• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.361-374
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• 2016

When the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure is generated significantly due to pore volume change associated with rearrangement soil grains. This effect leads a seabed liquefaction around and under structures as a result from decrease in the effective stress, and the possibility of structure failure is increased eventually. These facts shown above have been investigated in the previous studies related to regular and irregular waves. This study suggested a concrete mat for preventing the seabed liquefaction near the submerged breakwater. The concrete mat was mainly used as a countermeasure for scouring protection in riverbed. According to installation of the concrete mattress, the time and spatial series of the deformation of submerged breakwater, the pore water pressure, and the pore water pressure ratio in the seabed were investigated. Their results were also compared with those of the seabed unprotected with the concrete mat. The results presented were confirmed that the liquefaction potential of seabed under the concrete mattress is significantly reduced under regular wave field.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.35-43
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• 2016

With the development of construction technology, constructions of dam and levee (dike) as well as the environmental problems are becoming issues. Recently, many countries have tried to develop and used CSG (Cemented Sand and Gravel), which needs fewer requirements than others in aggregates, constructability and ground condition during the dam construction. Mixing up with small amount of cement, CSG is able to increase the strength and proceed accelerated construction without artificial gradation adjustment of riverbed aggregate and crushed rock on construction site. Thus, CSG can minimize environmental damage resulted from quarries mining and reduce cost of construction. Unlike heat of hydration condition that regular concrete usually met, CSG exposes to repeated dry-wet and freezing and thawing environment. Thus, consider the importance of structure of dam or levee, intensive study on the durability of CSG is needed. In this study, freezing and thawing experiment was carried out to evaluate the durability of CSG. In results, the durability factor of CSG is 30~40 or >40 when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. The unconfined compressive strength is reduced to 30~50% or 40~70% when the amount of cement is $0.4{\sim}0.6kN/m^3$ or $0.8{\sim}1.0kN/m^3$, respectively. Taken together, the strength and durability of CSG is reliable when the amount of cement is over $0.8kN/m^3$.

• Korean Journal of Ichthyology
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• v.19 no.3
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• pp.225-235
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• 2007

The freshwater fish fauna and physical characteristics of streams in Yeosu peninsula and Geumo Islands were surveyed at thirty nine stations in the period of 2003 and 2005. Most of the streams were short in length and narrow in flowing water width. Main materials of riverbed in most stations were cobble, pebble and gravel; those in the stations adjacent river mouth gravel and sand. In the river type, eighteen stations out of surveyed stations were upstream type: Aa. Thirty nine fish species belonging sixteen families were caught in this survey region. Among them twenty seven species were primary freshwater fishes and nine were peripheral. In the species composition of each family, there were the most species in Cyprinidae and Gobiidae, twelve and ten species, respectively. Endemic species of Korean peninsula in this region were eight species. One exotic fish species, Lepomis macrochirus was found in Yeosu peninsula. Dominant species in each district was Zacco temminckii in Yeosu peninsula, Rhinogobius brunneus in Dolsan Island, Leucopsarion petersii in Geumo island and Oryzias latipes in Gae island. In the analysis of community structure, it was appeared that the community of Yeosu peninsula was the most diverse and stable in this region; as the size of island became smaller, diversity and richness of community decreased. Kichulchoia brevifasciata did not caught in this survey, and it is possible that the species was extincted in this island. Acanthorhodeus gracilis and L. petersii were reported firstly in this region.

• 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.

• Journal of Environmental Impact Assessment
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• v.28 no.2
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• pp.129-140
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• 2019

Majangcheon is a small agricultural stream which is located in Chuncheon-si, Gangwon-do. To understand ecological characteristics of Majangcheon as biological habitats, we surveyed its physical environment and fishes from June 2016 to September 2016. The altitudinal difference between lowest and highest point of the stream was 3 meters and the first-order stream under a map drawn on a scale of 1:25,000. The flow rate of stream was slow in overall with $0.09-0.48m{\cdot}s^{-1}$. More than 50% of clay were found in all points except for the point St. 3 in the riverbed structure surveyed. A total of 2,532 individuals of 22 species in nine families were collected from Majangcheon. Of them, stillwater-living species (Acheilognathinae and Carassius auratus) and floating species (Zacco platypus and Oryzias sinensis) were mainly collected. In Majangcheon, thus, both of stillwater-living and floating fishes were specifically coexisted. The correspondence analysis, based on fishes collected from Majangcheon and past research, showed that Majangcheon is closer to the flat streams in Gyeonggi-do rather than the mountainous streams in Gangwon-do but it appeared as an independent group from those of two regions. As a result, Majangcheon is a stream with specificity of fish community.

