• Journal of Korea Water Resources Association
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• v.41 no.12
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• pp.1199-1210
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• 2008

The mean residence time is the time scale for intermediate status between infiltration and runoff and one of the critical factors for understanding runoff response, erosion, and eco-hydrological processes. This research explored a direct method to estimate the mean residence time over existing indirect, isotope tracer method. Spatial and temporal distributions of soil moisture have been monitored for a year with 2-hours monitoring interval. Mean residence time for soil moisture showed apparent increasing tendency to deeper depth and decreasing trend during summer periods, which had intensive rainfall events. The mean residence times obtained from this research showed similar trend to those obtained from other isotope methods, which means the direct method can be an efficient approach to obtain the mean residence time.

• Journal of the Korean Geotechnical Society
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• v.29 no.5
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• pp.19-27
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• 2013

Most of the landslides induced by rainfall in summer rainy season appear in the type of debris flow. Debris flow gives a lot of economic losses and human casualties due to high moving velocity and volume of debris flow. In order to analyze movement and deposition characteristics of debris flow, numerical analysis using FLO-2D program was conducted with various viscosities and yield stresses. As a result of numerical analysis, velocity and runout distance of debris flow decreased as its viscosity increased due to resisting force between particles of debris flow. Consequently, flow depth of debris flow increased and impact force decreased. Yield stress of debris flow affected its initiation and deposition characteristics. As yield stress increased, runout distance of debris flow decreased and its impact force increased. Based on the results of numerical analysis, it was found that velocity of debris flow mainly depended on viscosity, while deposition characteristics (runout distance, deposition width, deposition area) of debris flow depended on both viscosity and yield stress.

• Journal of the Korean Society of Safety
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• v.33 no.4
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• pp.84-89
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• 2018

The number of landslides has increased since the 2000s due to the increased frequency of heavy rainfall caused by abnormal weather. A variety of debris flow prevention facilities have been installed as a countermeasure against this problem. However, it is not easy to evaluate the efficiency of debris flow prevention structures except for the structures with constant volume such as the erosion dam, because the other structures are limited to be reproduced in simulation program for debris flow. Therefore, the methods by which the debris flow prevention structures were modeled were proposed, and the efficiency of four prevention structures installed in Baekyang Mt. in Busan was evaluated with UDS, which accuracy had been verified, using these methods. The initial amount of debris flow was determined based on landslide which occurred in 2014, and specifications of the complex retaining walls around the settlements were measured and applied modeling for terrain. The numerical results showed that the efficiency of debris flow prevention structures could be quantitatively presented. Among the debris flow prevention structures installed in Baekyang Mt., prevention structure of barrier type for debris flow was the most efficiency and debris flow prevention device was the lowest efficiency when the only depth of debris was evaluated. It seems that this study is meaningful to propose the methods which were used to model the debris flow prevention structures that could not be reproduced in most 2D debris flow numerical analysis programs. If precise verification of the presented methods is carried out, it will be possible to provide clear criteria for the efficiency evaluation method of disaster prevention structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.1
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• pp.61-72
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• 2017

Due to the climate change, damages of human life and property caused by natural disaster have recently been increasing consistently. In South Korea, total damage by natural disasters over 20 years from 1994 to 2013 is about 1.0 million dollars. The 13% of total damage caused by heavy snow. This is smaller amount than the damage by heavy rainfall or typhoon, but still could cause severe damage in the society. In this study, the snow damage in Gangwon region was estimated using climate variables (daily maximum snow depth, relative humidity, minimum temperature) and scoio-economic variables (Farm population density, GRDP). Multiple regression analysis with enter method was applied to estimate snow damage. As the results, adjusted R-square is above 0.7 in some sub-regions and shows the good applicability although the extreme values are not predicted well. The developed model might be applied for the prompt disaster response.

• Journal of the Korean Geotechnical Society
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• v.32 no.5
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• pp.49-55
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• 2016

This study aims to present the practical Nitrogen monoxide (NO) removal capacity of cement mortar with Titanium dioxide ($TiO_2$) which is one of the paving materials by considering the environment of pavement in urban areas. NO removal capacity test under designated conditions of humidity of inflow gas and the test with variation of the degree of saturation of specimen were conducted. In the test for humidity, dry specimen is subject to the test and NO removal ratio was observed. Humidity-NO removal ratio curve is a log normal distribution in shape, and the maximum NO removal ratio appears at specific humidity. NO removal capacity test relying on the degree of saturation was carried out with wet specimen to reflect the unsaturated pavement by rainfall and domestic sewage. Wet specimen presents less NO removal capacity than dry specimen and the recovering evolution of NO removal capacity follows evaporation. Moreover, $TiO_2$ under the specific depth of specimen hardly contributes to NO removal capacity.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.57-65
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• 2001

In this study, the seepage behavior and the stability of the extension embankment were estimated for three cases the permeability coefficient of an extension part and the rising velocity due to the rainfall of flood period. In parallel flow condition, the unstability of the slope due to embankment erosion was examined by analyzing the variation of seepage line by the seepage modeling tests and FEM analysis, and the stability of the embankment slope accompanied by the sudden rise of the water level after the flood. The seepage behavior of extension embankment indicates that the larger permeability of the extension part the longer initial seepage distance, and the exit point from embankment slope is gradually increased, and then shows unstable seepage behavior that occurs a partial collapse as safety factor decreases with time. It is because of the increment of exit points due to variation of seepage line and rising velocities of water level. Also, the collapse aspect of embankment slope shows that the increment rising velocities of water level causes the increment collapse height and depth.

