• Journal of the Korean Geosynthetics Society
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• v.9 no.3
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• pp.77-85
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• 2010

The change of water level in reservoirs is an important factor causing failure of bank slopes, i.e. landslide. The water level of Three Gorges reservoir in China fluctuate between 145 m and 175 m, as a matter of flood control. During its normal operational state, the rate of water level fluctuation is supposed to range from 0.67 m/d to 3.0 m/d. Majiagou slope is located on the left bank of Zhaxi River, 2.1 km up from the outlet. Zhaxi River is a tributary of the Yangtze River within the Three Gorges area, of which the water level changes with the reservoir. At the back of Majiagou slope, a 20 m long and 3~10 cm wide fissure developed just after the reservoir water level rose from 95 m to 135 m in 2003. This big fissure was a full suggestion of potential failure of this slope. In this study, unsaturated-saturated seepage analyses were carried out to simulate the change of pore-water pressures in the bank slope subjected to the reservoir water level change. The obtained pore-water pressures were then used to evaluate the change in factor of safety (FS) with reservoir water level. It was found that the phreatic line showed a delayed response with respect to the change of the reservoir water level, because the seepage through soil layer was generally slower than water flows itself. During the rising and drawdown process, the phreatic lines take the shapes of concave and convex, respectively. And the fluctuation of reservoir water level just affected the front part of the bank slope, but had little influence on the back of the slope.

• Journal of the Korean Geosynthetics Society
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• v.9 no.3
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• pp.87-93
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• 2010

The change of water level in reservoirs is an important factor causing failure of bank slopes, i.e. landslide. The water level of Three Gorges reservoir in China fluctuate between 145 m and 175 m, as a matter of flood control. During its normal operational state, the rate of water level fluctuation is supposed to range from 0.67 m/d to 3.0 m/d. Majiagou slope is located on the left bank of Zhaxi River, 2.1 km up from the outlet. Zhaxi River is a tributary of the Yangtze River within the Three Gorges area, of which the water level changes with the reservoir. At the back of Majiagou slope, a 20 m long and 3~10 cm wide fissure developed just after the reservoir water level rose from 95 m to 135 m in 2003. This big fissure was a full suggestion of potential failure of this slope. In this study, the pore water pressure files obtained from seepage analysis were used to evaluate the change in factor of safety (FS) with reservoir water level. Slope stability analyses then were carried out, with fully specified slip surface and limit equilibrium method. In the limit equilibrium analysis, the contribution of negative pore water pressure to shear strength was considered by the use of Fredlund's shear strength equation for unsaturated soils. On the base of the analyses, the change of FS with reservoir water level was interpreted in detail. It was found that FS against bank slopes decreases with the rise of the reservoir water level and increases with the drawdown of the reservoir water level. The most dangerous state was when the reservoir water level stays at the highest for a long time.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.165-174
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• 2011

The purpose of this research is to develop the model for analyzing the hydraulic behavior of off-stream reservoir whose purpose is to reduce a peak flood. When a flood occurs in river, off-stream reservoir has a capability of sharing a part of peak flood. It is accomplished by flowing over a off-line weir that is built by lowering a portion of bank and connecting river with off-line reservoir. Since flood control depends on river elevation, characteristics of off-line weir (elevation, length, position et al.) and reservoir capacities, an integrated model linking the one dimensional unsteady river flow model, off-line weir model and two dimensional unsteady flood model is developed to analyze the behavior of off-stream reservoir and off-line weir. The results show that a flood control capability of off-stream reservoir strongly depends on facilities of off-line weir and storage capacity of offstream reservoir.

• KCID journal
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• v.17 no.2
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• pp.28-34
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• 2010

This study re-exams hydrologic stability on spillway outlet capacity of agricultural reservoirs using hydrologic data with current rainfall condition instead of project hydrologic data applied at design on Backgok reservoir located in Chungbuk province. It is concluded that Backgok reservoir is not hydrologically stable and therefore structural measures including the extension of spillway and non structural measures should be taken. Continuous basic plan for river maintenance including additional bank reinforcement to bottom river shall be carried out. Due to high peak flood with more than 290% compared to 200 year frequency probability flood which was design standard of the past in view of the results of calculating PMF according to revised design standard for reservoirs, there could a problem for securing rationality in case of applying PMF with design flood. Therefore, hydrological stability, construction, and maintenance cost shall be synthetically studied and reasonal application shall be made if the decision is made on applying PMF with design flood.

• Journal of The Korean Society of Agricultural Engineers
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• v.60 no.3
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• pp.135-148
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• 2018

Reservoir sedimentation is a major environmental issue, and various sediment load controls and plans have been proposed to secure clean and safe water resources. The objectives of this study were to estimate soil loss in the upper basins and predict sediment deposition in Ipjang reservoir using hydrologic and hydraulic model. To do so, SWAT (Soil and Water Assessment Tool) and EFDC (Environmental Fluid Dynamics Code) was used to estimate soil loss in two upper basins and to predict spatial distribution and amount of sediment deposition in the Ipjang reservoir, respectively. The hydrologic modeling results showed that annual average soil loss from the upper basins was 500 ton. The hydraulic modeling results demonstrated that sediment particles transported to the reservoir were mostly trapped in the vicinity of the reservoir inlet and then moved toward the bank over time. If long-term water quality monitoring and sediment survey are performed, this study can be used as a tool for predicting the dredging amount, dredging location and proper dredging cycle in the reservoir. The study findings are expected to be used as a basis to establish management solutions for sediment reduction.