• Korean Journal of Environment and Ecology
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• v.34 no.6
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• pp.551-557
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• 2020

This study surveyed the ecological characteristics of Ladislabia taczanowskii at Songcheon Stream from March to November 2019. The species inhabited upstream, where the riverbed structure was mostly covered with boulders and cobbles. The water depth was 31-148 cm, and the stream velocity was fast at 0.94±0.23 (0.51-1.39) m/sec. The gender ratio of females to males was 1 : 0.89. The age according to the total length frequency distribution indicated that the group with 38-70 mm below in total length was one year old, the group with 70-100 mm was two years old, the group with 100-120 mm was three years old, and the group over 120-128 mm was over four years old. The total length of sexually mature fishes was 70 mm for females and 75 mm or more for males. The spawning season was from May to August, and the water temperature was 15.5-20.1℃ during the period. The prosperous spawning season was from June to July, and the water temperature was 15.8-17.2℃ during the period. The spawning ground was where the riffle began in the pool, and its bottom was formed of sand and gravel. The width was about 150 cm, and the water depth was 20 to 50 cm. The average number of eggs in the ovaries was 821 (401-1,314) per matured female, and the matured eggs were yellowish and spherical with a mean diameter of 1.62±0.02 (1.43-2.01) mm. The live foods of L. taczanowskii Cyanophyta, Chlorophyta, Bacillariophyta, Ephemeroptera, and Diptera. The feeding habit of L. taczanowskii is omnivorous, but more than 90% of the stomach content was attached algae.

• Korean Journal of Environmental Biology
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• v.37 no.4
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• pp.664-671
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• 2019

This study was conducted to investigate the environmental impact of the construction of the Yeongju Dam, located near the upper stream of the Nakdong River, on benthic macroinvertebrates. The investigation was conducted four times from 2015 to 2016 and the composition of the benthic macroinvertebrate fauna from the four surveyed sites was compared. After the dam construction, the number of benthic macroinvertebrate species decreased and the species composition ratio of the E.P.T taxa(Ephemeroptera, Plecoptera, and Trichoptera) decreased, which favored the previous environment and the large riverbed structure. However, the species composition ratio of the O.C.H taxa (Odonata, Coleoptera, and Hemiptera), which favored the reservoir environment, increased. For the pattern of changes in the functional habitat groups, the proportion of 'Clinger(CL)' taxa decreased and the 'Burrower(BU), Climber(CB), Sprawler(SP), Swimmer(SW)' taxa increased in all surveys after the dam construction. A cluster stability comparison showed that the 'Stability Group II' species of St.2 and St.3 showed a drastic decrease. The average Benthic Macroinvertebrate Index(BMI) of all the survey sites in 2016 was lower than that in 2015. This research confirmed the temporal and spatial changes in the habitat type and community structure of the benthic macroinvertebrates resulting from the dam construction.

• Journal of Wetlands Research
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• v.22 no.3
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• pp.194-199
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• 2020

