• Journal of the Korean Geotechnical Society
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• v.30 no.1
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• pp.37-47
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• 2014

Unsaturated hydraulic conductivity (HC) is integrated theoretically from soil water retention curves (SWRC) by Mualem capillary model, but the prediction of HC is extremely sensitive to small variation of matric suction near saturation. Near saturation, the Mualem HC based on smooth SWRC decreases abruptly and has problems in the reliability of hydraulic behavior and the stability of numerical solutions. To improve van Genuchten-Mualem (VGM) HC, the van Genuchten SWRC model is modified within range of low matric suction (arbitrary air entry pressure). At an arbitrary air entry pressure, the VG SWRC is linearized in log scale until full saturation. The modified VG SWRC does not affect the fit of actual retention behavior and either the parameters of original VG SWRC fit. Using the modified VG SWRC, the VGM HC is modified to integrate for each interval decomposed by arbitrary air entry pressure. An analytical solution on modified VGM HC is proposed each interval, to protect the rapid change in HC near saturation. For silty soils, VGM models of HC function underestimate the unsaturated permeability characteristics and especially show rapid reduction near saturation. The modified VGM model predicts more accurate HC functions for Korean weathered soils. Furthermore, near saturation, the saturated HC is conserved by the modified VGM model. After 2-D infiltration analysis of an actual slope, the hydraulic behaviors are compared for VGM and the modified models. The prediction by the proposed model conserved the convergence of solutions on various rainfall conditions. However, the solution by VGM model did not converge since the conductivity near saturation reduced abruptly for heavy rainfall condition. Using VGM model, the factor of safety is overestimated in both initial and final stage during heavy rainfall. Stability analysis based on infiltration analysis could simulate the actual slope failure by the proposed model on HC.

• Journal of Wetlands Research
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• v.17 no.1
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• pp.38-44
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• 2015

In Korea, most rainfall events occur during summer which then leads to an increasing concern regarding high influx of non-point source pollutants since the pollutant loadings from these non-point sources are very significant. In particular, the first flush of roof-harvested rainfall is said to contain the most highest concentration of nutrients and heavy metals. Accordingly, it is important to develope the possible water quality management options in treating the contaminants and considering reclaimed water reuse. The rain garden could be one of suitable alternatives in addressing this issue. In this study, the development of an effective adsorption media and its application to a lab-scale rain garden was tested to evaluate the removal rate of various nutrient and organic matter (TN, TP, CODcr), and heavy metals (Cu, Cd, Pb). Results showed that carbonized peatmoss produced at higher temperature have better adsorption capacity as compared to the one produced at a lower temperature. When the carbonized peatmoss was applied as rain garden media, the highest removal of TN, TP, and CODcr was observed compared to no carbonized peatmoss applied rain garden. Therefore, this study showed that the carbonized peatmoss would be effectively applied to the rain garden for removing nutrients and heavy metals from roof-harvested rainwater.

• Journal of Wetlands Research
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• v.20 no.1
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• pp.72-79
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• 2018

Two planter boxes were monitored during their initial year of operation to be able to assess their stormwater runoff and pollutant reduction capabilities and investigate on the design factors affecting their performance. One of the planter boxes provided 85-100% runoff volume reduction for rainfall less than 15 mm and rainfall intensities lower than 5 mm/hr. This reduced to 50-64% during higher rainfall intensities and depths of up to 50 mm. Suspended solids, organics, nutrients, and heavy metals were satisfactorily removed at a range of 40-95%. The other planter box, however, did not produce outflow in all the events and allowed total capture of stormwater. The uncertainty regarding the fate of the runoff in that case required an investigation of the planter box's actual drainage and underground conditions which was deemed outside the scope of the study. Nonetheless, several design improvements and retrofits were suggested based on the provisions of current design guidelines to ensure that the hydraulic and water quality goals are achieved without potential damage to nearby structures. Moreover, continuous monitoring data is required to provide more accurate design evaluation and can serve as a guide in the construction of similar facilities in the future.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.35 no.4
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• pp.126-133
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• 2017

