• Korean Journal of Ecology and Environment
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• v.34 no.1 s.93
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• pp.45-53
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• 2001

Transport of cyanobacterial toxins (microcystin-LR, -RR, -YR) were assessed from a eutrophic lake, Lake Suwa, through the outflowing river, the Tenryu River, and its irrigation channel branch. Temporal variation of phytoplankton species composition in the river coincided with those of the lake; Microcystis ichthyoblabe dominated from June to July, and M. viridis dominated from August to September. When cyanobacterial bloom occurred, microcystins were continuously detected at the concentration of $0.3{\sim}3.2\;{\mu}g/l$ even at 32 km downstream. The change of the content of three microcystin variants were related both with the total cell density of Microcystis and with the change of Microcystis species composition. When Microcystis ichthyoblabe dominated during July, only microcystin-RR (MC-RR) and -LR (MC-LR) were detected, while when Microcystis viridis dominated between August and October, microcystin-RR,-YR (MC -YR) and -LR were detected. Along 29 km flowing distance (flow time 11 hours) between site 2 and site 5 in the Tenryu River, cyanobacterial density and microcystin concentration were reduced by 73% and 72%, respectively, which is mostly contributed by the dilution effect of tributary waters (61% and 57%, respectively) . In the artificial irrigation channel microcystins and cyanobacterial cells were decreased less than in the natural river. The results indicate that cyanobacterial toxins can be transported far downstream without much removal and give hazards to water usage in downstream of eutrophic lakes with cyanobacterial blooms.

• Korean Journal of Ecology and Environment
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• v.55 no.4
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• pp.398-405
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• 2022

The research was based on long-term studies on the major physico-chemical and hydrological factors and zooplankton community dynamics in the Hwang River. We had 341 times survey and collected zooplankton samples in the Hwang River of mid-Nakdong River from 1995 to 2013. We identified 97 zooplankton species, including 77 rotifers, 16 cladocerans, and 4 copepods. The total zooplankton abundance and species diversity were shown distinctive temporal variation (ANOVA, p<0.001). Annual average of zooplankton population density was 58.4±3.2 ind L^-1 (n=341) and the lowest was 17.0±3.8 ind L^-1 (1996, n=20), while the highest was 151.5±32.3 ind L^-1 (2010, n=22). For zooplankton, small rotifer groups(e.g., Keratella sp., Brachionus sp., Trichotria sp.) dominated the study site for 19 years survey. Statistical analysis revealed that there were positive relationships with SiO₂ (p=0.002) and water level (p<0.001) for the high abundance of rotifer community. There were considerable variations both the total cladocerans population and the number of cladocerans' species concerning annual precipitation. Despite the appearance of various zooplankton in the Hwang River, the mean population density remained low. Due to the lateral structures in the Nakdong River, the downstream basin of the Hwang River is inevitably affected. The zooplankton community in our study site is considered to be mainly influenced by external factors that can stably increase and maintain the volume of the water body and internal factors that induce an increase in food sources through the inflow of nutrients into the water body.

• Journal of Korea Water Resources Association
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• v.43 no.1
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• pp.95-104
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• 2010

The tap water supply in Korea mainly depends on the surface water. However, the advanced water purification process becomes a necessity due to the deterioration of surface water quality and the risk of accidental spill. High cost of water treatment and public concerns make the decision makers turn to riverbank filtration as an alternative to the surface water. Riverbank filtration has been employed for water supply in many developed countries for more than 150 years. In Korea, riverbank filtration has drawn attention since 1990s as a supply source having potential to stably meet the ever-increasing water demand. Some cities located in the Nakdong River Basin are currently supplying water through riverbank filtration. This work studies the site suitability analysis for riverbank filtration using game theory. Theory of games, which is a branch of applied mathematics used in social sciences (most notably economics), biology, engineering and computer science, was applied to candidate locations for the selection of riverbank filtration site. We proposed a policy game model as a new method adopting a probabilistic approach. The model developed turned out to be an effective tool for site selection.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.20 no.6
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• pp.107-115
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• 2017

