Water under liner while building

[conley2112]

I have a hole (not a pond yet), 23x30ish. I put down underlayment and the the liner.
The liner is big enough that it covers the berm all the way around and we'll edges are on the down hill outside and we held down by rocks.
The berm is at least a foot higher than surrounding ground all the way around, higher in most places.
I can see no way water could have gotten underneath the liner, but I've got two feet of water under the deep section after a lot of rain.

There are no rocks placed yet, no water in it other than what gathered with the rain, but when I went to start building up rock I stepped in and sank in the liner because of the large pool underneath.

I can't figure out of this is a big problem or if I had a full pond it wouldn't have collected there, but I'm ready to smash my head into the rocks over it.

I'm at a loss as to what to do. I'm pumping out the water, but if it's going to bubble up once I fill it I've got a problem that I don't know how to fix.

Unless someone can convince me it's just because the pond is empty and water seeped in that wouldn't were it full.

Please help. I'm at my wits end with what to do.

 

[brokensword]

@GBBUDD is the pro on this subject, but I believe the solution is to establish a pipe UNDER your liner and have it ported/vented out one side by running it vertically above the pond height. The idea is that the water will collect in this under-liner piping and the natural pressures will force it up and out because it's the path of least resistance now, thus no collecting beneath your pond liner. This is probably happening because the water table is higher than you want it. If I'm wrong about the above fix, GB will correct it. Btw, when this happens, it's called a 'hippo'. Don't ask.

 

[combatwombat]

Agree w/ @brokensword. Sounds like high water table. Imagine right now is the highest it will ever be and pressure from rocks/water once pond is full MIGHT fix it, but that's a big gamble.

Believe best solution is to install a french drain across the area in question leading to a sump pit/pump. There are some good videos on Youtube about how to do it. I think the Team Aquascape channel just did rec pond where they had to do this. I remember them showing some of the details of the installation.

 

[GBBUDD]

As @brokensword mentioned you want to give the water underneath a easier path then it is to build up under the liner. This is done like mentioned above with very similar to a French drain but you should not need a pump expecialy if you are adding stone in the pond when water below the liner and water above the liner meat for lack of a better word the pressures are very similar even with rubber between them . So the empty pipe is less pressure and the path of least resistance. The exit however does not and actually should not be higher then the pond it's self as that will add head pressure for the water to have to build up in order to get that high. Let's say your ground slopes away some 10 feet away from the pond I'd run that discard pipe to that area pitched so the water will run on its own. For a larger pond you may need to make a baffle of pipes across the bottom it all depends on your soils and how much water you get. There are commercialy made drain tiles made, some of your better pond stores have these I do know underwater warehouse sells one type . But it is a real dyi possibility as well with just some perforated pipe. Just make sure it can take being buried and that it's not going to collapse and ruin your efforts.

 

[j.w]

@conley2112
Good info given and hope you can get that hippo taken care of!

 

[Pondguy]

GBBUDD

We are also looking at using this type of system with 3” pipe.

Our best route is a vertical run opposed to a 45° run From our pit.

I think head pressure would be the same in both cases but one might think the sloped pipe would drain more easily.

I think we might need an extra 90° fitting which would lead into the next question of how many bends maximum to prevent restrictions?


How did the OP make out with your design?

Hope you got the Hippo under control lol….

Hippo …. Never heard that before.. Can be a big problem..

 

[GBBUDD]

your not looking a pressures like a pump its just a path of least resistance while i am not a engineer in fluid dynamics i would safely bet you could have a 100 elbows , as long as the elbows stay lower than water level it is on open no restriction way for water to drain

 

[Pondguy]

Thanks for your reply GBBUDD

that would be a lot of elbows lol

I was mostly concerned about going against a recommendation of leaving the drainage pit from below the liner on a 45°.

Instead in our case it would be much easier exiting with a vertical run straight up and 90° out.

Unrestricted with the 3” pipe and a couple of elbows with the water having to push up and out 4.5 ft appx from bottom of drainage pit to just below the water level of pond Is what we are roughly dealing with for our design.

I was trying to convince my wife that I didn’t think it would matter if the exit run went on a 45° and out or 90° and straight up and out Just as long as it was unrestricted.

If not a problem going straight up we can continue with the build. If a problem going straight up dig more to accommodate the 45° exit run.

Either way the water would take the path of least resistance. Either out the end of the pipe or if too much resistance from I assume head pressure in the pipe/low flow would then back up and flow elsewhere With a path of least resistance Back in the ground somewhere.

The drainage we are trying to overcome is seasonal and not a lot of volume but want to build this pond right This time.

