River Basins In Korea Research Articles

Estimation of river discharge using Monte Carlo simulations and a 1D hydraulic model based on the artificial multi-segmented rating curves at the confluence of two rivers

During extreme floods caused by climate change, reliable flow discharge data are essential for successful reservoir operation to mitigate downstream flood damage. Generally, the flow discharge is computed using the rating curve (RC) established from the relationship between the flow rate and water stage level. Determining the parameters of rating curves is subject to uncertainties related to the difficulties and limitations of flow monitoring in covering a wide range of flow variations. Especially at river confluences, the uncertainties are pronounced when floods occur owing to several factors such as roughness change, backwaters, and levee overflow. The Seomjin River Basin in Korea suffered from flood inundation that occurred at the tributary confluence during an extreme flood in 2020. To identify a reliable flow rate of the main stream and tributary, this study proposes an indirect flow assessment scheme using a 1D hydrodynamic simulation model to find the best simulated water level in an iterative manner based on Monte Carlo (MC) simulations. With a large amount of discharge data generated from random-number combinations, it is possible to obtain the best results automatically by specifying the reliability limitation considering the uncertainty of the predetermined RC parameters associated with the roughness coefficient. Nash Sutcliffe Efficiency (NSE) was incorporated to evaluate the reproduced water level to meet the threshold specified for NSE ≥ 0.75. The simulated flowrates computed from the revised RC and roughness coefficients revealed an error range of 8%–36.6% compared with the design flood. The approach proposed in this study is applicable for determining the valid parameters necessary to create a revised RC at an existing water level gauge station, where the uncertainties of the RC are pronounced, particularly in the vicinity of the channel confluence.

The Impact Evaluation of Acid Mine Drainage on Zebrafish (Danio rerio) and Water Fleas (Daphnia magna) in the Vicinity of the Geum River Basin in Korea

Heavy metals, such as copper, lead, and cadmium, carried by acid mine drainage are pollutants of the aquatic ecosystem, posing a significant health risk to the water resource for humans. Environmental technologies to reduce metal contamination are applied for post-mining prevention and improvement. Despite detailed pollution management, water contaminated by heavy metals still flows into the natural water system. This study investigated the impact of drainage discharged from abandoned mines near the major river in South Korea on aquatic organisms. The toxicity of the field water showed a more significant effect than observed through the experiment for each heavy-metal concentration. Various toxic substances coexisted in the field water around the mine, such that the overall toxic intensity was high even when the concentration of each heavy metal was low. As a result, the inhibition of activity of aquatic organisms was observed at low individual concentrations, and further investigation on the effect of long-term exposure to trace amounts of heavy metals is required.

Characterization of the Propagation of Meteorological Drought Using the Copula Model

Drought is a phenomenon that is caused by several factors and can be divided into meteorological drought, agricultural drought, hydrological drought, and socioeconomic drought. In this study, the characteristics of propagating from meteorological drought to agricultural (or hydrological) drought in the Andong Dam basin and Hapcheon Dam basin located in the Nakdong River basin in Korea were investigated. Standardized precipitation index (SPI), standardized soil moisture index (SMI), and standardized runoff index (SRI) were used to characterize meteorological, agricultural, and hydrological droughts, respectively. SPI-m (1–12) on various timescales and SMI-1 (or SRI-1) were selected as drought propagation timeseries, such that a correlation analysis was performed to evaluate the correlation and propagation time between meteorological and agricultural (or hydrological) drought. Propagation probability was quantified using a copula-based model. The correlation between meteorological and agricultural (or hydrological) droughts was not significantly affected by seasons. A relatively strong correlation was found in summer. A relatively weak correlation was shown in autumn. In addition, it was found that there was a difference in correlation between the Andong Dam basin and the Hapcheon Dam basin. On the other hand, in both watersheds, the propagation time was as long as 2 to 4 months in spring and decreased to 1 month in summer.

Status of Helminthic Infections in Residents around River Basins in the Republic of Korea for 10 Years (2011-2020).