This study illustrated the process of bar structure and vegetation coverage to understand historical changes of riverbed and suppose adaptive management in Tan-chun ecological landscape reserve. The study site that lower reach of the Tan-chun are known as habitats of migratory bird and aquatic species with dynamic riverbed. Aerial photos from 2006 to 2016 and surveyed vegetation data in 2006 and 2016 were used by analysis of landscape changes and comparison of vegetation coverage. Study area is classified into 3 sites (A: straight site, B: meandering site, C: meandering and junction with Yangjae-cheon). The result showed that bar area of A and C sites gradually increased, B site decreased during 10 years. Also, ratio of bar area to vegetation coverage and level of vegetation coverage increased in all sites during 10 years. All sites seem to have experienced the terrestrialization with time. On the other hand, ratio of annual vegetation increased and ratio of perennial vegetation decreased in C site in 2016 compare to 2006. Because area of Japanese Hops (Humulus japonicas) as one type of annual vegetation increased, other vegetation could not grow up by its powerful expandability. It is time to make active adaptive management based on not only continuos monitoring but also revaluation of river conditions in order to enhance habitat quality and quantity in Tan-chun ecological landscape reserve.

• Korean Journal of Environmental Biology
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• v.26 no.4
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• pp.367-376
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• 2008

The seasonality of phytoplankton in Dongbok lake was analysed from March to November 2003. The concentrations of TN and TP showed nearly constant level except high concentrations in May at dam site of Dongbok lake. Chlorophyll ${\alpha}$ concentration was highest at dam site in May with 225.3 ${\mu}g$ L$^{-1}$ and high in spring and fall and low in summer at upper and central regions of Dongbok lake. A total of 108 phytoplankton species was identified as an algal flora of Dongbok lake. They were 54 Chlorophyceae, 30 Bacillariophyceae, 12 Cyanophyceae, and 12 species of other taxa. Total cell biomass of phytoplankton showed peaks in May$\sim$June and August$\sim$September, and low biomass in July at dam site. However, upper and central regions of Dongbok lake showed no clear patterns in cell biomass. Maximum biomass was 7,158 cells mL$^{-1}$ at dam site in May with the blooms of Peridinium bipes f. occulatum. The general seasonality of phytoplankton in Dongbok lake was Bacillariophyceae-Dinophyceae/Bacillariophyceae-Cyanophyceae/Chlorophyceae/Bacillariophyceae-Bacillariophyceae in 2003.

• Water for future
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• v.25 no.1
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• pp.93-100
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• 1992

A study on the Derivation of the Unit Hydrograph using Multiple Regression Moe이. The purpose of this study is to deriver an optimal unit hydrograph suing the multiple regression model, particularly when only small amount of data is available. The presence of multicollinearity among the input data can cause serious oscillations in the derivation of the unit hydrograph. In this case, the oscillations in the unit hydrograph ordinate are eliminated by combining the data. The data used in this study are based upon the collection and arrangement of rainfall-runoff data(1977-1989) at the Soyang-river Dam site. When the matrix X is the rainfall series, the condition number and the reciprocal of the minimum eigenvalue of XTX are calculated by the Jacobi an method, and are compared with the oscillation in the unit hydrograph. The optimal unit hydrograph is derived by combining the numerous rainfall-runoff data. The conclusions are as follows; 1)The oscillations in the derived unit hydrograph are reduced by combining the data from each flood event. 2) The reciprocals of the minimum eigen\value of XTX, 1/k and the condition number CN are increased when the oscillations are active in the derived unit hydrograph. 3)The parameter estimates are validated by extending the model to the Soyang river Dam site with elimination of the autocorrelation in the disturbances. Finally, this paper illustrates the application of the multiple regression model to drive an optimal unit hydrograph dealing with the multicollinearity and the autocorrelation which cause some problems.

• Journal of The Geomorphological Association of Korea
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• v.20 no.3
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• pp.15-25
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• 2013

The purpose of this study is to identify the environment of optimal location of the dwelling (hereafter referred as dwelling site) in the Neolithic Age found in Unseo-dong relics group, Yeongjong-do, Incheon from the geographical and geomorphological perspectives. For this purpose, micro-landform, altitude, gradient, distance from the river of water available for use and the difference between the highest altitude and lowest altitude of river bed of water available for use based on change of dwelling site over periods were analyzed targeting ground surface of hills where individual dwelling sites (a total of 68 sites) discovered in investigation area so far. As a result, it was shown that the Upper sideslope were selected as the primary dwelling location standard in investigation area where the Neolithic people lived upon selecting the dwelling site (or settlement). In addition, the ground surface of dwelling site had the altitude of 21-31m and slope of $5-10^{\circ}$ (gentle slope) as the secondary and it had distance of 514-549m from the river of water available for use and difference of 11-23m between the highest altitude and lowest altitude of river bed of water available for use. Thus, it was shown that the space to get water relatively easy from two places at the same time was the secondary dwelling location standard.

