• Journal of Korean Society of Forest Science
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• v.105 no.2
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• pp.216-222
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• 2016

In relation to the impact of cumulative rainfall on landslides in accordance with the cumulative number of days, for the more than 100 mm rainfall, the 3 days cumulative rainfall experienced 64.9% of the total points, which is 986 points out of the 1520 points. The 5 days cumulative rainfall period experienced 60% of the total landslides, which is 846 points out of 1520 points analyzed. The 3 days or 5 days cumulative rainfall thus had a greater effect on landslides than the other days. In addition, for the 101-200 mm rainfall, more landslides occurred in the 10 days cumulative number of days, for the 201-300 mm, more landslides occurred in the 14 days cumulative number of days, whereas the 18 days cumulative number of days had more landslides for the 301-400 mm rainfall. Thus, it is imperative to take into consideration cumulative rainfall and the cumulative number of days of rainfall in the establishment of forecasting and warning systems for landslides, to minimize the damage caused to life and property by landslides.

• Journal of the Korean GEO-environmental Society
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• v.17 no.12
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• pp.5-16
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• 2016

This study aims to assess the influence of rainfall patterns on shallow landslides initiation. Doing so, five typical rainfall patterns with the same cumulative amount and intensity components comprising Advanced (A1 and A2), Centralized (C), and Delayed (D1 and D2) were designed based on a historical rainstorm event in Jinbu. Mt area. Those patterns were incorporated as the hydrological conditions into the Transient Rainfall Infiltration and Grid-based Regional Slope-stability Model (TRIGRS) to assess their influences on groundwater pressure and changes in the stability of the slope. The results revealed that not only the cumulative rainfall thresholds necessary to initiate landslides, but also the rate at which the factor of safety decreases and the time required to reach the critical state, are governed by rainfall patterns. The sooner the peak rainfall intensity, the smaller the cumulative rainfall threshold, and the shorter the time until landslide occurrence. Left-skewed patterns were found to have a greater effect on landslide initiation. Specifically, among five rainfalls, pattern (A1) produced the most critical state. The severity of response was followed by patterns A2, C, D1, and D2. Our conclusion is that rainfall patterns have a significant effect on the cumulative rainfall threshold, the build-up of groundwater pressure, and the occurrence of shallow landslides.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.202-202
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• 2016

Despite the potentially major influence of rainstorm patterns on the prediction of shallow landslides, this relationship has not yet received significant attention. In this study, five typical temporal rainstorm patterns with the same cumulative amount and intensity components comprising Advanced (A1 and A2), Centralized (C), and Delayed (D1 and D2) were designed based on a historical rainstorm event occurred in 2006 in Mt. Jinbu area. The patterns were incorporated as the hydrological conditions into the Transient Rainfall Infiltration and Grid-based Regional Slope-stability Model (TRIGRS), in order to assess their influences on pore pressure variation and changes in the stability of the covering soil layer in the study area. The results revealed that not only the cumulative rainfall thresholds necessary to initiate landslides, but also the rate at which the factor of safety (FS) decreases and the time required to reach the critical state, are governed by rainstorm pattern. The sooner the peak rainfall intensity occurs, the smaller the cumulative rainfall threshold, and the shorter the time until landslide occurrence. Left-skewed rainfall patterns were found to have a greater effect on landslide initiation. More specifically, among the five different patterns, the Advanced storm pattern (A1) produced the most critical state, as it resulted in the highest pore pressure across the entire area for the shortest duration; the severity of response was then followed by patterns A2, C, D1, and D2. Thus, it can be concluded that rainfall patterns have a significant effect on the cumulative rainfall threshold, the build-up of pore pressure, and the occurrence of shallow landslides, both in space and time.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5B
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• pp.519-528
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• 2006

In the construction of hydraulic structures deciding a design flood is one of the most important works. It should be especially noted that the time distribution of the design rainfall method makes a significant effect on the results of the design flood. Thus, choosing an appropriate time distribution method for the design rainfall is a very important process. In recent years, Huff's method is usually used in Korea. This method presents dimensionless rainfall-time cumulative curves, which are made through the analyses of storm data. In this study, the annual maximum rainfall data, from 1961 to 2004 were analyzed to make the dimensionless rainfall-time cumulative curves and hyetographs in Seoul. The results were compared with the "Regional Time Distribution of the Design Rainfall", (KICT, 1989 and MCT, 2000). As a result, the dimensionless rainfall-time cumulative curves are smoother than Huff's results when the duration of an annual maximum rainfall is short. In addition, the curves are similar with the Huff's results as the duration is longer.

• Journal of Korea Water Resources Association
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• v.39 no.9 s.170
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• pp.767-777
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• 2006

The goal of this study is to improve Huff's method which is the most popular method for rainfall time distribution in Korea. As the first step, we reevaluated the context of Huff's original research motivations, geography and rainfall pattern of study area, and compared that to Korean situations. In original Huff's results, no change in temporal distribution characteristics were found for different rainfall durations. This was found to be different from Korean situations. Furthermore, results from the MOCT(Ministry of Construction and Transportation) version of Huff's method is on a gage basis not on a watershed basis, thus making it difficult to select cumulative rainfall curves representative of a watershed. In addition, all rainfall data regardless of their magnitude were used in the MOCT version of Huff' method which is different from original Huff's which screened out data by using a threshold value of 25.4mm. For both point and areal mean rainfall, time distribution characteristics of rainfall for various durations were found to be different. This was statistically proven by K-S test at 5% significance level as some cumulative rainfall curves developed from the rainfall data of certain durations were found to be not significant with cumulative rainfall curves developed from the rainfall data of all durations. Therefore, in order to apply Huff's method to Korean situations, it is recommended that dimensionless cumulative curve must be developed for various rainfall duration intervals using rainfall data greater than a certain threshold value.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.509-512
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• 2003

