How to alleviate hydrostatic pressure under liner

[MajorDan]

No surface water gets in my pond as the liner terminates 18” above ground. Every time we get heavy rains my sump pumps in our craw space run for days and the outlet from under the pond runs clear water. Liner has never ballooned. So for my area and our soil conditions and the small limestone mountains all above our house, the drain solution works great.

 

[MajorDan]

Thank you Dan, I'm not trying to be controversial and certainly can't argue with science, I'm just trying to reconcile this in my mind. I understand the concept in your illustration, but in a container the "ground water" outside the bag is constrained by the container walls and with just ambient pressure the water can't overcome the static pressure of the water within the bag. In the earth there is the potential for lateral movement. Granted, an empty liner in a hole would be the path of least resistance hence the bubble on the bottom, but once the pond is full of water the forces should cancel each other out. I'm trying to figure out why thousands of full, established ponds haven't been pushed out of the ground based on the premise we're discussing.
I did notice that most of the bubbles in the video's were at the upper areas of the sides. The video that made the most impact to me and I would think be the easiest to accomplish in an established pond was the dry well approach.
Please don't consider this an affront, I'm just a thick-headed old duffer that has to think things over and over until the "light" comes on over my head - it'll come to me, it just may take some time.......

It happens with a high water table and the clay soil that acts exactly like a container when the water gets in it since all of the soil around it is saturated. I am sure this condition would not happen in porous soils with a low water table. In the recent past we have had so much rain that water came up through the street drains as the creek they empty into flooded and kids kayaked in the streets.

 

[Lisak1]

I guess there are circumstances were air pockets can Occur in clay soil under the liner and cause issues.

OK - now that's a new one. I mean, go ahead and do it if you want, but I have literally never heard of air coming up out of the ground and lifting a liner. We live in an area with heavy clay soil too - but I won't question the pros if they've had it happen.

 

[brc]

It's basic physics - if water pressure above the liner is higher than the water pressure below it, then any water under the liner will be pushed out of the way.

If the water level in the pond is higher than the water level in the ground, then you're good.

So, there's no need to worry about what happens at the bottom - you just need to ensure that the ground water can't get higher than the pond water. I did this in my pond by putting a drain next to it.

 

[paco]

I am currently digging a pond approximately 10 feet by 10 feet and 3 feet deep. I live in an area where the ground is mostly clay. I get a lot of ground water in my lawn after a rain. It was suggested that I install perforated pipe Along the bottom of my pond and vent it out to An opening so I can relieve pressure. I'm Trying to understand this process.I guess this is not like a French drain that is supposed to drain the water out from underneath the pond.Can someone please explain is to me so I install it properly?

Hydrostaic pressure can be a real problem in ponds deeper than 3' that are dug into clay.. We had this problem with one of our ponds a few years back. The liner would bulge/herniate whenever the ground water was high. Our first attempt was to dig a well adjacent to the pond with a sump pump in it. This worked to a point but did not eliminate all the liner issues. Adding two PVC pipes with pressure relieving valves at the top still didn't completely solve the problem either. We finally gave in and just had fiberglass reinforced concrete poured into the bottom of the pond with the relief valves installed down through the liner. Although this played with our PH for a while, it did solve the problem and actually makes spring cleaning a lot easier.

Hopes this helps,
paul

 

[Hop2it2022]

It sounds crazy but it does happen.

I live in West Tennessee. We installed a preformed pond liner (165 gallon) last weekend. I was happy. It was cute. We had a downpour Saturday night and believe it or not the entire thing, water and all, was rocking like a boat Sunday morning. I am searching now for a solution. I believe I'm understanding that most here are discussing regular pond liners that are not preformed.

 

[j.w]

@Hop2it2022

 

[GBBUDD]

FIRST solution is like rocks in the bottom of the pond adding weight. but if that doesn't work creating a berm so that the run off from rains does not get to the pond and is diverted around the pond and not into the pond

 

[poconojoe]

Don't doubt this can happen. It does. It has been called a water hippo here on this forum. The liner can bubble up by ground water.
There have been many discussions on this.

Take the advice in post #3.
Lay your perforated pipe on the bottom and run the pipe vertically up the side between the liner and pond wall.
I think the suggestion is a good one that the vertical pipe ends at a level that is below the pond's water level. If the pipe exits too high, maybe dig a hole and create a sort of culvert so the pipe ends lower.