  We present experimental findings on the flow rule for granular flows on a
rough inclined plane using various materials including sand and glass beads of
various sizes and four types of copper particles with different shapes. We
characterize the materials by measuring $h_s$ (the thickness at which the flow
subsides) as a function of the plane inclination $\theta$ on various surfaces.
Measuring the surface velocity $u$ of the flow as a function of flow thickness
$h$, we find that for sand and glass beads the Pouliquen flow rule $u/\sqrt{gh}
\sim \beta h/h_s$ provides reasonable but not perfect collapse of the $u(h)$
curves measured for various $\theta$ and mean particle diameter $d$. Improved
collapse is obtained for sand and glass beads by using a recently proposed
scaling of the form $u/\sqrt{gh} =\beta \cdot h \tan^2\theta /h_s\
\tan^2\theta_1$ where $\theta_1$ is the angle at which the $h_s(\theta)$ curves
diverge. Measuring the slope $\beta$ for ten different sizes of sand and glass
beads, we find a systematic, strong increase of $\beta$ with the divergence
angle $\theta_1$ of $h_s$. The copper materials with different shapes are not
well described by either flow rule with $u \sim h^{3/2}$.