This study analyzed hydrological changes of stormwater runoff of Seolleung Jeongneung zone according to the application of LID system based on landscape Architectural technology. The results are as follows. First, when flooding occurred in Gwanghwamun in July 27, 2011, the maximum instantaneous rainfall amount was 183 mm/hr recorded at 10:00 on 27th for 10 minutes, and it was confirmed that rainfall intensity more than three times as high as the maximum rainfall of 57.5 mm/hr. Second, it is possible to control peak flow rate in the case of 1,500mm of soil thickness, so that it is possible to improve the vulnerability of flood damage in Seolleung and Jeongneung zone when applying the LID system. Third, in the berm height scenario, peak flow rate control was not controled in all depth level models, but the first stormwater runoff was delayed by 4 hours and 10 minutes compared to the soil thickness scenario. It was interpreted as a relatively important indicator the soil thickness for the initial stromwater runoff reduction and the berm height for the peak runoff. Through this, the systematic adaptation of landscape-friendly ecological factors within the cultural property protection zone could theoretically confirm the effects of flood disaster prevention.

• Journal of Korea Water Resources Association
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• v.52 no.9
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• pp.615-626
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• 2019

Soil moisture and runoff have very close relationship. Especially the water retention capacity and drainage characteristics of the soil are determined by various factors of the soil. In this study, a total of 40 rainfall events were identified from the entire rainfall events of Sulma basin in 2016 and 2017. For each selected events, the constant-K method was used to separate direct runoff and baseflow from total flow and calculate the runoff coefficient which shows positive exponential curve with Antecedent Soil Moisture (ASM). In addition to that, the threshold of soil moisture was determined at the point where the runoff coefficient starts increasing dramatically. The threshold of soil moisture shows great correlation with runoff and depth to water table. It was founded that not only ASM but also various factors, such as Initial Soil Moisture (ISM), storage capacity of soil and precipitation, affect the results of runoff response. Furthermore, wet condition and dry condition are separated by ASM threshold and the start and peak response are analyzed. And the results show that the response under wet condition occurred more quickly than that of dry condition. In most events occurred in dry condition, factors reached peak in order of soil moisture, depth to water table and runoff. However, in wet condition, they reached peak in order of depth to water table, runoff and soil moisture. These results will help identify the interaction among factors which affect the runoff, and it will help establish the relationship between various soil conditions and runoff.

• Journal of the Korean GEO-environmental Society
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• v.17 no.4
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• pp.17-31
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• 2016

Many researchers have evaluated the influence of vegetation cover on slope stability. However, due to the extensive variety of site conditions and vegetation types, different studies have often provided inconsistent results, especially when evaluating in different regions. Therefore, additional studies need to be conducted to identify the positive impacts of vegetation cover for slope stabilization. This study used the Transient Rainfall Infiltration and Grid-based Regional Slope-stability Model (TRIGRS) to predict the occurrence of landslides in a watershed in Jinbu-Myeon, Pyeongchang-gun, Korea. The influence of vegetation cover was assessed by spatially and temporally comparing the predicted landslides corresponding to multiple trials of cohesion values (which include the role of root cohesion) and real observed landslide scars to back-calculate the contribution of vegetation cover to slope stabilization. The lower bound of cohesion was defined based on the fact that there are no unstable cells in the raster stability map at initial conditions, and the modified success rate was used to evaluate the model performance. In the next step, the most reliable value representing the contribution of vegetation cover in the study area was applied for landslide assessment. The analyzed results showed that the role of vegetation cover could be replaced by increasing the soil cohesion by 3.8 kPa. Without considering the influence of vegetation cover, a large area of the studied watershed is unconditionally unstable in the initial condition. However, when tree root cohesion is taken into account, the model produces more realistic results with about 76.7% of observed unstable cells and 78.6% of observed stable cells being well predicted.

