  We model driven two-dimensional charge-density waves in random media via a
modified Swift-Hohenberg equation, which includes both amplitude and phase
fluctuations of the condensate. As the driving force is increased, we find that
the defect density first increases and then decreases. Furthermore, we find
switching phenomena, due to the formation of channels of dislocations. These
results are in qualitative accord with recent dynamical x-ray scattering
experiments by Ringlandet al. and transport experiments by Lemay et al.
