When closing the pool for the season, how far can you drain a fiberglass pool?

[Mark McLeroy]

When closing the pool for the season, how far can I drain my fiberglass pool? From what I understand there are 2 things to be concerned about when lowering the water of a fiberglass pool.
1) The pool floating out of the ground from high ground water and,
2) The walls bowing in of twisting from the lack of counter pressure the gravel backfill exerts on the pool.
My PB did install an 8" pipe next to the deep end of the pool to inspect the ground water, and if necessary, drop a pump down it; so that address the 1st concern. Burt what about the backfill pressure? Bottom line is you have to drain down some water at closing. Last year I drained just blow the bottom of my skimmer but with a rainy winter and early spring, the water was overflowing the pool when I removed the cover.
I would love to hear some opinions on this. Thanks.

 

[Texas Splash]

EDIT: I wanted to come back and clarify a few things I said initially. You may find different guidance in FG pool manuals that say anything from never drain water, to some that state it's safe to lower the water level down a few inches. While there are cases where it is safe to lower to just below the return jets, that is primarily reserved for repairs on the return jets and not so much for long-term winterization.

In general, we try to remove the least amount of water needed for the situation. Each pool scenario is different when it comes to closing for winter. How far you "really" need to lower the water depends on the type cover, amount of seasonal snow/rainfall, if you have a waterline tile, condition of your grout line between the decking and shell, etc. Any potential water table pressure from below and soil pressure against the sides of the shell are always a concern. For some FG pool owners, they will do like you did previously and only lower the water about an inch or so below the skimmer because they know it's safe and they need the water's support for the (solid) cover. They'll blow out the lines and plug the submerged jets. Some owners take the water level down further to about 6 inches for the reasons noted above (i.e. mesh cover, rainfall, etc).

The general rule, only lower what is absolutely needed. Since you experienced enough rainfall last winter to overflow, periodic draining with a small sump pump may be an option as long as the water surface hasn't frozen solid. I believe @Newdude may have some info from your local area to validate.

I hope that helps.