• Journal of Korea Water Resources Association
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• v.45 no.7
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• pp.675-684
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• 2012

Recently, a heavy rainfall under climate change causes the flood exceeded river's conveyance. Flood control methods under the limited river width are the increase of embankment, the construction of storage pockets and diversion channel, the dredging of river bed. Hwasun flood control reservoir of washland is designed as the storage pockets and the regulating gate for the control of water level. In this study, the propriety of design was investigated through hydraulic experiments for the circumstances to exclude the constant flood discharge during operation period. In the results, the over flow rate of side weir exceeded the flow of design and indicated to be able to discharge the designed flow in the regulating gate opened 1.1 m. The high velocity 7.1 m/s behind the gate has investigated to reduce under 3.3 m/s by the baffle block.

• Journal of the Korean association of regional geographers
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• v.10 no.3
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• pp.568-578
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• 2004

This study is aimed at investigating floodgate characteristics and environmental issues in Gwangjucheon and examining possible problems of expanding river maintenance water being carried on in the context of river recovery works. In general, the obtained results show the following. The treatment water provisioned in the restoration project of the drying stream going through the water circulation device can pollute the land and groundwater in the Gwangjucheon Basin. Besides, although about $17,565m^3$/day of water is available in the upper ground, most of it go to the junction and exhausting directly to the waste water treatment or going into the groundwater. Because of the drying stream, the amount of water going to the ground is increased. Therefore, efficient land use along with regulations to protect cultivated land and ensure recovery works of city stream through the recovery of water circulation by constructing and expanding a special drainage system are of vital importance.

• Korean Journal of Ecology and Environment
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• v.53 no.4
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• pp.453-460
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• 2020

Bolboschoenus planiculmis is an important prey species for winter migratory birds in the Nakdong River Estuary region, but its population has declined in the last decade due to a physio-chemical shift. To identify the growth and development characteristics of B. planiculmis, we carried out an experimental survey on the aboveground and belowground sections of B. planiculmis specimens in the Eulsuk tidal flat from April to September 2019. We divided the belowground area into two groups: a vegetation group in which B. planiculmis exists and a non-vegetation group in which B. planiculmis does not exist and measured the rate of tubers. We observed a 45% appearance frequency in the vegetation group and only a 5% frequency in the non-vegetation group, indicating that there were no supplies for plant growth. The mean density, length, and biomass of B. planiculmis aboveground were 166.90±149.62 n m^-2, 44.39±5.45 cm, and 67.63±54.46 g DW m^-2, respectively, which was approximately half of those obtained from the study in the Eulsuk tidal flat in 2002. Tuber number was the highest in the 15~25 cm deep layer(41.50%). The mean number of total tubers belowground was related to different sediment conditions(FS: flat surface, DS: disturbed surface) 251.75±16.86 n pot^-1 for FS and 171.00±25.18 n pot^-1 for DS, which was significantly different(total tubers: p<0.005). The mean biomass of B. planiculmis above-ground was 21.11±1.60 g DW pot^-1 for FS and 15.41±1.38 g DW pot^-1 for DS, which was significantly different(p<0.05). This research provides primary materials for the restoration of the Nakdong River Estuary, wintering sites for migratory birds, and protection of B. planiculmis.

• Journal of Korea Water Resources Association
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• v.44 no.10
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• pp.787-795
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• 2011

Extreme water events such as heavy rainfalls due to recent climate change are continually increasing and their scale has also shown an increasing trend. To overcome these natural disasters, this policy study suggests securing lateral river space as an effective method for extreme flood. To support the importance of restoration and expansion of lateral river space, Gumi upstream region of the Nakdong River basin was chosen as a target area and flood reduction analysis of the washland by using LISFLOOD model have been examined. The 500-year frequency flood was simulated for the estimation of possibly occurable flood level and it turns out that the secured lateral river space on the selected site effectively lowers about 0.53 m flood level and reduces the flood damage of the city on the lower reaches of the river. In addition, based on this result, multilateral river space securing plans were compared, and conservation easement and natural disaster insurance were suggested for sustainable and cost-effective alternatives. The costs of land purchase and conservation easement for securing the river space were also compared.