The positive rate of Clonorchis sinensis is the highest among intestinal parasites in the Republic of Korea (Korea). More than 1.2 million people were at risk of C. sinensis infection in Korea in 2012. An intensive control program is being implemented for residents of the 5 major river basins to reduce helminthic infections, including C. sinensis infection. This study evaluated the continuous intensive control program for parasitic diseases including clonorchiasis in areas near the 5 major river basins in Korea over the past 10 years (2011–2020). A total of 335,020 fecal samples (one sample per resident) prepared by the modified sedimentation technic were microscopically examined. Those who expelled helminth eggs were treated with anthelmintics through local health centers and re-examined 3 months later. The overall positive rate of helminths egg was 7.1%. The annual positive rates were dramatically decreased from 14.4% (2011) to 5.9% (2020). The egg positive rate was highest in C. sinensis (5.3%), followed by heterophyid flukes (1.5%) and Trichuris trichiura (0.2%). The prevalence of C. sinensis was significantly higher in males (7.6%) than in females (3.7%), and the highest in the 50–59 years (7.0%) age group. Our results are beneficial to establish prevention and control policies against helminthiases including clonorchiasis in endemic areas in this country.

Equivalent Horton’s ratios of channel network within the framework of variable source basin area

Study regionThe Seolmacheon Experimental Basin, Korea. Study focusTo estimate the equivalent Horton’s ratios for channel network which are independent of the magnitude of threshold area or source basin area New hydrological insights for the regionThis paper aims to estimate the equivalent Horton’s ratios for a small experimental river basin in Korea, which are independent of the magnitude of threshold area or source basin area. To this end, various pattern of channel networks is extracted with the correspondence to the variable source basin area. It turns out that the original Horton’s ratios are highly variable and sensitive to the scale of observation for channel networks. Nevertheless, the combination of those such as the logarithmic rate between bifurcation ratio and area ratio might have a relatively constant trend implying scale invariance, which could be considered as an avenue to Horton’s ratios independent of the source basin area. Thereby, the equivalent Horton’s ratios could be regarded as the representative values for the basin of interest, so that they can provide a reliable description of channel network regardless of the scale of observation. It is confirmed that the scale invariance of channel network closely related to Hortons’ ratios would be the result stemming from cooperation or competition between the elongation and expansion of channel network due to variable source basin area.

Water quality risk assessment for drought conditions: A case study of the Korean Nakdong River basin

As the frequency of drought from climate change increases and the severity of drought become worse, it is imperative to prepare appropriate countermeasures against severe droughts. Despite the severe impacts of droughts on coupled humans and environmental systems, we do not fully understand the consequences of severe droughts affecting the environment. Therefore, the present study proposed a quantitative assessment index for water quality risk for extreme droughts to improve the safety of water environment management by providing flows to areas vulnerable to the drought. The application of this study is the Nakdong River basin in Korea, which has assessed the vulnerability of water quality to severe droughts as water quality deterioration problems continue to be experienced event after the river restoration project was completed. The results of this study are expected to provide scientific environmental drought monitoring information in a changing climate.

Changes in butterfly communities over a 10‐year period in Geum river basin in Korea

AbstractOne conclusion of this study is that as the road network expands in rural and remote areas the surrounding butterfly populations are generally noted to be decreasing or even disappearing. However, there is one exception, Libythea celtis. This common species, living close to forested areas, have actually increased while thier competing species have decreased according to this study. The endangered species of Korea, Parnassius bremeri, Sinia divina and Argynnis nerippe, which inhabit the area of the study have also decreased or disappeared. Another result of this study is that, while the number of species which inhabit the grasslands have decreased, no similar changes have been noted in the number for the species which inhabit the shrubs. Furthermore, there has been a growth in the numbers of the species that inhabit trees. In addition, the number of individuals has decreased in the grasslands and shrubs but increased in the trees. Overall, the general conclusion of this study is that, while the development of rural and remote areas showed a decrease in the number of specific butterfly species, they are being replaced by more common species.

