Kegs02

You can use a syringe / needle to dye the rivers with, or find and old rapidograph pen, fill with dye to "draw" in the rivers. The pen may work better than the syringe, as you can use it more writing instrument style. You could also find colored epoxies, once in place and in a semi-hard state, cut surface flush with wood background with a very sharp chisel. Try this out on scrap first :-)

Vellum