• Journal of Ecology and Environment
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• v.43 no.2
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• pp.271-281
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• 2019

Background: The plant communities within reservoir drawdown zones are ecologically important as they provide a range of ecosystem services such as stabilizing the shoreline, improving water quality, enhancing biodiversity, and mitigating climate change. The aim of the study was therefore to identify the major environmental factors affecting these plant communities within the drawdown zone of the Soyangho Reservoir in South Korea, which experiences a monsoonal climate, and thereafter to (1) elucidate the plant species responses and (2) compare the soil seedbank composition along main environmental gradients. Results: Two main environmental gradients affecting the plant community structure were identified within the drawdown zone; these were a vertical and longitudinal gradient. On the vertical dimension, a hydrological gradient of flood/exposure, the annual-dominated plant community near the water edge changed to a perennial-dominated community at the highest elevation. On the longitudinal dimension from the dam to the upstream, plant species composition changed from an upland forest-edge community to a lowland riverine community, and this was correlated with slope degree, soil particle size, and soil moisture content. Simultaneously, the composition of the soil seedbank was separated along the vertical gradient of the drawdown zone, with mainly annuals near the water edge and some perennials at higher elevations. The species composition similarity between the seedbank and extant vegetation was greater in the annual communities at low elevation than in the perennial communities at higher elevation. Conclusions: The structures of plant community and soil seedbank in the drawdown zone of a monsoonal riverine reservoir were changed first along the vertical and secondly along the longitudinal gradients. The soil seedbank could play an important role on the vegetation regeneration after the disturbances of flood/exposure in the drawdown zone. These results indicate that it is important to understand the vertical and longitudinal environmental gradients affecting shoreline plant community structure and the role of soil seedbanks on the rapid vegetation regeneration for conserving and restoring the drawdown zone of a monsoonal reservoir.

• Journal of Korean Society on Water Environment
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• v.22 no.6
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• pp.1060-1067
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• 2006

Water quality in the Daecheong reservoir has been deteriorated by algal bloom due to nutrient supply from the upstream of the Daecheong reservoir after heavy rainfall. Algal bloom is propagated from eutrophicated tributary into the main body of the reservoir according to the hydrological conditions. This study is aimed to estimate the water current and temperature effect by the simulation of dam spill flow control using water quality model, CE-QUAL-W2 in 2003. Water current was resulted in nutrient transport from upstream of main reservoir and nutrients were delivered up to downstream by fast water velocity. Algal blooms occurred in stagnate zone of reservoir downstream as the current of downstream was retarded according to dam outflow control. Consequently water balance in stagnate zone triggered a rise of water temperature in summer. It affected algal bloom in the embayment of the reservoir. The simulation result by outflow control scenarios showed that spill flow augmentation induced in water body instability of stagnate zone so that water temperature declined. It could be suggested that outflow control minimize algal bloom in the downstream in the flooding season as long as water elevation level is maintained properly.

• Journal of environmental and Sanitary engineering
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• v.13 no.3
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• pp.1-8
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• 1998

Chungju reservoir is a multipurpose dam lake located at the upstream of Nm Han river and known as having the biggest watershed and the second water volume in korea. Conclusions are made as follows. 1. Environmental characteristics of the reservoir appear to be as follows. Chungju reservoir has long hydaulic retention time, 60-160 days. Water column has oxygen depletion zone in hypolimnion. Chungju reservoir is found to be in the midst of eutrophication. Chlorophyll-a and other physical parameters are found to be significantly dependent. 2. Nitrogen to phosphorus ratio was 50-350 for the water samples taken from the reservoir in 1996. It is very important clue for water quality management in relation to phytoplankton growing kinetics. Variations in chlorophyll-a contents appear to be related closely to total phosphorus concentration.

