• The Korean Journal of Ecology
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• v.27 no.4
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• pp.211-216
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• 2004

The complex ecological researches were made in the broad-leaved forest zone of Central Europe in nature reserves and national parks located on the banks of the river (hydrology, vegetation, soils, unconfined ground waters). The natural conditions of terrestrial ecosystems and natural sites were compared along the course of the rivers. The significant negative influence of low-dammed (low-confined hydrotechnic) construction and small reservoirs on vegetation and soils of floodplain was revealed. On the basis of analysis of mean annual water level and flow trends on the multi-years series (60-100 years) of the hydrometric stations on the rivers under consideration the significant influence of natural long-term variability of watering on vegetation dynamics in the floodplains was revealed.

• Journal of Magnetics
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• v.21 no.3
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• pp.431-436
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• 2016

In the design of transformer winding, natural vibration frequency is an important parameter. This paper presents a 2D model to calculate axial vibration natural frequency of power transformer winding based on the elastic dynamics theory, and according to the elastic support equivalent principle of radial pressboards. The 3D model to calculate natural vibration frequency can be simplified as a 2D one as the support of pressboards on the winding is same. It is verified that results of the 2D model are consistent with those of 3D one, but the former can achieve much higher calculation efficiency. It shows that increasing the width and number of pressboards can improve axial natural frequency through formula analysis and simulation, and also the relations between the changes of axial pre-compression and axial natural vibration frequency on the windings are investigated. Finally, the proposed 2D model's effectiveness is proved when compared with tested ones.

• Structural Monitoring and Maintenance
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• v.6 no.2
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• pp.85-101
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• 2019

The effects of foundation scour depth and riverbed condition on the natural frequencies of a typical cross-river integral abutment bridge have been studied. The conventional operational modal analysis technique has been employed in order to extract the modal properties of the bridge and the results have been used in the Finite Element (FE) model updating procedure. Two tests have been carried out in two different levels of water and wet condition of the riverbed. In the first test, the riverbed was in dry condition for two subsequent years and the level of water was 10 meter lower than the natural riverbed. In the second test, the river was opened to water flow from the upstream dam and the level of water was 2 meter higher than the natural riverbed. The results of these two tests have also been used in order to find to what extend the presence of water flow in the river and saturation of the surrounding soil affect the bridge natural frequencies. Finally, the updated FE model of the bridge has been applied in a series of parametric analyses incorporating the effect of piles' relative scour depth on the bridge natural frequency of the first four vibration modes.

• Water Engineering Research
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• v.6 no.3
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• pp.131-147
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• 2005

Today, a trend that tries to return the artificial space of a river to a natural one is expanding. But in Korea, which lies in the monsoon climate zone, rivers endure flood damage every year. Moreover, climatic change from global warming causes severe variations in precipitation patterns. Until recently, river restoration practices in Korea have followed partial restoration. These restorative treatments transformed artificial structures of the stream to natural ones and introduced natural vegetation by imitating natural or semi-natural streams. Treatment transformed the riparian structure and increased the diversity of micro-topography and vegetation. Furthermore, restoration recovered species composition, increased species diversity, and inhibited the establishment of exotic species. In particular, the Suip stream, which was left to its natural process for approximately 50 years, recovered its natural features almost completely through passive restoration. An urban stream, the Yangjae, and a rural stream, the Dongmoon, were restored partially by applying ecological principles. On the contrary, technological treatment applied to recover flood damage induced species composition far from the natural vegetation and decreased species diversity. Additionally, this treatment increased exotic species. The same results were found also in benthic invertebrate and fish fauna. The above-mentioned results reflect the importance of ecological considerations in river management.

• Fisheries and Aquatic Sciences
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• v.23 no.6
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• pp.15.1-15.14
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• 2020

Background: Large rivers are ecological treasures with high human value, but most have experienced decades of degradation from industrial and municipal sewage, row-crop agricultural practices, and hydrologic alteration. We reviewed published analyses of long-term fish diversity publications from three intensively managed large river ecosystems to demonstrate the conservation potential of large river ecosystems. Results: We show how the incorporation of recent advances in river concepts will allow a better understanding of river ecosystem functioning and conservation. Lastly, we focus on the Wabash River ecosystem based on high conservation value and provide a list of actions to maintain and support the ecosystem. In the Wabash River, there were originally 66 species of freshwater mussels, but now only 30 species with reproducing populations remain. Although there were multiple stressors over the last century, the largest change in Wabash River fish biodiversity was associated with rapid increases in municipal nutrient loading and invasive bigheaded carps. Conclusions: Like similarly neglected large river systems worldwide, the Wabash River has a surprising amount of ecological resilience and recovery. For instance, of the 151 native fish species found in the 1800s, only three species have experienced local extinctions, making the modern assemblage more intact than many comparable rivers in the Mississippi River basin. However, not all the changes are positive or support the idea of recovery. Primary production underpins the productivity of these ecosystems, and the Wabash River phytoplankton assemblages shifted from high-quality green algae in the 1970s to lower less nutritional blue-green algae as nutrient and invasive species have recently increased. Our recommendations for the Wabash River and other altered rivers include the restoration of natural hydrology for the mainstem and tributaries, nutrient reductions, mechanisms to restore historical hydrologic patterns, additional sediment controls, and improved local hydraulics.

