To extend the Powell analogy: He ran in a wooden boat and they ran with their backs to the rapids. You run in rubber/plastic boats with fiberglass oars/paddles and very effective PFDs, etc. It is hypocritical to berate someone's desire to use a GPS based on your arguments. True, it's both unfortunate and wonderful that we have tools that can reduce a great deal of guess work in our navigation. But, if you run a named rapid and know it's on the river well then, sorry, you're not only running it second, you're running it last (at least until the next boater comes along
) and no amount of river enthusiasm will change the fact that the water way you're on has been mapped, measured, and plotted, visible on google maps, and talked about ad nauseam. And no amount gps beeping will enable a boater to successfully get a boat out of a sticky hole.
There is a point to be made on failing tech though, and one tool is not something to rely on fully. Don't get out on a river only to find your gps has failed then blame the tech for your inability to complete the trip.
Oh.. and any garmin will do the trick. Water proof is better and some have better mapping.. but based on your requirements, any will do what you want it to do.