[dcsobral]

The topography of the rivers is lacking the "erosion" effect. For example, here's an image I took from a topographical map of Kauai, one of Hawaii islands:



It's hard to see the river in this image, but it goes from bottom left to top right. You can see the "U" shape of the topological lines around it. The elevation drops rapidly on the river path, until it gets to a valley. That river above joins the river in the central valley here:



So the river on the right looks reasonable, but I'd extend the contour line on the top to make it more U-shaped. To "explain" why it didn't just continue downhill to the North.

The left one looks weird to me. It feels right in some spots but in others the elevation line is too flat where the river crosses it.

I might also add one or two elevation lines on each side of the river once they reach the "plains", to make it more valley-like and explain why they go south instead of north.