Actually, to the left of this picture, there is infact a waterfall with quite a large pool attached to it at the bottom. (I'll attach a picture of it when I'm on the computer tonight).
Also, the entire outdoor exhibit is surrounded by a water barrier, which the elephants have access to, and is deeper than the actual height of an adult elephant
that reminds me of one of the threads on here (can't remember which one) in which there was a discussion of how zoo exhibit designers put waterfalls everywhere, however irrelevant and unnatural they may appear
