• Journal of Wetlands Research
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• v.13 no.3
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• pp.481-488
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• 2011

Various development activities have lead to the destruction of the ecosystem such as natural wetlands. In order to protect these natural wetlands, the Ministry of Environment (MOE) in Korea enacted the Wetland Conservation Act in 1999 and designated protected areas for wetland conservation. The MOE adapted the use of Best Management Practices (BMP) such as retention ponds and constructed wetlands to treat the polluted water before entering the water system. One of these projects was a free-water surface flow (FWS) constructed wetland built as a secondary treatment unit for piggery wastewater effluent coming from a livestock wastewater treatment facility. Water quality monitoring for the constructed wetland was conducted during rainfall events. The results showed that the average removal efficiencies of TSS, BOD, TN, TP were 86, 60, 45, 70%, respectively. It was observed that the removal efficiency of particulate matter and phosphorus was high compared to nitrogen. Therefore, a longer hydraulic retention time was needed in order to improve the treatment efficiency of nitrogen. The results of this study can contribute to the wetland design, operation and maintenance of constructed wetlands.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.752-757
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• 2009

In the last decade, many methods such as greet chamber, reservoir, or debris barrier, have been utilized to manage and prevent muddy water problem. The Vegetative Filter Strip (VFS) has been thought to be one of the most effective methods to trap sediment effectively. The VFS are usually installed at the edge of agricultural areas adjacent to stream or drainage ditches, and it has been shown that the VFS effectively removes pollutants transported with upland runoff. But, if the VFS is installed without any scientific analysis of rainfall-runoff characteristics, soil erosion, and sediment analysis, it may not reduce the sediment as much as expected. Although Soil and Water Assessment Tool (SWAT) model has been used worldwide for many hydrologic and Non-Point Source Pollution (NPSP) analysis at a watershed scale. but it has many limitations in simulating the VFS. Because it considers only 'filter strip width' when the model estimates sediment trapping efficiency, and does not consider the routing of sediment with overland flow option which is expected to maximize the sediment trapping efficiency from upper agricultural subbasin to lower spatially-explicit filter strip. Therefore, the SWAT overland flow option between landuse-subbasins with sediment routing capability was enhanced with modifications in SWAT watershed configuration and SWAT engine. The enhanced SWAT can simulate the sediment trapping efficiency of the VFS in the similar way as the desktop VFSMOD-w system does. Also it now can simulate the effects of overland flow from upper subbasin to reflect the increased runoff volume at the receiving subbasin, which is what is occurring at the field if no diversion channel is installed. In this study, the enhanced SWAT model was applied to small watershed located at Jaun-ri in South Korea to simulate diversion channel and spatially-explicit VFS. It was found that approximately sediment can be reduced by 31%, 65%, 68%, with diversion channel, the VFS, and the VFS with diversion channel, respectively.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.1817-1821
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• 2009

최근 전자제품 사용의 증가로 인해 버려지는 전자제품의 양도 함께 증가하고 있으며 이렇게 늘어난 전자폐기물이 부적절한 방식으로 처리될 경우 우리에게 악영향을 미치는 위험물질이 될 수 있다. 본 연구에서는 이러한 전자폐기물 중 하나인 폐 LCD 유리를 이용한 수질정화용 여재를 이용하여 전자폐기물에 의한 오염을 줄이고, 동시에 강우시 표면 유출로 인하여 발생되는 비점오염을 제어하고자 하였다. 본 연구에서 이용한 수처리 여재는 기존 수처리 여재의 단점을 보완하는 대체 여재 개발이라는 목적에 적합할 것으로 판단된다. 이에 본 연구에서 발포기술이 적용된 폐 LCD 유리 여재의 비점오염에 의한 수질정화능력평가를 하기 위해 실험 장치를 구성하여 실험하였다. 반응조는 직경 0.10 m, 높이 0.75 m 크기(총용량= 5.89 $\ell$)로 두께 10mm의 투명 아크릴판으로 3조를 제작하였다. 유입수는 미량 펌프를 이용하여 유입하였다. 각 반응조의 체류시간에 의한 수질정화능력을 평가하였다. 연구 결과, 오염물질에 대한 제거효율 범위는 SS $64.1%\sim88.2%$, BOD $29.8\sim52.4%$, COD $56.8\sim66.1%$, T-N $39.4\sim\;52.3%$, T-P $14.1\sim36.8%$로 나타났다. 체류시간이 가장 길었던 반응조의 경우, 대부분의 측정항목에서 높은 처리 효율을 볼 수 있었다. 초기에 처리 효율이 낮은 것은 미생물이 부착되지 않았기 때문이라고 판단되며, 실험의 중반과 후반에서 미생물이 부착이 되는 시점부터 높은 처리효율을 보이는 것으로 나타났다.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.2
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• pp.29-36
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• 2013