• Ecology and Resilient Infrastructure
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• v.5 no.2
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• pp.94-104
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• 2018

The Soyangho Reservoir in Korea has a large drawdown zone, with an annual maximum water level fluctuation of 37 m due to dam operations to maintain a stable water supply and control flooding, especially during the monsoon period. The floristic composition, distribution and biomass of the major plant communities in the drawdown zone of the Soyangho Reservoir were assessed in order to understand their responses to the wide water level fluctuation. Species richness of vascular plants was low, and species composition was dominated by herbaceous annuals. Principal coordinates analysis using both flora and environmental data identified slope angle and the distance from the dam as important factors determining floristic composition. The species richness was low in the steep drawdown zone close to the dam, where much of the soil surface was almost devoid of vegetation. In shallower slopes, distant from the dam plant communities composed of mainly annuals were found. The large fluctuation in water level exposed soil where these annuals could establish. An overall biomass of 122 t (metric tons) Dry Matter was estimated for the reservoir, containing ca 3.6 t N (nitrogen) and ca 0.3 t P (phosphorus); the role of the vegetation of the drawdown zone in carbon sequestration and water pollution were briefly discussed.

• Journal of Korean Society on Water Environment
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• v.22 no.5
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• pp.887-894
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• 2006

Water quality in the Daecheong reservoir has been deteriorated by algal bloom every year. Algal bloom is propagated from eutrophicated tributary into the main body of the reservoir during the wet season. Nutrients from diffuse sources trigger the propagation of the algal bloom. This study is aimed to analyze relationship between the water current by the simulation and algae transport from the main body in the Daecheong reservoir including tributary where algal bloom has occurred seriously every year. Water quality model CE-QUAL-W2 was applied to analyze water movement in draught season (2001) and flooding season (2003). The result of simulation corresponded with the observed water elevation level, 63~80 m and showed stratification of the Daecheong reservoir. In the draught season, as velocity and direction off low in the reservoir was estimated to affect algae transport including nutrient supply from small tributary, algal blooms occurred in the stagnate zone of middle stream of the reservoir. On the other hand, in the flooding season, it was resulted in nutrient transport from upstream of main reservoir and nutrients were delivered up to downstream by fast water velocity. In result, algal blooms occurred in stagnate zone of reservoir downstream as the current of downstream was retarded according to dam outflow control.

• Journal of Environmental Science International
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• v.23 no.9
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• pp.1537-1549
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• 2014

The objectives of this study were to analyze reservoir trophic state, based on Trophic State Index (TSI), spatial variation patterns of three zones (riverine, transition, and lacustrine zone), and empirical models through 20-years long-term data analysis. Trophic variables of TP and CHL-a were highest during the summer monsoon, and decreased along the main axis from the riverine to lacustrine zone. In the mean time, TN did not show the trend. Ratios of N:P and Secchi disc transparency (SD) increased from the riverine to lacustrine zone. The analysis of trophic state index (TSI) showed that mean TSI (TP) and TSI (CHL-a) were 62 and 57, respectively, and these values were highest in the transition zone during the summer. This zone should be managed well due to highest lake water pollution. The analysis of Trophic State Index Deviation (TSID) showed that algal growth was primarily limited by light penetration, and this was most pronounced in the monsoon season. The analysis of empirical models showed that the value of $R^2$, based on CHL-SD model, was 0.30 (p < 0.0001) in the transition zone and the $R^2$, based on TP-SD model, was 0.41 (p < 0.0001) in the transition zone.

• Journal of Korea Water Resources Association
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• v.47 no.10
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• pp.921-934
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• 2014

The purpose of the study is to derive a long term reservoir operation method that is easy to understand and apply to practical use for dam operators. The zone based operation rule is a simple method to make operation decisions by criteria corresponding to storage zones. The reservoir storage levels dividing a reservoir, however, must be determined by some methods. We developed a reservoir operation model based on the zone based operation rule and the shuffled complex evolution algorithm (SCE-UA) was used to determine storage levels for zone division. The model was applied to Angat Dam in the Philippines that has trouble in water supply due to imbalance between supply and demand. We derived a zone based operation rule for Angat Dam and applied it to the reservoir simulation of Angat Dam using the historical inflow. The simulation results showed water supply deficit and power generation were improved by 34.5% and 21.2%, respectively, when compared with the historical records. The current study results may be used to derive a long term reservoir operation rule.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.585-585
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• 2012