• Korean Journal of Ecology and Environment
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• v.41 no.spc
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• pp.1-10
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• 2008

We patterned water quality of agricultural reservoirs according to the differences of six physico-chemical environmental factors (TN, TP, DO, BOD, COD, and SS) using four different ordination methods: Principal Components Analysis (PCA), Detrended Correspondence Analysis (DCA), Nonmetric Multidimensional Scaling (NMS), and Isometric Feature Mapping (Isomap). The data set was obtained from the water quality monitoring networks operated by the Ministry of Agriculture and Forestry and the Ministry of Environments. Chlorophyll-${\alpha}$ displayed the highest correlation with COD, followed by TP, BOD, SS, and TN (p<0.01), while negatively correlated with altitude and bank height of the reservoirs (p<0.01). Although four different ordination methods similarly patterned the reservoirs according to the gradient of nutrient concentration, PCA and NMS appeared to be the most efficient methods to pattern water quality of reservoirs based on the explanation power. Considering variable scores in the ordination map, the concentration of nutrients was positively correlated with Chl-${\alpha}$, while negatively correlated with altitude and bank height. These ordination methods may help to pattern agricultural reservoirs according to their water quality characteristics.

• KCID journal
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• v.17 no.2
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• pp.95-104
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• 2010

Water quality data for 10 years (2000~2009) from about 826 reservoirs that are operated as a agricultural water quality survey network were analyzed in order to seek water quality management plan based on physical and chemical characteristics of agricultural reservoirs. The 95% reservoirs that exceed agricultural water quality standard of Chl-a (35mg/ $m^3$) had effective water depth shallower than 5m. The reason was that the reservoirs had more inflows of nutrient salts from the watershed, bigger surface water area of weak structure to algae occurrence. As the reservoirs of effective water depth shallower than 5m cover 49% of benefited area for irrigation, it is critical for agricultural water quality management of the reservoirs. The water quality of reservoir with shallower than 5m effective water depth was worse than reservoir with deeper than 5m effective water depth. Therefore, it is desirable that effective water depth of reservoirs make more than 5m for water quality management by building the bank higher and dredging the bottom of reservoirs.

• Magazine of the Korean Society of Agricultural Engineers
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• v.37 no.3_4
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• pp.48-60
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• 1995

A flood - flow forecasting system model of river basins has been developed in this study. The system model consists of the data management system(the observation and telemetering system, the rainfall forecasting and data-bank system), the flood runoff simulation system, the reservoir operation simulation system, the flood forecasting simulation system, the flood warning system and the user's menu system. The Multivariate Rainfall Forecasting model, Meteorological factor regression model and Zone expected rainfall model for rainfall forecasting and the Streamflow synthesis and reservoir regulation(SSARR) model for flood runoff simulation have been adopted for the development of a new system model for flood - flow forecasting. These models are calibrated to determine the optimal parameters on the basis of observed rainfall, 7 streamfiow and other hydrological data during the past flood periods.

• Parasites, Hosts and Diseases
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• v.54 no.4
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• pp.509-518
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• 2016

Parasites are recorded from the red squirrel, Sciurus vulgaris, from Cheongju, the Republic of Korea. A total of 5 road-killed squirrels were thoroughly examined for internal and external parasites from November 2011 to May 2014. Total 4 parasite species, including 1 tapeworm and 3 ectoparasite species were recovered. They were morphologically identified as Catenotaenia dendritica (Cestoda: Catenotaeniidae), Hirstionyssus sciurinus, Leptotrombidium pallidum, and Ceratophyllus (Monopsyllus) indages. Among them, C. dendritica and H. sciurinus are recorded for the first time in the Korean parasite fauna. In addition, the possibility that the red squirrel could act as a reservoir host for a zoonotic disease like tsutsugamushi disease with L. pallidum as its vector has been raised.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.12 no.5
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• pp.77-91
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• 2009

The purpose of this study is to define the species composition of the soil seed banks at major wetlands in Nakdong river basin and central korea and to investigate how soil seed banks relate to aboveground vegetation and soil texture. In 2005, we sampled seed banks at Baksil reservoir, Jillal marsh, Deapyeng marsh, Hwapo marsh, Upo marsh and Junam reservoir in Nakdong river basin and Osan stream and Amsa-dong in Seoul. The soil seeds were estimated with the emergence method from April to October. Total numbers of species at the seed banks were 33 at Baksil, 18 at Daepyeong, 35 at Jillal, 56 at Upo, 32 at Hwapo, 47 at Osan stream, 54 at Amsa waterside, 31 at Amsa meadow. The species diversity in the soil seed banks of Upo marsh was the highest as 0.95. The community overlap index that compares aboveground with underground vegetation is high in the Upo marsh (0.34), Jilla marsh (0.36), and Osan stream (0.27). Soil texture affected distribution of 8 species, Lindernia procumbens, L. attenuata, Arenaria serpyllifolia, Juncus effusus, Persicaria thunbergii, Eragrostis multicaulis, Cyperus nipponicus, Scirpus fluviatilis. Considering the social and cultural values, soils at Amsa meadow, Hwapo marsh and Osan stream have worth to use for wetland restoration.