Critical rainfall thresholds for debris flows in Sanyanyu, Zhouqu County, Gansu Province, China

Abstract

Critical rainfall thresholds can be the key to ensuring effective debris-flow forecasting. They are significant for the study of the trigger mechanisms of debris flows, for the forecast of the characteristics of future events, and for the development of engineering guidance for mitigation. Using a hydrological approach, we first calculated the flood peak discharge at different frequencies and then the corresponding rainfall thresholds for the initiation of different scales of debris flows in Zhouqu County, China. This was followed by the establishment of a functional relation between the intensity and duration of rainfall events that trigger debris flows of different warning levels in two initial soil conditions (dry and moist). This, in turn, yielded four warning levels and two preliminary warning levels. For the two early soil conditions (dry and moist) in the Sanyanyu Gully of Zhouqu County, the Level I (red) warning values for rainfall triggering debris flow are 56 and 51 mm h −1 , respectively; the Level II (orange) warning values are 41 and 38 mm h −1 , respectively; the Level III (yellow) warning values are 32 and 30 mm h −1 , respectively; and the Level IV (blue) warning values are 24 and 22 mm h −1 , respectively. The Level V preliminary warning values are 17 and 16 mm h −1 , respectively; and the Level VI preliminary warning values are 10 and 9.5 mm h −1 , respectively. The rainfall intensity and duration were found to exhibit a power function relation, I = αD β , where the values of α and β vary with the warning levels. Rainfall events capable of triggering debris flows in the new thresholds and intensity–duration relations presented here can be used for forecasting purposes and in operational geohazard warning systems. These research results also provide a scientific basis for regional hazard mitigation and reduction in Zhouqu County.

Investigating slow-moving landslides in the Zhouqu region of China using InSAR time series

“…The topography is characterized by rugged mountains and deeply incised valleys with elevations ranging from 1200 m to more than 4000 m a.s.l. which has a strong influence on local climate: high relative relief causes rainfall to concentrate in the high-altitude areas, with much less precipitation in the valleys, resulting in the so-called dry and hot valleys system in this region as defined in Yu et al (2015).…”

Comparison of satellite-estimated and model-forecasted rainfall data during a deadly debris-flow event in Zhouqu, Northwest China

“…Several countermeasures against this type of event happening again in the future have been presented on the basis of its factors of influence, characteristics, and trends (Hu et al 2010;Yan et al 2010;Liu et al 2011). However, under the same conditions, the likelihood of fatal flows occurring when it rains heavily remains high (Yu et al 2010).…”

Risk assessment of debris flow in Yushu seismic area in China: a perspective for the reconstruction

“…They posed high risk to human lives. Since 12 May 2008, large numbers of debris flow events have occurred in the Wenchuan seismic area and have caused thousands of deaths (Xie et al, 2009;Tang and Tie, 2009;Cui et al, 2010;Xu, 2010;Yu et al, 2010). The debris flow event that took place on 7 August 2010 in Zhouqu led to more than one thousand people losing their lives (Yu et al, 2010).…”

“…Since 12 May 2008, large numbers of debris flow events have occurred in the Wenchuan seismic area and have caused thousands of deaths (Xie et al, 2009;Tang and Tie, 2009;Cui et al, 2010;Xu, 2010;Yu et al, 2010). The debris flow event that took place on 7 August 2010 in Zhouqu led to more than one thousand people losing their lives (Yu et al, 2010). Studies on the Chi-Chi seismic area have shown that the threshold of accumulated rainfall for triggering debris flow would drop significantly after a large earthquake (Chen, 2008;Liu et al, 2008).…”