Applying Logistic Regression Method to Analyze the Effect of Landslide on Rainfall Threshold Value for Debris Flow Warning –Using the Site of Shenmu, Nantou as An Example
Date Issued
2011
Date
2011
Author(s)
Chang, Lun-Hsien
Abstract
The main purpose of this study is to investigate the effects of landslides and other physiographic factors on the rainfall threshold value for debris flow warning and then to evaluate it. In Taiwan, the rainfall threshold value for debris flow warning has been used for years as a basis to announce debris flow warning and it is amended annually or after the event of great mass movement disasters.
The site of this study was selected at Shen-mu, Nan-tou. The debris flow events occurred in the site were collected and the method of logistic regression was used for analysis. Statistical analysis was made on the physiographic factors which were mostly commonly used in the previous studies to investigate the occurrence of debris flow. In this study, average riverbed slope steepness, landslide area and effective watershed area were used to estimate the rainfall threshold value for debris flow warning. From the results, it was found that when the ratio of the data in proportion to the occurrence of debris flow and non occurrence of debris flow was 1 to 1,the sensitivity was higher and up to 87%. This indicated that when the debris flow events of occurrence and non occurrence were similar, there would be a better prediction.
In addition, the equation for evaluating rainfall threshold value for debris flow using the logistic regression analysis was obtained. The parameters used for evaluation were average riverbed slope steepness, landslide area, effective watershed area and effective cumulative rainfall. The event occurred during Herb typhoon was used as an example for validation. If the physiographic factors are similar to that during Herb typhoon, debris flow may occur while the effective cumulative rainfall reach 713.5mm .
Subjects
rainfall threshold value for debris flow warning
logistic regression
landslide
debris flow
Type
thesis
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