Ground water prohibiting laying pool liner

[Peter Kirby]

After digging out the pool ground water has appeared. If I remove this water, lay the liner and fill with water. What will happen to the ground water and what effect will it have on the pool? Pool size 3x4 met depth 80cm ground water 50cm deep.

 

[Meyer Jordan]

The pressure exerted by the ground water can overcome any pressure exerted by the water in the pond resulting in the liner bulging up at the bottom of the pond. Do you live in a flood plain or near a natural wetlands?
My advice would be to rethink the construction of the pond and have it partially above ground. This would avoid any potential problems with ground water.

 

[Jimmy Gibson]

The pressure exerted by the ground water can overcome any pressure exerted by the water in the pond resulting in the liner bulging up at the bottom of the pond. Do you live in a flood plain or near a natural wetlands?
My advice would be to rethink the construction of the pond and have it partially above ground. This would avoid any potential problems with ground water.

Twenty five years ago when we put our pool in the they dug the hole and did the plumbing for the bottom drain the next morning there was four feet of water in it..... The contractor worked with it until he dug a pit put a sump pump in it filled it up with pea gravel so he could keep the water out to finish the pool.... In the case of my pool I have 10 foot of water pressure to hold the liner down against the water..... And have not had any problems.... But in the case of a two or three foot pond deep pond the ground water could float your liner.....

 

[Waterbug]

Yeah the water level in the pond just has to be a little above the surrounding area. With the dirt dug out of the pond it's normally pretty easy to do with the pond still appearing to not be raised.

This is of course just a precaution. Normally soil near the surface is porous enough for there not to be an issue. And for ponds without ground water issues the problem is the same when rain over fills the pond and goes behind the liner it can float. So given that floating liners can happen in many ponds it actually appears rarely. Although some "leaks" can be attributed to floating liner. Liner flows, and as water drains back down the liner goes back but now the pond is 1/2 empty or whatever and the owner looks for a leak that doesn't exist. So it's hard to tell how often floating liners are a problem.

So it isn't a certainty, but worth a little designing to reduce risk...in all ponds regardless of ground water To that end rocks, or my preference, mortared rock, can reduce the risk to almost zero even if the water level in the pond is below the surrounding ground. Rock is almost 3 times the density of water and if mortared then the sides help hold down the bottom a bit more than loose rock. So if you lay say an average of 4" of rock in just the bottom it would mean the water level in the pond could be about 6-8" lower than the surrounding ground and still be safe from floating. 6" of rock allows for 9-12" lower which is way lower than most people would want.

But sides can "float" inward too so for me mortared rock over the entire liner is the way to go. And it looks nice imo, be easier to clean, protects liner from UV (to a large degree) and walking.

You can also lay the liner with standing water in the hole. Have to be careful walking on the liner if the soil beneath is muddy as you can sink in and leave footprints. Carpet under the liner can reduce that problem, but still, socking feet is better than shoes imo.

 

[Peter Kirby]

The pressure exerted by the ground water can overcome any pressure exerted by the water in the pond resulting in the liner bulging up at the bottom of the pond. Do you live in a flood plain or near a natural wetlands?
My advice would be to rethink the construction of the pond and have it partially above ground. This would avoid any potential problems with ground water.

Many thanks, I thought this would be the case. Will take your advise.

 

[Jimmy Gibson]

Yeah the water level in the pond just has to be a little above the surrounding area. With the dirt dug out of the pond it's normally pretty easy to do with the pond still appearing to not be raised.

This is of course just a precaution. Normally soil near the surface is porous enough for there not to be an issue. And for ponds without ground water issues the problem is the same when rain over fills the pond and goes behind the liner it can float. So given that floating liners can happen in many ponds it actually appears rarely. Although some "leaks" can be attributed to floating liner. Liner flows, and as water drains back down the liner goes back but now the pond is 1/2 empty or whatever and the owner looks for a leak that doesn't exist. So it's hard to tell how often floating liners are a problem.

So it isn't a certainty, but worth a little designing to reduce risk...in all ponds regardless of ground water To that end rocks, or my preference, mortared rock, can reduce the risk to almost zero even if the water level in the pond is below the surrounding ground. Rock is almost 3 times the density of water and if mortared then the sides help hold down the bottom a bit more than loose rock. So if you lay say an average of 4" of rock in just the bottom it would mean the water level in the pond could be about 6-8" lower than the surrounding ground and still be safe from floating. 6" of rock allows for 9-12" lower which is way lower than most people would want.

But sides can "float" inward too so for me mortared rock over the entire liner is the way to go. And it looks nice imo, be easier to clean, protects liner from UV (to a large degree) and walking.

You can also lay the liner with standing water in the hole. Have to be careful walking on the liner if the soil beneath is muddy as you can sink in and leave footprints. Carpet under the liner can reduce that problem, but still, socking feet is better than shoes imo.

Lol..... Although you only see them at night when the pool light is on..... Even after 25 years I still have a set of footprints going from the shallow end to the deep