• Journal of Korean Society on Water Environment
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• v.27 no.1
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• pp.9-18
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• 2011

In this study the optimal volume for non-point source control retention is estimated considering spatio-temporal variation of land surface. The 3-parameter mixed exponential probability density function is used to represent the statistical properties of rainfall events, and NRCS-CN method is applied as rainfall-runoff transformation. The catchment drainage area is divided into individual $30m{\times}30m$ cells, and runoff curve number is estimated at each cell. Using the derived probability density function theory, the stormwater probability density function at each cell is derived from the rainfall probability density function and NRCS-CN rainfall-runoff transformation. Considering the antecedent soil moisture condition at each cell and the spatial variation of CN value at the whole catchment drainage area, the ensemble stormwater capture curve is established to estimate the optimal volume for an non-point source control retention. The comparison between spatio-temporally varied land surface and constant land surface is presented as a case study for a urban drainage area.

• Journal of Korea Water Resources Association
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• v.33 no.S1
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• pp.124-129
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• 2000

• Journal of the Korean GEO-environmental Society
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• v.15 no.4
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• pp.13-27
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• 2014

Catchments soil erosion, one of the most serious problems in the mountainous environment of the world, consists of a complex phenomenon involving the detachment of individual soil particles from the soil mass and their transport, storage and overland flow of rainfall, and infiltration. Sediment size distribution during erosion processes appear to depend on many factors such as rainfall characteristics, vegetation cover, hydraulic flow, soil properties and slope. This study involved laboratory flume experiments carried out under simulated rainfall in a 3.0 m long ${\times}$ 0.8 m wide ${\times}$ 0.7 m deep flume, set at $17^{\circ}$ slope. Five experimental cases, consisting of twelve experiments using three different sediments with two different rainfall conditions, are reported. The experiments consisted of detailed observations of particle size distribution of the out-flow sediment. Sediment water mixture out-flow hydrograph and sediment mass out-flow rate over time, moisture profiles at different points within the soil domain, and seepage outflow were also reported. Moisture profiles, seepage outflow, and movement of overland flow were clearly found to be controlled by water retention function and hydraulic function of the soil. The difference of grain size distribution of original soil bed and the out-flow sediment was found to be insignificant in the cases of uniform sediment used experiments. However, in the cases of non-uniform sediment used experiments the outflow sediment was found to be coarser than the original soil domain. The results indicated that the sediment transport mechanism is the combination of particle segregation, suspension/saltation and rolling along the travel distance.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.153-153
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• 2022

Large-scale and accurate observations at fine spatial resolution through a means of remote sensing offer an effective tool for capturing rainfall variability over the traditional rain gauges and weather radars. Although satellite rainfall products (SRPs) derived using two major estimation approaches were evaluated worldwide, their practical applications suffered from limitations. In particular, the traditional top-down SRPs (e.g., IMERG), which are based on direct estimation of rain rate from microwave satellite observations, are mainly restricted with their coarse spatial resolution, while applications of the bottom-up approach, which allows backward estimation of rainfall from soil moisture signals, to novel high spatial resolution soil moisture satellite sensors over South Korea are not introduced. Thus, this study aims to evaluate the performances of a state-of-the-art bottom-up SRP (the self-calibrated SM2RAIN model) applied to the C-band SAR Sentinel-1, a statistically downscaled version of the conventional top-down IMERG SRP, and their integration for a targeted high spatial resolution of 0.01° (~ 1-km) over central South Korea, where the differences in climate zones (coastal region vs. mainland region) and vegetation covers (croplands vs. mixed forests) are highlighted. The results indicated that each single SRP can provide plus points in distinct climatic and vegetated conditions, while their drawbacks have existed. Superior performance was obtained by merging these individual SRPs, providing preliminary results on a complementary high spatial resolution SRP over central South Korea. This study results shed light on the further development of integration framework and a complementary high spatial resolution rainfall product from multi-satellite sensors as well as multi-observing systems (integrated gauge-radar-satellite) extending for entire South Korea, toward the demands for urban hydrology and microscale agriculture.

• Journal of The Korean Society of Agricultural Engineers
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• v.48 no.7
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• pp.3-14
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• 2006

The objective of this study was to develop a GIS-based decision support system (GIS-USLE system) to estimate soil erosion and evaluate its effect on concentrated upland plots in Godang district, Korea. This system was developed for the ArcView environment using A VENUE script. Three modules were used in the GIS-USLE system, namely pre-processing, the USLE factors calculator module, and post-processing. This system benefits from a user friendly environment that allows users with limited computer knowledge to use it. This system was applied to 1,285 individual upland plots ranging from 0.005 to 1.347 ha in size with an average slope steepness of 14 %. The rainfall distributions were estimated using the three methods, namely Mononobe and Yen-Chow with Triangle and with Trapezoid type, and then used to calculate the rainfall erosivity factor. The soil erosion amounts from the 1,285 individual plots in the study area by 2 year return period with a 24h maximum rainfall amount of 154.6 mm were estimated at 5 tons/ha on average. Slope appeared to be the most important factor affecting soil erosion estimation, as expected. The prototype model was applied to the project area, and the results appeared to support the practical applications. By examining many fields simultaneously, this system can easily provide fast estimation of soil erosion and thus reveal the spatial pattern of erosion from fields in a region. This study will help estimate and evaluate soil erosion in concentrated upland districts and identify the best management practices.

