• Journal of Ocean Engineering and Technology
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• v.20 no.6 s.73
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• pp.54-60
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• 2006

This study discusses characteristic of spatiotemporal changes of the sand barrier in the Nakdong estuarine for the last century, focusing on geomarphologic evolution and mobility of sand barriers in the view of coastal engineering. The Nakdong estuarine, the research subject, has a complexly changing natural environment by interaction between ground and marine elements such as ocean wave, tidal current, sediment, etc. Moreover, recently, unnatural geomorphologic changes (e.g., seaside reclamation, new harbor construction, etc.) has been radically increased in this area with increasing desire for coastal development. Because of this, its sand barrier has developed quite unstable condition. Therefore, to identify the development process of geomorphologic changes in this area, required is a close examination on historical characteristics of spatiotemporal changes of the sand barrier in relation to surrounding seaside reclamation and physical environmental changes. This study, based on the marine charts published in between 1927 and 1995 year, analyzes the length and area of the sand barrier for the last hundred years, and investigates the cause of the changes by looking into the change of water depth for the last two years and doing ocean-physical site observations. In conclusion, the sand barrier of the Nakdong estuarine expands toward the open sea by $7.4{\sim}26m$ in annual average, maintaining a fixed distance of $1,241{\sim}1.279m$, and its area is expected to increase about $2.8km^2$ annually. This is characterized by the wocean wave from the open sea and the discharge of Nakdong River.

• Journal of Ocean Engineering and Technology
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• v.21 no.2 s.75
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• pp.22-34
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• 2007

We present basic data for developing new research topics and closely examine the existing data on the development and organization of the Nakdong River Estuary Delta by analyzing various studies of the area, including ocean engineering, coastal engineering, ocean environmental engineering, geomorphological, and geological studies. We first defined the general concepts related to the estuary and delta and reviewed the historical development of the Nakdong River Estuary Delta over the past 100 years. We then examined the origin and core elements of the estuary deposits that constitute the delta. In addition, we scrutinized the main factors affecting the development of the delta and analyzed existing research on delta development mechanisms by core researchers. The construction of an estuary barrage is one of the main factors effecting estuarine circulation and has altered the physical oceanic environment, area of deposition, atmospheric environment, and vegetation community of the delta. These factors affect the estuary circulation in turn, altering the delta. Along the Nakdong River, an unsteady-state sandy barrier appears at approximately three times the distance of the wavelength of incident offshore waves, and this terrain forms approximately 10-15 years after reclamation in the interdistributary upper stream and transforms the shoreline. It is necessary to develop a technique to predict terrain change that reproduces the erosion and accumulation of estuarine deposits. To determine the parameters and variables necessary to reproduce this system, continuous on-site monitoring is necessary. The existing research did not fully examine the terrain changes in Nakdong River Estuary or the periodic developmental characteristics. To understand the future process of estuary delta development, it is necessary to establish an integrated management system.

• 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.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1013-1022
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• 2005

Because depth of deposit is deeper as well as compressibility is very larger than the other regions in Korea, behaviour of settlement at Nak-Dong river estuarine causes hot issue at ground improvement. Defined properties for design differ from measurement. Therefore it affects cost of construction. This study presents design standard to engineers as it defined properties of compressibility at Jangyu Area of Nak-Dong river estuarine. To search value of representation for region, back analysis was performed using the measurement. To verify that, the measurement of recently designed site was confirmed, and the cost of construction with properties of consolidation was calculated.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.1
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• pp.11-20
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• 2006

The Nakdong Estuary is complex water system, where sea water and fresh water meet each other. It has undergone the significant change of its environmental conditions since the construction of the Nakdong River Barrier in 1987. Prior to its construction, mixing and circulation processes in the Nakdong Estuary was dominated by tidal current. However, after the dam construction, those processes were greatly altered by the artificial control of the fresh river water discharge. In this paper, the influence of opening and closing the floodgate of Nakdong River on the outflow behavior of estuarine water from the Nakdong Estuary is analyzed in detail.

• Korean Journal of Ecology and Environment
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• v.38 no.2 s.112
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• pp.160-180
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• 2005

Long-term data (Ministry of Environment Water Quality Monitoring data) of phytoplankton biomass (chlorophyll a) and water quality were analyzed to investigate trends in biomass of the primary producers and water quality for the estuarine systems in Korea: Sumjin River, Han River, Asan Lake- Bay, Youngsan River, Keum River and Nakdong River. The literatures were also reviewed to examine the characteristics of phytoplankton biomass and water quality in the estuarine systems. The Sumjin River estuary, the single estuary without a dike in Korea showed the characteristics similar to other typical estuarine systems. Phytoplankton biomass was high during the fall at transitional regions (5 ${\sim}$ 15 psu) after riverine freshwater inputs were increased in summer. Concentrations of the nitrate and silicate were increased with the high river discharge rates. Phytoplankton biomass and nutrient concentrations were high during spring at the lower regions in the Han River whereas phytoplankton biomass and nutrient concentrations were high during spring at the upper regions in the Youngsan River. Phytoplankton biomass was the highest in the Asan Lake and nutrient concentrations were high at the upper region of the lake. In Nakdong River, phytoplankton biomass was high during winter and the biomass was slightly higher at upper region than at lower region. Long-term trends showed that total nitrogen and total phosphorus were mostly increased in the river systems. Implications of these results relevant to the water quality management for the river systems were also discussed.

