• Geomechanics and Engineering
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• v.23 no.2
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• pp.151-163
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• 2020

Grouting method is an effective way of reinforcing cracked rock masses and plugging water gushing. Current grouting diffusion models are generally developed for horizontal cracks, which is contradictory to the fact that the crack generally occurs in rock masses with irregular spatial distribution characteristics in real underground environments. To solve this problem, this study selected a cement-sodium silicate slurry (C-S slurry) generally used in engineering as a fast-curing grouting material and regarded the C-S slurry as a Bingham fluid with time-varying viscosity for analysis. Based on the theory of fluid mechanics, and by simultaneously considering the deadweight of slurry and characteristics of non-uniform spatial distribution of viscosity of fast-curing grouts, a theoretical model of slurry diffusion in an oblique crack in rock masses at constant grouting rate was established. Moreover, the viscosity and pressure distribution equations in the slurry diffusion zone were deduced, thus quantifying the relationship between grouting pressure, grouting time, and slurry diffusion distance. On this basis, by using a 3-d finite element program in multi-field coupled software Comsol, the numerical simulation results were compared with theoretical calculation values, further verifying the effectiveness of the theoretical model. In addition, through the analysis of two engineering case studies, the theoretical calculations and measured slurry diffusion radius were compared, to evaluate the application effects of the model in engineering practice. Finally, by using the established theoretical model, the influence of cracking in rock masses on the diffusion characteristics of slurry was analysed. The results demonstrate that the inclination angle of the crack in rock masses and azimuth angle of slurry diffusion affect slurry diffusion characteristics. More attention should be paid to the actual grouting process. The results can provide references for determining grouting parameters of fast-curing grouts in engineering practice.

• Journal of the Korean Association of Geographic Information Studies
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• v.13 no.4
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• pp.111-124
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• 2010

To monitor the environment of land surface change is considered as an important research field since those parameters are related with land use, climate change, meteorological study, agriculture modulation, surface energy balance, and surface environment system. For the change detection, many different methods have been presented for distributing more detailed information with various tools from ground based measurement to satellite multi-spectral sensor. Recently, using high resolution satellite data is considered the most efficient way to monitor extensive land environmental system especially for higher spatial and temporal resolution. In this study, we use two different spatial resolution satellites; the one is SPOT/VEGETATION with 1 km spatial resolution to detect coarse resolution of the area change and determine objective threshold. The other is Landsat satellite having high resolution to figure out detailed land environmental change. According to their spatial resolution, they show different observation characteristics such as repeat cycle, and the global coverage. By correlating two kinds of satellites, we can detect land surface change from mid resolution to high resolution. The K-mean clustering algorithm is applied to detect changed area with two different temporal images. When using solar spectral band, there are complicate surface reflectance scattering characteristics which make surface change detection difficult. That effect would be leading serious problems when interpreting surface characteristics. For example, in spite of constant their own surface reflectance value, it could be changed according to solar, and sensor relative observation location. To reduce those affects, in this study, long-term Normalized Difference Vegetation Index (NDVI) with solar spectral channels performed for atmospheric and bi-directional correction from SPOT/VEGETATION data are utilized to offer objective threshold value for detecting land surface change, since that NDVI has less sensitivity for solar geometry than solar channel. The surface change detection based on long-term NDVI shows improved results than when only using Landsat.

• Journal of the Korean Geographical Society
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• v.42 no.4
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• pp.469-487
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• 2007

Grain-Size Trend Analysis is the methodology to identify net sediment transport pathways, based on the assumption that the movement of sediment from the source to deposit leaves the identifiable spatial pattern of mean, sorting, and skewness of grain size. It can easily be implemented with low cost, so it has great potentials to contribute to geomorphological research, whereas it can also be used inadequately without recognition of its limitations. This research aims to compare three established methods of grain-size trend analysis to search for the adequate way of application, and also suggest the research tasks needed in improving this methodology 1D pathway method can corporate the field experience into analyzing the pathway, provide the useful information of depositional environments through X-distribution, and identify the long-term trend effectively. However, it has disadvantage of the dependence on subjective interpretation, and a relatively coarse temporal scale. Gao-Collins's 2D transport vector method has the objective procedure, has the capability to visualize the transport pattern in 2D format, and to identify the pattern at a finer temporal scale, whereas characteristic distance and semiquantitative filtering are controversial. Le Roux's alternative 2D transport vector method has two improvement of Gao-Collins's in that it expands the empirical rules, considers the gradient of each parameters as well as the order, and has the ability to identify the pattern at a finer temporal scale, while the basic concepts are arbitrary and complicated. The application of grain sire trend analysis requires the selection of adequate method and the design of proper sampling scheme, based on the field knowledge of researcher, the temporal scale of sediment transport pattern targeted, and information needed. Besides, the relationship between the depth of sample and representative temporal scale should be systematically investigated in improving this methodology.