• Korean Journal of Environment and Ecology
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• v.34 no.3
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• pp.191-197
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• 2020

The purpose of this was to examine the differences of large whopper swan (Cygnus cygnus) in wintering habitat preference among bridge sections of the lower Nakdong River of the Nakdong River Estuary, the largest whopper swan's wintering habitat in Korea. This species is designated and protected as Natural Monument in Korea. The survey was conducted in six time-series during the 2018~2019 wintering season, and it found up to 500 whopper swans were wintering in the lower Nakdong River. For the survey, a seven sections were set up based on the bridges across the river. Whopper swans were rarely observed in five narrow sections where the distance between bridges was less than 2 km. The stable population of the whopper swan was observed only in two broader sections where the distance between bridges was is over 4 km. As these sections were relatively little affected by artificial interference, the distance from the mouth of the Nakdong River was not a factor. Securing a stable space is considered as one of the most important factors for wintering of whopper swans, which are an endangered species. The survey results indicate that the distance between bridges should be at least 4 km to secure the whopper swan's stable habitat. These results are expected to be a reference to the development or restoration of the river ecosystems, especially bridge construction.

• Journal of Advanced Marine Engineering and Technology
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• v.40 no.1
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• pp.69-74
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• 2016

Bathymetric changes were studied in the southern sea off the Jinwoo-do Island, which is one of the deltaic barrier islands surrounding the Nakddong river estuary. In this study, 16 bathymetry data sets were obtained from June 2006 to April 2015. Two narrow channels, the one lying between Jinwoo-do and Shinja-do, and the other one lying between Nulcha-do and Jinwoo-do extended into the eastern and western parts of the study area, respectively. The eastern extension of the channel contained a passage of mixed estuarine waters of seawater and river water discharged from the Nakdong river barrier and the west Nakdong River. The western channel connected the Nakdong River estuary with the Busan New Port via a connecting pier. Total volumetric changes of sediments in study area and discharge flow of the Nakdong river barrier were analyzed. Bottom topographical changes occurred mainly in the eastern extension of the channel. These changes were initially characterized by gradual erosion or deposition followed by rapid restoration. The total volume of sediment gradually increased from June 2006 to March 2013, but experienced a sudden decrease in October 2013 because of typhoon Danas. Few fluctuations were observed from October 2013 to April 2015. Analysis of the cross-sectional bathymetry of the north-south direction showed that the deepest point of the eastern channel moved 100-130 m westward and 200 m northward between June 2006 and April 2015.

• Journal of Korean Society on Water Environment
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• v.28 no.4
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• pp.561-573
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• 2012

The object of this study was to analyze long-term water quality gradients during 1992-2008 at six sites of Geumho River and near-by two sites of Nakdong River and their influences on fish trophic guilds and tolerance guilds along with ecological health. Water quality including biological oxygen demand (BOD), chemical oxygen demand (COD), conductivity, total phosphorus (TP), total nitrogen (TN), and total suspended solids (TSS) varied largely depending on the sampling locations and seasons. Values of ambient BOD, COD, TP, and TN were greater in the downstream than in the upstream reach, and seasonal and interannual variabilities were also higher in the downstreams. This phenomenon was evident due to a dilution by the Asian monsoon rainfall during the monsoon. These outcomes indicate that point sources near the downstream are important for the chemical conditions, but also seasonal stream runoff was considered as an important factor regulating the chemical conditions. Conductivity decreased rapidly during the summer due to ionic dilution, and nutrients (N, P), BOD, COD had an inverse function of seasonal precipitation. Based on the water quality, we selected two sites (control site = $C_s$ vs. impacted site = $I_s$) for impact analysis of water chemistry on fish community and trophic/tolerant guilds. Fish guild analysis showed that species diversity was higher in the headwater stream ($C_s$) than the impacted downstream ($I_s$), and that the proportion of tolerant and omnivore species were greater in the impacted site of downstream. Comparisons of water quality between Geumho River and Nakdong River indicated that Geumho River was considered as a point source which degradated water quality to the Nakdong River. Overall, chemical water quality and fish guild analysis suggest that even if current chemical quality got better after 1996 due to continuous constructions of wastewater disposal plants near the downstreams, fish compositions of tolerant and omnivores were still dominated the community. Thus, biological restoration based on ecological health is required for the ecosystem conservation.

