• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.877-882
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• 2010

This paper is a result of investigating causes and main characteristics of landslides, occurred at Hongcheon area in Gangwondo during July in 2006, by collecting relevant data and visiting site. The main cause of landslides in this area has been found to be saturation of the ground wetted by a series of precipitations during 10~13 July and the heavy rainfall during 15 July. The pattern of the landslides could be classified as translational failure, occurred at the boundary between the relatively thin weathered residual soil and the mother rock. By analyzing a number of failed slopes based on site visit and reviewing collected data, typical widths of failed slopes are in the range of 10~20m (minimum: 5m, maximum: 70m). Lengths of landslide area are in the wide range of 10~450m. Most of area are less than 20m in width and 100m in length so that their shapes are long and narrow, frequently observed in Korea, and their areas are relatively small size of around $1000m^2$. The inclinations of the failed slopes are in the range of $10{\sim}60^{\circ}$ while the most probable slope angle is about $20{\sim}25^{\circ}$.

• 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.

• Korean Journal of Agricultural Science
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• v.2 no.1
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• pp.281-300
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• 1975

The precipitation data and water level data in twenty-four sampling places, to investigate same hydrological quantities along the basin of Geum River, have been analyzed, and the findings for the first report are summarized as follows. 1. The mean annual precipitation in the basin of Geum River is of 1203mm, and the areal weight of areal rainfall by Thiessen's method shows as Table 1. 2. The areas where have maximum annual precipitation of 1501 to 2000mm, are seventeen placed among twentyfour gauging stations, and it is founded to be the highest rate with 71 percents. The precipitation of below 1500mm is measured in the other three statinons, and that of above 2001mm in four stations, too. 3. The areas where have maximum rainfall of 201 to 300mm within a day, are fifteen places, and that comes in the highest rate of distribution with 63 percents. 4. As to distribution of the places with maximum rainfall of below and above 300mm within two days, it shows respectively 50 percents. 5. The areas where have maximum rainfall of 301 to 400mm within three days, are fifteen places, and it is the highest rate of distribution with 63 percents. 6. The fourteen places have maximum rainfall of 401 to 600mm within a continuous day, it is the highest rate of distribution with 58 percents. 7. Table 5 shows probable maximum rainfall within a day, and it does the most rainfall a long the upper stream of Daecheong dam site around Muju, and the next shows in the areas around Ganggyeung, Gongju and Buyeu. 8. During irrigation period on paddy corp, for 100 days from early ten days in June to early ten days in September the areas where have rainfall of 601 to 800mm are sixteen places, and it is the highest rate of distribution with 76 percents, as Table 6 9. The areas where have effective rainfall of 501 to 600mm, are fifteen places, and it is the highest rate of distribution with 71 percents. Thirteen places have the effective ratio of 66 to 75 percents, and it means 62 percents of distribution, and the next, 76 to 85 percents in the seven places, and it comes 33 percents. 10. The areas where have probable effective rainfall of 401 to 500mm, are fourteen places, which is about 100mm less than mean effective rainfall in each area, and that comes 67 percents of distribution. 11. A particular year can not be appointed as once -in-10 year drought in the same year as a whole in the basin of Geum River. 12. The basin of Geum River, s/S being 0.53 to 0.74, has relatively proper conditions in the aspect of water resources.

• Journal of the Korean Society of Hazard Mitigation
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• v.3 no.3 s.10
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• pp.125-132
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• 2003

In this study, safety analysis of river in flash flood due to local extraordinary rainfall was conducted for the Hong-Je river, which was selected as a representative sample basin because it is one of the most urbanized rivers in Seoul. The rainfall data of precipitation 310.1 mm and probable maximum precipitation (PMP) 740.0 mm in July $14{\sim}15$, 2001 was used to perform safety analysis. Resulting of safety analysis of the flood control in Hong-Je river, case of the 50 year of design frequency, safety section, management section, and danger section were represented to be 85%, 15%, and 0% respectively. For the 200 year of design frequency, safety section decreased by 6% and management section and danger section increment by 4% and 2%, respectively, The variation of management section was not observed with respect to 200 year of frequency. Little variation of safety value for management section for 300 and 500 of frequency increased by 8% and 12% relative to 50 year of frequency, respectively. management section and danger section for 1000 year of frequency increased by 19% and 13% relative to 50 year of frequency.

