• Journal of Environmental Science International
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• v.23 no.4
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• pp.553-560
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• 2014

The rainfall-runoff characteristics in Jeju Island significantly differ from those in inland, due to highly permeable geologic features driven by volcanic island. Streams are usually sustained in the dry conditions and thereby the rainfall-runoff characteristics changes in terms of initiating stream discharge and its types, depending highly on the antecedent precipitation. Among various the rainfall-runoff characteristics, lag time mainly used for flood warning system in river and direct runoff ratio for determining water budget to estimate groundwater recharge quantity are practically crucial. They are expected to vary accordingly with the given antecedent precipitation. This study assessed the lag time in the measured hydrograph and direct runoff ratio, which are especially in the upstream watershed having the outlet as $2^{nd}$ Dongsan bridge of Han stream, Jeju, based upon several typhoon events such as Khanun, Bolaven, Tembin, Sanba as well as a specific heavy rainfall event in August 23, 2012. As results, considering that the lag time changed a bit over the rainfall events, the averaged lag time without antecedent precipitation was around 1.5 hour, but it became increased with antecedent precipitation. Though the direct run-off ratio showed similar percentages (i.e., 23%)without antecedent precipitation, it was substantially increased up to around 45% when antecedent precipitation existed. In addition, the direct run-off ration without antecedent precipitation was also very high (43.8%), especially when there was extremely heavy rainfall event in the more than five hundreds return period such as typhoon Sanba.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1073-1082
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• 2015

The behavior of the unsaturated soil slope can be influenced by the various factors such as the hydraulic characteristics, the mechanical characteristics, the coefficient of conductivity, the stratifications, the rainfall conditions i.e. the rainfall intensity, the rainfall pattern, the duration time of the rainfall and the antecedent rainfall etc. It is known that the slope failure is influenced greatly by the antecedent rainfall rather than the rainfall condition at the failure time, so the antecedent rainfall is supposed to be a very important factor in slope stability analysis among these factors. To predict and to prevent the slope failure by the rainfall, the distribution of the matric suction by the antecedent rainfall must be considered first of all and the slope stability analysis should be carried out by considering the successive rainfall characteristics. In this research, 3 samples with different quantity (5%, 10%, 20%) of silts were prepared and the SWCC (Soil-water characteristic curve) tests were carried out and the associated parameters were analyzed. After analyzing the distribution of the matric suction and the change of the mechanical characteristics such as the stress and the strength when applying the antecedent rainfall for one month and the successive intensive rainfall for 12 hours, the slope stability analyses were carried out numerically. And the influence of the antecedent rainfall for one month and the SWCC on the stability of a slope were compared and analyzed.

• Journal of Wetlands Research
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• v.7 no.3
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• pp.41-48
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• 2005

Generally the estimation of effective rainfall is important in the rainfall-runoff analysis. So, we must pay attention to selecting more accurate effective rainfall estimation method. Although there are many effective rainfall estimation methods, the NRCS method is widely used for the estimation of effective rainfall in the ungaged basin. However, the NRCS method was developed based on the characteristics of the river basin in USA. So, it may have problems to use the NRSC method in Korea without its verification. In the NRCS method, the antecedent precipitation of 5-day is usually used for the estimation of effective rainfall. The main purpose of this study is to investigate the suitable antecedent precipitation day in Korea river basin through the case study. This study performs the rainfall-runoff simulation for the Tanbu river basin by HEC-HMS model under the condition of varying the antecedent precipitation day from 1-day to 7-day and performs goodness of fit test by Monte Carlo simulation method. The antecedent precipitation of 2-day shows the most preferable result in the analysis. This result indicates that the NRCS method should be applied with caution according to the characteristics of the river basin.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.09a
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• pp.822-823
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• 2005

• Journal of Environmental Science International
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• v.27 no.10
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• pp.845-851
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• 2018

In this study, the runoff characteristics of the non-rainfall period were examined using daily rainfall data from 1977 to 2017 and the data of runoff into the dam. Results showed that, the mean runoff decreases with longer non-rainfall periods in the Andong dam basin. The correlation coefficient between non-rainfall days and average runoff reaches 0.85. The results of the analysis of the runoff characteristics during the non-rainfall period, based on the preceding rainfall of Andong dam are as follows. The runoff characteristics of the entire non-rainfall period, shows that, for a rainfall of 1.0 mm or less, the runoff height was larger than the rainfall size and the base runoff larger. The correlation between the antecedent rainfall and runoff height was reached as high as 0.9864 in the 30 ~ 50 mm interval of the antecedent rainfall period, and this is the interval where the linearity of rainfall and runoff was at its maximum in the Andong dam basin. The correlation between the antecedent rainfall and the runoff height reached 0.92 for rainfalls of 100.0 mm. However, for rainfalls of 100.0 mm greater, the correlation between the antecedent rainfall and runoff height during the rainfall period was 0.64, which is relatively small. In this study, we investigated the runoff characteristics of the rainfall period in the Andong dam watershed. As a result, it was confirmed that the mean runoff decreased with rainfall duration. The linearity was found to be weak for rainfall events greater than 100.0 mm. The results of this study can be used as data for water balance analysis and for formulating a water supply plan to establish water resource management of Andong dam.

• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.11-24
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• 2013

This study presents a design method for typical rainfall-induced landslide considering in-situ matric suction. Actual landslide data are used to validate the proposed method. The soil-water characteristic curve (SWCC) and unsaturated permeability are experimentally determined to estimate hydraulic properties of testing site. The field measurement of matric suction is carried out to monitor in-situ matric suction in a natural slope subjected to rainfall infiltration, which is incorporated in the landslide analysis. The wetting band depth and safety factor of the slope are assessed to clarify the effect of domestic rainfall pattern. Especially, the effect of antecedent rainfall on the slope stability is investigated and discussed in terms of wetting band depth using parametric study. It is found from the result of this study that proposed design method can consider the characteristic of unsaturated soil and effect of antecedent rainfall. The location of the scarp zone is fairly well predicted by proposed design method. Moreover, heavy rainfall, concentrated in the backward part with time, causes the lowest safety factor of the slope. These results demonstrate that decrease in matric suction due to antecedent rainfall may trigger slope instability. After the antecedent rainfall, additional rainfall may cause the slope failure due to increasing wetting band depth.

• Journal of the Korean Geotechnical Society
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• v.32 no.4
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• pp.15-27
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• 2016

This study was conducted to suggest a landslide triggering rainfall threshold (ID curve) for landslide prediction by considering the effect of antecedent rainfall. 202 rainfall data including domestic landslide and rainfall records were used in this study. In order to consider the effect of antecedent rainfall, rainfall data were analyzed by changing Inter Event Time Definition (IETD) and IETD based ID curve were presented by regression analysis. Compared to the findings of the previous studies, the presented ID curve has a tendency to predict the landslides occurring at a relatively low rainfall intensity. It is shown that the proposed ID curve is appropriate and realistic for predicting landslides through the validation of proposed ID curve using records of landslides in 2014. Based on this analysis, it is found that the longer IETD, the greater the effect of antecedent rainfall, and the steeper the gradient of ID curve. It is also found that the rainfall threshold (intensity) is higher for the short period rainfall and lower for the long period rainfall.

• Journal of the Korean Geotechnical Society
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• v.31 no.8
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• pp.5-15
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• 2015

One-dimensional rainfall laboratory tests using gneissic weathered soil were conducted to investigate effect of antecedent rainfall on infiltration characteristics. Experimental results using samples from Chuncheon and Chungju sites showed that rainfall onto the ground surface decreased initial negative pore water pressure of unsaturated soils, which recovered gradually after the end of rainfall. Rainfall intensity increases water infiltration rate, and infiltration rate during main rainfall is faster than that of the preceding rainfall. It is considered that higher water saturation after antecedent rainfall increases water infiltration rate during main rainfall. In particular, Chungju sample with higher clay content had slower recovery of negative pore water pressure and infiltration rate. Numerical results using finite element slope stability analysis showed that reduction of initial negative pore pressure due to rainfall infiltration deteriorates slope stability, and diffusion of pore water pressure after the end of rainfall further reduces FS of the slope in the short term. Main rainfall after prior rainfall further reduced factor of safety of the unsaturated slope. Pattern of antecedent rainfall has a significant impact on the magnitude and distribution of initial pore water pressure in unsaturated soils which are controlling factor to assess factor of safety of unsaturated slope during rainfall.

• Proceedings of the Korea Water Resources Association Conference
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• 2005.05b
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• pp.578-582
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• 2005

In this study, the conceptual foundation and development process of the Antecedent soil Moisture Condition(AMC) in SCS runoff curve number method are reviewed. Although the runoff volume is very sensitive with AMC condition, the AMC class limits developed in SCS(1972) are used in rainfall-runoff analysis without careful consideration. Tn this study, following the SCS curve number development process, rainfall-runoff characteristics of the Jang-Pyung subbasin subject to the Pyung-Chang River basin are analyzed to evaluate the reasonability of the AMC class limits at present. The New AMC class limits are proposed by the sensitive analysis of the antecedent rainfall - curve number value. As a result, the classification value of AMC-I with II is 22mm of antecedent 5-day rainfall amount, and the classification of AMC-II with III is 117mm in growing season. When the New AMC class limits are applied to Jang-Pyung subbasin, AMC probability distribution shows that the AMC-II has increased remarkably even though the AMC-I has a little higher value. But the AMC-III has the smallest one. According to the conceptual basis of the curve number method, the AMC probability distribution, the New AMC class limits adopted, gives reasonable results.

• Journal of Korea Water Resources Association
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• v.38 no.11
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• pp.963-972
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• 2005

This study searched the criterion of AMC with respect to the rainfall amount for the periods of antecedent 5 to 2 days. This criterion was decided as the rainfall amount with which the frequency of the observed CN(I) and CN(III) events being categorized as the true CN(I) and CW(III) become highest. Among four cases considered, the cases with antecedent 4 and 5 days provided a reasonable results, but the others not due to limited rainfall events available. For both cases with antecedent 4 and 5 days, the frequency of AMC-II increases, but that of AMC-III decreases significantly to become a more reasonable distribution. Among the cases with antecedent 4 and S days, the latter seems to be better as the occurrence of AMC-II and the relative frequency of CN(I) are higher. If adopting the rainfall amount of antecedent 5 days for the AMC, the criteria for AMC-I and AMC-III for the Jangpyung subbasin becomes 22 mm and 117 mm, respectively.