Flow behavior of head of stony debris flow on unsaturated erodible bed

The dynamic behavior of the head of stony debris flow on unsaturated erodible bed was studied by laboratory experiments and particle image analysis. During the laboratory experiments, the debris flow was generated by supplying water into uniform gravel material, and the head was photographed by a CCD video camera which was moved at the translation velocity of the head. During the image analysis, the instantaneous velocity fields inside the head were estimated by a correlation method. The temporal fluctuations of the head height and front velocity and the instantaneous velocity profiles of the particles inside the head were studied. It was found that the deceleration and acceleration of the head during the steadily fluctuating period was closely correlated with the accumulation of particles caused by resistance owing to the internal friction and sliding friction against the bed, and the sliding down of accumulated particles caused by the shear failure.