• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.79-86
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• 2012

Cemented soils have been used for subbase or base materials of roads, backfill materials of retaining walls and cofferdam. Such cemented soils can be degraded due to repeated wetting and drying or various weathering actions. Unlike rocks, a standard method was not defined for evaluating the durability of cemented soils. In this study, a slaking durability test and an ultrasound cleaner were used for developing a new durability test method for cemented soils. For durability tests, cemented sands with different cement ratios (4, 6, 8, and 12%) with cylindrical specimens were prepared and then air cured or under-water cured for three days. Three-day-cured specimens were dried for one day and then submerged for one day before testing. The weight loss after the slake durability test or ultrasonic cleaner operation for 10 or 20 min was measured and used for assessing durability. When a cement ratio was 4%, the weight loss from ultrasonic cleaner test was 7-25% but that from slake durability test was as much as 30-60%. For specimens with cement ratio of more than 8%, the weight loss was less than 10% from both tests. A durability index increased with increasing a cement ratio. The durability index of under-water cured specimen was higher than that of air cured specimen. The ultrasonic cleaner test was found to be an effective tool for durability assessment of cemented sands rather than the slake durability test.

• Journal of Wetlands Research
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• v.16 no.2
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• pp.213-220
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• 2014

Recently, river maintenance is change due to concern for the environment increases. Thus, the river restoration and river environment is best part of river maintenance. In case of Korea, existing river is improvement straightly for flood control and transportation. When the stream channel is straightly, maintain stability is important. Thus, construction of levees along the river. The various river structures for the purpose of flood control and transportation are inhibit factors of longitudinal and lateral connectivity. Connectivity is defined as the maintenance of lateral, longitudinal, and vertical pathways for biological, hydrological, and physical processes. Long-term point of view, increased connectivity is very important for a healthy ecosystem composition. As the first step of river restoration, this study described theory and concept of river continuum and the numerical model was applied to a real topography to simulate the flow analysis with or without segregated and blocked space in the Mankyung river. The results of this study can be utilized to develop the watershed connectivity assessments methods in order to the river restoration.

• Journal of Korea Water Resources Association
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• v.50 no.9
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• pp.627-635
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• 2017

It is required to estimate reliable design floods for hydraulic structures in order to respond more effectively to recent climate change. In this study, differences of design floods that were estimated the flood frequency analysis (FFA) and the design rainfall-runoff analysis (DRRA) were analyzed. In Korea, due to lack of measured flood data, the DRRA method is used in practice to determine the design floods. However, assuming the design floods estimated by the FFA as true values, the DRRA method over estimated the design floods by 79%. Thus, this study proposed a practical method to estimated design flood in ungauaged watersheds through regressive adjustment of flood quantiles estimated from the DRRA method. To this end, after investigating the differences between design floods acquired from the FFA and the DRRA method, nonlinear regression analyses were performed to develop the adjustment formulas for 8 large-dam watersheds. Applying the adjustment formula, the accuracy was improved by 65.0% on average over the DRRA method. In addition, when considering the watershed size, the adjustment formula increases the accuracy by 2.1%p on average over when not considering the watershed size.

• Geophysics and Geophysical Exploration
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• v.5 no.4
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• pp.257-261
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• 2002

We have carried out integrated research including field survey and numerical modeling to appraise the applicability of SP method to the leakage problems of irrigation facilities. The leakage pattern of the dike studied here can be classified into the three categories: leakage through the abutment, leakage by piping through dike, and leakage due to the composite effects of landslide and distortion of the dike structure. for the numerical modeling to interpret quantitatively SP survey results acquired at dike, we have modified the computer code proposed by Sill (1983) to apply to the leakage problems. The numerical studies match the characteristic patterns of SP anomalies according to the leakage types and appear to be very useful to interpret the leakage zone and path. The SP monitoring results were also well coincided with tidal variations observed at every embankment so we found the SP method is quite effective not only to detect the leakage zone but also to determine the leakage trend. The numerical modeling results also reproduced the SP anomalies due to seawater leakage in the embankment.