Our country is serious difference of precipitation seasonally and about 66% of yearly mean rainfall is happening in concentration rainfall form between September on June. It requires consideration because of a lot of natural disasters by this downpour are produced. Slope failure is happened by artificial factor of creation of slope according to the land development, fill slope etc. and natural factor of rainfall, topography, nature of soil, soil quality, rock floor. Usually, Direct factor of failure slope is downpour. In this study, the Slope about among 55 places happened failure by downpour investigated occurrence position, geological etc and executed and inquire into character of rainfall connected with failure slope. Among character of rainfall, executed analysis about Max. hourly rainfall and cumulative rainfall of place that failure slope is situated and grasped the geological character of failure slope. Through this, inquire to character of failure slope by rainfall and take advantage of basis study for Hazard map creation.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.1
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• pp.57-65
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• 2007

In Korea, most landslides occurr during the rainy season and have shallow failure planes parallel to the slope. For these types of rainfall-induced failures, the most important factor triggering slope unstability is decrease in the matric suction of unsaturated soils with increasing saturation depth by rainfall infiltration. For this reason, estimation of cumulative infiltration has a significance. In this study, infiltration rate and cumulative infiltration are estimated by using both Mein & Larson model based on Green-Ampt infiltration model and using modified Mein & Larson model to which unsteady rainfall is applied. According to the results, the modified model is more reasonable than Mein & Larson method itself in estimation of infiltration rate and saturation depth because of considering real pending condition.

• Journal of the Korean GEO-environmental Society
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• v.19 no.12
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• pp.15-23
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• 2018

The occurrence of soil erosions in Korea is mostly driven by flowing water which has a close relationship with rainfalls. The soil eroded by rainfalls flows into and deposits in the river and it polluted the water resources and making the rivers become difficult to be managed. Recently, the frequency of heavy rainfall events that are more than 30 mm/hr has been increasing in Korea due to the influence of climate change, which creating a favourable condition for the occurrence of soil erosion within a short time. In this study, we proposed a method to estimate the distribution of rainfall intensity and to calculate the energy produced by a single rainfall event using the cumulative distribution function that take into account of the physical characteristics of rainfall. The raindrops kinetic energy estimated by the proposed method are compared with the measured data from the previous studies and it is noticed that the raindrops kinetic energy estimated by the rainfall intensity variation is very similar to the results concluded from the previous studies. In order to develop an equation for estimating rainfall kinetic energy, rainfall particle size data measured at a rainfall intensity of 0.254~152.4 mm/hr were used. The rainfall kinetic energy estimated by applying the cumulative distribution function tended to increase in the form of a power function in the relation of rainfall intensity. Based on the equation obtained from this relationship, the rainfall kinetic energy of 1~80 mm/hr rainfall intensity was estimated to be $0.03{\sim}48.26Jm^{-2}mm^{-1}$. Based on the relationship between rainfall intensity and rainfall energy, rainfall kinetic energy equation is proposed as a power function form and it is expected that it can be used in the design of short-term operated facility such as the sizing of sedimentation basin that requires prediction of soil loss by a single rainfall event.

• Journal of Korean Society of Forest Science
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• v.101 no.1
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• pp.28-35
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• 2012

Rainfall is widely recognized as a major landslide-triggering factor. Most of the latest landslides that occurred in South Korea were caused by short-duration heavy rainfall. However, the relationship between rainfall characteristics and landslide occurrence is poorly understood. To examine the effect of rainfall on landslide occurrence, cumulative rainfall(mm) and rainfall intensity(mm/hr) of serial rain and antecedent rainfall(mm) were analyzed for 18 landslide events that occurred in the southern and central regions of South Korea in June and July 2011. It was found that all of these landslides occurred by heavy rainfall for one or three days, with the rainfall intensity exceeding 30 mm/hr or with a cumulative rainfall of 200 mm. These plotted data are beyond the landslide warning criteria of Korea Forest Service and the critical line of landslide occurrence for Gyeongnam Province. It was also found that the time to landslide occurrence after rainfall start(T) was shortened with the increasing average rainfall intensity(ARI), showing an exponential-decay curve, and this relation can be expressed as "T = $94.569{\cdot}exp$($-0.068{\cdot}ARI$)($R^2$=0.64, p<0.001)". The findings in this study may provide important evidences for the landslide forecasting guidance service of Korea Forest Service as well as essential data for the establishment of non-structural measures such as a warning and evacuation system in the face of sediment disasters.

• The Journal of Engineering Geology
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• v.15 no.4 s.42
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• pp.435-445
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• 2005

Landslides induced by heavy rainfall from typhoon 'Rusa' in 2002 and typhoon 'Meami' in 2003 were investigated at Samcheok area, and the relationship between landslides and rainfall on that area was analyzed. The average annual rainfall at Samcheok area is generally $1,200mm\~1,300mm$. However, the average annual rainfall at samcheok for 2003 and ton was increased more than 2,000mm because of typhoon 'Rusa' and typhoon 'Meami'. The number of landslides and the landslides area are largely occurred in a area of the relatively high maximum hourly rainfall and 2days cumulative rainfall. Therefore, it confirmed that landslides are directly depended on the hourly rainfall and the cumulative rainfall. The landslides at Samcheok area induced by heavy rainfall due to typhoon are more influenced by the maximum hourly rainfall at the landslide occurrence day. In order to predict a rational landslide size, a new method included the maximum hourly rainfall and the landslide area in a traditional way was proposed. As the result of applying the new proposed method, the landslide size at Samcheok area is involved in the large scale landslide.