• Fisheries and Aquatic Sciences
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• v.24 no.7
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• pp.243-259
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• 2021

The spatial and temporal behaviors and fluctuations of the cold water that appeared in the South East Sea and the East Sea coast from 2016 to 2017 were investigated. The water temperature drop was large in the east coast from April to June and the southeast coast from July to September, and the temperature drop period was longer in the southeast coast. The water temperature fluctuated sensitively to the wind direction, and it gradually decreased in the southwest wind but rose as if jumping in the northeast wind. Wind stress and surface water temperature had an inverse correlation, which was larger in Bukhang-Idukseo, and decreased toward the north of Guryongpo. The cold water appeared mainly in Geojedo-Pohang after 1 to 2 days when the southwest wind was strong, but when the wind became weak, it shrank to the Idukseo (Ulgi-Gampo) and extended into the open sea in a tongue shape. Cold water was distributed only in Samcheok-Toseong in mid-May, Idukseo-Guryongpo and Hupo-Jukbyeon-Samcheok from late May to mid-July, and Bukhang-Idukseo in August-September. The intensity of cold water was greatest in mid-August, and the center of cold water descended from the east coast to the southeast coast from spring to summer. The water temperature fluctuation was dominant at the periods of 1 d and 7-21 d. In wavelet spectrum analysis of water temperature and wind, wind speed increase-water temperature decrease showed phase difference of 12 h in 2 d, 18 h in 3 d, 1.5 d in 4-8 d, and 2-3 d in 8-24 d period. The correlation between the two parameters was large in Geojedo and Namhang, Bukhang-Idukseo, Guryongpo-Jukbyeon, and Samcheok-Toseong. Monitoring stations with high correlation in all periods were generally parallel to the monsoon direction.

• Forest Science and Technology
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• v.14 no.4
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• pp.181-191
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• 2018

This study was carried out in the teaching and research forest of the University of Dschang in Belabo, with the aim of analysing land-cover and land-use changes as well as carbon stocks dynamic. The databases used are composed of three Landsat satellite images (5TM of 1984, 7ETM + of 2000 and 8OLI of 2016), enhanced by field missions. Satellite images were processed using ENVI and ArcGIS software. Interview, focus group discussion methods and participatory mapping were used to identify the activities carried out by the local population. An inventory design consisting of four transects was used to measure dendrometric parameters and to identify land-use types. An estimation of carbon stocks in aboveground and underground woody biomass was made using allometric models based on non-destructive method. Dynamic of land-cover showed that the average annual rate of deforestation is 0.48%. The main activities at the base of this change are agriculture, house built-up and logging. Seven types of land-use were identified; adult secondary forests (64.10%), young secondary forests (7.54%), wetlands (7.39%), fallows (3.63%), savannahs (9.59%), cocoa farms (4.28%) and mixed crop farms (3.47%). Adult secondary forests had the highest amount of carbon ($250.75\;t\;C\;ha^{-1}$). This value has decreased by more than 60% for mixed crop farms ($94.67\;t\;C\;ha^{-1}$), showing the impact of agricultural activities on both forest cover and carbon stocks. Agroforestry systems that allow conservation and introduction of woody species should be encouraged as part of a participatory management strategy of this forest.

• Journal of the korean society of oceanography
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• v.39 no.1
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• pp.46-56
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• 2004

Spectral attenuation of light and upwelling radiance were measured in the western coast of Korea on board the R/V Inchon 888 of the Korean National Fisheries Research and Development Institute(NFRDI) during four seasons. The goal of these efforts was to determine the spatial and temporal distribution of the inherent and apparent optical properties of the water, and the factors that control their distribution. Our data indicate that while stratification of the water column, phytoplankton, and wind stress determined the vertical distribution of the optical parameters offshore, it was the tidal current and sediment type that controlled both the vertical and horizontal distribution in the coastal areas. These findings led to the development of a model that estimates the spectral attenuation of light with respect to depth and time for the Yellow Sea. The model integrates water leaving radiance from satellites, sediment types, current vectors, sigma-t, bathymetry, and in situ optical measurements in a learning algorithm capable of extracting optical properties with only knowledge of the environmental conditions of the Yellow Sea. The performance of the model decreases with increase in depth. The mean absolute percentage error (MAPE) of the model is 2% for the upper five meters, 8-10% between 6 and 50 meters, and 15% below 51 meters.

• Parasites, Hosts and Diseases
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• v.56 no.2
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• pp.205-210
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• 2018

Waterborne parasitic protozoa, particularly Giardia lamblia and Cryptosporidium spp., are common causes of diarrhea and gastroenteritis worldwide. The most frequently identified source of infestation is water, and exposure involves either drinking water or recreation in swimming pools or natural bodies of water. In practice, studies on Cryptosporidium oocysts and Giardia cysts in surface water are challenging owing to the low concentrations of these microorganisms because of dilution. In this study, a 3-year monitoring of Cryptosporidium parvum, Giardia lamblia, and Naegleria fowleri was conducted from August 2014 to June 2016 at 5 surface water sites including 2 lakes, 1 river, and 2 water intake plants. A total of 50 water samples of 40 L were examined. Cryptosporidium oocysts were detected in 22% of samples and Giardia cysts in 32%. Water at the 5 sampling sites was all contaminated with Cryptosporidium oocysts (0-36/L), Giardia cysts (0-39/L), or both. The geometric mean concentrations of Cryptosporidium and Giardia were 1.14 oocysts/L and 4.62 cysts/L, respectively. Thus, effective monitoring plans must take into account the spatial and temporal parameters of contamination because they affect the prevalence and distribution of these protozoan cysts in local water resources.

