• Journal of Korea Water Resources Association
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• v.37 no.5
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• pp.425-435
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• 2004

Mainly, observed maximum rainfall has been evaluated by point rainfall, but actually it should be considered by means of average areal rainfall. Average areal rainfall is an estimated value computed through DAD(rainfall Depth-Area-Duration) analysis. By using this value, an average and maximum areal rainfall according to area-duration relationship could be computed. In this study, we assume that the whole Korea region is hydrologically homogeneous, and then analyze using the storm-centered DAD(moving-area DAD) method for the past century data. From this analysis, we evaluate the yearly variation of observed maximum areal rainfall through area-duration relationship. And we also construct an IDF(rainfall Intensity-Duration-Frequency) curve by using the annual time series data which is composed of maximum areal rainfall. The characteristics of IDF and observed maximum areal rainfall is also evaluated.

• Proceedings of the Korean Society of Agricultural Engineers Conference
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• 2005.10a
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• pp.375-380
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• 2005

In Korea, most landslides are occurred during the rainy season from June to September and have a shallow failure plane parallel to the slope. For these types of rainfall-induced failures, the most important factors triggering slope unstability is not the increase of pore water pressure but the decrease of the matric suction of unsaturated soils by rainfall infiltration. So it is essential to landslide hazard assessment that defines the characteristics of infiltration in natural slopes. In this study, field measurements have been carried out in order to monitor in-situ volumetric water contents and ground water table, at several depths and locations on a natural slope. The results show that rainfall infiltration is correlated with antecedent water contents, rainfall intensity and total rainfall. The ground water table was varied sensitively by every rainfall event.

• Economic and Environmental Geology
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• v.44 no.1
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• pp.71-82
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• 2011

The unsaturated soil column tests were carried out for weathered gneiss soil and weathered granite soil in order to obtain the relationship between rainfall intensity and infiltration velocity of rainfall on the basis of different unit weight conditions of soil. In this study, volumetric water content and pore water pressure were measured using TDR sensors and tensiometers at constant time interval. For the column test, three different unit weights were used as in-situ condition, loose condition and dense condition, and rainfall intensities were selected as 20 mm/h and 50 mm/h. In 20 mm/h rainfall intensity condition, average rainfall infiltration velocities for both gneiss and weathered granite soils were obtained as $2.854{\times}10^{-3}$ cm/s ~ $1.297{\times}10^{-3}$ cm/s for different unit weight values and $2.734{\times}10^{-3}$ cm/s ~ $1.707{\times}10^{-3}$ cm/s, respectively. In 50 mm/h rainfall intensity condition, rainfall infiltration velocities were obtained as $4.509{\times}10^{-3}$ cm/s ~ $2.016{\times}10^{-3}$ cm/s and $4.265{\times}10^{-3}$ cm/s ~ $3.764{\times}10^{-3}$ cm/s respectively. The test results showed that the higher rainfall intensity and the lower unit weight of soil, the faster average infiltration velocity. In addition, the weathered granite soils had faster rainfall infiltration velocities than those of the weathered gneiss soils except for the looser unit weight conditions. This is due to the fact that the weathered granite soil had more homogeneous particle size, smaller unit weight condition and larger porosity.

• Journal of Korea Water Resources Association
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• v.45 no.8
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• pp.795-804
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• 2012

Recently, changes in rainfall intensity and patterns have been causing increasing soil loss worldwide. As a result, the water ecosystem becomes worse and crops yield are reduced with soil loss and nutrient loss with it. Many studies have been proposed to estimate runoff and soil loss to predict or decrease non-point source pollution. Although the USLE has been used for many years in estimating soil losses, the USLE cannot reflect effects on soil loss of changes in rainfall intensity and patterns. The WEPP, physically based model, is capable of predicting soil loss and runoff using various rainfall intensity. In this study, the WEPP model was simulated for sediment yield, runoff and peak runoff using data of 5, 10, 30, 60 minute term rainfall, Huff's method and design rainfall. In case of rainfall interval of 5 minutes and 60 minutes, the sediment and runoff values decreased by 24% and 19%, respectively. The peak rate runoff values decreased by 16% when rainfall interval changed from 5 minutes to 60 minutes, indicating the peak rate runoff values are affected by rainfall intensity to some degrees. As a result of simulating using Huff's method, all values (sediment yield, runoff, peak runoff) were found to be the greatest at third quartile. According to the analysis under various design rainfall conditions (2, 3, 5, 10, 20, 30, 50, 100, 200, 300 years frequency), sediment yield, runoff, and peak runoff of 906.2%, 249.4% and 183.9% were estimated using 2 year to 300 year frequency rainfall data.

• International Journal of Highway Engineering
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• v.13 no.2
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• pp.133-138
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• 2011

This study aims to compare hydraulic & hydrologic design characteristics by examining generated on weak points for road drainage poor sites. More appropriated methodology of rainfall-intensity calculated is to consider minutely rainfall-intensity decision method for road drainage basins. To use non-uniform flow analysis methodology for road surface drainage facilities inlet spacing decision methods is better than present experience inlet spacing decision equations.