 

[GBBUDD]

Unrestricted with the 3” pipe

Just as long as it was unrestricted

LETS say you wanted to push the water 200 feet away and up the same 4.5 feet the waters weight will become head pressure. possibly making lifting the liner in the pond the least resistance.

 

[Pondguy]

That makes sense the volume is significant in a long run.

Our run would be less than 15’

2.5 ft into the gravel sump
90°
2.5 ft horizontal under top layer of gravel to wall.
90°
4 ft vertical run up (2 ft below pond water level)
90°
2.5 ft run out to slope away from feature.

If the water for some reason didn’t push up and out with a three inch line I could always run a hose down it and pull a siphon out him up a pump and suck the sump out below the liner in a worst case scenario.

 

[conley2112]

GBBUDD

We are also looking at using this type of system with 3” pipe.

Our best route is a vertical run opposed to a 45° run From our pit.

I think head pressure would be the same in both cases but one might think the sloped pipe would drain more easily.

I think we might need an extra 90° fitting which would lead into the next question of how many bends maximum to prevent restrictions?


How did the OP make out with your design?

Hope you got the Hippo under control lol….

Hippo …. Never heard that before.. Can be a big problem..

I thought I'd responded to this.
I ended up using a French drain with an exiting hose within a pipe that I can connect a pump to if needed, but since finishing and filling, I've never had another issue.
No water under at all, so I guess it was for nothing more than a cheap insurance policy.

 

[Marco]

I am joining the thread with a question, I have now added underlay and liner but no water and am being panicked about hippoing. I have a couple of questions. 1. Are the pipes mentioned hard plastic or thick water pipes 2. Could you just dig a pit and run a pipe out and have a pump on the end so if you see a hippo you just turn on? I have dug everything now so did not want to dig a huge sideways trench. I am unsure where to go with this. Picture attached.

 

[GBBUDD]

I thought I'd responded to this.
I ended up using a French drain with an exiting hose within a pipe that I can connect a pump to if needed, but since finishing and filling, I've never had another issue.
No water under at all, so I guess it was for nothing more than a cheap insurance policy.

It maybe. I did not add one to my pond because I have Rocky course soil and I never have drainage issues. Its a case by case , location and design question if one is needed or not down south in the clay or in Maine or florida with High water tables would demand more thought as to it need.

Often hippos don't show but on those 50 or 100 year rains, Or a hurricane. Like you said its cheap, 50 bucks or so to keep a path open for water to escape. While building uts quite abit easier than when theres 20 tons of stone or more to Re work.

 

[Mmathis]

@Marco I had a problem with “ hippos”, but mine were due to a high water table and clay soil. I solved my problem by raising the edge of the pond about 10” above ground level (not really sure, but about 10”). That put the water level at or just above ground level so the pressure of the water kept the “hippos” away.

 

[hammer]

I have a hole (not a pond yet), 23x30ish. I put down underlayment and the the liner.
The liner is big enough that it covers the berm all the way around and we'll edges are on the down hill outside and we held down by rocks.
The berm is at least a foot higher than surrounding ground all the way around, higher in most places.
I can see no way water could have gotten underneath the liner, but I've got two feet of water under the deep section after a lot of rain.

There are no rocks placed yet, no water in it other than what gathered with the rain, but when I went to start building up rock I stepped in and sank in the liner because of the large pool underneath.

I can't figure out of this is a big problem or if I had a full pond it wouldn't have collected there, but I'm ready to smash my head into the rocks over it.

I'm at a loss as to what to do. I'm pumping out the water, but if it's going to bubble up once I fill it I've got a problem that I don't know how to fix.

Unless someone can convince me it's just because the pond is empty and water seeped in that wouldn't were it full.

Please help. I'm at my wits end with what to do.

I'm a landscape architect who plays civil engineer on a daily basis for work professionally... if that qualifies my suggestion so be it, if not just as well lol.

we have situations where 500'x 250' underground water storage (under ground detention systems) are installed into ground water. we pitch the bottom to a corner at 1-2% (the dirt is called subgrade at this point). the hole is dewatered (pumped out) during the liner installation. as the liner is back filled with stone and the plastic pipes, it displaces the water beneath the liner.

all you need to do is pump the water out while you fill the pond with water and you'll be fine. put a pumping basin down in that low spot with 1-1/2" pipe up to the surface with a cover on it. when you goto empty the pond the future, you can suck the water out through that pipe.

you don't need drainage beneath the pond if it's full of water because the hydrostatic pressure of the water in the pond is equal to the same water outside the pond.... you might have some issues if it freezes but I wouldn't put a drain beneath it and we never put drainage beneath our underground detention in the same situations.