I generated two fresh survival world's in a row, both with the experimental "Caves and Cliffs" toggle enabled, and both times it spawned me in a shallow riverbed where I lost half of my health before even loading in. For obvious reasons, this is an issue.

Steps to replicate: 1) go to Create New world

2) enable "Caves and Cliffs experimental toggle

3) Create the world

4) Die

This might not have guaranteed results but it happened twice in a row for me so it's not too uncommon.