• Journal of Korea Water Resources Association
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• v.41 no.8
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• pp.845-854
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• 2008

The old bridge of Woljeong-gyo, which has the fluvial history and culture, represents the ancient construction and civil engineering techniques. It is the oldest stone bridge in Korea and currently restored with its vicinities. In this study, the experimental model was used to analyze the hydraulic characteristics, the local pier-scour depth without scour protection, and the stability of riprap protection using the old grid type panels and stones for Woljeong-gyo of the study area. The water levels were increased around 30cm due to the restored bridge piers and foundations and the effects went up to 200m upstream. The maximum scour depth of 5.4m was measured and the scour protection tests were performed with the riprap size calculated using empirical equations and the existing scour protection range. The riprap of the existing scour protection in the upstream side was broken away, while the riprap of extended scour protection was very stable for the design flood condition of Woljeong-gyo area.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.299-306
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• 2000

Korea IS one of countries to be predicted short of water in the 21st century. The government has been investigating various alternatives to resolve the problems including construction of reservoirs. Freshwater retention techniques using boom and skirt system is one of them. It is very difficult to intake water in the estuaries of south and west coast of Korea because a big tide penetrates into an upstream river. Thus, means or retaining and keeping separate freshwater from seawater could potentially be helpful in solving the water supply problems. In this study, the proposed means to achieve freshwater retention is by use of floating boom and skirt systems. The hydraulic viability of these systems in taking advantage of natural stratification tendencies between the fresh and seawaters has been investigated through hydraulic experiments. It is found that freshwater retention capacity depends on skirt length and the opening beneath the skirt. The choice of skirt length IS very important to optimize freshwater storage because longer skirt lengths cause faster mixing and shorter lengths retain less volume. Results show that the freshwater retention volume generally increases as the length of the skirt increases. However, they show that water storage might be insufficient if skirts were either too long or too short.

• Korean Journal of Ecology and Environment
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• v.33 no.1 s.89
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• pp.23-30
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• 2000

n situ sediment oxygen demand (SOD), which takes place with the uptake of dissolved oxygen for biological metabolism and chemical oxidation in sediments, ranged from 1.57 to $12.55\;mg\;O_2\;m^{-2}\;h^{-1}$ in onshore of Lake Paldang from April to November 1999. SOD was influenced by the amount of organics and oxygen diffusion. Comparing the oxygen demands partitioning between overlying water and sediment during initial phase, SOD accounted for $63.8{\sim}94%$ of total oxygen demand in Lake Paldang. The chemical SOD and nitrogenous oxygen demand ranged $1.2{\sim}18.3%$ and $8.3{\sim}51.7%$ of total SOD, respectively. This result indicated that SOD in Lake Paldang occurred mainly by aerobic respiration and nitrification. Although the flow velocity could increase SOD within a certain limit, the effect of sediment depth on SOD was dependent on physicochemical properties of the sediment. This study showed that SOD can represent a significant portion of the total oxygen up-take in Lake Paldang. Therefore, the assessment of SOD might be necessary for the control of water quality.

• Korean Journal of Ecology and Environment
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• v.45 no.2
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• pp.190-199
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• 2012

The reproductive ecology of an endangered species, Gobiobotia macrocephala (Pisces: Cyprinidae), was investigated in the Seom River, a tributary of the Han River drainage system, from March 2010 to February 2011. During the non-spawning season, no difference in the external morphology was observed between males and females; however, during the spawning season, clear differences merged for the depth and width of the body, preventral length and preanal length in the standard length. The sex ratio of females to males was 1 : 1.01. The spawning season was estimated to last from late April to middle of June, at water temperatures of $15{\sim}25^{\circ}C$. The number of mature eggs in the ovary averaged about $2,134{\pm}930$ (mean${\pm}$SD), and the mean diameter was approximately $0.88{\pm}0.04$ mm. The spawning area was composed of pebble and cobble bottoms (3~10 cm), with current velocities of 13~24 cm $s^{-1}$ and water depths of 12~18 cm. Spawning behavior between males and females was observed in a water tank 14~15 h after injecting females with Ovaprim to promote reproduction. Fish spawned near the water surface with monogamous pairing.