• Journal of The Korean Society of Agricultural Engineers
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• v.59 no.1
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• pp.81-96
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• 2017

Along with climate change, it is reported that the scale and the frequency of extreme climate events (e.g. heavy rain, typhoon, etc.) show unstable tendency of increase. In case of Korea, also, the frequency of heavy rainfall shows increasing tendency, thus causing natural disaster damage in downtown and agricultural areas by rainfall that exceeds the design criteria of hydraulic structures. In order to minimize natural disaster damage, it is necessary to analyze how extreme precipitation event changes under climate change. Therefore a new design criteria based on non-stationarity frequency analysis is needed to consider a tendency of future extreme precipitation event and to prepare countermeasures to climate change. And a quantitative and objective characteristic analysis could be a key to preparing countermeasures to climate change impact. In this study, non-stationarity frequency analysis was performed and inundation risk indices developed by 4 inundation characteristics (e.g. inundation area, inundation depth, inundation duration, and inundation radius) were assessed. The study results showed that future probable rainfall could exceed the existing design criteria of hydraulic structures (rivers of state: 100yr-200yr, river banks: 50yr-100yr) reaching over 500yr frequency probable rainfall of the past. Inundation characteristics showed higher value in the future compared to the past, especially in sections with tributary stream inflow. Also, the inundation risk indices were estimated as 0.14 for the past period of 1973-2015, and 0.25, 0.29, 1.27 for the future period of 2016-2040, 2041-2070, 2071-2100, respectively. The study findings are expected to be used as a basis to analyze future inundation damage and to establish management solutions for rivers with inundation risks.

• Journal of Korea Water Resources Association
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• v.48 no.2
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• pp.115-126
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• 2015

In recent years, debris flow disaster has occurred in multiple locations between high and low mountainous areas simultaneously with a flooding disaster in urban areas caused by heavy and torrential rainfall due to the changing global climate and environment. As a result, these disasters frequently lead to large-scale destruction of infrastructures or individual properties and cause psychological harm or human death. In order to mitigate these disasters more effectively, it is necessary to investigate what causes the damage with an integrated model of both disasters at once. The objectives of this study are to analyze the mechanism of debris flow for real basin, to determine the PMP and run-off discharge due to the DAD analysis, and to estimate the influence range of debris flow for fan area according to the scenario. To analyse the characteristics of debris flow at the real basin, the parameters such as the deposition pattern, deposit thickness, approaching velocity, occurrence of sediment volume and travel length are estimated from DAD analysis. As a results, the peak time precipitation is estimated by 135 mm/hr as torrential rainfall and maximum total amount of rainfall is estimated by 544 mm as typhoon related rainfall.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.1
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• pp.77-84
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• 2011

The methods of the rational formula and Kajiyama formula have been widely used for estimating the peak flood for design to all kind of hydraulic structure. However, there are many limitations and we have to apply these methods to ungauged basin. These methods require to calculate the Probable Maximum Precipitation (PMP) before determining the Probable Maximum Flood (PMF). Creager's method (Creager et al., 1945) is a kind of estimation of specipic flood and this method provided nonlinear equations based on relationship between the drainage area and PMF in order to calculate the PMF of multipurpose dams over medium-sized. But this method has not much applied in Korea. Creager's coefficient is not clear about its application because this method has never been applied to dams in Korea. Based on the PMP for rainfull-runoff models with the PMF of small and larger dams in this research, the range and standard of Creager's coefficients with parameters are proposed to apply basin areas in Korea.