• Journal of Ecology and Environment
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• v.37 no.4
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• pp.217-223
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• 2014

We conducted a distributional survey of Pectinatella magnifica, an invasive species, in the Geum River and the Nakdong River from July 12 to July 25, 2014. The spacing between the study sites was 10 km along the main channels for the Geum River (n = 12, 120 km) and the Nakdong River (n = 38, 380 km) from the estuarine barrage to upper part of main channel. Pectinatella magnifica was detected along the riparian zone (within 100 m) at each of the study sites. Presence rate of P. magnifica in Geum River and Nakdong River was 25% and 32.6%, respectively. The colony number of P. magnifica at Geum River ($9.5{\pm}3.1colony/m$, n = 3) was over 94 fold higher than that in the Nakdong River ($0.1{\pm}0.1colony/m$, n = 16). The Total length distribution of P. magnifica had a truncated bell shape at each rivers (mean length: $14.0{\pm}1.2cm$ for Geum River (n = 32), and $16.8{\pm}1.4cm$ for Nakdong River (n = 52)). These findings could provide basic information regarding the distribution pattern of P. magnifica in a new invasion area.

• Korean Journal of Environmental Biology
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• v.35 no.3
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• pp.227-239
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• 2017

To find unrecorded diatom species in the Nakdong River Estuary and Yeongil Bay, bottom sediments in the estuary, and seagrasses in the bay were collected from 12 sampling sites. Eighteen species and four genera are added to the national flora of diatom as newly recorded one. In the Nakdong River Estuary, twelve species are new records to Korea, Martyana atomus (Hustedt) Snoeijs, Pseudostaurosira perminuta (Grunow) Sabbe & Vyverman, Trachysphenia acuminata M. Peragallo, Trachysphenia australis Petit, Fallacia clipeiformis ($K{\ddot{o}}nig$) D.G. Mann, Amphora graeffeana Hendey, Amphora jostesorum Witkowski, Metzeltin & Lange-Bertalot, Amphora ostrearia var. vitrea (Cleve) Cleve, Amphora wisei (Salah) Simonsen, Halamphora eunotia (Cleve) Levkov, Halamphora lineata (Gregory) Levkov, Nitzschia littorea Grunow. In Yeongil Bay, four species are added as new, Licmophora gracilis var. anglica ($K{\ddot{u}}tzing$) H. Peragallo & M. Peragallo, Tabularia investiens (W. Smith) Williams & Round, Nitzschia composita Giffen, Nagumoea neritica Witkowski & Kociolek. Two species occurred simultaneously in both regions, Fragilaria cassubica Witkowski & Lange-Bertalot and Hyalinella lateripunctata Witkowski et al.

• Journal of the korean society of oceanography
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• v.38 no.2
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• pp.80-86
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• 2003

The horizontal distributions of $^{224}Ra$ (half life=3.4 days) and $^{223}Ra$ (half life=11.3 days) were measured in surface seawaters of the Nakdong River estuary and the South Sea of Korea in April and October 2002. In order to determine these short-lived Ra isotopes, we used a delayed coincidence counter which is much more rapid and accurate than traditional methods. In an estuarine mixing zone (salinity, ~l6 ppt), the activities of $^{224}Ra\;and\;^{223}Ra$ were much greater than what would be expected from a mixture of freshwater and seawater in the Nakdong River estuary. This excess Ra may be a result of Ra desorption from fresh sediments originating from the river upstream. However, in the more open areas of the Nakdong River estuary (salinity>30 ppt) and the South Sea of Korea, $^{224}Ra\;and\;^{^{223}Ra$ activities decreased exponentially as a function of distance offshore. Using the decrease of $^{223}Ra$ with distance offshore in the South Sea of Korea, we estimated the apparent horizontal eddy diffusivities. The apparent eddy diffusion coefficients in South Sea of Korea are calculated to be approximately $3500-8000\;\textrm{m}^2/sec$.

• Korean Journal of Ecology and Environment
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• v.40 no.4
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• pp.576-580
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• 2007

Phytoplankton community dynamics were studied from 2004 to 2006 with two and four weeks interval at mid to lower part of the Nakdong River (Waegwan: RK 194, Goryeong: RK 157, Jukpo: RK 112, Namji: RK 75 and Hanam: RK 63: RK: distance from the Estuarine Barrage), South Korea. Annual averages of water temperature was about $16^{\circ}C$, and dissolved oxygen was ranged between 10.0 and 11.5 mg $L^{-1}$ (percent saturation, 106.5 to 112.8%). Diatoms were dominant group with over 60% of phytoplankton abundance in all study sites (Waegwan: 64%, Goryeong: 69%, Jukpo: 73%, Namji: 79%, and Hanam: 83%). However, the occasional dominances of other groups such as green algae and blue-green algae were observed from March to October. Stephanodiscus hantzschii was dominant species and the relative abundances were highat all study sites (48-72%). The ratio of S. hantzschiiltotal phytoplankton abundance were showed a clear increasing tendency toward the estuarine barrage: i.e. 0.31 at Waegwan, 0.39: Goryeong, 0.50: Jukpo, 0.56: Namji, 0.60: Hanam. The results of this study provide the information that the phytoplankton community structure in a regulated river system is basically affected by the physical properties such as water velocity and retention time, resulting in single species dominance by the stagnancy of river flow.