• Journal of Environmental Impact Assessment
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• v.23 no.4
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• pp.271-284
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• 2014

The objectives of this research were to analyse the microhabitat of Cobitis choii which is designated as an endangered fish species (I) and national monument species in Korea (No. 454), and provide valuable information of suitable replacement habitat in the future for a conservation of the population with rapid decreases by environmental pollution. Sampling and microhabitat analysis in three streams such as Baekgok, Yugu and Gap Stream, known as one of the least habitats in Korea showed that the mean number of Cobitis choii observed was 2.6. This result indicated that the richness was too low, so the species conservation was very urgent. Optimal physical microhabitat of the population was determined as environmental conditions with > 60% sand with 1 mm particle size, optimal water depth of 20 - 60 cm in the habitats, and the optimal current velocity of < 0.4 m/s. Under the circumstances of the microhabitat, optimal water volume (discharge) was 0 - 2 m3/s in the each sectional analysis and this reach was mainly composed of the stream section with intermittant slow runs and pools. These microhabitats were largely disturbed by physical modifications of habitat and chemical pollutions due to direct influences of nutrient-rich water inputs from the urban area and intensive agricultural pollutants. For these reasons, optimal habitat replacement are required in the future for the conservation of the species.

• Journal of Korea Water Resources Association
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• v.46 no.11
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• pp.1115-1128
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• 2013

The purpose of this study is to evaluate the suspended solids and eutrophication processes relationships in Chungju lake using CE-QUAL-W2, two-dimensional (2D) longitudinal/vertical hydrodynamic and water quality model. For water quality modeling, the lake segmentation was configured as 7 branches system according to their shape and tributary distribution. The model was calibrated (2010) and validated (2008) using 2 years of field data of water temperature, suspended solids (SS), total nitrogen (TN), total phosphorus (TP) and algae (Chl-a). The water temperature began to increase in depth from April and the stratification occurred at about 10 m early July heavy rain. The high SS concentration of the interflow density currents entering from the watershed was well simulated especially for July 2008 heavy rainfall event. The simulated concentration range of TN and TP was acceptable, but the errors might occur form the poor reflection for sedimentation velocity of nitrogen component and adsorption-sediment of phosphorus in model. The concentration of Chl-a was simulated well with the algal growth patterns in summer of 2010 and 2008, but the error of under estimation may come from the use of width-averaged velocity and concentration, not considering the actual to one side inclination by wind effect.

• Journal of the Korean Geosynthetics Society
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• v.6 no.1
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• pp.9-16
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• 2007

Geotextile is one of the most useful and effective polymer material in civil construction works and the main function of geotextile is separation, reinforcement, filtering and drainage. Recently, because of the shortage of natural rock, traditional forms of river and coastal structures have become very expensive to build and maintain. Therefore, the materials used in hydraulic and coastal structures are changing from the traditional rubble and concrete systems to the cheaper materials and systems. One of these alternatives employs geotextile tube technology in the construction of coastal and shore protection structures, such as embankment, see dyke, groins, jetties, detached breakwaters and so on. Geotextile tube technology has changed from being an alternative construction technique and, in fact, has advanced to become the most effective solution of choice. This paper presents case history of sea dyke filter construction using geotextile tube mattress and also, various issues related to the tube mattress design and construction technology.