• Journal of the Korean Professional Engineers Association
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• v.1 no.1
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• pp.18-25
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• 1968

Higher yield in rice paddies is greatly dependent on adequately balanced and timely supply of water. A majority of rice paddy in Korea is generally irrigated by rainfall, but in many cases it has to be supplemented by artificial irrigation for optimum rice culture. Although the water requirement of rice plant is for higher Than that of athec crops, submerged condition of rice paddy is not Necessarily required. The moisture requirement of rice plant varies with its growing stages, and it is possible to increase the irrigation efficiency through reduction of water loss due to percolation in rice paddies. An experimental plots were set up by means of sandomized block design with three duplication; (a) All time submerged, (b) Economically controlled, and (c) Extremely controlled. Three different irrigation periods Were (a) Initial sage, (b) Inter-stage, and (c) Yast stage. The topsoil of the three plots were excavated to the depth of 30 cm and then compacted with clay of 6 cm thickness. There after, they were piled up with the excavated top soils, leveled and cored with clay of 6 cm thickness around footpath in order to prevent leakage. The results obtained from the experiments are as follows, 1. There is no difference among the three experiments plots in terms of physical and chemical conditions, soil properties, and other characteristics. 2. Culm length and ear length are not affected by different irrigation methods. 3. There is no difference in the mature rate and 1, 000 grain weight of rice for the three plots. 4. The control plot which was irrigated every three days shows an increased yield over the all the time submerged plot by 17.8 percent. 5. The clay lined plot whose water holding capacity was held 5 days long, needs only to be irrigated every 7 days. 6. The clay lined plot shows an increased yield over the untreated plot ; over all-the-time submerged plot by 18 percent ; extremely controlled plot by 18 percent, and economically controlled plot by 33 percent. 7. It may be saved in water requirement about one Thirds.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.1 no.1
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• pp.63-69
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• 1998

The slope revegetation methods in Korea are generally the hydroseeding mixed with perennial herbs, soil, fibers, and fertilizer in consideration of scenic landscape rather than ecological and engineering effect. But perennial herbs can't protect the slope from deep surface erosion and they are not tall enough to create the original naturalness at the boundary parts of existing woodlands. This study is about the slope revegetation method using nutritional propagation capacity of plants and the experimental construction was carried out on the cut-slope of Yongin Hoam C.C. We dug several trenches to a depth of 80cm and at intervals of 150cm from each other. After placing various kinds of live branches(Salix species) into the trench, we backfilled with the excavated soils and finally sprayed water mixed with soil-stabilizer, fertilizer. As six months passed, we made a vegetation research and check the slope surface erosion. Vegetation research was performed in examining the frequency of each block using transect method. 31 kinds of plant species appeared in total area($113.6m^2$) and the dominant species are Setaria viridis, Artemisia rubripes, Persicaria pubescens, Plantago asiatica, Cyperus amuricus, Commelina communis. Among the examined blocks, '아', the top part of the slope, showed the ratio of 1.4 as the highest Alpha-diversity. With regard to life form, therophytes were shown dominant distribution of 58% of total species and neophytes relatively low distribution of 16%. It can be estimated that there is no ecological stabilization of this slope, because of ruderal species' occupation of 74% in total area. Regarding the slope stabilization, the serious surface erosion didn't take place in spite of heavy rainfall this year, but a little surface erosion took place at the block where no other species coming from outside of the site were found.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.13 no.5
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• pp.81-89
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• 2010

This study was conducted to evaluate the effects of early revegetation by analyzing the characteristics of germination and growth of Chrysanthemum zawadskii using vegetation-plant in rock slopes. After making up a growing basis of approximately 20-cm depth and 10-cm diameter by using a boring machine, the surface of rock slopes was planted with vegetation-plant. The number of germinating populations by soil media was 41 in H.s, 4 in T.s, 3 in M.s, and 0 in M.g.s. The germination rate (%) by soil media was 20.0% in H.s, 3.3% in T.s, 2.5% in M.s and 0% in M.g.s. In monthly changes of growth rate, the aspect was northwest direction, the soil media was H.s, and the treatment was microorganism plot. The main factors affecting survivorship and growth of population were soil media and treatment plot. The interaction between each factor had a good effects in bearing x treatment plot, soil media x treatment plot. but, it is recommended that the mulching of vegetation plant is highly needed to help the germination of seed and growth of vegetation because of loss of seed and soil media occurred due to rainfall. Therefore, The result suggests that the revegetation technique using boring in rock slope was very efficient in respect of the early revegetation and the landscape.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.126-134
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• 1995

The salinity data taken by Fishery Research Development Agency were analyzed to investigate the salinity decrease in the South Sea of Korea in summer. Decrease of depth-averaged salinity in June and August can not be accounted for the input of river discharge and rainfall. The low salinity water in the Cheju Strait is the only possible source for the decrease of salinities in the South Sea. A box model of the salt conservation shows that the transport in the Cheju Strait is 0.5-0.6${\times}$10$\^$6/ ㎥/sec (mean velocity is 10-13 cm/sec) which is 31-36% of the transport in the western channel of Korea Strait and the transport in the section between Cheju island and Tsushima island is 0.9-1.4${\times}$10$\^$6/ ㎥/sec when the transport in the western channel of the Korea Strait is 1.4-2.0${\times}$10$\^$6/ ㎥/sec.