What to do with groundwater that comes up when digging for pond

[addy1]

This pond is specifically for my lotus and they need at least 30 in deep underground water for it not to freeze

My lotus are in a 2.5 feet deep stock tank, about 6-8 inches below water level in kitty litter. The lotus are growing in about 2 feet of litter. The tank is 1/2 in ground 1/2 out, that 1/2 is diagonal not height. The 1/2 is due to the slope of our yard, up slope is in ground, down slope is out of ground. Those lotus have survived some hard winters where the ice went down to the top of the litter and mild winters.

So in your zone 7b you don't need them that deep. Is the long and short of what I am typing

 

[Heruga]

I’m in zone 7a if that makes a difference. What should the maximum depth be then? So far I dug a total of about 22-24 inches and I bought some all purpose sand to spread on the surface on the hole so that’ll probably add like 1 or 2 inches on it and the total depth would be like 20-22 inches in total. Would that be enough?
Also what if my lotus were in a pot? Would that make a difference to their hardiness?

 

[addy1]

Mine were in pots before I dumped them into the stock tank to run free, those pots were about 1.5 feet deep but they were in the stock tank which over all were 2.5 feet deep. They like to jump the pot.

I have no clue how deep the tubers live but they are doing great in the stock tank.

Do you ever get a good ice layer? We have off and on, one time it froze down to the litter and the lotus still survived. Most of the time not much more than 6 inches only if we have a cold winter.

IMHO what you have should be fine.

" Set the container in the pond so that the top of the soil is two to four inches under water. Taller varieties of lotus can grow in water up to 18 inches or deeper, while dwarf varieties do best in water two to 12 inches deep. In winter, lotuses can be left in the pond so long as the tubers are protected from ice. "