• Korean Journal of Environment and Ecology
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• v.30 no.5
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• pp.888-895
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• 2016

The population ecology (Ecological characteristics) of Squalidus chankaensis tsuchigae were investigated at Geum River from March to November, 2013. This species inhabited midstream of the river where was mostly covered with cobble and sand. The depth of the habitat was 30~60 cm and velocity of stream was 2.27~4.88 cm/sec. The sex ratio of female to male was 1 : 0.86. They were sexually mature when they were over two years of age. The spawning period was from June to July with water temperatures from $25^{\circ}C$ to $25^{\circ}C$. Sexually matured individuals appeared over the two year of age. Frequency analysis of total length indicated that the group with 55~70 mm in total length was one year old, the 71~90 mm was two years old, and the group over 91 mm was three years old. The average number of eggs in the ovaries was estimated as 2,219 per matured female. The number of matured eggs size in ovaries was 0.64~0.98 (mean: 0.85) mm. Calulation length-weight relation of S. chankaensis tsuchigae show the value of contant a as 0.0002 and b as 2.81, and condition factor (K) was 1.06 on average. The stomach contents were Cyanophyta, Chlorophyta, Bacillariophyta, Crustaceae, Copepoda, Nematota, Actithocephala, and Ephemeroptera, Hemiptera, Diptera, and Trichoptera that belong to Aquatic insect, and dormant bud of Pectinatella that belongs to Phylactolaemata. The diet of S. chankaensis tsuchigae was omnivorous, mainly vegetable feed on attached algae (filament form), and mainly animality feeded on benthic invertebrates such as Chironomidae larvae.

• Journal of Korea Water Resources Association
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• v.51 no.12
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• pp.1273-1284
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• 2018

The flow and bed change were analyzed using the CCHE2D model, which is a two-dimensional numerical model, at a confluence of the Namhan River and Seom River where deposition occurs predominantly after the "Four Major Rivers Restoration Project." The characteristic of the junction is that the tributary of Seom River joined into the curved channel of the main reach of the Namhan River. The CCHE2D model analyzes the non-equilibrium sediment transport, and the adaptation lengths for the bed load and suspended load are important variables in the model. At the target area, the adaptation length for the bed load showed the greatest influence on the river bed change. Numerical simulation results demonstrated that the discharge ratio ($Q_r$) change affected the flow and bed change in the Namhan River and Seom river junction. When $Q_r{\leq}2.5$, the flow velocity of the main reach increased before confluence, thereby reducing the flow separation zone and decreasing the deposition inside the junction. When $Q_r$>2.5, there was a high possibility that deposition would be increased, thereby forming sand bar. Numerical simulation showed that a fixed sand bar has been formed at the junction due to the change of discharge ratio, which occurred in 2013.

• Korean Journal of Environment and Ecology
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• v.36 no.4
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• pp.381-389
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• 2022

This study investigated the ecological characteristics of Microphysogobio yaluensis at Dugye Stream of Geum River basin from January to December 2021. The river bed structure of this species' habitat was rich in pebbles and gravel. The water depth ranged from 12 to 85 cm with an average of 23 cm, which was shallow. The stream velocity was rapid at 1.03±0.34(0.72-1.47) m/sec. The ratio of females to males was 1:0.86. The age according to the total length-frequency distribution as of summer (June, July) indicated that the group with less than 50 mm (30.4-49 mm) in total length was one year old, the group with 50-69 mm was two years old, and the group over 70-92 mm was three years old. Both male and female fish sexually matured at 50 mm long and two years old in June and July. The spawning season was from July to August, and the water temperature was between 25.8℃ and 28.2℃ during the period. The prosperous spawning season was July. The matured eggs were yellowish and spherical with a mean diameter of 0.52±0.16 (0.33-0.77) mm, and the average number of eggs found in the ovaries of mature female fish was 2,593 (1,343-4,672). As for the food of M. yaluensis, only attached algae, which grow by attaching to stones and gravel of the stream rapids, were identified. The feeding habit of M. yaluensis was reported to be herbivorous, ingesting Cyanophyta, Chlorophyta and Bacillariophya. Also, the species belonging to Bacillariophya and Chlorophyta were abundant in Dugye Stream.