$Cu(In_{1-x}Ga_x)Se_2$(CIGS) 박막 태양전지는 Chalcopyrite 계 박막 태양전지로 Cu, In, Ga, Se 각 원소의 조성을 적절히 조절하여 박막을 성장시킨다. 성장시킨 CIGS 박막은 광흡수계수가 $10^5cm^{-1}$로 다른 물질보다 뛰어나고 직접 천이형 반도체로서 얇은 두께로도 고효율의 박막 제작이 가능하다. CIGS 태양전지를 제조하는 방법은 3-stage 동시 증착법, 금속 전구체의 셀렌화 공정법, 전기 증착법 등이 있다. 그 중에 금속 전구체의 셀렌화 공정법은 다른 제조 방법에 비해 대면적 생산에 유리한 장점이 있다. 하지만 아직 상대적으로 3-stage 동시 증착법에 비해 낮은 에너지 변환 효율이 보고된다. 본 실험에서는 기존의 금속 전구체의 셀렌화 공정법과는 달리 전구체 증착과 셀렌화 공정을 동시에 하고, Se cracker를 통하여 Se 원료를 주입하는 방식인 반응성 스퍼터링 공정에서 reservoir zone의 온도 변화에 따른 특성을 분석하였다. Se cracker의 reservoir zone 온도가 증가할수록 Cu/(In+Ga) 비가 증가한다. CIGS 박막 태양전지의 구조는 Al/Ni/ITO/i-ZnO/CdS/CIGS/Mo/Soda lime glass이다. CIGS 박막의 조성비가 Cu/(In+Ga)=0.89, Ga/(In+Ga)=0.17인 박막 태양전지에서 개방전압 0.34 V, 단락전류밀도 $32.61mA/cm^2$, 충실도 56.2% 그리고 변환 효율 6.19%를 얻었다. 본 연구는 2011년도 지식경제부의 재원으로 한국에너지 기술평가원(KTEP)의 지원을 받아 수행한 연구 과제입니다(No.20093020010030).

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.199-210
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• 2023

The physical properties of rocks in reservoirs change after CO₂ injection, we modeled a reservoir with a transition zone within which the physical properties change linearly. The function of the Wolf reflection coefficient consists of the velocity ratio of the upper and lower layers, the frequency, and the thickness of the transition zone. This function can be used to estimate the thickness of a reservoir or seafloor transition zone. In this study, we propose a method for predicting the thickness of the transition zone using deep learning. To apply deep learning, we modeled the thickness-dependent Wolf reflection coefficient on an artificial transition zone formation model consisting of sandstone reservoir and shale cap rock and generated time-frequency spectral images using the continuous wavelet transform. Although thickness estimation performed by comparing spectral images according to different thicknesses and a spectral image from a trace of the seismic stack did not always provide accurate thicknesses, it can be applied to field data by obtaining training data in various environments and thus improving its accuracy.

• Korean Journal of Ecology and Environment
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• v.45 no.1
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• pp.52-61
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• 2012

Distribution, abundance and biomass of submerged macrophytes were assessed using a double-headed rake and an echo-sounder in the Keumpoong Reservoir to investigate the temporal and spatial variations of submerged macrophytes in a small agricultural reservoir located upstream. Slope steepness and water depth in the littoral zone were important controlling factors on flora and vegetation structure of submerged macrophytes. Biodiversity of submerged macrophytes was increased at a gentle slope of the littoral zone. The results of DCA (detrended correspondence analysis) showed that the structure of submerged vegetation depended on the depth of water. Submerged macrophytes were distributed at the maximum water depth of 2.8 m in the Keumpoong Reservoir. The area occupied by the submerged macrophytes was estimated at only 6% of the total reservoir area because of the steep slope of the littoral zone and the large annual water-level fluctuation of 3.5 m. The increase of water level and inflow of turbid water in the rainy season might reduce the biomass of submerged macrophytes in the reservoir. It may be concluded that submerged vegetation in the Keumpoong Reservoir, a small agricultural reservoir located at the upstream, appears to be particularly susceptible to water level fluctuations and slope steepness of the littoral zone.