• KSCE Journal of Civil and Environmental Engineering Research
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• v.44 no.3
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• pp.303-314
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• 2024

Precipitation data are an integral part of water management planning, especially the design of hydroelectric structures and the study of floods and droughts. However, it is difficult to obtain accurate data due to space-time constraints. The recent increase in hydrological variability due to climate change has further emphasized the importance of precipitation simulation techniques. Therefore, in this study, the Modified Bartlett-Lewis Rectangular Pulse model was utilized to apply the parameters necessary to predict daily precipitation. The effect of this parameter on the daily precipitation prediction was analyzed by applying exponential distribution, Gamma distribution, and Weibull distribution to evaluate the suitability of daily precipitation prediction according to each distribution type. As a result, it is judged that parameters should be selected in consideration of regional and seasonal characteristics when simulating precipitation using the MBLRP model.

• Korean Journal of Ecology and Environment
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• v.41 no.2
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• pp.206-215
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• 2008

Temporal and spatial distributions of salinity, temperature, dissolved oxygen (DO), and turbidity were investigated at seven sites in the upper regions of brackish Lake Sihwa with a limited water exchange, from March to October 2005. During the study period, salinity and temperature varied $0.1{\sim}29.9\;psu$ and $4.7{\sim}28.1^{\circ}C$, respectively, depending on seasons and sites sampled. A distinct halocline profile showing the maximum density gradient (difference over $20\;psu\;m^{-1}$ between surface and bottom layers) was observed during the rainy season, due to the decrease of salinity in surface layers by freshwater inflow. This result implies that rainfall event is the important factor forming the halocline. On the other hand, the depth and location of haloeline varied with the amount of seawater through the sluice gates and the operation systems (inflow or outflow). High DO (over 300% saturation) was observed at surface layer above the halocline in April when red tide occurred, whereas low DO (below 20% saturation) was at the bottom layer below the halocline in the rainy season. Turbidity ranged $1.5{\sim}80.3\;NTU$ showing the maximum turbidity at the layers above or upper the halocline. As a result, the distributions of DO and turbidity in the upper regions of brackish Lake Sihwa were largely affected by the variation of salinity. Also, when the halocline was formed, the water quality between upper and lower water layers may be expected completely different. This study suggests that the physicochemical characteristics of water in the brackish regions are closely associated with the causes of eutrophication such as red tide and DO deficit.

• Journal of Korea Water Resources Association
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• v.55 no.8
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• pp.623-634
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• 2022

Due to river maintenance projects such as the creation of hydrophilic areas around rivers and the Four Rivers Project, the flow characteristics of rivers are continuously changing, and the risk of water quality accidents due to the inflow of various pollutants is increasing. In the event of a water quality accident, it is necessary to minimize the effect on the downstream side by predicting the concentration and arrival time of pollutants in consideration of the flow characteristics of the river. In order to track the behavior of these pollutants, it is necessary to calculate the diffusion coefficient and dispersion coefficient for each section of the river. Among them, the dispersion coefficient is used to analyze the diffusion range of soluble pollutants. Existing experimental research cases for tracking the behavior of pollutants require a lot of manpower and cost, and it is difficult to obtain spatially high-resolution data due to limited equipment operation. Recently, research on tracking contaminants using RGB drones has been conducted, but RGB images also have a limitation in that spectral information is limitedly collected. In this study, to supplement the limitations of existing studies, a hyperspectral sensor was mounted on a remote sensing platform using a drone to collect temporally and spatially higher-resolution data than conventional contact measurement. Using the collected spatio-temporal hyperspectral images, the tracer concentration was calculated and the transverse dispersion coefficient was derived. It is expected that by overcoming the limitations of the drone platform through future research and upgrading the dispersion coefficient calculation technology, it will be possible to detect various pollutants leaking into the water system, and to detect changes in various water quality items and river factors.

