  We report an experimental study of a binary sand bed under an oscillating
water flow. The formation and evolution of ripples is observed. The appearance
of a granular segregation is shown to strongly depend on the sand bed
preparation. The initial wavelength of the mixture is measured. In the final
steady state, a segregation in volume is observed instead of a segregation at
the surface as reported before. The correlation between this phenomenon and the
fluid flow is emphasised. Finally, different ``exotic'' patterns and their
geophysical implications are presented.