• Proceedings of the Korea Water Resources Association Conference
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• 2008.05a
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• pp.629-633
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• 2008

Frequently occurring flood and drought have increased the necessity of an effective water resources control and management of river flows. Therefore, the simulation of the flow distribution in natural rivers is very important to the solution of a wide variety of practical flow problems in water resources engineering. Usually in many flow problems, two-dimensional approach can provide good estimates of complex flow features in the flow around islands and obstructions, flow at confluence and flow in braided channel. The objective of this study is to examine validation of developed an accurate and robust two-dimensional finite element method with wet and dry simulation in complex natural rivers. Milyang river, and Kumho river and Keum river were performed for tests. The results were compared with those of existing model. The suggested model displayed reasonable flow distribution compared with existing model in dry area for application of natural river flow. As a result of this study, the developed general two-dimensional model provide a reliable results for flow distribution of wet and dry domain, it could be further developed to basis for extending to water quality and sediment transport analysis.

• Journal of Environmental Science International
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• v.10 no.4
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• pp.253-258
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• 2001

A macroeconomic minimodel was simulatedto suggest the public for sustainable us of Nakdong River Basin. The minimodel for the simulation shows the interrelationships between natural environment and economic activity. Topsoil, water, economic assets, and money stock are plotted for 300 years, beginning with 1996 in each simulation. The computer simulation runs suggest that the Nakdong River Basin system in the near future may strongly be influenced by the favorable availability of outside resources, while the economic assets and money stock may be declined by indigenous environmental stock depletion. The simulation run made under the constant decrease in systems purchased inputs with investment ratio of developed country and for sustainable use. The results of simulation shows the recover of natural environment and decrease of economic activity under these condition. Therefore, the economic structure of Nakdong River Basin should be transformed from the present industrial structure to the social-economic structure based on an ecological-recycling concept which depend on renewable resources rather than industrial structural which depend on outside resources.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.33 no.1
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• pp.13-29
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• 2021

A 3-D hydrodynamic model is applied in the Han River Estuary system, Gyeonggi Bay, to understand the mechanisms of salt transport. The model run is conducted for 245 days (January 20 to September 20, 2020), including dry and wet seasons. The reproducibility of the model about variation of current velocity and salinity is validated by comparing model results with observation data. The salt transport (FS) is calculated for the northern and southern part of Yeomha channel where salt exchange is active. To analyze the mechanisms of salt transport, FS is decomposed into three components, i.e. advective salt transport derived from river flow (QfS0), diffusive salt transport due to lateral and vertical shear velocity (FE), and tidal oscillatory salt transport due to phase lag between current velocity and salinity (FT). According to the monthly average salt transport, the salt in both dry and wet seasons enters through the southern channel of Ganghwa-do by FT. On the other hand, the salt exits through the eastern channel of Yeongjong-do by QfS0. The salt at Han River Estuary enters towards the upper Han River by FT in dry season, whereas that exits to the open sea by QfS0 in wet season. As a result, mechanisms of salt transport in the Han River Estuary depend on the interaction between QfS0 causing transport to open sea and FT causing transport to the upper Han River.

• Journal of the Korean housing association
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• v.11 no.3
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• pp.43-51
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• 2000

This study aims to find the characteristics of the folk houses in the upper area of Seomjin river in the view point of generating housing floor plans by their human and natural elements of environment. Because they are formed differently as them and have the characteristics as the houses in the upper area of Seomjin river. Seomjin river flows from mid-west area of the Korean peninsula to the southern sea. This is about 212.3km long and the fourth in the south of the Korean peninsula. It is surrounded high mountains in the upper area and makes open field in the mid and lower area of river. The study is surveyed and analyzed to the folk houses of the middle and lower class people in the area of Seomjin river. Because they have been formed by their natural and human elements of environment gradually. They are 35 houses - 13 in Jinan-kun, 4 in Imsil-kun, 10 in Namwon city, 10 in Sunchang-kun. They are analyzed by their floor plans and their spatial relations. The result of this study is that they are made by their natural and human elements of environment. There are some houses with semi-several wings and with storage that are appeared in the mountain village. It reflects that they are surrounded by high mountains. And there are some houses with wooden floor room that are appeared in the area of river little in the area of mountain. To prevent wind from the river the houses are layouted as a form . open ㄴ type, open ㄷ type, and their wall is made of stone and planted bamboo trees around their houses.

• Journal of Korean Society on Water Environment
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• v.21 no.2
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• pp.125-131
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• 2005

Natural organic matter(NOM) is defined as the complex matrix of organic material and abundant in natural waters. It affects the performance of unit operations for water purification. Several kinds of analytical indicators such as DOC, specific ultraviolet absorbance(SUVA), apparent molecular weight (AMW), fractionation and high performance size exclusive chromatography(HPSEC) have been used to understand characteristics and variations of NOM. This study aims to evaluate the characteristics of NOM in the Geum River system comprising with stream flows and reservoirs. It was identified that SUVA denoting the portion of humic substance in water ranged within 1.60~3.36. Using resin adsorbents, dissolved organic carbon(DOC) was fractionated into three classes: hydrophobic bases(HOB), hydrophobic acids(HOA) and hydrophilic substances(HI). HI dominates in all samples, collectively accounting for more than 62% of the DOC. HOA was the second dominated fraction and it varied considerably but accounted for about 30% of the DOC. The distribution of high molecular weight(HMW) measured by HPSEC being used to determine the molecular weight distribution of aquatic humic substances was 40.1% and 38.7% in reservoir and stream flow, respectively. The distribution of low molecular weight(LMW) in stream flow was 13.2% higher than that in reservoir. And apparent molecular weight less than 1KDa, which include the molecular weight of hydrophilic organic matter, occupied with 69.2% and 68.2% in stream flow and reservoir, respectively. While the molecular weight of 1 to 100 KDa including humic substances ranged with 18.6% and 21.6% in stream flow and reservoir, respectively. Seasonal variation of refractory dissolved organic carbon was similar to that of SUVA.