• Water for future
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• v.27 no.3
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• pp.71-82
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• 1994

A statistical characteristics, relations of calendar and water year, and frequencies of precipitaion which are necessary for water resources planning were analyzed with long historical data(1905-1991 years). And the analysis of precipitation of the drought periods in 1967-1968 years was carried out. The study basins are the five major rivers in Korea. As a results of this study, annual precipitation shows an increasing trend but its variation has no statistical significance. The rellations of calendar and water year precipitation is presented, it shows that there are little difference of the total precipitation between them. The annual minimum series of total precipitation for the periods of 3, 6, 9, and 12 months by water year are constructed, and frequency precipitation for each periods using 2-parameter lognormal distribution is presented. The analysis of the precipitation in 1967-1968 years shows in a natural river basins that it would be a moderate drought, if dry seasons(Oct-May) or wet seasons(Jun-Sep) has 75 percents of historical mean precipitation of the same periods. And if it has less than 60 percents of historical mean precipitation, it would be a severe drought.

• Journal of Korea Water Resources Association
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• v.44 no.5
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• pp.363-376
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• 2011

1-D hydrodynamic numerical models have been most widely used in the field of flood analysis. The model's input data are upstream/downstream boundaries, roughness coefficients, cross-sections, and so on, and computational distance step and time step are the most important factors in order to guarantee the computational accuracy, stability, and efficiency. In this study, a theoretical explanation is presented for the basis of the previous empirical selection criteria of cross-section's location; also, the estimation technique of computationally variable distance step is proposed to reflect the properties of flow at every computational time step. Combining this technique with 1-D unsteady numerical model, it was applied to two events of Teton dam failure flood and the Han River flood. The numerical experimental results demonstrate that the accuracy and stability is increased when used more interpolated cross-sections and show that the proposed technique of computationally variable distance step has the same order of accuracy with smaller numbers of cross-section than previous empirical selection criteria. The practical use of this technique will be possible to analyze the river floods with high efficiency as well as accuracy and stability.

• Resources Recycling
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• v.19 no.6
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• pp.61-69
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• 2010

S.M.C (DSME), only operating gold mine in Korea, is processing about 160 ton/day to recover gold and more than 150 ton/day of tailing is produced. Some portion of the tailings are used as a filler material after drying, but most of them are stored on the tailing dam. As a result of chemical analysis by a fire assay method, it contained Au 1.5~2.0 g/ton and 225~300 g per day of gold is getting discarded. It is urgent to develop a technology to recover and reutilize Au. In the present study, flotation tests were carried out to recovery gold for the tailings. Test results show that products with gold grade 21.31 g/ton(Au grade) and 62.73% (Au recovery) were obtained under the optimal conditions including KAX addition rate 97.2 g/ton, frother AF 65 (0.248 l/ton) and depressant sodium silicate (4 kg/ton), it's possible to recover one of the most valuable metal Au, by re-feeding to rougher flotation.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.535-535
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• 2012

