Zhang, Jun, Li, Yong, Guo, Xiaojun, Song, Dongri, Turowski, Jens M.
Abstract. Debris flows often occur as intermittent surges in succession; a single event may comprise tens to hundreds of separate surges. While previous studies have focused primarily on isolated surge dynamics, the temporal evolution and statistical properties of the surge sequences as an entirety remain poorly understood. Here, we present a comprehensive analysis of global debris flow datasets, including velocity, discharge, sediment volume, and inter-surge intervals. We quantitatively characterize the surge sequences by the statistic features of the key parameters, revealing 1) a general decay trend in fluctuating discharge, 2) universal distributions for flow velocity (Weibull), discharge/sediment volume (exponentially-modified power-law), and inter-surge intervals (exponential), and 3) self-similar structure in sequence organization. These findings motivate the development of a novel stochastic modeling framework that conceptualizes surge sequences through three key components: 1) The cascading thinning of mass sequences originating from Poisson processes of source failures and inter-processes of bank and bed erosions driven by hydrologic process, 2) a selection coefficient generated through Gaussian process to integrate the effective contributions of mass from multi-sources, 3) model parameter calibration using local monitoring data and experimental validation. Numerical simulations demonstrate the model's ability to accurately replicate observed surge sequences. Notably, the framework spontaneously generates a unified distribution of discharge and sediment volume in the form of a truncated power-law with an exponential cutoff. This provides a novel magnitude–frequency relationship for mass movements and can also be applied to large-scale sediment transport studies.