• Journal of Korea Water Resources Association
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• v.44 no.9
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• pp.765-776
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• 2011

Flood discharge capacity in a dam downstream reach has been decreased after dam construction because of the river cross section reduction impacted by farm lands, sand-bars and parking lots, etc. in river flood plains. Those obstacles being in the river inside areas have caused negative influences to the dam operation policy. Therefore, the dam downstream river improvement work associated with the dam operation improvement plan is under construction for removing reduction factors on the dam effective storage, assuring flood safety in the dam downstream river and incrementing dam operation benefits. But the project has issued some problems such as project feasibility, economic evaluation, cost allocation and benefit share, etc. Since a dam enterpriser has not committed such kind of project before, it is necessary to set up an objective analysis process and a quantitative financial valuation. This study examines the measurable economic benefits and the cost allocation of the project for the fairness between benefit owners (central government and water electricity enterprisers). As a result, the total economic benefit from 3 dams (Imha, Daechung and Youngdam Dam) accounts for 14.41 Billion Won/year. The financial valuation of K-water as a project enterpriser is approximately estimated at 40% of the total value and the government is 60%.

• Journal of Korean Society on Water Environment
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• v.22 no.2
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• pp.277-287
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• 2006

Production loads of the contaminants near the Nakdong-river are, BOD : $1,006ton{\cdot}day^{-1}$, TN : $117ton{\cdot}day^{-1}$, and TP : $21ton{\cdot}day^{-1}$. Among the sources of contamination, the biggest contribution to the production load was shared by the human population, which maintains 40.7% of BOD, 44.2% of TN, and 52.5% of TP production. Similarly, among the sources of discharge load, the human population contributed 45.0% of BOD, 34.5% of TN, and 45.8% of TP. Results of flow investigation in 2001 and 2002 indicate that among the side streams, Nam-river showed the greatest average flow. In case of main stream flow, it was increased in the downstream due to the increase of the influents from the side streams. In case of BOD, COD, TOC and SS, high values were detected at Keumho-river where industrial wastewater was discharged as high level concentration. In case of the main stream, Koryoung point where direct influence of Keumho-river and Seongseo industrial complex is evident showed high BOD, COD and TOC. Oxidized nitrogen compounds and total nitrogen showed similar patterns of BOD, COD, and TOC. Especially, nitrate nitrogen was relatively high at all points. However, in case of Chlorophyll-a, relatively high values were observed at mid- and downstream areas such as Koryoung, Namjee, Soosan, Moolkeum and Hakooeun. This could be caused by the slow flow rate and the abundant nutrient salts attributed by the side streams. Relatively better water quality was observed in 2002 when the flow was relatively abundant than that in 2001. Results of investigation during 2001-2002 showed that delivery load increased as the flow reaches downstream. In 2001, delivery loads at the downstream Soosan-bridge were BOD $22,152ton{\cdot}day^{-1}$, COD $45,467ton{\cdot}day^{-1}$, TN $22,062ton{\cdot}day^{-1}$, TP $926ton{\cdot}day^{-1}$. Delivery loads in 2002 were increased due to the increase of the rainfall. They are BOD $25,876ton{\cdot}day^{-1}$, COD $64,200ton{\cdot}day^{-1}$, TN $41,101ton{\cdot}day^{-1}$, and TP $1,362ton{\cdot}day^{-1}$.