• Journal of Korea Water Resources Association
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• v.51 no.4
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• pp.371-381
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• 2018

Domestic agricultural reservoir dam facilities are difficult to manage water resources because of the in summer rainfall increase due to aging and climate change, it is expected that the dam risk will be large due to the overflow. In this study, author selected study basin in order to evaluate hydrological safety of agricultural reservoir dam facilities. And calculated the probable rainfall, Present PMP, Future PMP considering climate change. Also, author carried quantitative analysis out for increasing rainfall due to climate change, analyze freeboard assessment of agricultural reservoir by calculate flood discharge, reservoir flood routing according to rainfall scenarios. As a result of evaluate hydrological safety of agricultural reservoir dam facilities using Future PMP considering climate change, Gosam, Kumkwang, Miho, Cheongcheon reservoir had the Highest Water Level over the design flood level, it is analyzed that it would be vulnerable to overflow risk.

• Current Research on Agriculture and Life Sciences
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• v.5
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• pp.143-157
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• 1987

In order to determine the design precipitation, the most probable daily precipitation and annual precipitation at every spot are calculated and iso - precipitation line are drawn. Probability of precipitation and drought phenomena of each gage station are analyzied by the method of frequency analysis from the statistical conceptions. The results summarized in this study are as the follows. 1. Annual mean precipitation in kyungpook area are 1044 mm, about 115 mm less than annual mean precipitation of Korea amounts to l1S9mm, and found to regionally unequal. 2. Monthly mean rainfall of July is 242.2mm, 23.2%, August 174.2mm, 16.7%, June 115mm, 11% and September 114.2mm, 10.9% and Rainfall depth of July-August are more than 40% of annual precipition. This shows notable summer rainy weather by typoon and low pressure storm and seasonal unbalance of water supply. 3. The relation among the maximum precipi.tation per day, per two continuous days and per three contnous days are caculated and the latter is found 31.0% increased rate of the first and the last 48.2% increased rate of first. 4. Probability precipitation in Kyungpook area are shown as 9.0%(5 year), 13.3%(10 year), 17.7%(20 year), 23.1%(50 year), 27.0%(100 year) and 31.1%(200 year) increased rate of each recurrence year compared with observed average annual precipitation. 5. From annual precipitation and maximum daily rainfall data probability of precipitation and precipitation isohyetal line are derived which shown as Table 11 and Fig. 8. 6. Drought days are divided 6 class and analysed results are shown on table 12. Average occurrence time of 10-14 continuous drought days are 2.3 time per year, 15-19 days are 0.9 time per year, 20-24 days are one per six years, 30-34 days are once per nine years and over than 35days are once per 25 years.

• Current Research on Agriculture and Life Sciences
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• v.16
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• pp.37-44
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• 1998

The estimation of PMP (Probable Maximum Precipitation) and the analysis of characteristics of PMF (Probable Maximum Flood) according to the types of time distribution of rainfall and variations of base flow for the determination of design flood of major hydraulic structures in the watershed area of Wi stream were analysed. The PMP was estimated by the hydro-meteorological method suggested by the guideline of the World Meteorological Organization(WMO). The Blocking method was cited to transpose from PMP to PMS (Probable Maximum Storm) with time distribution. The unit hydrograph, applied for the estimation of PMF was derived by Clark's method. The summaryzed results : (1) The 72 hrs duration PMP in the area is 477.3mm which is 80mm less than the PMP map in Korea and 134 mm lager than the maximum precipitation of 342.9mm in Taegu, near the Wi stream watershed. (2) According to the types of time distribution and variations of base flow, the ranges of PMF for advanced type, central type and delayed type are 3,145.3~3,348.3cms, 3,774.6~3,977.7cms and 3,814.6~4,017.3cms, respectively. Those mean that peak discharge of advanced type is 600cms less than the central type and delayed type. (3) Delayed type among three types by Blocking method has been estimated the largest PMF of 4,017.3cms, and the advanced type has been estimated the smallest PMF of 3,145.3cms. The mean value of the peak PMF of 3,653.6cms may probably be resonable PMF in the Wi stream watershed. The mean PMF could probably be 1.7 times lager than the result of Gajiyama's equation. It is equivalent to the flood of return period 1,000 to 10,000 yrs.