If you take water from underneath your ice, is your ice is going to lower. Is it actually 'floating' on the water or is it frozen to the sides of your rink? Will this rip your tarp? Stretch your tarp? If the ice is frozen to the sides of the rink and not floating, then removing water from below will cause the airpockets.
If you have 17" of water in one section, then your yard isn't completely level. If you remove enough water, ice in low areas will continue to drop while ice in high areas could possibly end up sitting on the ground, if your ice stays in one piece it's going to start sloping at some point.
This is all theory as I'm just speculating scenarios to think about. Again, it's not something I would ever do. I have 5" of water on my thin side and 14" in my deep end, I just let it freeze as is. My rink is 32' x 71' and I run everything off my house spigot - although I have more leeway on the vertical plane than you do. You need higher boards. :-)
If you try it, I'm sure others out there would appreciate hearing about the experience.
Making Backyard Rinks from 1999-2015
Twitter: @kevmac_5 or @macisaac_odr
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