• Journal of Korea Water Resources Association
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• v.32 no.6
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• pp.697-709
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• 1999

Two dimensional finite element model(RMA) is applied to examine sediment transport behavior near Buyeo water intake station of the Keum River. The simulation results of bed change with various discharge conditions agree with those of observation. As the alternatives of channel modification and resulting bed lowering near intake station, construction of jetties and removal of small island are considered. The station of jetties diverted the main stream toward the other side and the width of the main stream did not change so much. The bed elevation of the main channel is reduced about 5~20 cm, when flow condition of 12,030㎥/sec applied. The removal of small island provides the less significant effect on sediment movement. This study shows that the construction of jetties would be effective to reduce the entrainment of sediment.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.7 no.4
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• pp.195-203
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• 1974

The individual production rate of Plecoglossus altivelis was studied from the 18th of June to the 25th of September (99 days) 1973, when the fish grow best at Gangjeong Stream, Jeju Do, as one of the ways to find out the reasons why the size of P. altivelis of Jeju Island is smaller than that of other places. The results obtained are as follows : 1) The indivudual production rate of the fish in the Gangjeong Stream during the summer 1973, was estimated as shown in Table 6. 2) The individual production rate of the fish and standing crop of algae on stones in the Gang-jeon Stream were no more than $7.2\%$ and $6.2\%$ respectively, when compared with those of the Ukawa River (which is located in Japan), thus the individual production rate of the fish at Gang-jeong Stream being very poor. 3) Population density was 5.2 individuals average per square meter during the research period. This is beyond the estimated density limit, i. e., 4.8 individuals per square meter, for the standing crop of algae on stones. 4) The period that the individual production rate of the fish was the most brisk during the summer in this stream was from August to September in 1973. 5) The poor individual production rate is primarily regarded due to insufficient gross ingestion. The reasons seemed to be insufficeient productivity of algae on the bottom stones, over-population density of the fish, and the lowered activity of ingestion due to low water temperature in daytime as compared with other places. Thus, the production rate of Plecoglossus altivelis in the Gangjeong Stream during the summer was greatly influenced by these factors.

• Journal of Environmental Science International
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• v.21 no.8
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• pp.939-951
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• 2012

This study is conducted to estimate the air temperature decreasing effects by restoring urban streams using WRF/CALMET coupled system. The types of land use on covered streams are constructed with the land cover map from Korea ministry of environment. Restoring covered streams changes the types of land use on covered areas to water. Two different types of land use(CASE 1 and CASE 2) are inputted to the WRF/CALMET coupled system in order to calculate the temperature difference. The results of the WRF/CALMET coupled system are similar to the observed values at automatic weather stations(AWS) in Busan area. Restoring covered streams causes temperature to be decreased by about $0.34{\sim}2^{\circ}C$ according to the locations of streams and the regions that temperature is reduced are widely distributed over the restored area. Reduction of temperature is increased rapidly from morning and maximus at 13LST. Natural restoration of streams will reduce the built-up area within urban. With this, temperature reductions which are the cause to weaken the urban heat island appear. Relief of urban heat island will help to improve the air quality such as accumulation of air pollutants in within urban area.

• Journal of the korean society of oceanography
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• v.32 no.1
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• pp.1-7
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• 1997

Surface current fields in the eastern East China Sea (ECS) were constructed by analyzing trajectories of 58 satellite-tracked surface drifters released during 1991-1996. Composite trajectories and 20-minute-by-20-minute box-averaged current vectors show that the basic current pattern composes of: the Kuroshio main stream, which turns eastward toward the Tokara Strait; a northward branch current of the Kuroshio on the ECS outer shelf deeper than 100 m; and an anticyclonic circulation in the northern Okinawa Trough west of Kyushu. The northward branch current sharply changes its direction to the northeast when it crosses a line connecting Cheju Island, Korea and Goto Islands, Japan. The basic pattern of current field changes slightly from winter to summer, and the main axis of the Tsushima Current in the Korea Strait is found to shift seasonally. The drifter experiment does not support the claim that the Yellow Sea Warm Current is separated from the northward branch current on the outer shelf southeast of Cheju Island. We suggest that the use of the term 'Tsushima Current' be limited to the northeast channel flow in the Korea Strait. The new term 'Kuroshio Branch Current' is suggested for the northward branch current on the outer shelf south of Cheju-do, which is separated from the Kuroshio.

• Proceedings of the Korea Water Resources Association Conference
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• 2015.05a
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• pp.427-427
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• 2015

The storm water management and drainage relation are the key variable that plays a vital role on hydrological design and risk analysis. These require knowledge about spatial variability over a specified area. Generally, design rainfall values are expressed from the fixed point rainfall, which is depth at a specific location. Concurrently, determine the areal rainfall amount is also very important. Therefore, a spatial rainfall interpolation (point rainfall converting to areal rainfall) can be solved by areal reduction factor (ARF) estimation. In mainland of South Korea, for dam design and its operation, public safety, other surface water projects concerned about ARF for extreme hydrological events. In spite of the long term average rainfall (2,061 mm) and increasing extreme rainfall events, ARF estimation is also essential for Jeju Island's water control structures. To meet up this purpose, five fixed rainfall stations of automatic weather stations (AWS) near the "Hancheon Stream Watershed" area has been considered and more than 50 years of high quality rainfall data have been analyzed for estimating design rainfall. The relationship approach for the 24 hour design storm is assessed based on ARF. Furthermore, this presentation will provide an outline of ARF standards that can be used to assist the decision makers and water resources engineers for other streams of Jeju Island.

