My neighbor is having a pool put in water is going in today. The pool has a cascading end (Vanishing end heard a lot of names for it) Just great if your on a hill and have a view, witch he dose. The water rolls over the edge and droops about 3 feet, into a trough . Now what I'm curious about the trough is about 4 feet deep 16 inches wide. The pool contractor says it has to be the same dept as the deepest point of the pool ( total is about 7 feet) I can't figure out why, It had to just a pain in the ass to plaster the trough, it can't balance ( level) the water out, there are pump inlets in the bottom. Any ideas of why the trough has to match the pool dept?