OPEN ACCESS
This article studied the debris-flow occurrence and the corresponding extreme rainfall events, as well as a severe earthquake, the Chi–Chi earthquake (CCE), in Chenyulan watershed, Taiwan. By examining the associations between the rainfall index (RI), defined as the product of the maximum 24-h rainfall and maximum hourly rainfall of a rainfall event, the return period (T), and the probability (P) of debris flow after an event, an empirical model of the P–T relationship was developed and this model was applied to evaluate an extreme rainfall event, Typhoon Morakot. Results of this study showed that debris flows could be triggered at lower RI values, corresponding with lower T values, for rainfall events after extreme rainfalls or after the CCE. The extreme events mostly had T values exceeding eight years. The T value for the critical RI affected by the CCE was approximately one year, much smaller than that affected by extreme events. P rose significantly after an extreme rainfall event or the CCE at the same T. The P value affected by CCE was markedly higher than that affected by extreme rainfalls. In addition, field data of debris-flow occurrence and rainfall between 2012 and 2014 were collected to assess the proposed model. The model was successfully applied to evaluate the probability of debris-flow occurrence after extreme rainfalls.
Chenyulan watershed, probability of debris-flow occurrence, rainfall index, return period
[1] Dong, J.J., Lee, C.T., Tung, Y.H., Liu, C.N., Lin, K.P. & Lee, J.F., The role of the sediment budget in understanding debris flow susceptibility. Earth Surface Processes and Landforms, 34, pp. 1612–1624, 2009. DOI: 10.1007/978-94-015-8404-3_6.
[2] Chen, J.C., Huang, W.S., Jan, C.D. & Yang, Y.H., Recent changes in the number of rainfall events related to debris flow occurrence in the Chenyulan Stream Watershed, Taiwan. Natural Hazards and Earth System Science, 12, pp. 1539–1549, 2012. DOI: 10.5194/nhess-12-1539-2012.
[3] Jakob, M., Bovis, M. & Oden, M., The significance of channel recharge rates for estimating debris flow magnitude and frequency. Earth Surface Processes and Landforms, 30, pp. 755–766, 2005. DOI: 10.2113/gseegeosci.I.1.11.
[4] Lin, C.W., Shieh, C.L., Yuan, B.D., Shieh, Y.C., Liu, S.H. & Lee, S.Y., Impact of Chi–Chi earthquake on the occurrence of landslides and debris flows: Example from the Chenyulan River watershed, Nantou, Taiwan. Engineering Geology, 71, pp. 49–61, 2003. DOI: 10.1016/S0013-7952(03)00125-X.
[5] Liu, C.N., Huang, H.F. & Dong, J.J., Impacts of September 21, 1999 Chi–Chi earthquake on the characteristics of gully-type debris flows in central Taiwan. Nature Hazards, 47, pp. 349–368, 2008. DOI: 10.1007/s11069-008-9223-9.
[6] Chen, J.C., Variability of impact of earthquake on debris flow triggering conditions: Case study of Chen-Yu-Lan Watershed, Taiwan. Environmental Earth Sciences, 64(7), pp. 1787–1794, 2011. DOI: 10.1130/REG7-p93.
[7] Zhang, A.B. & Zhang, L.M., Impact of the 2008 Wenchuan earthquake in China on subsequent long-term debris flow activities in the epicentral area. Geomorphology, 276, pp. 86–103, 2017. DOI: 10.1016/j.geomorph.2016.10.009.
[8] Chen, J.C., Jan, C.D. & Huang, W.S., Characteristics of rainfall triggering of debris flows in the Chenyulan Watershed, Taiwan. Natural Hazards and Earth System Science,13, pp. 1015–1023, 2013. DOI: 10.5194/nhess-13-1015-2013.
[9] Shin, T.C. & Teng, T.L., An overview of the 1999 Chi–Chi, Taiwan earthquake. Bulletin of the Seismological Society of America, 91, pp. 895–913, 2001. DOI: 10.1785/0120000738.
[10] Chen, J.C., Study on the criteria of debris flow occurrence after extreme rainfalls. Report of Minister of Science and Technology, Taiwan (No. MOST 104-2625-M-211-001), 2016 (in Chinese).
[11] Chen, J.C., Huang, W.S., Jan, C.D. & Tsai, Y.F., Rainfall conditions for the initiation of debris flows during Typhoon Morakot in the Chen-Yu-Lan watershed in central Taiwan. Proceedings of the 5th International Conference on Debris flow Hazards Mitigation, Padua, Italy, eds. R. Genevois, D.L. Hamilton & A. Prestininzi, pp. 31–36, 2011.
[12] Makkonen, L., Plotting positions in extreme value analysis, Journal of Applied Meteorology and Climatology, 45, pp. 334–340, 2006. DOI: 10.1175/JAM2349.1.
[13] Hosmer, D.W. & Lemeshow, S., Applied Logistic Regression, 2nd ed., Wiley Series in Probability and Statistics, New York, 2000.