Very rarely will you NEED a snorkel here. I know that the Dugas road run takes you across the Verde river and although it's not neccissarily needed for that crossing, you can't ever be positive of that rivers depth. It's always changing. Christopher creek, oak creek (down range from Sedona), some of the local rivers an tributarys during the monsoon floods will require a snorkel...of course if your planning on crossing a flood you're an idiot; snorkel or not.
Around here a snorkel is nothing more than an extra piece of mind. You almost never run into water, but when you do, you'll wish you had a snorkel. Lol
Everyone IS out to get you, if you just believe in yourself and try hard enough!