• KSCE Journal of Civil and Environmental Engineering Research
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• v.11 no.4
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• pp.81-89
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• 1991

An interesting property of meandering river patterns is that they slowly deform, as bank erosion on one side of a channel and deposition on the other side result in the location of the channel. In this study we used a sine-generated meander pattern proposed by Langbein and Leopold(1966) to develop a solution of a linear, second-order differential equation of transverse bed slope(bed topography) proposed by Odgaard(1986). A new model for transverse bed slope(bed topography), that accounts for the phase lag and the influence of the width to depth aspect ratio, was developed in this study and compared with results of field measurements.

• Journal of Forest and Environmental Science
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• v.33 no.2
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• pp.130-135
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• 2017

In temperate monsoon regions, extensive shallow landslides triggered by heavy rainfall are recurrent phenomena in mountainous areas. 1,357 landslides over Jinbu area, Korea that totaled 127 km2 were identified from aerial photographs and field survey. We examined characteristics of rainfall-induced shallow landslides and casual factors affecting landslide distribution with respect to topographic and forest settings, and land use. Most landslides occurred in the study area were the results of a complex combination of precondition, preparatory factors and triggering factors. Cumulative rainfall and high intensity rainfall during short period of time made the study area very sensitive to landslides and played as catalysts to enable other factors including topographic and forest settings, and land use to act more effectively. In addition, some landslides at lower elevation involved channel incision or bank erosion influenced by land use changes such as deforestation and intensification of agriculture surrounding riparian forests or hillslopes. The results suggest that most of landslide were triggered by heavy rainstorms while topographic, forest settings, and land use affected landslide distribution occurred in the study area.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.12 no.3
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• pp.173-180
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• 1992

A feature typical of natural rivers is the bend. The purpose of this study is to examine hydraulic and morphometric characteristics in channel bend reach by the deterministic approach. Cross section shape factor, "As" is suggested for a new cahracteristic factor of channel bend reach analysis. The variation of this new factor along the river reach showed the location of the concentration of the force due to the current all over the reach, that is curved or not. Some general meander factors are used for correlation with new factor suggested, and the applicability of "As" is verified. The range R/W values are concentrated 2~4, the meanning of this value can be regarded to the warning for bank erosion or breaking. And this paper dealt with prediction of cross section bed shape variation.

• Journal of Korean Society of Rural Planning
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• v.8 no.1 s.15
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• pp.41-59
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• 2002

The condition and management of land resources has become an increasing matter of concern in recent years, because of the pressure placed upon land for agricultural use by expanding populations and economic development. Pressures upon land quality can lead to various forms of land degradation, such as in soil erosion, soil fertility decline, adverse changes in water resources, salinization of irrigated areas, or decline in the biological condition of forests or rangelands. In 1992, World Bank estimates that the cost of degraded areas has been estimated as 10-50 times higher than that of measures to prevent degradation. Based upon a survey interviewed with people living in rural areas, the present study argue that it is important to establish policies for preventing changes in agricultural land use, to provide early warning of adverse trends and identification of problem areas. The present study also stresses that stewardship of agricultural land resources plays a leading role in achieving sustainable rural development not to mention agricultural and forestry production.

• Korean Journal of Social Welfare
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• v.44
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• pp.117-145
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• 2001

This paper attempts to assess the impact and implication of globalization on social welfare in Korea. It is no easy task to give an exact definition of globalization and the concept has been used in many different senses, that is, economic, social, cultural, political globalization. In particular, the meaning of globalization is connected to the rise and expansion of neo-liberalism. Globalization tends to undermine national welfare systems by the social dumping, race to the bottom, privatization of social services, labor market flexibility. On the other hand, in many studies the negative impact of globalization on social welfare has been questioned. Instead of end or erosion of the welfare systems, it is emphasized that competitiveness and welfare may go hand in hand. We investigate the question what and how the social welfare system in Korea has been changed in globalization process. In order to answer, this paper examines the changes in welfare ideology, welfare programs, social stratification level after economic crisis. The result of analysis is that in contrast to globalist expectations which is to retrench social welfare, paradoxically, the welfare system in Korea has been reinforced in globalization process. Therefore, the alleged impact of globalization on social welfare will be independent on the structure of domestic institution, political legacies, and on the socialization of global politics such as IMF, World Bank, ILO, UNDP, etc., on the welfare politics of stakeholders in national state.

