  We introduce and investigate a simple model to describe recent experiments by
Douady and Daerr on flowing sand. The model reproduces experimentally observed
compact avalanches, whose opening angle decreases linearly as a threshold is
approached. On large scales the model exhibits a crossover from compact
directed percolation to directed percolation; we predict similar behavior for
the experimental system. We estimate the regime where "true" directed
percolation morphology and exponents will be observed, providing the first
experimental realization for this class of models.
