Spatial-temporal characteristics of sediment transport by intermittent surges

Debris flows move as surge waves and they transport volumes of sediment of various magnitudes at irregular time intervals. As exemplified by Jiangjia Gully (JJG; Yunnan Province, China), the sediment transport of such surges can fluctuate by up to four orders of magnitude within a single debris flow event. This study investigated the variation of the sediment transported by a series of surges based on observations of 3000 surges in JJG. It was found that the fluctuation in sediment transport evolved with surge progress and then finally decayed in a power law form with a decay coefficient of 0.1-0.5, which can be considered a representative of the under-lying dynamics. Moreover, the cumulative sediment yield followed a unified sediment size distribution (SSD) that can be expressed as P(S) = CS-beta exp(-S/S-c), with parameters well associated with the material composition of the surges. Moreover, this distribution also applies to transport processes in large-scale rivers, which suggests that the SSD could be used to predict the scale of sediment transport in rivers.