• Journal of Energy Engineering
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• v.26 no.1
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• pp.68-75
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• 2017

Global warming affects water supply and water resources throughout the world. In many countries, climate change affects significantly on the fresh water resources. Vietnam is exposed mainly, to landslides and floods triggered by tropical storms and monsoon rains, although storm surge, whirlwind, river bank and coastal line erosion, hail rain. In addition to the prevalent drought, there are many major water challenges, including water availability, stress, scarcity and accessibility, because of poor resource management. Fast growth of urbanization, industrialization and population growth, agricultural activities and climate change cause heavy pressure on water quality. Both domestic and industrial wastewater, as well as storm water shares the same drainage. The common facilities for wastewater treatment are not available. Therefore, wastewater is treated only superficially and then discharged directly into rivers and lakes causing serious pollution of surface water environment. In this paper, we reported the severe water crisis and massive green algal blooms formation in Vietnam rivers and lakes. This is the biggest evidence of climate change variations in Vietnam.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.86-86
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• 2019

일반적으로 하천에 설치하는 각종 이수 및 치수 시설물들은 각각의 고유기능을 충분히 발휘하도록 계획하고 설치하고 있으나, 이러한 하천 시설물 중에는 하천의 자연 환경에 부정적인 영향을 일으킬 수 있는 환경과 조화롭지 못한 시설물이 있기도 하다. 하도 만곡부에 설치하는 전통적인 수제, 즉 하안부에서 수로 중심방향으로 돌출하는 형식의 횡수제, 역시 외곽부 하안의 침식을 방지하기 위해 설치하는 시설물이지만 하천의 자연환경 측면에서는 바람직하지 못 한 현상을 일으키기도 한다. 본 연구에서 소개하는 잠형의 방틀공 수제는 하안부에 돌출하여 설치하는 기존 수제와 달리 만곡부 외측 하안에 근접하여 유수 방향으로 하상에 고정시키고 홍수 시에는 잠길 수 있는 높이로 방틀공을 설치하여 하천수의 흐름을 제어하는 시설물이다. 이와 같은 시설물은 만곡부에서 발생하는 2차류 흐름을 방지하고 유수의 수충력을 흡수 혹은 반사시킴으로써 하안부를 세굴로부터 보호할 뿐만 아니라 심각한 하상 세굴과 퇴적을 완화하는 하도의 안정 기능도 발휘하게 된다. 치수의 기능 외에도 하천 환경 측면에서는 수제의 안쪽에 형성되는 못 (pool)에 다양한 생물이 서식하는 서식기능을 담당하기도 한다. 본 고에서는 현재까지 국내에 설치한 사례가 없는 잠형 방틀형 수제의 효과를 검증하기 위해 강원도 양양 남대천에 구축하는 Test bed를 소개하고자 한다. 산지하천의 만곡부 하안부를 세굴로부터 보호하기 위해 설치하는 잠형 수제에 대한 Test bed 구축 배경과 설치 과정 등을 소개하여 이와 관련한 하천 기술자들에게 새로운 패러다임의 수제 설계가 이루어질 수 있는 계기를 제공하고자 한다.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.480-480
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• 2023