• Journal of Environmental Science International
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• v.27 no.11
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• pp.1029-1048
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• 2018

In this study, seasonal Mann - Kendall test method was applied to 12 stations of the water quality measurement network of Nam-River based on data of BOD, COD, TN and TP for 11 years from January 2005 to December 2015 The changes of water quality at each station were examined through linear trends and the tendency of water quality change during the study period was analyzed by applying the locally weighted scatter plot smoother (LOWESS) method. In addition, spatial trends of the whole Nam-River were examined by items. The flow-adjusted seasonal Kendall test was performed to remove the flow at the water quality measurement station. As a result, BOD, COD concentration showed "no trand" and TN and TP concentration showed "down trand" in regional Kendall test throughout the study period. BOD and TP concentration in "no trand", COD, and TN concentration showed an "up trand" tendency in Nam-River dam. LOWESS analysis showed no significant water quality change in most of the analysis items and stations, but water quality fluctuation characteristics were shown at some stations such as NR1 (Kyungho-River 1), NR2 (Kyungho-River 2), NR3 (Nam-River), NR6 (Nam-River 2A). In addition, the flow-adjusted seasonal Kendall results showed that the BOD concentration was "up trand" due to the flow at the NR3 (Nam-River) station. The COD concentration was "up trand" due to the flow at NR1 (Kyungho-River 1) and NR2 (Kyungho-River 2) located upstream of the Nam-River. The effect of influent flow on water quality varies according to each site and analysis item. Therefore, for the effective water quality management in the Nam-River, it is necessary to take measures to improve the water quality at the point where the water quality is continuously "up trand" during the study period.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.16 no.2
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• pp.137-153
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• 2013

In order to assess the effects of ecosystem and landscape in around spur dikes, this study had carried out monitoring on the changes of ecosystem and morphologic characteristics in around spur dikes that had been settled in bend of Youngcheon River. The study site was a short reach with length 190m, spur dikes were installed in March, 2008. Monitoring of the site had been started in May 2008 and had been completed September 2011. The results are as follow ; 1) Spur dikes that were installed for channel stabilization are performing effectively hydraulic functions at flooding time. 2) Spur dikes that were installed in water colliding front of river bend brought about sediment deposition between those and formed pools around front of those. Therefore, it was verified to create various physical characteristics in the aspect of channel topography and flow consequently. 3) The survey results that was carried out in October 2008 showed to emerge 25 species of plant, 9 species of fish and 17 species of benthic macroinvertebrates, but the survey results in October 2010 showed to emerge 74 species of plant, 12 species of fish and 19 species of benthic macroinvertebrates. In particular, plant species that emerged in 2011 increased about three times more than those in 2008.

• Journal of the Korean association of regional geographers
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• v.15 no.2
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• pp.192-203
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• 2009

The purpose of this paper is to elucidate the formative processes of depositional landforms in Jiwoo drainage basin which located in the most upstream reach of Namgang River. Through the analysis of morphologic characteristics and sedimentary facies, the formative processes can be summarized as follow: First, the high depositional landforms(Sapyeong, Eungam, Naedongdyttle site) were formed by gelifluction process in the periglacial environment during the last glacial period. And the relative height over river bed of them is getting lower from upper to downstream. The extent of the high depositional landforms is assumed about 1 kilometer downstream far from the confluence of Jiwoo stream and Namgang River. Second, the sediments in the gentle slope at Jangseungbuldle were carried by gelifluction process during the last glacial stage after the deep-weathered bedrock had formed a gentle slope. Third, the high depositional landforms were dissected during warm and humid environment of postglacial stage, and some sediments of them were left in the river bed. Later, as the more upstream high depositional landforms were dissected completely, stream power was getting more than resistance(sediment storage) and the low depositional landforms(Sapyeong, Yongchusa, Deungbangdle site) were formed.