  In this note, we announce a complete classification of stability of periodic
roll-wave solutions of the viscous shallow-water equations, from their onset at
Froude number $F\approx 2$ up to the infinite-Froude limit. For intermediate
Froude numbers, we obtain numerically a particularly simple power-law relation
between $F$ and the boundaries of the region of stable periods, that appears
potentially useful in hydraulic engineering applications. In the asymptotic
regime $F\to 2$ (onset), we provide an analytic expression of the stability
boundaries whereas in the limit $F\to\infty$, we show that roll-waves are
always unstable.
