Dam breaks of viscoplastic material on an inclined plane.

We report experimental results related to the dam-break problem for viscoplastic fluids. Using image processing techniques, we were able to accurately reconstruct the free-surface evolution of fixed volumes of fluid suddenly released on an inclined plane. Carbopol Ultrez 10 was used as a viscoplastic material. Varying the Carbopol concentration allowed us to change the yield stress and bulk viscosity. We investigated the behaviour of a 43-kg mass released on a plane, whose inclination ranged from 0◦ to 18◦. For each run, we observed that the behaviour was nearly the same: at short times, the mass accelerated vigorously on gate opening and very quickly reached a nearly constant velocity. At time t = 1 s, independently of plane inclination and yield stress, the mass reached a nearequilibrium regime, where the front position varied as a power function of time over several decades.