Abstract
The basic geometric parameters of 236 debris flow catchments were determined by interpreting SPOT5 remote sensing images with a resolution of 2.5 m in a 209 km section along the Jinsha River in the Panxi area, China. A total of 27 large-scale debris flow catchments were selected for detailed in situ investigation. Samples were taken from two profiles in the deposition zone for each debris flow catchment. The φ value gradation method of the grain size was used to obtain 54 histograms with abscissa in a logarithmic scale. Five types of debris flows were summarized from the outline of the histogram. Four grain size parameters were calculated: mean grain size, standard deviation, coefficient of skewness, and coefficient of kurtosis. These four values were used to evaluate the features of the histogram. The grain index that reflects the transport (kinetic) energy information of debris flows was defined to describe the characteristics of the debris-flow materials. Furthermore, a normalized grain index based on the catchment area was proposed to allow evaluation of the debris flow mobility. The characteristics of the debris-flow materials were well-described by the histogram of grain-size distribution and the normalized grain index.
Highlights
The Wenchuan Earthquake triggered more than 15,000 landslides and rock collapses [1]
The 236 debris flow catchments can be detected by interpreting the SPOT5 remote sensing images in the study region along the Jinsha River [24,25].Only large-scale debris flows affect the stability of the dam site
The catchment areas for the 27 debris flow catchments investigated in the study region vary widely from around 1 to 621 km2 (Table 6).To identify the differences in the characteristics of the debris flow materials, the 27 debris flows were divided into four categories based on the size of catchment area as described
Summary
The Wenchuan Earthquake triggered more than 15,000 landslides and rock collapses [1]. Damage caused by debris flows occurs during the transportation of material and in deposition zones. The size of the largest transported boulders provided by deposits (such as screes) in the basin can be used to estimate the kinetic energy of debris flows. The grain-size distribution can reflect the characteristics of the debris flow transport, including the transport energy. Wang [22] and Zhang et al [23] indicated that the kinetic energy and the head height of a debris flow surge increased with an increase of transported materials. Current research places emphasis on the grain-size distribution of debris-flow materials. This study proposed two parameters, which are based on the grain size distribution and the catchment area, to quantitatively describe these types of debris flows
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