Estimation of flow in various sizes of streams using the Sentinel-1 Synthetic Aperture Radar (SAR) data in Han River Basin, Korea

This study proposes a novel approach of estimating stream discharge using the European Space Agency Sentinel-1 satellite data. Fifteen hydrological stations with a mean discharge ranging between 2 m3 s−1 and 305 m3 s−1 in the Han River Basin in Korea were chosen as test sites. A series of Sentinel-1 Synthetic Aperture Radar (SAR) images and observed streamflow data were selected to develop and validate the methodology. The methodology relates the stream discharge to the water area that is extracted from the satellite image analysis. The satellite image analysis involved the following sequential steps: (1) A series of SAR images for a given test site is pre-processed for thermal noise, radiometric calibration, speckle filtering and terrain correction; (2) The histogram matching technique is applied to all images to unify the backscatter distribution; (3) The polygonal area including the stream is manually delineated along the reach and the image filter with the shape of the polygon is applied to all images so that only the water area of the stream is extracted; (4) A single backscatter threshold value is applied to all images to extract a series of water area; (5) the power-law relationship between the series of the water area and the corresponding stream discharge is established and the correlation coefficient of the relationship is calculated; (6) The process of (4) and (5) was repeated to identify the optimal backscatter threshold that maximizes the correlation coefficient of the relationship. A clear relationship was developed for the 13 stations except for the two at which flow is highly influenced by hydraulic structures such as dam. At the 13 stream locations, the R value of the power-law relationship varied between 0.68 and 0.98 with a mean value of 0.89. The relationship was influenced by the geometric properties of the stream such as the size and side slope.

Natural and Human-Induced Drivers of Groundwater Sustainability: A Case Study of the Mangyeong River Basin in Korea

The sustainability of rural areas depends on the availability of water resources. The Mangyeong River Basin (MRB) in Korea faces a water supply shortage for agriculture and industry. Based on 11-year (2005–2015) precipitation and groundwater monitoring data, groundwater sustainability was evaluated in terms of natural and man-made factors and their spatio-temporal variations. A precipitation time-series revealed a declining trend, but there were different seasonal trends between wet and dry periods, with declining and rising trends, respectively. Groundwater hydrographs from five national groundwater monitoring wells showed temporal variations. Groundwater wells located in downstream areas showed both recharge from upgradient areas and local man-made impacts (e.g. from pumping), resulting in an ambiguous relationship between precipitation and water levels. However, other monitoring wells in the upstream areas displayed water level responses to precipitation events, with a declining trend. Using the standardized precipitation index at a time scale of 12 months (SPI-12) and the standardized groundwater level anomaly, meteorological and groundwater drought conditions were compared to infer the relationship between precipitation deficit and groundwater shortage in the aquifer. The SPI results indicated severely dry to extremely dry conditions during 2008–2009 and 2015. However, the standardized groundwater level anomaly showed various drought conditions for groundwater, which were dependent on the site-specific hydrogeological characteristics. Finally, groundwater sustainability was assessed using water budget modelling and water quality data. Presently, if groundwater is used above 39.2% of the recharge value in the MRB, groundwater drought conditions occur throughout the basin. Considering water quality issues, with nitrate being elevated above the natural background, this critical abstraction value becomes 28.4%. Consequently, in the MRB, sustainable groundwater management should embrace both natural and human-induced factors to regulate over-exploitation and prevent contamination.

Streamflow response to climate change during the wet and dry seasons in South Korea under a CMIP5 climate model

Having knowledge regarding to which region is prone to drought or flood is a crucial issue in water resources planning and management. This could be more challenging when the occurrence of these hazards affected by climate change. In this study the future streamflow during the wet season (July to September) and dry season (October to March) for the twenty first century of South Korea was investigated. This study used the statistics of precipitation, maximum and minimum temperature of one global climate model (i.e., INMCM4) with 2 RCPs (RCP4.5 and RCP8.5) scenarios as inputs for The Precipitation-Runoff Modelling System (PRMS) model. The PRMS model was tested for the historical periods (1966-2016) and then the parameters of model were used to project the future changes of 5 large River basins in Korea for three future periods (2025s, 2055s, and 2085s) compared to the reference period (1976-2005). Then, the different responses in climate and streamflow projection during these two seasons (wet and dry) was investigated. The results showed that under INMCM4 scenario, the occurrence of drought in dry season is projected to be stronger in 2025s than 2055s from decreasing -7.23% (-7.06%) in 2025s to -3.81% (-0.71%) in 2055s for RCP4.5 (RCP8.5). Regarding to the far future (2085s), for RCP 4.5 is projected to increase streamflow in the northern part, and decrease streamflow in the southern part (-3.24%), however under RCP8.5 almost all basins are vulnerable to drought, especially in the southern part (-16.51%). Also, during the wet season both increasing (Almost in northern and western part) and decreasing (almost in the southern part) in streamflow relative to the reference period are projected for all periods and RCPs under INMCM4 scenario.

