  Current-voltage measurements of type-II superconductors are described by a
coarse-grained model of superconducting vortex dynamics. We find that the power
spectra of the voltage fluctuations, and the noise power, are related to the
large scale morphology of the plastic flux flow. At currents corresponding to
the peak in differential resistance, the flux flow forms a braided river, the
noise power is maximal, and the power spectra has a 1/f^{\alpha} form with
\alpha \approx 1.8 over a wide frequency range. This agrees with recent
experiments on NbSe_2. The observed variation of \alpha with applied current is
a crossover phenomenon.