The objective of the research was to describe the effect of straw mat cover and soil amendments on the reduction of runoff and non-point source load from steep sloped highland agricultural fields. Four $5{\times}30$ m plots on sandy loam soil with 28 % slope were prepared. Experimental treatments were bare (control), rice straw mat cover (3,000 kg/ha) (S), PAM (5 kg/ha)+Gypsum (1 ton/ha) (PG) and rice straw mat cover+PAM+Gypsum (SPG). A variety of lettuce was cultivated and runoff was monitored during a growing season in 2011. Natural monitoring was conducted to three times. Runoff rate of S, PG and SPG plots were significantly lower than those of control plot. Especially, the runoff rate is zero in SPG plot at a first rainfall events. The reduction rate of runoff from the S, PG and SPG plots was 30.8 %, 29.0 % and 81.8 % compared to control plots, respectively. The reduction rate of NPS pollution load of S, PG and SPG was ranged of 50~90 %, 30~70 % and 90~100 %, respectively. Yield of lettuce from S, PG and SPG plots was respectively 400 (567 kg/ha), 320 (453 kg/ha) and 760 (1,067 kg/ha) that of compared to control plots greater than that from control plots (140 kg/ha). We speculated that the experimental treated plots could hold more nutrients and moisture than the control and helped the crop grow healthier. When analyzing the above results, in terms of reduction of runoff and NPS pollution load and crop yields, SPG experimental treatment had the best effect. It was concluded that the use of rice straw mats cover and soil amendments on soil surface could not only reduce the NPS pollution loads in receiving waters but also help increase the crop yield.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.11 no.2
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• pp.75-86
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• 2008

The wetlands have functions those were retention of diverse biota, purification of water quality, control of climate and flood, eco-tourism and supply of agricultural water, and that was the ecosystem of high biodiversity as the zone of transition between inland and water. Therefore, this study showed the conservation and management plan by analyzing in the abiotic and biotic environment of forest swamp, Gyeongsangbuk-do. The results were as follows. Examining the management plan of the abiotic environment, there will need to establish the hydrological plan in continuous expediting the supply of water to maintain a humid soil of swamp, and to try to find the organic farming, use of low toxic agrichemicals and so on to prevent occurring a non-point source pollutants. To prevent changing the flowing of ground water and inflow of earth and sand in modifying the land character, there will be needed to restrict the construction of farmland and slope around swamp. To manage the biotic environment, there needed to offer the habitat by removing the regular interval and individual of a dead tree, and to improve the growth environment of vegetation. Because the naturalized plants disturb the natural vegetation, they will be removed. The afforested trees like Robinia pseudoacacia and Amorpha truticosa will be renewed to prevent the heterogeneity of landscape ecology, and the active conservation plan on wetland species will be established. As this study was carried out to study on the partial swamp, Gyeongsanbuk-do, the ecological environments distributing a swamp in Korea show a some problem. In the future, the study will accomplish to study the accurately and objectively ecological environment and management of a swamp by analyzing the extensive sites.

• Structural Engineering and Mechanics
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• v.56 no.4
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• pp.549-567
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• 2015

A first-order moment method (FORM) reliability analysis is commonly used for structural stability analysis. It requires the values and partial derivatives of the performance to function with respect to the random variables for the design. These calculations can be cumbersome when the performance functions are implicit. A Gaussian process (GP)-based response surface is adopted in this study to approximate the limit state function. By using a trained GP model, a large number of values and partial derivatives of the performance functions can be obtained for conventional reliability analysis with a FORM, thereby reducing the number of stability analysis calculations. This dynamic renewed knowledge source can provide great assistance in improving the predictive capacity of GP during the iterative process, particularly from the view of machine learning. An iterative algorithm is therefore proposed to improve the precision of GP approximation around the design point by constantly adding new design points to the initial training set. Examples are provided to illustrate the GP-based response surface for both structural and non-structural reliability analyses. The results show that the proposed approach is applicable to structural reliability analyses that involve implicit performance functions and structural response evaluations that entail time-consuming finite element analyses.

