• Korean Journal of Ecology and Environment
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• v.37 no.1 s.106
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• pp.57-63
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• 2004

Primary productivity of phytoplankton was measured by $^{14}C$ method from January to October of 1996 in Seonakdong River. This river was a highly productive freshwater showing the euphotic depth of 1.4 m in August and 2.1 m in the remaining season. Chlorophyll-a concentrations of phytoplankton ranged from 67 ${\mu}g\;L^{-1}$ to 894 ${\mu}g\;L^{-1}$ and showed the great increase in August. Maximum specific productivity was 2.1 ${\sim}$4.3 mg C mg $chl-a{-1}\;hr^{-1}$ and occurred above 0.4m depth. In photosynthesis-irradiance relation, photoinhibition or photosynthetic suppression of phytoplankton occurred clearly in the cold seasons, while phytoplankton (mainly Microcystis aeruginosa and its relatives) in August did not show any symptom of the photosynthetic inhibition against the high irradiance. The specific productivity of phytoplankton was eventually dependant upon incident irradiance to show the linear correlation with received irradiance infield, and the areal productivity of phytoplankton upon chlorophyll-a standing crops. In the downstream of the Nakdong River, phytoplankton productions have linearly increased since the estuarine barrage construction to reflect the gradual eutrophication in the estuarine area. Average chlorophyll-a increase of 10 ${\mu}g\;chl-a\;L{-1}$ absolutely corresponded to the primary production acceleration of 30 mg C $m^{-2}\;day^{-1}$ on the annual basis.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.4
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• pp.821-834
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• 2015

This study presents the analysis of flow and bed change characteristics considering bed protection work built on the immediate downstream of weir to protect river bed from scouring. The study area is 37km reach from Hyunpoong station to Masuwon station including Hapcheon- Changryoung multi-function weir in the Nakdong river. CCHE2D model is calibrated and validated for evaluating the flow and bed change characteristics during Typhoon Kompasu in 2010. Three simulation conditions are set up: Case 1 is a natural channel without installation of weir. Case 2 involves an installation of weir in the natural channel. Case 3 involves an installation of weir with bed protection in the natural channel. Flood frequency (50, 100 and 200yr) is applied to each scenario to analyze the effects of bed protection work. While the sediment rate is increased in the downstream of fixed gate and sluice-type gate, river bed scouring rate is increased in the downstream of lift-type gate in Case 2 comparing with the results of Case 1. The river bed scouring is not occurred in the immediate downstream of weir (~30m) due to the effect of bed protection, but larger amount of sediment is occurred in the downstream of weir (60m~) which the bed protection is not installed comparing with the results Case 1. Through the results of simulation considering bed protection work, this study would be helpful to expect bed change and operate the weir as well as manage.

• Journal of the Korean association of regional geographers
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• v.16 no.2
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• pp.85-99
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• 2010

This study analyzes the geomorphic environments of river channels and properties of sediments in the Naeseong-River basin, a branch of Nakdong-River. While the area at NU1 located in the uppermost reaches indicates the landscapes with the gravel riverbeds, the sand riverbeds can be seen in the downstream of NU2 whose basin consists mostly of the granite regolith. The downstream of NU2 has the braided channels in the beds and this may be due to the large quantities of sand particles supply to the bed under the favorable geologic and geomorphic conditions, properties of river flowing within the floodplains less resistant to the erosion and great fluctuations of discharges. Whereas the river at NU2 may seem that sand particles are actively eroded during the high water-level periods, the particles may be actively deposited during the periods at NM2 and NL2. Moreover, in the reaches of NU2 to NM1 and NL1 to NL2, the mean grain sizes of sediments increase downstream suggesting the other supplies of coarse sediments from the lower order streams running the steep slopes because the river flows in the areas consisting of the metamorphic rocks rather than the granites and shows the properties of incised meander.