• Economic and Environmental Geology
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• v.56 no.2
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• pp.139-153
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• 2023

This study aimed to understand the spatiotemporal variations in nitrogen content in the Gyeongan stream along the main stream and at the discharge points of the sub-basins, and to identify the origin of the nitrogen. Field surveys and laboratory analyses, including chemical compositions and isotope ratios of nitrate and boron, were performed from November 2021 to November 2022. Based on the flow duration curve (FDC) derived for the Gyeongan stream, the dry season (mid-December 2021 to mid-June 2022) and wet season (mid-June to early November 2022) were established. In the dry season, most samples had the highest total nitrogen(T-N) concentrations, specifically in January and February, and the concentrations continued to decrease until May and June. However, after the flood season from July to September, the uppermost subbasin points (Group 1: MS-0, OS-0, GS-0) where T-N concentrations continually decreased were separated from the main stream and lower sub-basin points (Group 2: MS-1~8, OS-1, GS-1) where concentrations increased. Along the main stream, the T-N concentration showed an increasing trend from the upper to the lower reaches. However, it was affected by those of the Osan-cheon and Gonjiamcheon, the tributaries that flow into the main stream, resulting in respective increases or decreases in T-N concentration in the main stream. The nitrate and boron isotope ratios indicated that the nitrogen in all samples originated from manure. Mechanisms for nitrogen inflow from manure-related sources to the stream were suggested, including (1) manure from livestock wastes and rainfall runoff, (2) inflow through the discharge of wastewater treatment plants, and (3) inflow through the groundwater discharge (baseflow) of accumulated nitrogen during agricultural activities. Ultimately, water quality management of the Gyeongan stream basin requires pollution source management at the sub-basin level, including its tributaries, from a regional context. To manage the pollution load effectively, it is necessary to separate the hydrological components of the stream discharge and establish a monitoring system to track the flow and water quality of each component.

• 한국해양학회지
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• v.30 no.6
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• pp.550-564
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• 1995

The temporal and spatial characteristics of wind fields over the neighbouring seas of the Korean peninsula are investigated using 10-years daily wind data during 1978${\sim}$1987 which have been spatially smoothed and low-pass filtered. Long term annual and monthly means are examined for synoptic patterns and spectral analyses are made for temporal variability and spatial coherence. Spatial patterns of the annual mean wind stress and curl have a strong resemblance with those of monthly means during the winter season. Two outstanding periodicities are observed at 1 and 2 cycles per year. The synoptic winds over the study area are highly coherent at both the annual and semi-annual periodicities. However, each basin has its own characteristic spatial pattern. For instance, the prevailing wind during the winter season is northerIy over the northern East Sea (ES), Yellow Sea (YS), and northern East China Sea (ECS), while it is northwesterly over the southern ES and northesterly over the northern ES and southern ECS. At the same time, the wind stress curl is positive over the northern ES and southern ECS, while it is negative over the southern ES, YS and northern ECS. On the other hand, the wind field during the summer season, with its strength being much reduced, is completely different from that during the winter season, and frequent passage of tropical storms provokes large temporal variability over ECS. One remarkable point is that the annual cycle, dominated by the Siberian High, tends to propagate from northeast to southwest, i.e., from northern 25 toward southern ES, YS and ECS, while the semi-annual cycle propagates in the opposite direction, from southwest to northeast. The semi-annual periodicity may reflect development of extratropical cyclones in spring and fall which frequently cross the Korean peninsula. In higher frequencies, there are no dominant periodicities, but local winds over YS and ES are highly correlated for frequencies larger than 0.1 cycles per day and phase difference increases linearly with frequency. This linear increase of phase corresponds to phase speed of 550 and 730 km/d at 0.1 and 0.3 cpd, respectively, The phase speed is apparently coincident with moving speed of extratropical cyclones across the Korean peninsula in the west-east direction.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.4
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• pp.362-371
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• 2016