• The Journal of Engineering Geology
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• v.26 no.2
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• pp.251-260
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• 2016

Groundwater flow due to hydraulic gradients across a geologic barrier surrounding a dam reservoir can cause swamps or wetlands to form on the downstream side of the dam, thereby restricting land use. The difference in head between the reservoir level and the downstream groundwater level creates a hydraulic gradient, allowing water to flow through the geologic barrier. We constructed a drainage system at the Daecheong dam to study the effects on groundwater levels and soil moisture contents. The drainage system consisted of a buried screened pipe spanning a depth of 1-1.5 m below a land surface. Groundwater levels were monitored at several monitoring wells before and after the drainage system was installed. Most well sites recorded a decline in groundwater level on the order of 1 m. The high-elevated site (monitoring well W1) close to the reservoir showed a significant decline in groundwater level of more than 2 m, likely due to rapid discharge by the drainage system. Soil moisture contents were also analyzed and found to have decreased after the installation of the drainage system, even considering standard deviations in the soil moisture contents. We conclude that the drainage system effectively lowered groundwater levels on the downstream side of the dam. Furthermore, we emphasize that water seepage analyses are critical to embankment dam design and construction, especially in areas where downstream land use is of interest.

• Journal of Korea Water Resources Association
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• v.48 no.6
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• pp.501-509
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• 2015

Lately multipurpose dam is required to consider various interests such as quality, ecological environment as well as flood control, water supply, hydropower generation, etc. The objective of this study is to investigation and analysis of water temperature in the areas where there are social conflicts due to cold water outflow. In this study, we monitored water temperature of Juam regulation dam, downstream river, Suncheon bay in a long term period and performed comparative analysis on a change of water temperature in downstream river and Suncheon bay by using three-dimensional numerical mode (EFDC) considering various external factors such as water outflow amount. The result of monitoring and numerical modelling indicates that effects of cold water outflow takes place from april to september. Also effects of the low temperature discharge of dam was complicatedly altered by various factors such as outflow time and amount, weather and tide level conditions etc. The result of this study can be utilized as a basic data for establishing improvement of dam operation plan to minimize negative effects of dam's cold temperature water outflow to downstream river and coastal area.

• Ecology and Resilient Infrastructure
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• v.9 no.1
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• pp.1-14
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• 2022

The total maximum daily load (TMDL) implemented in Korea mainly manages the mainstream considering a single common pollutant and river discharge, and the river system is divided into unit watersheds. Changes in the water quality of managed rivers owing to the water quality management in tributaries and unit watersheds are not considered when implementing the TMDL. In addition, it is difficult to consider the difference in the load of pollutants generated in the tributary depending on the conditions of the water quality change in each unit watershed, even if the target water quality was maintained in the managed water system. Therefore, it is necessary to introduce the total maximum load management at tributaries to manage the pollution load of tributaries with a high degree of pollution. In this study, the HSPF model, a watershed runoff model, was applied to the target areas consisting of 53 sub-watersheds to analyze the effect of water quality changes the in tributaries on the mainstream. Sub-watersheds were selected from the three major areas of the Paldang water system, including the drainage basins of the downstream of the South Han-River, Gyeongan stream, and North Han-River. As a result, BOD ranged from 0.17 mg/L to 4.30 mg/L, and was generally high in tributaries and decreased in the downstream watershed. TP ranged from 0.02 mg/L - 0.22 mg/L, and the watersheds that had a large impact on urbanization and livestock industry were high, and the North Han-River basin was generally low. In addition, a pollution source reduction scenario was selected to analyze the change in water quality by the amount of pollution load discharged at each unit watershed. The reduction rate of BOD and TP according to the scenario changes was simulated higher in the watershed of the downstream of the North Han-River and downstream and midstream of the Gyeongan stream. It was found that the benefits of water quality reduction from each sub-watershed efforts to improve water quality are greatest in the middle and downstream of each main stream, and it is judged that it can be served as basic data for the management of total tributaries.