Improving Reservoir Operation Criteria to Stabilize Water Supplies in a Multipurpose Dam: Focused on Nakdong River Basin in Korea

Recently, torrential rain and drought have occurred in close temporal proximity and for similar durations due to changes in the spatiotemporal patterns of rainfall owing to climate change. In particular, when a drought occurs, it tends to be prolonged, making it necessary to improve the operation of multipurpose dams that not only control flooding but also serve as water supplies. In this study, standard water volume lines and action plans by response stage were improved so that water could be stored in advance of a drought instead of reservoir operation criteria set based on data from the past. The minimum water demand by use (domestic water, industrial water, and agricultural water) was also calculated. The improved reservoir operation criteria were applied to multipurpose dams in the Nakdong River Basin, and their effects were analyzed by calculating additionally secured water volumes. In the future, in case of lowered water volumes in multipurpose dams owing to a drought, the application of these improved reservoir operation criteria is expected to contribute to water supply stability by delaying entry into the drought stage and minimizing the damages caused by limited water supplies.

A new blind groundwater-dwelling genus of the Cladocera (Crustacea: Branchiopoda) from the Korean Peninsula.

Groundwater-dwelling Cladocera are to date known only from the caves and hyporheic zones of the rivers in Europe (Belgium, England, France, Bosnia and Herzegovina, Macedonia, Slovenia, Spain), Turkey (European part) and Arabian Peninsula (Yemen). All these animals belong to the subfamily Aloninae Dybowski & Grochowski of the family Chydoridae Dybowski & Grochowski (Cladocera: Anomopoda). Examination of some samples collected by our colleagues - experts in Copepoda, Bathynellidae and Amphipoda-in South Korea led us to discovery of a new stygobiotic alonine genus, which is also the first record of a groundwater-dwelling cladoceran in Asia. Aims of this paper are: (1) to describe Korealona gen. nov., represented by two species, Korealona karanovici gen. nov., sp. nov. found in three different localities, and K. choi sp. nov., also found in three different localities; and (2) to discuss its differences from other genera of this subfamily and possible phylogenetic position of this genus among the aloninse. Distribution ranges of two species of Korealona gen. nov. are not unequivocally associated with present-day main river basins in Korea, but more sampling efforts are needed for final conclusions on their distribution ranges in Korea and closest countries and understanding of the genus evolutionary history.

Application of real option analysis for planning under climate change uncertainty: a case study for evaluation of flood mitigation plans in Korea

With concerns regarding global climate change increasing, recent studies on adapting to nonstationary climate change recommended a different planning strategy that could spread risks. Uncertainty in global climate change should be considered in any decision-making processes for flood mitigation strategies, especially in areas within a monsoon climate regime. This study applied a novel planning method called real option analysis (ROA) to an important water resources planning practice in Korea. The proposed method can easily be applied to other watersheds that are threatened by flood risk under climate change. ROA offers flexibility for decision-makers to reflect uncertainty at every stage during the project planning period. We successfully implemented ROA using a binomial tree model, including two real options—delay and abandon—to evaluate flood mitigation alternatives for the Yeongsan River Basin in Korea. The priority ranking of the four alternatives between the traditional discount cash flow (DCF) and ROA remained the same; however, two alternatives that were assessed as economically infeasible using DCF, were economically feasible using ROA. The binomial decision trees generated in this study are expected to be informative for decision-makers to conceptualize their adaptive planning procedure.

