  We discuss the problem of breaking of a nonlinear wave in the process of its
propagation into a medium at rest. It is supposed that the profile of the wave
is described at the breaking moment by the function $(-x)^{1/n}$ ($x<0$,
positive pulse) or $-x^{1/n}$ ($x>0$, negative pulse) of the coordinate $x$.
Evolution of the wave is governed by the Korteweg-de Vries equation resulting
in formation of a dispersive shock wave. In the positive pulse case, the
dispersive shock wave forms at the leading edge of the wave structure, and in
the negative pulse case at its rear edge. The dynamics of dispersive shock
waves is described by the Whitham modulation equations. For power law initial
profiles, this dynamics is self-similar and the solution of the Whitham
equations is obtained in a closed form for arbitrary $n>1$.
