The surface of any large river ought to work fairly well. Nothing much on the surface. If you “land” a meter too high or too low, no biggie.
Rivers don’t stay in the same place over time. There are spots in states east of the Missourissippi River which are on the west side, and vice-versa, due to the river changing course. So you might start off right above the surface, but at your destination time find yourself buried in an alluvial deposit.