were examined along ca. 100-km section of the middle to lower Seomjin River (without estuary dam in river mouth) and Youngsan River (with estuary dam in river mouth) systems during study periods (2004. Nov.${\sim}$2006. Aug.) based on a monthly sampling intervals. The spatial variation of zooplankton biomass at both river ecosystems was distinct. There was considerable longitudinal variation in total zooplankton abundance in Youngsan R. stretch. The increase in total zooplankton abundance were observed along the longitudinal stretch toward the estuary dam. In contrast, there were not statistically significant longitudinal differences in total zooplankton abundance in Seomjin R. stretch. In Youngsan R. stretch, average abundance of total zooplankton (average ranges: $199{\sim}817$ Ind. $L^{-1}$ at 3 sampling sites, n=20) were nearly $4{\sim}60$ fold higher than that of Seomjin R. stretch (average ranges: $12{\sim}43$ Ind. $L^{-1}$ at 4 sampling sites, n=20). Relative abundance of rotifers (over 80% of total zooplankton abundance) at the whole sampling sites in Youngsan R. stretch were Much higher than that of the Seomjin R. stretch. The most abundant rotifers were Polyarthra spp., Brachionus spp., Colurella spp., and Keratella spp. at the both river ecosystems. In Seomjin R. stretch, copepods carbon biomass sharply increased toward in river mouth (over 40% of total zooplankton carbon biomass). Average ranges of total zooplankton filtering rates for phytoplankton at both river ecosystems varied from 21.2 to 92.9 mL $L^{-1}\;D^{-1}$ in Youngsan R. stretch and from 2.1 to 2.6 mL $L^{-1}\;D^{-1}$ in Seomjin R. stretch. Considering the zooplankton filtering rates, zooplankton as grazers of phytoplankton in Youngsan R. stretch seemed to play the more important role in planktonic food web than that of the Seomjin R. stretch.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.519-519
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• 2023

Estuarine dams are a recent and global phenomenon. While estuarine dams can provide the benefit of improved freshwater resources, they can also alter estuarine processes. Due to the wide range of estuarine types and estuarine dam configurations, the effect of estuarine dams on estuaries is not well understood in general. To develop a systematic understanding of the effect of estuarine dam location and freshwater discharge interval on a range of estuarine types (strongly stratified, partially mixed, periodically stratified, and well-mixed), this study used a coupled hydrodynamic-sediment dynamic numerical model (COAWST) and compared flow, sediment transport, and morphological conditions in the pre- and post-dam estuaries. For each estuarine type, scenarios with dam locations at 20, 55 and 90 km from the mouth and discharge intervals of a discharge every 0.5, 3, and 7 days were investigated. The results were analyzed in terms of change in tide, river discharge, estuarine classification, and sediment flux mechanism. The estuarine dam location primarily affected the tide-dominated estuaries, and the resonance length was an important length scale affecting the tidal currents and Stokes return flow. When the location was less than the resonance length, the tidal currents and Stokes return flow were most reduced due to the loss of tidal prism, the dead-end channel, and the shift from mixed to standing tides. The discharge interval primarily affected the river-dominated estuaries, and the tidal cycle period was an important time scale. When the interval was greater than the tidal cycle period, notable seaward discharge pulses and freshwater fronts occurred. Dams located near the mouth with large discharge interval differed the most from their pre-dam condition based on the estuarine classification. Greater discharge intervals, associated with large discharge magnitudes, resulted in scour and seaward sediment flux in the river-dominated estuaries, and the dam located near the resonance length resulted in the greatest landward tidal pumping sediment flux and deposition in the tide-dominated estuaries.

• Korean Journal of Ecology and Environment
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• v.46 no.4
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• pp.524-540
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• 2013

After the construction of the Geum River estuary dam, we investigated the ecological property of phytoplankton community with physicochemical property in 9 stations of Geum River estuary 4 times seasonally in 2010 about the environmental changes through the change of phytoplankton. Physicochemical property seems to show eutrophication which developed from the tendency of accruing of the nutrients (those involved in intermittency of freshwater which flows from the dike and the surrounding cities), caused by the changing of tidal flow, the decreasing of the inflow of seawater after the construction of the Geum River estuary dam (dike). A total of 233 species of species composition of phytoplankton emerged, showing a highly increased result compared to that of the former research. The reason for the increase in number is considered as a phenomenon resulting from the mix of blackish and freshwater marine species in the flow of intermittency of freshwater discharge. Also, the standing crops of phytoplankton considerably increased compared to when the dike had not yet been built. Highly affected by the discharge of occasional freshwater, the diatoms of blackish water zone dominated in spring and winter, while freshwater species appeared to dominate in summer and autumn. The species diversity showed over 2.0 except in winter season. After a cluster analysis, the result showed that the Geum River estuary was influenced by runoff from cities like Gunsan, the sewage which flows from Gyeongpo River, and the intermittency of freshwater discharge from the Geum River estuary dam.

