In Wilbur, try Texture>>Shader Setup:Intensity page and set Azimuth to 135. It should have the same lighting as on your rivers. Human are preconditioned to see lights from above (that's where the sun is in most cases); putting the light from below will frequently result in the illusion of depth inversion. It's why the "traditional" lighting direction on maps is from the upper left (well, upper from lighting and shadows on the right because the right-handed scribe won't smudge the existing work by going from left to right).