• Structural Engineering and Mechanics
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• v.28 no.2
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• pp.207-220
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• 2008

The shear lag has been studied for many years. Nevertheless, existing research gives a variety of stress concentration factors. Unlike the elementary beam theory, the application of load is not unique in reality. For example, concentrated load can be applied as point load or distributed load along the height of the web. This non-uniqueness may be a reason for the discrepancy of the stress concentration factors in the existing studies. The finite element method has been often employed for studying the effect of the shear lag. However, not many researches have taken into account the influence of the finite element mesh on the shear lag phenomenon, although stress concentration can be quite sensitive to the mesh employed in the finite element analysis. This may be another source for the discrepancy of the stress concentration factors. It also needs to be noted that much less studies seem to have been conducted for the shear lag effect on deflection while some design codes have formulas. The present study investigates the shear lag effect in a simply supported box girder by the three-dimensional finite element method using shell elements. The whole girder is modeled by shell elements, and extensive parametric study with respect to the geometry of a box girder is carried out. Not only stress concentration but also deflection is computed. The effect of the way load is applied and the dependency of finite element mesh on the shear lag are carefully treated. Based on the numerical results thus obtained, empirical formulas are proposed to compute stress concentration and deflection that includes the shear lag effect.

• Structural Engineering and Mechanics
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• v.75 no.4
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• pp.435-444
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• 2020

Ultrasonic guided wave testing is a very promising non-destructive testing method for rails, which is of great significance for ensuring the safe operation of railways. On the basis of the semi-analytical finite element (SAFE) method, a analytical model of 59R2 grooved rail was proposed, which is commonly used in the ballastless track of modern tram. The dispersion curves of ultrasonic guided waves in free rail and supported rail were obtained. Sensitivity analysis was then undertaken to evaluate the effect of rail elastic modulus on the phase velocity and group velocity dispersion curves of ultrasonic guided waves. The optimal guided wave mode, optimal excitation point and excitation direction suitable for detecting rail integrity were identified by analyzing the frequency, number of modes, and mode shapes. A sinusoidal signal modulated by a Hanning window with a center frequency of 25 kHz was used as the excitation source, and the propagation characteristics of high-frequency ultrasonic guided waves in the rail were obtained. The results show that the rail pad has a relatively little influence on the dispersion curves of ultrasonic guided waves in the high frequency band, and has a relatively large influence on the dispersion curves of ultrasonic guided waves in the low frequency band below 4 kHz. The rail elastic modulus has significant influence on the phase velocity in the high frequency band, while the group velocity is greatly affected by the rail elastic modulus in the low frequency band.

• Environmental Engineering Research
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• v.13 no.4
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• pp.184-191
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• 2008

Long term monitoring was conducted to investigate a surface runoff of pollution from urban highway. The monitoring data was collected for 18 rainfall events and was used to correlate pollution load to various parameters, such as rainfall intensity, antecedent dry days and total discharge flow. Runoff coefficient and seasonal variation were also evaluated. The mean runoff coefficient of the highway was 0.823(range; $0.4687{\sim}0.9884$), and wash-off ratio for $COD_{Mn}$ and SS loads was 72.6% and 64.3%, respectively. For the initial rainfall event, the runoff EMC of $COD_{Mn}$ was high in summer and the EMC of SS was high in autumn season. However the seasonal variation of T-N and T-P was not significant. The discharged $COD_{Mn}$-EMC was $147.6\;mg/L{\sim}9.0\;mg/L$ on the generated $COD_{Mn}$-EMC of $98.8\;mg/L{\sim}8.9\;mg/L$. While the generated EMC of SS was in $285.7\;mg/L{\sim}20.0\;mg/L$ and its discharged EMC was in $190.4\;mg/L{\sim}8.0\;mg/L$. EMC of pollutants was not directly related to the first flush rainfall intensity and the antecedent dry days. But the correlation was relatively high between EMC and cumulative runoff flow volume. The trend of EMC was reduced with the cumulative runoff flow volume.

• Journal of The Korean Society of Agricultural Engineers
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• v.53 no.3
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• pp.13-17
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• 2011

There was a transition from participatory irrigation management (PIM) to public irrigation management (PubIM) in Korea when Korea Rural corporation and Community (KRC) merged with Farm Land Improvement Associations (FLIAs), which had managed 60 % of irrigation areas. While making a number of achievements, some problems occurred in the public irrigation management, such as lack of farmers' participation, increased amount of water usage, and elevating operating costs. Accordingly, this paper suggested ways to increase efficiency in water usage and reduce operating costs under the public management through the motive power of farmers participation. First, WUGs replaced the discarded water management committee should be reorganized to revive the concept of PIM in the form of autonomously reinforced one and the roles and functions of WUGs and the board of representatives should be strengthened. The member of new type of WUGs should participate in the national and regional water management committees as a stakeholder of irrigation water user. And also new type of WUGs initiates not only the management of irrigation water but also the management of irrigation water quality and non-point source pollution in the watersheds. Those additional activities of WUGs should be properly compensated. Second, subsidies (direct payments) should be provided to faithful farmers as an incentive for their labor supply. Third, water fees could be charged to large scale agriculture companies. Fourth, professional managers could be hired, management targets would be adjusted, and incentives should be offered. These efforts are expected to improve the irrigation management by encouraging farmers' participation under public system.