Abstract:

The runoff yield and slope failures are the source of debris flows in watersheds. The previous study focuses on the deterministic mechanism formation of slope failures for debris flow initiation and hydrological processes for debris flow runoff calculation. This paper aims to reveal and discuss the randomness process of slope failures. Artificial rainfall experiment was conducted on selected typical debris flow source region to observe the movement features of slope runoff and soil body. Results showed that slope failure and runoff formation are two separated processes. Runoff generation was continuous, evenly and stably distributed on slope. Slope failure presented a sequence of soil body collapse with the features of intermittence in time, aggregation in space, and remarkable fluctuation in magnitude. Slope failures time interval fit the Poisson distribution and its magnitude fit the powerlaw. The soil and water supplies were unsynchronized, the debris flow initiation depend not only on the flood generation, but also on the spatiotemporal characteristics of the slope failure processes, which leads to high variety and fluctuation of debris flows even under the same rainfall condition. This study contributes the debris flow formation and runoff calculation by taking debris flow formation as a randomness and discontinuous process and revealing the spatial characteristics of slope failures.

Key words: debris flow source region, soil collapses, runoff yield, debris flow surges