• Journal of Korean Society on Water Environment
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• v.37 no.6
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• pp.531-538
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• 2021

In this study, the TOC in six estuarine reservoirs in the West Sea (Ganwol, Namyang, Daeho, Bunam, Sapkyo, and Asan) was estimated using optically-active water quality factors by the water environment monitoring network. First, specification data and land use maps of each estuarine reservoir were collected. Subsequently, water quality data from 2013 to 2020 were collected. The data comprised of 11 parameters: pH, dissolved oxygen, BOD, COD, suspended solids (SS), total nitrogen, total phosphorus, water temperature, electrical conductivity, total coliforms, and chlorophyll-a (Chl-a). The TOC in the estuarine reservoirs was 4.9~7.0 mg/L, with the highest TOC of 7.0 mg/L observed at the Namyang reservoir, which has a low shape coefficient and high drainage density. The correlation of TOC with water quality factors was also analyzed, and the correlation coefficients of Chl-a and SS were 0.28 and 0.19, respectively, while the correlation coefficients of these factors in the Namyang reservoir were 0.42 and 0.27, respectively. To improve the estimation of TOC using Chl-a and SS, the TOC was averaged in 5 mg/L units, and Chl-a and SS were averaged. Correlation analysis was then performed and the R² of Chl-a-TOC was 0.73. The R² of SS-TOC was 0.73 with a non-linear relationship. TOC had a significant non-linear relationship with Chl-a and SS. However, the relationship should be assessed in terms of the spatial and temporal variations to construct a reliable remote sensing system.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.4
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• pp.1-15
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• 2017

Eutrophication of surface waters is of concern worldwide, because it can result in many undesirable water-quality and ecological problems, such as hypoxic 'dead' zones and harmful algal blooms, both associated with considerable economic costs. In this study, we used LSM (Land Surface Model) to simulate nitrogen in five major rivers in the Southern Korean Peninsula. The main objective of this research was to enhance nitrogen data for input of LM3V model in South Korea. Input data for nitrogen fluxes were categorized into three sections including agriculture fertilizer, livestock manure, atmosphere deposition, biological fixation, and sewage pollutants were used as the nitrogen input. For using LM3V model, the nitrogen input data were regenerated by considering states of agriculture and industry in South Korea at a $1/8^{\circ}$ resolution. Then, we simulated stream/river flows and N loads throughout the entire drainage networks in South Korea at a $1/8^{\circ}$ resolution. By using the same parameters for the entire country ($100,210km^2$), composed of 5 river basins with varying climate and land use, the model simulates spatial (11 sites) and temporal (1999~2010) patterns of flows and nitrate-N loads are resonable by comparing observed flow and nitrate-N loads. The r (Pearson's linear correlation) for water temperature, flow and nitrate-N at river were 080~0.93, 0.62~0.92 and 0.5~0.9 respectively. Based on enhanced N input data and model results, we find that LM3V model as land surface model can be applied in South Korea with interaction of atmosphere and land conditions.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09b
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• pp.1189-1192
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• 2005

Due to their slow degradation properties, hydrophobic organic contaminants in estuarine sediment have been a concern for risks to human health and aquatic organisms. Studies of fate and transport of these contaminants in estuaries are further complicated by the fact that hydrodynamics and sediment transport processes in these regions are complex, involving processes with various temporal and spatial scales. In order to simulate and quantify long-term attenuation of Polycyclic Aromatic Hydrocarbons (PAH) in the Elizabeth River, VA, we develop a modeling approach, which employs the U.S. Environmental Protection Agency's water quality model, WASP, and encompasses key physical and chemical processes that govern long-term fate and transport of PAHs in the river. In this box-model configuration, freshwater inflows mix with ocean saline water and tidally averaged dispersion coefficients are obtained by calibration using measured salinity data. Sediment core field data is used to estimate the net deposition/erosion rate, treating only either the gross resuspension or deposition rate as the calibration parameter. Once calibrated, the model simulates fate and transport PAHs following the loading input to the river in 1967, nearly 4 decades ago. Sediment PAH concentrations are simulated over 1967-2022 and model results for Year 2002 are compared with field data measured at various locations of the river during that year. Sediment concentrations for Year 2012 and 2022 are also projected for various remedial actions. Since all the model parameters are based on empirical field data, model predictions should reflect responses based on the assumptions that have been governing the fate and sediment transport for the past decades.