• Journal of the Korean GEO-environmental Society
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• v.13 no.9
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• pp.75-82
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• 2012

This paper is the results of analysis for the causes and characteristics of landslide according to heavy rain occurred in west area of Gangwon province which is affected by typhoon such as Ewiniar and Bilis in 2006. West side of Gangwon province is topographically weak for the landslide and debris flow since it is covered by soil of weathered rock such as Gneiss and Granite. From the results of analysis for the rainfall characteristics, it was found that landslide occurrence is closely related to the accumulated rainfall amount less than 3 days. Furthermore, it was found that regional difference of occurrence frequency is effected by 1-hour maximum rainfall intensity. From the results of analysis for the landslide data of 860 locations occurred in west side, it was shown that failure mode was changed from transition slide to liquidity slide. Occurrence frequency was high at the slope angle of $20{\sim}30^{\circ}$ slope length of 11~20, and slope width of 6~10. Landslide of west side is the typical landslide of Gneiss and Granite and the type of small scale which has narrow slope width.

• Atmosphere
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• v.33 no.1
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• pp.1-20
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• 2023

Holding the longest observation data from April 1904, Busan is one of the essential points to understand the climate variability of the Korean Peninsula without missing data since implementing the modern weather observation of the South Korea. Busan is featured by coastal areas and affected by various climate factors and fluctuations. This study aims to investigate climate variability and changes in climatic variables, extremes, and several weather indexes. The statistically significant change points in daily mean rainfall intensity and temperature were found in 1964 and 1965. Based on the change point detection, 117 years were divided into two periods for daily mean rainfall intensity and temperature, respectively. In the long-term temperature analysis of Busan, the increasing trend of the daily maximum temperature during the period of 1965~2021 was larger than the daily mean temperature and the daily minimum temperature. Applying Ensemble Empirical Mode Decomposition, daily maximum temperature is largely affected by the decadal variability compared to the daily mean and minimum temperature. In addition, the trend of daily precipitation intensity from 1964~2021 shows a value of about 0.50 mm day^-1, suggesting that the rainfall intensity has increased compared to the preceding period. The results in extremes analysis demonstrate that return values of both extreme temperatures and precipitation show higher values in the latter than in the former period, indicating that the intensity of the current extreme phenomenon increases. For Wet-Bulb Globe Temperature (effective humidity), increasing (decreasing) trend is significant in Busan with the second (third)-largest change among four stations.

• Journal of the Korean Geotechnical Society
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• v.21 no.9
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• pp.77-86
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• 2005

Since slope sliding and loss of railway triggered by a rainfall produce instability in the operation of trains, a proper method to estimate the slope stability considering rainfall Is required. from the field study, sliding induced by rainfall depends on the engineering properties of soils, three dimensional aspect of the slope, rainfall intensity and geological conditions of the soil layers. In this study, among various types of sliding, slope Instability caused by the surface runoff water at the concave zones in a slope is investigated. The depth of runoff water is calculated by using the Rational method and Manning equation. The occurrence of runoff water is evaluated by a comparison between the calculated infiltration rate and rainfall intensity. Pressure heads which can be calculated from the modified Iverson model are used to calculate the factor of safety along the vertical depth of the slope. The modified Iverson model considers the depth of runoff water, thus the maximum hydraulic gradient along the depth of slope is greater than one.

• Journal of Environmental Science International
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• v.22 no.6
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• pp.733-744
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• 2013

This study was to investigate characteristics of Seoho watershed in Suwon city. $BOD_5$ and SS were selected due to the one of the important factors of the water qualities. Monitoring was conducted monthly for four years during the non-rainfall time. Also, we have been monitored $BOD_5$, $COD_{Mn}$, SS, TN and TP with two times sampling after the rainfalls. The highest concentrations of $BOD_5$ and SS were observed in downstream compare with upstream and midstream during the non-rainfall time. No change was observed in $BOD_5$ and $COD_{Mn}$ during the non-rainfall time and after the rainfalls. The monitoring result indicated that the concentration of SS was the highest in downstream after the rainfalls. We have collected the samples two times after the rainfalls. The rainfall intensity in first sampling was two times higher than second sampling. TN and TP concentrations were increased with increasing the rainfall intensity at all stream. The ESB (Ecological Score of Benthic macroinverterbrate community) index was used to evaluate the statement of stream. ESB results were identified that the upstream is protected waters and the down and midstream is reformed waters. EBS analysis results indicated that the Seoho watershed was ${\beta}$-mesosaprobic at all stream.

• Journal of the Korean earth science society
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• v.36 no.5
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• pp.460-475
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• 2015

A number of heavy rainfall events on the Korean Peninsula are indirectly influenced by tropical cyclones (TCs) when they are located in southeastern China. In this study, a heavy rainfall case in the middle Korean region is selected to examine the influence of typhoon simulation performance on predictability of remote rainfall over Korea as well as direct rainfall over Taiwan. Four different numerical experiments are conducted using Weather Research and Forecasting (WRF) model, toggling on and off two different improvements on typhoon in the model initial condition (IC), which are TC bogussing initialization and dropwindsonde observation data assimilation (DA). The Geophysical Fluid Dynamics Laboratory TC initialization algorithm is implemented to generate the bogused vortex instead of the initial typhoon, while the airborne observation obtained from dropwindsonde is applied by WRF Three-dimensional variational data assimilation. Results show that use of both TC initialization and DA improves predictability of TC track as well as rainfall over Korea and Taiwan. Without any of IC improvement usage, the intensity of TC is underestimated during the simulation. Using TC initialization alone improves simulation of direct rainfall but not of indirect rainfall, while using DA alone has a negative impact on the TC track forecast. This study confirms that the well-suited TC simulation over southeastern China improves remote rainfall predictability over Korea as well as TC direct rainfall over Taiwan.