• Journal of The Korean Society of Agricultural Engineers
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• v.57 no.5
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• pp.61-67
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• 2015

Effect of tillage on time of initial runoff, runoff coefficient, NPS pollution load, soil erosion and crop productivity were studied. Eight runoff plots of $5{\times}30m$ on loamy sand field that were 4 respective plots of 3 % and 8% slope were prepared. Treatment included conventional tillage (CT) and no-till (NT). Time of initial runoff from NT retarded between 247~261 % compared with that from CT. Under 3% slope, runoff coefficient in NT was 63.5 % lower than that in CT. The reduction under 8 % slope was 61.7 %. Differences in runoff reduction between 3% and 8% plots were not significant. NT could reduce more than 60 % of NPS pollution and between 50~85 % of sediment if compared with CT. Productivity of NT was also shown that it was not lower than that of CT. It was expected that the results could be used as a fundamental data for estimating a reduction load in Korea TMDL from a no-till BMP on loamy sand agricultural fields.

• The Korean Journal of Ecology
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• v.12 no.1
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• pp.9-20
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• 1989

Annual production and decomposition of litter were studied in piuns rigida platation in Mt. Kwan-ak. The peak time of litter production was October-November. The litterfalll at that time was 54% of annual litter production. But the peak time of litterfall of reproductive parts was Junejuly. The peak times of litter production in Alnus hirsuta plantation were June-July, and November. It is thought that difference of seasonal distribution of letterfall between two forest types were assigned to litter falling factors such as temperature and insects. Total amount of letter loss increased according to time. Particulary, the peak time of loss rate was July-August. It was shown that the protein and phosphorus were accumulated in the letter for an experimental period. The amount of crude protein increased to 150% of initial amount. The amount of potassium was increased by August and then decreased rapidly. The contents of crude fat, holocellulose, lignin, and Na were decreased slowly. The loss of holocellulose was the largiest among them. Calcium was in steady state. It was thought that this variation pattern was assigned to leaching of soluble parts by high temperature, rainfall and growth rate of microorganisms.

• Water for future
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• v.9 no.2
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• pp.67-75
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• 1976

With 9 existng reservoirs selected in the Sab-Gyo River Basin, the sedimentation of the reservoirs has been calculated by comparing the present capacity with the original value, which revealed its reduced reservoirs capacity. The reservoirs has a total drainage area of 6,792 ha, with a total capacity of 1,204.09 ha-m, and are short of water supply due to reduction of reservoirs capacity. Annual sedimention in the reservcire is relation to the drainage area, the mean of annual rain fall, and the slop of drainage area. The results of obtained from the investigation are summarized as follow; (1) A sediment deposition rate is very high, being about $9.19{m}^3/ha$ of drainage area, and resulting in the average decrease of reservoir capacity by 19.1%. This high rate of deposition could be mainly attributed to the serve denvdation of forests due to disor derly cuttings of tree. (2) An average unit storage of 415.8mm as the time of initial construation is decreesed to 315.59mm at present, as resultting, we could'nt supply water at 566.24ha. (3) A sediment deposition rate as a relation to the capacity of unit drainage area is as follow; $Qs=1.43 (c/a)^{0.531}$ (4) A sediment deposition rate as a relation to the mean of annval rainfall is as follow; $Qs=672.61 p^{0.024}$ (5) A sediment deposition rate as a relation to the mean slop of drainage area is follow; $Qs=267.21 S^{0.597}$

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.749-758
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• 2010

Embankment Slope (or Fill Slope) is defined as artificial slope formed by the filling of soil or rocks on the original ground. Recently a lot of embankment failures and collapse has occurred due to the increase of torrential rainfall and typhoons. Embankment collapse has lead to a great loss of lives and property therefore there is a need to establish a systematic embankment slope management system that will handle the maintenance and repair of risky embankment slopes. The objective of this study is to establish an "Embankment Slope Management Method" for embankment slopes located along national highways all over Korea. The method for field investigation of embankment slopes was recommended and the system for investment priority determination was also developed. The factors that lead to the collapse of embankment slopes caused by natural calamities were also determined through the initial survey of embankment slopes located along river fronts and mountainous areas.