  Titan's surface was revealed by Cassini's instruments, showing the presence
of liquid hydrocarbons in lakes, and features like dry riverbed. In order to
study the sediment transport in Titan's channels and to map distribution of the
water-ice signature in these terrains, we use a radiative transfer model to
retrieve the surface albedo, after we estimated VIMS error via an original
method. We also establish a criteria related to the intensity of the water ice
signature. The tuning of the radiative transfer model shows that the fractal
dimension of Titan's aerosols is higher than previously thought, around 2.3 -
2.4. We find spots of increasing signal of water ice downstream, at the margins
of Tui Regio, that could correspond to alluvial fans, deltas or crater rims. We
also observe a very low water ice signal on Tui Regio, with a positive gradient
between the central region and the boundary of the area, possibly due to the
thickness variation of an evaporitic layer. The riverbeds show within the error
bars a decreasing grain size from the top to the bottom of the channels.