Interrelationship between geochemical elements of sediment and groundwater at Samrak Park Delta of Nakdong River Basin in Korea: multivariate statistical analyses and artificial neural network approaches

This research was conducted at Samrak Park Delta of Nakdong River Basin in Busan Metropolitan City, Korea. The main objective of this study was to evaluate the interrelationship of geochemical elements in sediments and groundwater through multivariate statistical analyses and a multilayer perceptron artificial neural network model. The mean concentrations of chemical elements were Si (46%), Fe (16.9%), Al (15.7%), K (7.5%) and Ca (4.5%) in sediments, and Na (8650 mg/L), Mg (999 mg/L), Ca (432 mg/L), K (293 mg/L) and Cl (17,640 mg/L) in groundwater, respectively. The principal component analysis produced 3 kinds of factors with the variances of 63.37, 27.02 and 9.62%, respectively. It is suggested that the chemical components of sediments and groundwater were mainly originated from source rocks and seawater intrusion, with the minor impacts of irrigation and industry. Cluster analysis also showed that chemical elements were mainly controlled by the natural geogenic sources and seawater intrusion. Multilayer perceptron of artificial neural network (ANN) presented the good interrelationship between sediment and groundwater. The determination coefficients (R 2) between ANN predicted values and observed values in groundwater showed the high values of 0.61–0.97 except Mg, Mn and Sr. It is revealed that the chemical components of sediment and groundwater were derived from local geological origin and from the minor impact of anthropogenic sources. Multivariate analyses and ANN contributed to the identification of the mutual relationship between the geochemical elements of sediment and those of groundwater.

Development of an ecological impact assessment model for dam construction

The purpose of this study was to develop a model for assessing the ecological value of a dam reservoir. Various evaluable characteristics (“elements”) that influence the ecology of the target area around the dam were grouped into three classes: (1) physical elements, such as altitude, slope, and aspect; (2) vegetation elements, such as forest physiognomy, vegetation type, age class, diameter at breast height (DBH) class, and density; and (3) habitat elements, such as ecological conditions, vegetation conservation classification, and frequency of wildlife appearances. The evaluation standard was quantified considering the ecological function of each element. The developed assessment model was applied to the Yeongju Dam in the Nakdong River basin in Korea. This study assumed that the ecological condition before the dam construction was 100 %. The results of this study showed that the physical, vegetation, and habitat elements were downgraded to 82.8, 95.5, and 90.7 %, respectively, after the construction of the dam. The overall ecological value was estimated to be 90.0 % and thus decreased by 10.0 % due to dam construction. Additionally, by combining the results for the evaluation elements, an ecologically healthy area was selected. The results of this study should prove useful for quantifying ecological impact and for establishing an ecological restoration plan for dam reservoirs.

Assessment of the Impacts of Global Climate Change and Regional Water Projects on Streamflow Characteristics in the Geum River Basin in Korea

The impacts of two factors on future regional-scale runoff were assessed: the external factor of climate change and the internal factor of a recently completed large-scale water resources project. A rainfall-runoff model was built (using the Soil and Water Assessment Tool, SWAT) for the Geum River, where three weirs were recently constructed along the main stream. RCP (Representative Concentration Pathways) climate change scenarios from the HadGEM3-RA RCM model were used to generate future climate scenarios, and daily runoff series were constructed based on the SWAT model. The indicators of the hydrologic alteration (IHA) program was used to carry out a quantitative assessment on the variability of runoff during two future periods (2011–2050, 2051–2100) compared to a reference period (1981–2006). Analyses of changes in the runoff characteristics of the lower Geum River showed that climate change is likely to lead to an increase of the future runoff ratio and that weirs contributed to an increase in the minimum discharge and a decrease in the maximum discharge. The influence of the weirs on the runoff characteristics of the Geum River basin was projected to be greater than that of climate change.