• Asian Journal of Atmospheric Environment
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• v.8 no.4
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• pp.202-211
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• 2014

In this study, long-term rainfall data with irregular spatial distribution in Seoul, Korea, were separated into individual precipitation events by the inter-event time definition of 6 hours. Precipitation washout of $PM_{10}$ and $NO_2$ concentrations in the air considering various complex factors were analyzed quantitatively. Concentrations of $PM_{10}$ and $NO_2$ in the atmosphere were lower under condition of rainfall compared to that of non-precipitation, and a noticeable difference in average $PM_{10}$ concentrations was observed. The reduction of concentrations of $PM_{10}$ and $NO_2$ by rainfall monitored at road-side air monitoring sites was also lower than that of urban air monitoring sites due to continuous pollutant emissions by transportation sources. Meanwhile, a relatively smaller reduction of average $PM_{10}$ concentration in the atmosphere was observed under conditions of light rainfall below 1 mm, presumably because the impact of pollutant emission was higher than that of precipitation scavenging effect, whereas an obvious reduction of pollutants was shown under conditions of rainfall greater than 1 mm. A log-shaped regression equation was most suitable for the expression of pollutant reduction by precipitation amount. In urban areas, a lower correlation between precipitation and reduction of $NO_2$ concentration was also observed due to the mobile emission effect.

• Journal of Korean Society on Water Environment
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• v.35 no.1
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• pp.35-42
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• 2019

Urbanization has led to extreme changes in land use on urban watersheds. Most cities are becoming residential, commercial and industrial areas, making infiltration and storage of rainfall less favorable. The demand for LID (Low Impact Development) technology is increasing in order to mitigate this water cycle distortion and return to existing hydrological conditions. The LID technique is effective in reducing runoff by permeating the urban impervious area. However, considering the limit of the installation area and the financial requirement of the installation, there is not much research on the linkage of each LID component technology for optimum efficiency according to the appropriate scale. In this study, the effects of the LID facilities applied to the target site were simulated using the SWMM model, suggesting the optimal linkage method considering interconnectivity, and applying the effects as an existing installation of individual facilities. The water balance at the time of application of the LID technology, short-term and long-term rainfall event were compared. Also, the individual application and the linkage application were compared with each other. If each component technology has sufficient processing size, then linkage application is more effective than individual application.

• Journal of Environmental Science International
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• v.10 no.3
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• pp.217-223
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• 2001

Where no records are available at a site, a preliminary estimate may be made from relations between floods and catchment chatacteristics. A number of these chatacteristics were chosen for testing and were measured for those catchments where mean annual flood estimates were available. Although the improvement using extended data in regression of flood estimates on catchment characteristics was small, this may be due to the limitations of the regression model. When an individual short term record is to be extended, more detailed attention can be given; an example is presented of the technique which should be adopted in practice, particularly when a short term record covers a period which is known to be biassed. A method of extending the peaks over a threshold series is presented with a numerical example. The extension of records directly from rainfall by means of a conceptual model is discussed, although the application of such methods is likely to be limited by lack of recording raingauge information. Methods of combining information from various sources are discussed in terms of information from catchment characteristics supplemented by records. but are generally applicable to different sources of information. The application of this technique to estimating the probable maximum flood requires more conservative assumptions about the antecedent condition, storm profile and unit hydrograph. It is suggested that the profile and catchment wetness index at the start of the design duration should be based on the assumption that the estimated maximum rainfall occurs in all durations centered on the storm peak.

• Journal of The Korean Society of Agricultural Engineers
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• v.56 no.6
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• pp.103-111
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• 2014

This study was to develop the flood analysis module (FAM) for implementation of a web-based real-time agricultural flood management system. The FAM was developed to apply for an individual watershed, including agricultural reservoir. This module calculates the flood inflow hydrograph to the reservoir using effective rainfall by NRCS-CN method and unit hydrograph calculated by Clark, SCS, and Nakayasu synthetic unit hydrograph methods, and then perform the reservoir routing by modified Puls method. It was programmed to consider the automatic reservoir operation method (AutoROM) based on flood control water level of reservoir. For a $15.7km^2$ Gyeryong watershed including $472{\times}10^4m^3$ agricultural reservoir, rainfall loss, rainfall excess, peak inflow, total inflow, maximum discharge, and maximum water level for each duration time were compared between the FAM and HEC-HMS (applied SCS and Clark unit hydrograph methods). The FAM results showed entirely consistent for all components with simulated results by HEC-HMS. It means that the applied methods to the FAM were implemented properly.

• Atmosphere
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• v.27 no.2
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• pp.151-162
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• 2017

The rainfall amount data measured by 'Wootaek', a method of measuring how far the moisture had absorbed into the soil when it rains during the Joseon Dynasty, were estimated with the Chugugi data in the 12 sites where both the 'Wootaek' and 'Chugugi' data are available. Excluding the 5 sites (Ganghwa, Jinju, Jeonju, Chuncheon, Hamheung) poor in sample data, the 'Wootaek' data 1 'Ri' and 1 'Seo' in 'Chugugi' unit (Bun) in the 7 sites; Suwon, Gwangju (Gyeonggi-do), Gongju, Daegu, Wonju, Haeju and Pyeongyang, were 11.1/5.6 Bun, 9.4/3.2 Bun, 14.0/5.7 Bun, 9.3/3.9 Bun, 13.6/4.3 Bun, 11.3/4.8 Bun and 16.8/7.4 Bun, respectively. The Chugugi unit 1 'Bun' is equall to approximately 2 'mm'. The average of the 7 sites is 13.1/5.7 Bun, however it becomes small to 11.7/4.5 Bun when the Pyeongyang of which data is considerably distributed over wide range is excluded, showing that the 'Wootaek' data 1 'Ri' is approximately the 2.3~2.6 times of 1 'Seo'. It is recommended to use the individual estimates of the sites in utilizing the 'Wootaek' rainfall data of 352 stations across the country restored from the "Gaksa-deungnok".