• Journal of Wetlands Research
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• v.6 no.1
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• pp.149-166
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• 2004

Water quality and ecological environment in the Han River estuary was analyzed using the longterm water quality monitoring data from National Fisheries Research and Development Institute (NFRDI) and the existing data collected in this area. Based on the salinity distribution and changes of current direction in the lower Han River and its estuary, boundaries of the estuary were identified and also, distribution patterns of the phyto- and zooplankton, benthos, ichthyoplankton and fish were discussed related with the salinity changes in the macrotidal subestuary of Han River. Seasonal and spatial distribution of salinity suggested that the direct impact of freshwater be limited to the Incheon North Harbour all the year round and even extended to the southern area of Gyunggi Bay near Palmi island during limited time, usually in summer. Upper limit of salt water intrusion through the Han River is likely to be Singok underwater dam located Gimpo, Gyunggi Province, and normally limited to much lower part of the river, Jeonryuri, Gimpo. Biological boundaries of the Han River estuary exceeded the physical boundaries based on the salinity distribution. Many estuarine species in plankton and fish were found at the totally freshwater or saltwater depending on the seasons and tidal cycles. Some estuarine ichthyoplanktons showed extremely limited distributions in the estuary whereas adult fish revealed wide ranges of salinity adaptation. Critical environmental issues in the Han River estuary and its drainage basin are likely to be 1) pressure on development-promoted district for new town in the drainage area of the estuary, 2) reduction of tidal flat by reclamation, 3) pollutant input through river from municipal sewages and industrial wastes, and 4) ecological barrier between river and terrestrial systems by the military wire fence and riverside road.

• The Korean Journal of Quaternary Research
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• v.13 no.1
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• pp.67-78
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• 1999

In present, the terminal area of the Nagdong River Delta consists of micro-depositional landforms with sand barrier islands, sand bars and tidal flats which are arranged parallel to the present shoreline, and have rapidly shifted toward sea during last 100 years due to human activities such as construction of estuary dam, industrial complex and residential area. To clarify the landform changes of the area, the author traced the morphologic change pattern based on interpretation of air-photos, topographic maps and old Korean traditional map, and the results are as follows ; Based on the Daedongyeojido, one of the old Korean map, published in 1861, the area including upper part of the delta was underlying by sea level except two larger sand barriers, which means the Nagdong River Delta was not completely formed as the present outline of morphology by 1860s. According to the topographic map(1 :50,000) of 1916, the delta resembled to the present morphology pattern was exposed in 1916, and at this time the area was mainly composed of one sand barrier island, four sand bars and tidal flats, which had slowly elongated southwards before construction of the Nagdong River Estuary Dam in 1987. But after 1987, the area has been rapidly and drastically shifted southwards in arrange with one chain of sand barrier islands (Elsugdo -Myeonghodo-Sinhodo ) and four chains of sand bars (first chain ; Jinwoodo -Daemadeung-Maenggeummeorideung, second chain : Jangjado-Baeghabdeung, third chain ; Saedeung-Namusitdeung, fourth : Doyodeung-Dadaedeung) parallel to shoreline. This rapid landform change of the area is now occurring, and is seemed to ascribed firstly, to the construction of the Nagdong River Estuary Dam on Elsugdo in 1987, the Sinho Industrial Complex on Sinhodo and Myeongji Residential Area on Myeonghodo in 1992, secondly, to artificial alteration of drainage channel and consequential breakdown of former energy system between riverflow and tidal-and wave-energy. From these facts, it is inferred that the landform change pattern of the area will continue until a new equilibrium between the factor available to this energy system is accomplished.

• Journal of Korean Society of Disaster and Security
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• v.16 no.4
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• pp.157-164
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• 2023

The estuary dam is a structure installed and operated in a closed state except when flood event occurs to prevent inland saltwater intrusion and secure freshwater supply. However, the closed state of dam leads to issues such as eutrophication, so it is necessary to examine the extent of saltwater intrusion resulting from the opening of sluice gates. Groundwater, due to its subsurface conditions and slow flow characteristics, is widely analyzed using numerical models. OpenGeoSys, an open-source software capable of simulating Thermal- Hydraulic- Mechanical- Chemical phenomena, was adopted for this study. Simulations were conducted assuming natural flow conditions without dam and operating considering busy farming season, mostly from March to September. Verification of the model through analytical solutions showed error of 3.7%, confirming that OpenGeoSys is capable of simulating saltwater intrusion for these cases. From results simulated for 10 years, considering for the busy farming season, resulted in about 46% reduction in saltwater intrusion length compared to natural flow conditions, approximately 74.36 m. It may be helpful to make choices to use groundwater as a water resource.