Unlike in the past, the world is facing water shortages due to climate change and difficulties in simultaneously managing the risks of flooding. The Four Major Rivers project was carried out with the aim of realizing a powerful nation of water by managing water resources and fostering the water industry, and the construction period was relatively short compared to the unprecedented scale. Therefore, the prediction and analysis of how the river environment changes after the Four Major Rivers Project is insufficient. Currently, part of the construction section of the Four Major Rivers Project is caused by repeated erosion and sedimentation due to the effects of sandification caused by large dredging and flood-time reservoirs, and the head erosion of the tributaries occurs. In order to solve these problems, the riverbed maintenance work was installed, but it resulted in erosion of both sides of the river and the development of new approaches and techniques to keep the river bed stable, such as erosion and excessive sedimentation, is required. The water agent plays a role of securing a certain depth of water for the main stream by concentrating the flow so much in the center and preventing levee erosion by controlling the flow direction and flow velocity. In addition, Groyne products provide various ecological environments by forming a natural form of riverbeds by inducing local erosion and deposition in addition to the protection functions of the river bank and embankment. Therefore, after reviewing the method of determining the shape of the Groyne structure currently in use by utilizing the mobile limit flow rate and marginal reflux force, a new Critical Movement Velocity(${\bar{U}}_d$) and a new resistance coefficient formula considering the mathematical factors applicable to the actual domestic stream were developed and the measures applicable to Groyne installation were proposed.

• Korean Journal of Environment and Ecology
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• v.37 no.1
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• pp.86-93
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• 2023

This study investigated the ecological characteristics of Odontobutis interrupta at the Geumdang Stream from January to December 2021. The riverbed structure of the species habitat was rich in sand and mud. The water was deep, ranging from 21 to 124 cm, with an average of 48 cm. The stream velocity was slow at 0.24 (0.08-0.36) m/sec. The ratio of females to males was 1:0.98, and the total length of collected individuals ranged from 23 mm to 162 mm. The age according to the total length-frequency distribution as of May indicated that the group with a total length of 23-59 mm was one year old, the group with 60-99 mm was two years old, the group with 100-139 mm was three years old, and the group with 140-162 mm was four years old. As a secondary gender characteristic, the females genital papilla had a cylindrical shape, a hollow inside of the tip, and a longer diameter than males. The males had a cone shape with a pointed end. Sexually mature males had the nuptial color, with a black abdomen and whole body. Some females with a length ranging from 60 to 69 mm and all females 70 mm longer were sexually mature. Some males with a length ranging from 70 to 79 mm and all males 80 mm longer were sexually mature. The spawning season was from May to July, and the water temperature was between 19.6℃ to 29℃ during that period. The prosperous spawning season was June (26℃). The average number of eggs in the ovaries was 2,473 (883-4,955) per matured female, and the matured eggs were yellowish and spherical with a mean diameter of 1.42 (1.20-0.54) mm. The correlation between total length and weight was BW=0.0000006TL^3.21 with the constant a as 0.0000006 and parameter b as 3.21. The condition factor (K) was 1.67 (1.18-2.43) on average, and the slope was 0.116.

• Korean Journal of Environment and Ecology
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• v.38 no.2
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• pp.148-155
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• 2024

This study investigated the ecological characteristics of Odontobutis platycephala at Jaho stream from January to December 2022. The riverbed structure of the species' habitat was rich in cobble and pebble. The water was deep, ranging from 22 to 153 cm, with an average of 64 cm, and the stream velocity was rapid at 0.89 (0.42-1.46) m/sec. The ratio of females to males was 1:1.02, and the total length of collected individuals ranged from 38 to 156 mm. The age according to the total length frequency distribution as of May indicated that the group with a total length of 38-69 mm was one year old, the group with 60-99 mm was two years old, the group with 100-139 mm was three years old, and the group 140-156 mm was four years or older. As a secondary gender characteristic, the genital papilla was cylindrical in females and cone-shaped with a pointed tip in males. Some females with a length ranging from 60 to 69 mm and all females 70 mm or longer were sexually mature. Some males with a length ranging from 70 to 79 mm and all males 80 mm or longer were sexually mature. The spawning season was from May to July, and the water temperature was between 17 ℃ and 28 ℃ during that period. The prosperous spawning season was June (24 ℃). The average number of eggs in the ovaries was 988 (284-2,722) per mature female, and the mature eggs were yellowish and spherical with a mean diameter of 1.46 (1.19-1.71) mm. The correlation between total length and body weight is BW=0.00000006TL^3.12 with the constant a as 0.00000006 and the parameter b as 3.12. The mean condition factor (K) was 1.44 (0.96-2.26), and the slope was negative at -0.0007