본 연구에서는 섬진강 하류에서 2차원 흐름 모형인 Nays2DH 활용하여 섬진강댐 하류, 송정 구간의 식생밀도를 고려한 부등류 계산을 통해 하도의 수위 및 유속을 예측 모의하는 방법론을 제시하고 모의결과를 분석하였다. 현장조사를 실시하여 하도의 식생밀도를 산정하였으며. 식생밀도는 섬진강댐 하류 1.15 m-1, 송정 0.35 m-1로 조사되었다. 모의결과, 섬진강댐 하류에서 원심력에 의해 만곡부 외측에서 수심이 가장 깊게 나타났으며(최대 7.48 m), 최대유속도 동일지점에서 5.58 m/s로 형성되었고 하안침식으로 인한 하도변화 예측결과, 유속이 빠른 만곡부 외측에서 세굴되었으며, 내측에서는 퇴적되었고 만곡부가 끝난 지점부터 중앙사주가 발달하며 흐름이 하도 좌안으로 집중하여 세굴이 진행되었다. 송정구간에서 저수로 폭이 좁아지는No.40+200 지점에서 수심이 가장 깊으며(15.8 m), 유속은 하폭이 좁고 경사가 급해지는 No.39+800 지점에서 최대 7.97 m/s 로 나타났다. 하안침식으로 인한 하도변화 예측결과, 하폭이 넓어지는 No.40+800에서 유속이 감소하여 사주가 발달하였다. 본 연구에서는 섬진강 하류의 실제 식생밀도를 반영하여 수치모의를 하였기 때문에 흐름과 식생관리에 따른 실무적 대책방안 마련에 도움이 될 것으로 판단되며, 본 연구에서 활용한 분석방법과 결과들은 섬진강 유역의 하천관리 방안을 구축하기 위한 기초자료로 활용될 수 있을 것으로 기대된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.63-63
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• 2021

Bed shear stress is important variable in river flow analysis. The bed shear stress has an effects on bed erosion, sediment transport, and mean flow characteristics. Quadratic formula to estimate bed shear stress is widely used, 𝜏=𝜌c_fu|u| in which friction coefficient, c_f, needs to be assigned to numerical models. The aim of this study is to estimate Chezy coefficient using bathymetry data measured by ADCP. Bed form geometry variables will be estimated form bed profile, then Chezy coefficient will be determined using estimated bed form geometry variables in order to set friction coefficient to numerical model. From the probability density function obtained from the bathymetry data, Chezy coefficient will be randomly generated since Chezy coefficient is not uniform over the space and it does not depend on spatial variables such as water depth and distance from river bank. Numerical test will be performed to find to demonstrate randomly extracted Chezy coefficient is appropriate. The result of this study is valuable in that the friction coefficient is estimated in consideration of the bed profile, and as a result, uncertainty of the friction coefficient can be reduced.

• Journal of Korea Water Resources Association
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• v.52 no.10
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• pp.743-752
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• 2019

The flow in the meandering channel is characterized by the spiral motion of secondary currents that typically cause the erosion along the outer bank. Hydraulic structures, such as spur dike and groyne, are commonly installed on the channel bottom near the outer bank to mitigate the strength of secondary currents. This study is to investigate the effects of submerged vanes installed in a $90^{\circ}$ meandering channel on the development of secondary currents through three-dimensional numerical modeling using the hybrid RANS/LES method for turbulence and the volume of fluid method, based on OpenFOAM open source toolbox, for capturing the free surface at the Froude number of 0.43. We employ the second-order-accurate finite volume methods in the space and time for the numerical modeling and compare numerical results with experimental measurements for evaluating the numerical predictions. Numerical results show that the present simulations well reproduce the experimental measurements, in terms of the time-averaged streamwise velocity and secondary velocity vector fields in the bend with submerged vanes. The computed flow fields reveal that the streamwise velocity near the bed along the outer bank at the end section of bend dramatically decrease by one third of mean velocity after the installation of vanes, which support that submerged vanes mitigate the strength of primary secondary flow and are helpful for the channel stability along the outer bank. The flow between the top of vanes and the free surface accelerates and the maximum velocity of free surface flow near the flow impingement along the outer bank increases about 20% due to the installation of submerged vanes. Numerical solutions show the formations of the horseshoe vortices at the front of vanes and the lee wakes behind the vanes, which are responsible for strong local scour around vanes. Additional study on the shapes and arrangement of vanes is required for mitigate the local scour.