The distribution patterns of Chromophoric Dissolved Organic Matter (CDOM) and the chemical characteristics of CDOM in the Seomjin river estuary were investigated in March, June and July 2012 in order to determine the spatial and temporal variability of CDOM along the salinity gradient considering the effects of mixing, nutrients and Chl a. The average CDOM values were $1.0{\pm}0.3m^{-1}$, $1.3{\pm}0.4m^{-1}$, and $1.4{\pm}0.3m^{-1}$ in March, June and July, respectively. A high concentration of CDOM (greater than $1.5m^{-1}$) was found at the head of the river which decreased towards the river mouth to as low as less than $0.5m^{-1}$. The average concentrations of CDOM increased from the dry season (March and June) to the wet season (July), and the average slope values ($S_{300-500}$), which were used as indicators of CDOM characteristics and sources, were in the range of $0.013-0.018m^{-1}$. The CDOM and $S_{300-50}$ values showed that not only the concentration of CDOM but also the chemical properties of DOM clearly changed between upstream and downstream in the Seomjin river. CDOM and FDOM showed a negative correlation with salinity ($R^2$ > 0.8), and CDOM was positively correlated with FDOM. Furthermore, the mixing pattern of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM was confirmed as conservative for all seasons. The main environmental factors influencing the concentration of CDOM were salinity (mixing) and water temperature, which meant the dilution of low CDOM seawater, was the controlling factor for the spatial distribution of CDOM. Increases in water temperature seemed to induce the production of CDOM during summer (June and July) through the biological degradation of DOM either by microbial activity or photo-degradation.

• Korean Journal of Ecology and Environment
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• v.50 no.1
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• pp.1-15
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• 2017

Daecheong Reservoir was made by the construction of a large dam (>15 m in height) on the middle to downstream of the Geum River and the discharge systems have the watergate-spillway (WS), a hydropower penstock (HPP), and two intake towers. The purpose of this study was to investigate the limnological anomalies of turbid water reduction, green algae phenomenon, and oligotrophic state in the lower part of reservoir dam site, and compared with hydro-meteorological factors. Field surveys were conducted in two stations of near dam and the outlet of HPP with one week intervals from January to December 2000. Rainfall was closely related to the fluctuations of inflow, outflow and water level. The rainfall pattern was depended on the storm of monsoon and typhoon, and the increase of discharge and turbidity responded more strongly to the intensity than the frequency. Water temperature and DO fluctuations within the reservoir water layer were influenced by meteorological and hydrological events, and these were mainly caused by water level fluctuation based on temperature stratification, density current and discharge types. The discharges of WS and HPP induced to the flow of water bodies and the outflows of turbid water and nutrients such as nitrogen and phosphorus, respectively. Especially, when hypoxic or low-oxygen condition was present in the bottom water, the discharge through HPP has contributed significantly to the outflow of phosphorus released from the sediment into the downstream of dam. In addition, HPP effluent which be continuously operated throughout the year, was the main factor that could change to a low trophic level in the downreservoir (lacustrine zone). And water-bloom (green-tide) occurring in the lower part of reservoir was the result that the water body of upreservoir being transported and diffused toward the downreseroir, when discharging through the WS. Finally, the hydropower effluent was included the importance and dynamics that could have a temporal and spatial impacts on the physical, chemical and biological factors of the reservoir ecosystem.

• Journal of the Korean Society of Marine Environment & Safety
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• v.19 no.5
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• pp.439-458
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• 2013

Temporal and spatial variations of water quality were investigated in the Cheonsu Bay of Yellow Sea, Korea from 2010 to 2011. Water samples were collected at 16 stations and physicochemical parameters were analyzed including water temperature, salinity, suspended solids (SS), chemical oxygen demand (COD), dissolved oxygen (DO), Chlorophyll a and nutrients. Spatial distribution patterns of all survey items were not clear among stations but the bimonthly variations were distinct except the bottom water of the suspended solids. The trend analysis by principal component analysis (PCA) during 2 years revealed the significant variations in water quality in the study area. Spatial water qualities were discriminated into 3 clusters by PCA; station cluster in the surface water 1, 2~11, and 12~16, the bottom water 1, 2~7, and 8~16. Annual bimonthly water qualities were clearly discriminated into 3 clusters by PCA. But tend of cluster in the surface and bottom water was difference, period most of the research was low in nutrient. Ecology-based water quality criteria was a good level of grade II. Bimonthly results are shown as III grade(normal) at June and August, II grade(good) at October and December and I grade for February and April. Water quality was showed by the input of fresh water same as those of Kyoungin coastal area, Asan coastal area, Gunsan coastal and Mokpo coastal area in the Cheonsu.

