  We have studied numerically the dynamics of sliding charge-density waves
(CDWs) in the presence of impurities in d=1,2. The model considered exhibits a
first order dynamical transition at a critical driving force $F_c$ between
``rough'' (disorder dominated) $(F<F_c)$ and ``flat'' $(F>F_c)$ sliding phases
where disorder is washed out by the external drive. The effective model for the
sliding CDWs in the presence of impurities can be mapped onto that of a
magnetic flux line pinned by columnar defects and tilted by an applied field.
The dynamical transition of sliding CDWs corresponds to the transverse Meissner
effect of the tilted flux line.
