Velocity of Debris Flow Determined by Grain Composition

Velocity is one of the most important parameters of debris flows, and it is usually calculated using Manning formula in hydraulics, mostly ignoring the granular effects due to flow materials. This study proposes a method in term of grain composition of debris flow, incorporating the physical effects of grain on roughness. It is found that the Manning resistance coefficient can be well related to the grain size distribution (GSD) and thus the method is expected to have a wide application. A new formula incorporating the influence of granular effects is built based on observation data of debris flows in Jiangjia Gully (JJG), China, and then it is tested by data from debris flows in other regions.