• Korean Journal of Ecology and Environment
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• v.47 no.spc
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• pp.48-56
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• 2014

Weekly changes of water environments and phytoplankton community with the salinity gradients were investigated at Gyoungpo Lake from April to November in 1998 and 2012. Underwater crossam in Gyoungpo Lake was removed in 2004. Thereafter, average salinity of Gyoungpo lake increased from 7.5 ppt in 1998 to 20 ppt in 2012. A total of 99 and 80 species of phytoplankton was observed from the sampled in 1998 and 2012, respectively. The number of common species during the 2 separate years was 40. Transparency, SS, $NO_3-N$ concentration and N/P ratio in 2012 were lower than those in 1998. During the period of water shortage (April, May) of 2012 transparency decreased due to decreased salinity and increased SS and Chl. a. Correlation coefficients between species and community scores of DCA ordination based on data matrix of the phytoplankton revealed larger variation among sampling seasons in 1998 than in 2012. The increase of seawater influx and conversion rates following the removal of the underwater crossbeam might explain such a differential variation. Gymnodium sp., Peridinium sp., Prorocentrum sp., Nitzschia longissima, Schroederia setigera, Lyngbya sp., Asterococcus limneticus, Asterococcus superbus and Cyclotella meneghiniana were found to well adapt at the high salinities in 2012. Comparatively, Asterrionella formosa, Nitzschia frustulum, Chlorella ellipsoidea, Scenedesmus bijuga and Scenedesmus ellipsoideus were observed at lower salinities in 1998. Two quite contrasting phytoplankton communities were found in the two seasons of a year, spring with limited precipitation and summer, the flood season.

• Korean Journal of Ecology and Environment
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• v.39 no.1 s.115
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• pp.73-84
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• 2006

The objective of this study was to analyze long-term temporal trends of water chemistry and spatial heterogeneity for 10 sampling sites of the Yeongsan River watershed using water quality dataset during 1995 to 2004 (obtained from the Ministry of Environment, Korea). The water quality, based on multi-parameters of biological oxygen demand (BOD), chemical oxygen demand (COD), conductivity, dissolved oxygen (Do), total phosphorus (TP), total nitrogen (TN) and total suspended solids (TSS), largely varied depending on the sampling sites, seasons and years. Largest seasonal variabilities in most parameters occurred during the two months of July to August and these were closely associated with large spate of summmer monsoon rain. Conductivity, used as a key indicator for a ionic dilution during rainy season, and nutrients of TN and TP had an inverse function of precipitation (absolute r values> 0.32, P< 0.01, n= 119), whereas BOD and COD had no significant relations(P> 0.05, n= 119) with rainfall. Minimum values in conductivity, TN, and TP were observed during the summer monsoon, indicating an ionic and nutrient dilution of river water by the rainwater. In contrast, major inputs of total suspended solids (TSS) occurred during the period of summer monsoon. BOD values varied with seasons and the values was closely associated (r=0.592: P< 0.01) with COD, while variations of TN were had high correlations (r=0.529 : P< 0.01) with TP. Seasonal fluctuations of DO showed that maximum values were in the cold winter season and minimum values were in the summer seasons, indicating an inverse relation with water temperature. The spatial trend analyses of TP, TN, BOD, COD and TSS, except for conductivity, showed that the values were greater in the mid-river reach than in the headwater and down-river reaches. Conductivity was greater in the down-river sites than any other sites. Overall data of BOD, COD, and nutrients (TN, TP) showed that water quality was worst in the Site 4, compared to those of others sites. This was due to continuous effluents from the wastewater treatment plants within the urban area of Gwangju city. Based on the overall dataset, efficient water quality management is required in the urban area for better water quality.