• Journal of Korea Water Resources Association
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• v.48 no.8
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• pp.685-693
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• 2015

We propose a method for deriving the relationship between channel width and discharge from remote sensing products. Stream widths at points distributed along a river network can be measured from high-resolution remote imagery. Further, corresponding drainage area for these points can be calculated using digital elevation models, making it possible to construct width-drainage area relation. On the other hand, the relationship between the flow discharge and the drainage area is obtained from historical data measured at ground stations. By coupling these two relationships, we can finally derive the width-discharge relationship which comprises an important component of downstream hydraulic geometry. The proposed method was tested for the Nakdong River and the Seomjin River, successfully capturing power-law exponents in the width-discharge relationships reported in earlier studies. The proposed approach can serve as an alternative for obtaining the hydraulic geometry relationship under the limits of ground data.

• Journal of Korea Water Resources Association
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• v.43 no.5
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• pp.455-469
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• 2010

Changes of geomorphology in alluvial river and vegetation recruitment on its floodplain downstream from dams are investigated both qualitatively and quantitatively focusing on the downstream of Andong dam and Imha dam on the Nakdong River. Results of the analyses of river morphology and bed material in the study site show a general trend of riverbed degradation with a max scour of 3 m and bed material coarsening from pre-dam value of 1.5 mm in D50 to post-dam value of 2.5 mm. Decrease in bed shear stress due to the decrease in flood discharge have caused vegetation recruitment on the once-naked sandbars. As result, the ratio of area of vegetated bars over total area of bars has drastically changed from only 7% in 1971 before the Andong dam (constructed in 1976) to 25% after it, and increased to 43% only three year after the Imha dam (constructed in 1992) and eventually to 74% by 2005. Analysis of the vegetation succession at Wicjeol subreach, one of the three subreaches selected in this study for detailed investigation, has clearly shown a succession of vegetation on once-naked sand bars to a pioneering stage, reed and grass stage, willow shrub and eventually to willow tree stages. At the second subreach selected, two large point bars in front of Hahoe Village seem to have maintained their sand surfaces without a signifiant vegetation recruitment until 2005. The sand bars, however, seem to have been invaded by vegetation recently, which warns river managers to have a countermeasure to protect the sand bars from vegetation invasion in order to conserve them for the historical village of Hahoe. On the other hand, recruitment and establishment of vegetation on the sand bars by artificial disturbance of the river, such as damming, can create an unique habitat of backmarsh in the sandy river, as shown in the case of Gudam Wetland, and may increase the biodiversity as compared with relatively monotonous sand bars. Last, the premise in this study that decrease in flood discharge due to upstream dams and decrease in bed shear stress can induce vegetation recruitment on the naked sand bars in the river has been verified with the analyses of the distribution of dimensionless bed shear stress along the selected cross section in each subreach.

• Economic and Environmental Geology
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• v.56 no.2
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• pp.185-199
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• 2023

This study aimed to predict the effects of water ecology on the supply of hydrothermal energy to model a housing complex in Eco Delta Smart Village in Busan. Based on the results, engineering measures were recommended to minimize problems due to possible temperature variations on the supply of hydrothermal energy from the river. The current distribution of fish, benthic macroinvertebrates, and phytoplankton in the Pyeonggang Stream was monitored to determine their effects on water ecology. In the research area, five species and three families of fish were observed. The dominant species was Lepomis macrochirus, and the subdominant species was Carassius auratus. Twenty-five species and 21 families of benthic macroinvertebrates were found. The distribution of aquatic insects was poor in this area. The dominant species were Chironomidae sp., Lymnaea auricularia, Appasus japonicus, and Caridina denticulata denticulata in February, May, July, and October. Dominant phytoplankton were Aulacoseira ambigua and Nitzschia palea in February and May. Microcystis sp. was dominant in July and October. The health of the ecology the Pyeonggang Stream was assessed as D (bad) according to the benthic macroinvertebrate index (BMI). Shifts in the location of the discharge point 150 m downstream from intake points and discharge through embedded rock layer after adding equal amounts of stream water as was taken at the beginning were suggested to minimize water temperature variations due to the application of hydrothermal energy. When the scenario (i.e., quantity of water intake and dilution water, 1,600 m³/d and water temp. difference ±5 ℃) was realized, variations in water temperature were assessed at -0.19 ℃ and 0.59 ℃ during cooling and heating, respectively, at a point 10 m downstream. Water temperatures recorded at -0.20 ℃ and 0.68 ℃ during cooling and heating, respectively, at a point 10 m upstream. All stream water temperatures after the application of hydrothermal energy recovered within 24 hours. Future work on the long-term monitoring of ecosystems is suggested, particularly to analyze the influence of the water environment on hydrothermal energy supply operations.

