Anti-backflow Needed?

Hello...need helo please and so far this site has been AWESOME!! We are building a 25k gallon pool. It will have 2 - 36" sheer decent that will be about 24" above pool and the a large 7' ft. Wide sheer rain waterfall on top of a pergola that is about 8-9' ft tall.
So question is....do I need Anti-backflows behind each of the sheer decents or is that not needed at all?

Thank you!