하천 환경의 변화는 자연적으로 일어나기도 하지만, 우리나라 경우 대부분 하천 정비, 골재 채취, 수중보와 하구둑 등 하천시설물의 건설, 그리고 댐 및 교량건설 등 인위적인 요인에 의한 변화가 지배적이다 이렇게 환경이 변화하면 하천의 평형 상태는 파괴되며 하천의 평형 상태를 복원하는 과정에서 하천의 침식 또는 퇴적이 일어나며 이러한 과정의 총체적인 결과로서 하상변동이 일어나게 된다. 하상변동은 단기적인 면에서는 하천에서의 취수, 배수, 주운동 하천관리에 직접적인 영향을 주며, 장기적인 면에서는 하천시설물의 안정, 홍수위 및 지하수위 변화, 홍수터와 같은 하천부지의 변화 등 하천 및 유역 관리에 광범위한 영향을 주고 있다 하천의 유황 및 하상재료의 인위적인 변화에 의한 장기적인 하상변동 효과를 예측하고 분석하는 것은 하천계획 및 관리 면에서 매우 중요하다. 또한 하천 정비사업 등에 의한 영향을 제대로 평가하기 위해서는 비교적 단기간의 홍수 또는 호우 사상에 대한 단기적인 하상변동 효과를 정확하게 예측하는 것은 필수적이다. 외국에서는 하상변동 예측의 필요성을 일찍이 인식하여 다수의 하상변동 예측모형이 개발되어 하천 실무에 사용되고 있으며, 국내에서도 하천 흐름의 등수 역학적 해석을 위해 여러 가지 수치 기법들에 대한 연구가 진행되고 발전되어져 왔다. 현재 국내에서는 측량 자료이용과 모형적용의 용이성을 이유로 1차원 점변 부정류 해석프로그램인 HEC-RAS 모형을 많이 사용하고 있으며 대부분의 하천 정비 기본계획 수립에 있어서도 1차원 해석 모형을 적용하고 있는 실정이다. 국내에 서 수행된 하상변동 예측에 관한 연구들은 대부분 1차원 모형이므로 하천의 사행의 진행이나 유사의 횡방향 분포 등은 고려할 수 없다. 또한 하상변동 계산 시 이동상 부분의 전체가 균일하게 상승 또는 하향하는 것으로 가정하기 때문에 흐름이 급변하는 데 적용하는 것은 적합하지 않다. 따라서 본 연구에서는 4대강살리기 사업이 진행중인 낙동강유역 구미보지점을 대상으로 2차원 흐름 및 하상변동 수치모형인 CCHE2D 모형을 적용하여 50년, 100년, 200년 빈도별로 모의를 실시, 보설치 전 후의 하상변동을 비교 분석 하였다. 모의 결과 보설치 후의 경우 보 상류단은 전반적으로 퇴적의 양상을 보였으며, 보 하류단의 만곡부의 경우 홍수량이 증가함에 따라 유속 및 소류력이 비슷한 패턴으로 증가하여 침식이 관찰되었다. 특히 보 직하류의 경우 수문을 기준으로 다량의 침식이 있음을 보였으며, 침식이 계속 진행된다면 보유실과 같은 심각한 결과를 초래할 수 있기 때문에 침식을 방지 할 수 있는 다양한 장치가 마련되어야 할 것으로 판단된다.

• Journal of Korea Water Resources Association
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• v.41 no.10
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• pp.1045-1058
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• 2008

Drought is a natural phenomena caused by long time lack of precipitation causing varying damages in several regions which increases yearly. Specifically, in 1994$\sim$1995 and 2001 severe drought occurred in almost every region of Korea. Small and medium sized water supply reservoirs exposed their bottoms and also raised considerable economic losses. In spite of this fact, damages and impacts from the drought can still be minimized by well defined drought management plans with optimal management of water supply facilities. Throughout this research, integrated drought information system is proposed to used in monitoring the drought of Korea in real time. And the expert system for the management of water supply facilities has developed using Shared Vision Model (SVM) to enable the Virtual Drought Exercise (VDE). To find a better way to manage water during drought and to develop the enhanced abilities to respond to drought, virtual drought exercise is the most effective approach and process. The proposed process of virtual drought exercise using integrated drought information system can be used as an effective tool to prepare the optimal water supply plans during the drought.

• Korean Journal of Environmental Biology
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• v.39 no.3
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• pp.273-288
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• 2021

We analyzed the spatio-temporal distribution characteristics of water quality and phytoplankton communities in the Isa Stream systems (ISS) from Sangsa Lake to Suncheon Bay. Sangsa Lake showed relatively oligotrophic and mesotrophic conditions, but the freshwater and mixed brackish water zones showed more severe eutrophication than Sangsa Lake and Suncheon Bay due to the influence of industrial waste such as livestock waste. In terms of the phytoplankton community, the number of phytoplankton species was higher in freshwater and mixed brackish water zones than in Sangsa Lake and Suncheon Bay, but the cell density and Chlorophyll-a concentrations (Chl-a) were relatively high in Sanga Lake and Suncheon Bay. In particular, the mesotrophic species Fragilaria crotonensis and Asterionella formosa showed different dominance in the surface and bottom layers, and the influence of A. formosa was significant in the freshwater and mixed brackish water zones in spring and summer. However, Skeletonema costatum-ls, a eutrophic indicator species, dominated in mixed brackish water zones to seawater in autumn and winter. Thus, the severe eutrophication and rapid environmental changes in the ISS could seriously damage the coastal ecosystem in Suncheon Bay. These ecosystem changes are threatening in terms of conservation and management of the UNESCO Suncheon Biosphere Reserve and Yeoja Bay including Suncheon Bay, which recorded the first Ramsar wetland in Korea. Therefore, further research is needed to establish an in-depth management plan.