• Korean Journal of Environment and Ecology
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• v.22 no.6
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• pp.658-665
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• 2008

One of the characteristics of fluvial river channel with sand bed-material is the existence of movable sand bars not occupied with vegetation. However, sand bars at the Hahoe's reach of the Nakdong River showing a double-meandering channel has been changed into expanding vegetation area. Moreover, sand material, in recent years, has stopped moving to downstream in channel and the number and area of bare bars which did not occupied by vegetation have been decreased. In order to find out the mechanism, we carried out the channel characteristics surveys such as hydro-geomorphologic, soil physio-chemical and vegetation surveys were conducted twice on autumn season in 2005,2006. The results so far achieved showed that the reduced discharge of transported sediment and duration of dry season might be critical factors for the spread of luxuriant vegetation. The vegetation area was significantly expanded by floods exceeding the subsequent dominant flow discharge. Furthermore, the expansion of vegetation area was highly correlated with the supply of organic matter, nutrients and alteration of soil texture by sediment deposition during the flooding event.

• Korean Journal of Ecology and Environment
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• v.49 no.2
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• pp.130-141
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• 2016

This study was conducted to elucidate the structure of river ecosystem in the watershed of the Seom River and Hoengseong Reservoir located in Hoengseong of Kangwon Province from February to October 2007. Topics of the survey were mainly rainfall, discharge, water quality in abiotic factors and attached algae, benthic macroinvertebrates, fish, birds and mammals of flora and fauna in a biotic factors, respectively. Specifically, the Seom River could be seen as a typical flow rate of the stream is controlled to the effect of the dam. Basic water qualities were great to seasonal effects, it was relatively clean. Diatom Achnanthes, Cymbella, Gomphonema, and Navicula were distributed predominantly in the periphytic algae. Benthic macroinvertebrates were mostly aquatic insects and freshwater shellfish, the aquatic insects were abundant Ephemeroptera and Trichoptera. Freshwater fish was the dominant Zacco platypus, fish species varied toward the downstream. Birds were mainly observed in four species, and species Egretta garzetta, which was distributed in a wide area of the Seom River. In mammals, Lutra lutra of Mustelidae was identified that the number of inhabit widely. In aspects of the ecological trophic level, the Seom River was maintained at a relatively stable state in the producer and the consumer relationship. The results of this study will expected to be utilized as a useful data for understanding the structure and function of the lotic and lentic ecosystems.

• Journal of the Korean earth science society
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• v.30 no.5
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• pp.622-629
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• 2009

This study intended to collect data for evaluating the meteorological value of Upo Wetland which is the largest wetland in the downstream of Nakdong River. The observations were conducted in summer at the Upo Wetland and its surrounding paddy field that is the converted areas from a wetland to a paddy field. The following results are obtained: 1) The temperature of Upo Wetland area was $1^{\circ}C$ lower than the surrounding area during the day while it was a little higher during the night.; 2) The maximum wind speed in the Upo Wetland area was 3.5 m/s which is stronger than 1.6 m/s of its surrounding area. The south wind was observed in the farmland for most of the day while north winds and south winds alternated between day and night in Upo Wetland.; 3) In heat budget analysis, Upo Wetland was wasted in the form of latent heat rather than sensible heat in daytime.

• Journal of Korea Water Resources Association
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• v.33 no.4
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• pp.447-459
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• 2000

Since the development of water resources is getting more difficult than ever before because of human-sociological condition, it would be necessary to develop a practically applicable technique for the management of water resources based on demand-side concept that could reduce unusable release for more effective and appropriate allocation of limited water resources. The objective of the study is to develop an optimal reservoir system operation model for water supply and energy augmentation by the combination of water budget analysis method in downstream area by MIP technique. The applicable study of the developed model was carried out and water supply capability of Nakdong river basin was re-evaluated by the developed model. The model has been found successful to guarantee appropriate water supply to the basin by means of deficit-supply management method and also turned out to be more practical tool for an optimal reservoir system operation model than other existing models.