• Korean Journal of Ecology and Environment
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• v.42 no.1
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• pp.58-66
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• 2009

The telemetry of eight adult manchurian trouts (Brachymystax lenok tsinlingensis) in the upper part of the Nakdong River, which is the southern limit of distribution of manchurian trout on the Korean peninsula, was used to examine migration patterns and evaluate characteristics of over-wintering and the spawning season between December, 2007 and May, 2008. Based on the tracking data, the tagged fish showed a limited migration between adjacent pools, moving only up to $8.6m\;day^{-1}$ during the winter season (December to February). Hydraulic conditions of over-wintering pool areas were, ca. 1m depth, slow moving surface water with areas of sand and gravel. The migration of tagged individuals was successful, moving up to $96.2m\;day^{-1}$ during the spawning season. Two tagged individuals (BL4, BL6) exhibited upstream migration, whereas others showed downstream movements. The timing of upstream migration of the two individuals was consistent with an increasing phases of water level and discharge. The fishes migrating toward the down stream moved to the wide pool areas downstream, where they spent the summer season for the growth.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.105-114
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• 2009

With urbanization in many countries, many pervious areas are being converted into impervious areas. These land use changes cause many negative impacts on runoff and water quality in the areas. Especially runoff volume and peak runoff are increasing with urbanization. In addition to the increased runoff, more pollutant transports to the downstream areas. For these reasons, Low Impact Development (LID) are nowadays being introduced in urban planning. For environment-friendly and economical urban development, the LID Integrated Management Practices (IMPs) are applied in various urban development. However, exact effects on runoff and water quality of various LID IMPs are not assessed with proper LID evaluation technique. Thus, the SWMM (Storm Water Management Model) 5.0 model was slightly modified to simulate the effect of infiltration manhole on runoff and water quality. For comparison of runoff and TSS (Total Suspended Solids) from the study area (26.5 ha), three scenarios were made in this study. It was found that runoff volume, peak runoff, and TSS could be reduced with infiltration manholes and pervious pavements to some degree. Although, there are many limitations in the analysis of LID effects on runoff and TSS, similar trends shown in this study would be expected with site-specific LID IMPs. Thus, it is strongly recommended that various site-specific LID IMPs, such as infiltration facilities, should be applied as much as possible for environment-friendly urban planning.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.5
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• pp.915-926
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• 2016

The purpose of this study is to classify debris flow hazard zones in urbanized areas using multivariate statistical analyses and to suggest customized management strategies to each areal type. Using field survey data set in Seoul, 49 sample debris hazard zones are selected. Clustering and discriminant analyses show that debris flow hazard zones are classified into two types. Surrounding land use and land slope are major factors influencing to the categorization. The results suggest that, by considering the characteristics of each areal type, more customized management strategies for debris flow hazard are necessary. Particularly, in addition to traditional structural measures, non-structural measures including land use and development control for downstream built-up areas should be emphasized in urbanized areas to mitigate human and property damages from debris flow hazard more fundamentally.

• Journal of Environmental Science International
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• v.17 no.6
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• pp.601-609
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• 2008

In this study for the development of area due to the increasing of industry, population and spreading of urbanization is rapidly increasing but about seventy percent of our nation's areas consists of the mountainous districts. In such case, when those areas have the heavy rains break, they are washed away by a fast-flowing stream of a valley and overflowed. Thus it could result on human life and property damage and also the widespread of flood damage in the downstream area. To decrease those damage, the construction of flood control reservoir is necessary. This research was aim to construct the flood runoff models of a mountainous small district and to determine the probability rainfall by analyzing precipitation. The study also examined the effects of location and size of flood control reservoir on flood reduction. The result showed that the construction of detention basin was an effective way to ensure the safety of flood control and multiple detention basin had superior result for reducing amount of runoff in the down stream area than the single detention basin.

• Water for future
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• v.28 no.5
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• pp.163-174
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• 1995

A diffusion hydrodynamic model named "DFLOW-2" for the floodwave analysis from levee-break in protected lowland has been developed. The model has been applied to Ilsan levee-break, which occurred on September 12-13, 1990 in the downstream of the Han River. An unsteady flow analysis has been made in the reach from Indokyo to Junryu. Overflow through broken levee has been treated as internal boundary condition in the channel. A post-processor has been also developed to demonstrate the simulation results. The velocity distributions and inundated depths have been presented. The computed results have good agreements with observed data in terms of inundation depth, flood arrival time and flooded areas.ded areas.