Water Under Liner

[Cypress Point Pond]

Our 2600 gallon pond is under reconstruction due to major leaks in the original liner. The pond is not yet filled.

Information:

a.)  The old liner was left in place due to a number of factors.

b.)  A number of puntures were made in the old liner to allow water to drain into the subsoil. 

c.)  Mixed sand and gravel cover the old liner and is directly underneth the new liners pad. 

d.)  The deep subsoil in our yard and is a very porus. 

e.)  I did not install a bottom drain. 

f.) This a DIY project.


Current Situation:

Over the past week we had two to three days of heavy rain.  As the rainwater makes its way through the subsoil it has also made a small pool in the bottom of the pond, specifically "over the old liner" and "under the new liner".  This has caused the new liner to swell in the bottom of the pond.


My questions are:

1.  Should I place large flat stone in the bottom of the pond to ensure the liner stays down?

Or

2.  Should I do nothing and just refill the pond when ready?


Thanks for your help.

[tinkster]

Not sure if this is similiar to you but when I was working on my pond I was on a very hard base of rock and clay.  I had the new liner in but not filled. The water did the same thing to me where rock/dirt underneath was so hard it didnt drain, dont think it ever would, but when I filled the pond the weight of the water holds the liner down fine now.  I am not sure if it would ever be  a problem as far as eroding the area under you pond or berms over time or if it will drain away since you have porus soil.    I know mine bottom/berms arent going anywhere since its so hard clay/rock.  Hope this help.

tinkster

[miguynmkoi]

I would think the weight of the water should be able hold down the liner.  If the soil is some what porous maybe spreading the liner out further around the pond on a berm may help.  Cover the excess liner with larger rocks would be my best guess.  Hope this helps.

[Julles]

I had a somewhat similar situation, where air got inbetween the liners, and caused a big bubble under the new one.  I just filled the pond with water, and the air found its way out.  No problems since.

[Don]

I had a similar problem with one of the ponds I tend to. The discharge from the waterfall was leaking behind the liner and settling in the middle of the pond underneath the liner.

The liner began to float as the water level decreased in the pond. Refilling the pond pushed the liner down, but the “bubble” did not go away until the water underneath was absorbed by the surrounding soil a few days later.

Don

[Esther]

I am not an engineer and have never had this problem but I don't understand how the weight of water above outweighs the pressure of water underneath. I have heard this discussed before when there has been a high ground water level. And I think they mentioned French drains to solve the problem.

[Don]

I am not an engineer and have never had this problem but I don't understand how the weight of water above outweighs the pressure of water underneath.

Once the pond was refilled, the greater volume (aka weight) of water on top of the liner pressed it down. The water under the liner was still there and noticeable but less mobile.

[Cypress Point Pond]

After discussing my situation with an engineer I learned that the hydrostatic pressure exerted by the water undernenth the liner can be as strong as or stronger than the water that fills the pond.  He went on to say that in some extreme causes the subsoil water can push up boulders from the bottom.

The engineer concluded by stating that the best solution is really to let nature takes its course that being the underliner water will disperse in time.  He also advised me to continue my work which as you can see I did.  Check out my new post "rebuilt cypress point pond filled today.

Thanks for all the help everyone.
Louis

[mascot]

I just proved the engineer's theory.  Well, I didn't prove it - mom nature did.  We had a bad rainstorm and the water got under my liner where the ground is very slow draining.  It pushed the liner up and raised the water level, which subsequently drained out, and now as the water starts soaking into the ground below the liner, the liner is starting to settle back down and the water level has dropped a couple inches.

[Don]

After discussing my situation with an engineer I learned that the hydrostatic pressure exerted by the water undernenth the liner can be as strong as or stronger than the water that fills the pond.

I just proved the engineer's theory.  Well, I didn't prove it - mom nature did.  We had a bad rainstorm and the water got under my liner where the ground is very slow draining.  It pushed the liner up and raised the water level, which subsequently drained out, and now as the water starts soaking into the ground below the liner, the liner is starting to settle back down and the water level has dropped a couple inches.

That makes perfect sense Blindtoo, water under the liner doesn't compress but displaces the water above the liner.

In the case I described above there was no excess water, it was just trading places.  I suspect some of the water below the liner was already receding when it was discovered because the pond level was low. Refilling the pond brought the level back to normal, however as the water below the liner continued to recede the pond needed filling again!

[mascot]

yeppir, Don, I'm sure of it.  I did try to push it down a little and all it did was displace the water underneath...like a water baloon does when you squich one end.  In two years this is the first time this happened...but it was a much bigger rainstorm than we've had.  I have pots out front that have about 6 inches of water in them just from the rain.

This picture was prior to digging the pond, and is a good indication of how slow the pond drains. 

[Esther]

Well guys, I didn't want to come off as a "know it all" but I knew all about the water pressure thingy and what it could do. You see about 30 years ago we had our inground pool redone to comply with the new codes about the depth of the diving end. They dug down about a foot and hit a spring that hadn't surfaced at the shallower depth. So they ran a pump and routed the water out from under and kept it pumped dry until they could cement part of the diving bowl. They also put in a hydrostatic valve in case the water pressure became "too much". The valve would open and allow the ground water to come into the pool which could be messy. It has never happened but at least I know it won't displace the pool liner.

[miguynmkoi]

After I read Blind'Too's post about his pond's dilemma I realized I misunderstood your problem, CypressPoint.  I can only shrug my shoulders  and hope you find an answer you can share with us.  Good Luck!

[Cypress Point Pond]

After I read Blind'Too's post about his pond's dilemma I realized I misunderstood your problem, CypressPoint.  I can only shrug my shoulders  and hope you find an answer you can share with us.  Good Luck!

After the pond filled the under-liner water was forced back into the subsoil through the punctures I made in the old liner.  I confirmed this by walking in the pond barefooted.  This may sound nuts but you can "sense" more about the bottom when barefooted just as you can when working without gloves.

Thank you all for the continued support.

lp