• Journal of Soil and Groundwater Environment
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• v.23 no.6
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• pp.37-45
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• 2018

The source of Chusan Spring water in the Ulleungdo is the precipitation in the Nari caldera basin, which permeates in the Trachitic pumice and tuff area and moves downward, outflowing at the lithologic boundary between the trachyte and Nari tuff. It is known that the discharge rate of the Chusan Spring is large enough to be used for the small hydroelectric power generation, but the exact discharge rate and hydrogeologic characteristics have not been known. The discharge rates of the Spring were measured 11 times, which ranged from $15,220m^3/d$ to $36,278m^3/d$. The discharge rates, measured by the automatic level recorder, for two-year period, were $20,000{\sim}38,000m^3/d$. The variation of discharge rates did not coincide with rainfall event, but showed daily increases of $3,000{\sim}5,000m^3/d$. The annual discharge rate excluding the evapotranspiration and the surrounding stream discharge corresponded to 70.6% of the annual precipitation of the recharge area. Therefore, meteorological observations at the Nari basin, rather than the Ulleung-do meteorological station, are more appropriate to properly interpret the discharge characteristics of the Chusam Spring and the recharge rate of the basin.

• Korean Journal of Environmental Biology
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• v.35 no.1
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• pp.57-63
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• 2017

This study was conducted to determined the status and geographical distribution of the alien invasive Red-eared slider (Trachemys scripta elegans) turtle on Jeju Island. We found thirty-two Red-eared slider habitats including twenty-five ponds, five agricultural reservoirs, a puddle and a stream. Among those, thirteen sites are newly determined habitats of the turtle. The remaining nineteen are previously reported. However, we could not find any turtles at nine sites, which were documented as turtle habitats in earlier reports. A total of one hundred thirty-three turtles were observed. Among them, we determined that thirty-nine were juvenile turtles, found in nineteen different habitats, indicating estimating that Red-eared sliders produced their progeny in the wild of this island. Because of geographical isolation by the ocean, no freshwater turtle had been found until $19^{th}$ Century. Therefore, the increased number of finding sites and Red-eared sliders indicate the possibility of human release of their pets or for other purposes, and natural propagation in the wild on Jeju Island. Our findings will be useful for management planning to deal with this invasive species, and implementation of a conservation program for native wildlife on Jeju Island.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.11 no.4
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• pp.165-171
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• 2006

This is the research to prepare a purification program for relatively less polluted stream by using phytoremediation. We calculated a treatment amount of nutrients followed by growth of Helianthus annuus (a kind of sunflower), setting up the plant reactor in the hothouse. Moreover, to investigate a field applicability, we could find increased contents of nitrogen, carbon and hydrogen in plants by setting up a H. annuus planted artificial floating island in an irrigation canal. When we changed the dissolved inorganic nitrogen(DIN) concentration of the influent from 28.5 to 199.2 mg/l and the dissolved inorganic phosphorus(DIP) concentration of the influent from 13.3 to 25.4 mg/l, growth disorder has not appeared though it is much higher than the criterion of water for irrigation. In this case, the removal rate of DIN was $81.7\sim98.6%$, and that of DIP was $81.9\sim98.4%$ in 3 days stay on average. It has appeared that the efficient hydraulic retention time(HRT) was 48 hours. The following contents of nitrogen, carbon and hydrogen of H. annuus appeared in the artificial floating island: nitrogen was $3.2\sim7.8%$ in the trunk and $3.0\sim6.3%$ in the root. Carbon was $40.1\sim57.7%$ in the trunk and $43.4\sim53.8%$ in the root.

• Journal of Environmental Science International
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• v.22 no.5
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• pp.563-570
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• 2013

Roughness coefficient was computed for review of applicability based on measurement of the representative grain diameter reflecting channel characteristics of Han Stream. After field survey, collection of bed material, and grain analysis on the collected bed material, roughness coefficient was computed using representative grain and existing empirical equation for roughness coefficient. Value of roughness coefficient calculated using equation by Meyer-Peter and Muller (1948) was 0.0417 for upstream, 0.0432 for midstream, and 0.0493 for downstream. As a result of comparing the computed roughness coefficient to other empirical equations for review of applicability, the coefficient was larger in Strickler (1923) equation by 0.006. Smaller coefficient was shown by Planning Report for River Improvement Works. Equation by Garde and Raju (1978) was larger by 0.004, and equations by Lane and Carlson (1953) and by Meyer-Peter and Muller (1948) were larger by 0.001. Such precise roughness coefficient is extremely important when computing the amount of flood in rivers to prevent destruction of downstream embankments and property damages from flooding. Since roughness coefficient is a factor determined by complicated elements and differs according to time and space, continued management of roughness coefficient in rivers and streams is deemed necessary.

• Journal of The Geomorphological Association of Korea
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• v.28 no.4
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• pp.1-13
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• 2021

In this study is aerial photos and UAV(Unmanned Aerial Vehicle) images were used to analyzed the characteristics of depositional landform changes in the Geum river channels before and after the opening gate of Gongju weir. Based on the depositional landform classification result, the main stream and the bare land occupied most of the area in all periods, and also found that the main stream, mid-channel island, and sand bar occupied a greater degree of area increase or decrease compared to other landforms in the classification items. As a result of analyzing the characteristics of depositional landform changes before and after the opening gate of Gongju weir, it is judged that the depositional landforms have changed due to the decreased water level of the Geum river after the opening of the weir, the summer rainy season and typhoons, river stabilization after the effluence of Daecheong dam, supply and deposition of river sediments and fixation of vegetation. The results derived from this study can be used as basic data for the study of river depositional landforms and the establishment of management and conservation plans for the landforms in river channels.