• Journal of Environmental Science International
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• v.18 no.9
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• pp.971-981
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• 2009

An objective of this study is as follows: 1) performing sensitivity analysis and parameter estimation of RMA2 and RMA4 models for the West-Nakdong River, 2) drawing up alternatives of gates-operation for water-quality enhancement, and 3) quantitative evaluation of methodology of 'flow-restoration by gates-operation' among 'Comprehensive Plan Improving Water-Quality in the West-Nakdong River(WNR)' with the target water-quality(BOD at Nakbon-N point: below 4.3 mg/L). The parameters for the RMA2 (depth-averaged two-dimensional flow model) and RMA4 (depth-averaged two-dimensional water-quality model) were determined by sensitivity analysis. Result of parameter estimation for RMA2 and RMA4 models is $1,000\;Pa{\cdot}s$ of the eddy viscosity, 20 of the Peclet number, 0.025 of the Manning coefficient, and $1.0\;m^2/s$ of the diffusion coefficient. We have evaluated the effects of water-quality enhancement of the selected alternatives by numerical simulation technique with the models under the steady-state flow condition and the time-variant transport condition. Because of no-resuspension from river bottom and considering BOD as conservative matter, these simulation results slightly differ from real phenomena. In the case of $50\;m^3/s$ of Daejeo-gate inflow, two-dimensional flow pn results result represents that small velocity occurs in the Pyungkang Stream and no flow in the Maekdo River. In the WNR, there occurs the most rapid flow near timhae-bridge. In the WNR, changes of water-quality for the four selected simulation cases(6, 10, 30, $50\;m^3/s$ of the Daejeo-gate inflow) were predicted. Since the Daejeo-Gate and the Noksan-Gate can be opened up to 7 days, it would be found that sustainable inflow of $30\;m^3/s$ at the Daejeo-gate makes BOD in the WNR to be under the target of water-quality.

• Journal of the Korean Geographical Society
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• v.49 no.3
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• pp.321-338
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• 2014

This study aims to identify spatial distribution of estuarine wetlands in Korea, and to assess temporal variation of the wetlands in the last few decades. Widely known in environmental and coastal management, watershed-based regions which composed with Han-river(western and eastern parts), Keum-river, Yeoungsan-river, Seomjin-river, Nakdong-river, and Jeju, are analyzed to evaluate temporal change of estuarine wetlands in the 1980s, 1990s, and 2000s, through the land-cover map. Results show that estuarine wetlands dramatically decreased in Han-river(western part), Keum-river, Yeoungsan-river that estuarine circulation have been interrupted with man-made structures such as dyke and drainage. But, estuarine wetlands surrounded by forests and grasslands has been relatively less damaged. Habitat diversity providing healthy estuary ecosystem is lower in interrupted estuaries than circulated estuaries, which are composed of tidal-flat, open water, salt marsh, rocky coasts and sandy shoreline. This study indicates that spatial distribution and temporal variation of estuarine wetlands are different with estuary type and region, so estuary type with seven regions can be applied to provides a framework for estuary management strategies and to establish estuary restoration plans.

• Journal of Korea Water Resources Association
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• v.49 no.10
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• pp.809-821
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• 2016

The study area is local river of 671 (total length 3,741 km) in Gyeongnam prefecture, the results are as follows. Total number of river-crossing structures was investigated as 7,730, and it was found that structures were installed in 2.1 sites per 1 km (river length) on average. Diversion weirs for agriculture were 4006 (51.82%) and drop structures for channel bed maintenance were 3670 (47.48%), but the rest (riverbed road etc.) were 54 (0.70%). The number of high structures (height > 1.0 m) that affect many impact in upstream and downstream was investigated as 3,897 (51%), and the number of low structures (height < 0.5 m) that affect negligibly was 1109 (14%). Fish ladders have been installed on 640 (8%) structures in 153 (23%) rivers. In flood control and environment conservation, river-crossing structures brought about various impact that flood water level is raises and the eco-corridor is intercept. In order to improve these problems, we proposed a few engineering measures that can be realize with respect to river-crossing structures.