Assessment of Meteorological Drought in Korea under Climate Change

Drought has become one of the most important elements for water resources planning and management in Korea. The objective of this study is to estimate the spatial distribution of drought and change in the drought characteristics over time due to climate change. For the spatial characterization of drought, the standardized precipitation index (SPI) is calculated from the 45 observatories in Korea and the spatial distribution is also estimated based on the joint probability analysis using the copula method. To analyze the effect of climate change, spatial distribution of drought in the future is analyzed using the SPI time series calculated from Representative Concentration Pathways (RCPs) scenarios and HADGEM3-RA regional climate model. The results show that the Youngsan River and the northwest of Nakdong River basins in Korea have nearly doubled drought amount compared to the present and are most vulnerable to drought in near future (2016 to 2039 years).

Evaluation of physico-chemical parameters in water and total heavy metals in sediments at Nakdong River Basin, Korea

Fourteen water and sediment samples were collected from the Nakdong River Basin in Korea to evaluate the physico-chemical parameters (pH, dissolved oxygen, chemical oxygen demand, biological oxygen demand, total organic carbon) in water and total heavy metals (Cu, Zn, Pb, Cd, As) in surface sediments. The assessment of physico-chemical parameters indicates that river water and sediments in the study area were strongly impacted by industrial wastewater, irrigational effluents and domestic sewage. The overall average concentrations of metals in sediments were Cu (6.41 mg/kg), Cd (0.11 mg/kg), Pb (4.72 mg/kg), Zn (16.8 mg/kg), As (0.19 mg/kg), and the order of the concentrations was Zn > Cu > Pb > As > Cd. Geo-accumulation index (Igeo) indicates that most of samples fall at unpolluted to medium category, while contamination factor values fall at the medium to very high pollution zone. Pollution load index also suggests that all samples fall at progressive pollution sector. Multivariate statistical analysis and pollution index methods were helpful for the classification on the basis of the contamination sources and origin of heavy metals. In conclusion, this study clearly infers the fact that the cause of metal pollution in this region is mainly due to the effluents discharged from factories, agricultural fields and sewers.

부하지속곡선(Load Duration Curve; LDC)을 이용한 한강수계 오염총량관리 목표수질 평가방법 적용 방안

Water quality in four major river basin in Korea was managed with Total Maximum Daily Load (TMDL) System. The unit watershed in TMDL system has been evaluated with Target Water Quality (TWQ) assessment using average water quality, without considering its volume of water quantity. As results, although unit watershed are obtained its TWQ, its allocated loads were not satisfied and vice versa. To solve these problems, a number of TWQ assessments with using Load Duration Curve (LDC) have been studied at other watersheds. The purpose of this study was to evaluate achievement of TWQ with Flow Duration Curve (FDC) and Load Duration Curve(LDC) at 26 unit watersheds in Han river basin. The results showed that achievement rates in TWQ assessment with current method and with LDC were 50~56 % and 69~73%, respectively. Because of increasing about 20% of achievement rates with using LDC, the number of exceeded unit watershed at Han river Basin was decreased about 4~6 unit watersheds.

개별배출시설 삭감잠재량 분석을 통한 수질오염총량제의 민간참여 활성화 방안 연구

AbstractFour major river basin in Korea has been managed with Total Maximum Daily Load(TMDL) System. Water quality indicators as targeted pollutants for TMDL were BOD and TP. In order to satisfy water quality criteria, government allocation using public treatment facilities and its action plan has been used. However, the role to improve water quality were recently faced to its limitation. It is time to require the role of non-government allocation in private discharge facilities to control good water quality. This study investigated three different scenarios in reduction demands of non-government allocations about industry and private sewages. The three different scenarios were discharge under 1) legal water quality standard, 2) water quality level in 2011 and 3) current water quality level with maximum value in group. The results showed that reduction potential in water discharge for TP indicator was 1,118kg/day, under second scenario with 20% of deduction. This results arrived at 42% of whole reduction potential costs and 0.012mg/L improvement in water quality. In conclusion, to intrigue voluntary participation in non-government allocation, various benefits such as tax reduction, tax exemption, and water quality trading should be provided.Key words: Non-government allocation, Private discharge facilities, Reduction potential, Total Maximum Daily Load (TMDL)