Liner & french drain vs. no liner and automatic filler.

[GardenStreet]

Hi. I can't decide whether to drain my pond (again) and put dig a french drain under it and reline with rubber, or just let it be a natural pond which needs topping off every week.
I dug my pond 20 months ago @ 24" deep. I lined it with rubber and added water as was necessary because of evaporation. In the spring of last year the ground water kept raising the pond bottom. We have quite a bit of clay, so the drainage is not at all good. 9 months ago ground water raised the liner all the way up so it was floating on the surface, and my fish were in a small pocket of water. I jumped in and cut a slit in the liner to allow a water exchange to above the liner and then removed the liner completely. The water seemed to stay with no problem, again because of poor drainage, although I would still have to watch and top it off everyweek. In the fall, I removed the 5 parent fish and their 60 babies, sucked all the water out and dug the center of the pond deeper and placed a large 20 gallon rubber bucket into the ground to make the pond 36" deep in the center and help keep water from seeping through the ground.
The water level has not gone below 24" all winter, but I do have to add water regularly because our winter has been so dry. Also a very mild winter, not nearly as cold as usual, and hardly any snow. I can't decide if I should try the rubber again... I would have to put in a french drain under the pond, run it 40' to a lower lying area, or leave it and put in an automatic filler. How expensive is it to have a trench 2-3' deep made? Has anyone else had this problem of too wet sometimes and too dry others? What do you suggest? Thanks, Becky

 

[DrCase]

Welcome to the Forum !!
I found in my ponds gone bad...If you build the ponds water level up higher than the ground around it ,
You will have more water weight in the pond than under it trying to float the liner up

 

[Waterbug]

Hi Becky,

I grew up near you, between Rochester and Buffalo near the lake. My first pond was there, mud bottom, which I kept for about 15 years. My sister lives on Canandaigua.

I know the water table thing well. And floating liners do happen. As you saw the water table only has to rise above the bottom of the pond for that part of the liner to start to float. As the water table rises further more liner floats. Liner doesn't actually float, but is more buoyant in water. At that point gas builds under the liner and it floats.

Even concrete pools can float and pop out of the ground. Empty pools can float with a water table 6' down. This is want code requires holes be punch into abandoned pools.

A trench and or French drain is problematic. Depends on grade but in general these would just fill with water as the water table rises. So they probably won't drain anything. All depends on grade.

Keeping a mud bottom pond is a whole other deal, very different hobby. Adding water in summer to keep these filled can be a problem. Other issues too. You can of course always try it. A liner can always be added later.

To keep liner from floating I would do 2 things. Shape the pond into more of a cone type shape. Gases then would have a better chance of working their way along the liner and escape at the surface. A flat bottom traps gas easily. You can also also put drain pipe on the sides of the dug pond before the liner is laid. Normally used to drain water, they'll drain gas too. You can also cover the pipe with sand which gas can travel through into the pipe or out through the ground surface.

The second thing I'd do is rock line over the liner. I personally like to mortar the rock in place as it makes it easy to clean. But many people use loose rock. I'm talking head size type river rock. This fixes the neutral buoyancy issue with bare liner.

Trapped gas under the liner can still float rocks, but it takes a lot more gas at much higher pressure. The higher pressure increases the chance of gas finding an easier path up out of the soil. In most cases this is enough.

Shame you cut the liner.

 

[taherrmann4]

Becky,
I had this problem when I first built my pond. My soil is clay and does not drain at all plus my pond is in a spot in the yard where a lot of water must travel through from the land next to me. When it did balloon up, I had bought a cheap harbor freight pump and would pull the liner up on one small section of the side of the pond, place the pump and let it do its thing until all the water was drained from under it or at least most of it. To keep this from happening again I strategically placed several large rocks throughout the bottom of the pond, plus my water lillies also weigh a lot so they help with it as well.

What I also did was dug down about 12" on the low side of the pond right next to the liner and placed some drain pipe then ran the drain pipe about 8 feet away from the pond. What I have noticed is when I get a lot of rain, water does get under the liner but it no longer balloons it up. The water now is forced from under the liner to up and around the sides of the pond to where the drain tile is and then drains out. I think the combination of doing this and adding weight to the bottom of the pond has fixed my problem. Last year in a week we had 10" of rain and it never ballooned up, there was some water pushing on the sides but it worked itself out within a day.

Never cut your liner just get a cheap pump and suck it out if it does balloon.

 

[j.w]

Becky
Never had that problem here as have sandy soil w/ really good drainage. Hope you can figure it out so it does not happen again!

 

[GardenStreet]

Thanks, guys, really useful information. I was aware that it was gas that builds up, but I didn't know how to let it escape. I also like the idea of getting rid of the flat bottom and adding more cone shape to the bottom. I'm not so sure about the adding rocks to the bottom... so many other pond folks warn about the the rocks floating and moving, and I did have that experience in the past with some pretty big ones. Plus it is harder to clean. When I first set the pond up, I had more rocks in the bottom, but it really was problematic. I will try some of your suggestions and let you know how it turns out. I will have to wait quite a few months though, since in the past trying to empty the pond and dig in spring, it just fills up again! As for the slit in the rubber, not a problem. Rubber patch on both sides, just like an innertube, good as new! Thanks again, and I will keep watching for other tidbits of information on this forum. Becky

 

[taherrmann4]

I only have a about 8 large strategically placed rocks in the bottom, it is not covered with them.

 

[Waterbug]

so many other pond folks warn about the the rocks floating and moving

Pond folk say the darndest things.

I also think loose rocks are problematic. Mortared rock solves those problems. But of course if you listen to pond folk you can't put mortar in a pond because it will kill all the fish.

 

[j.w]

Lol Waterbug, guess I have never seen a rock float either..............moved somehow but not float

 

[GardenStreet]

Oh, you guys! I think you may know I meant rocks sitting on floating liners! Thanks for the laugh.
So I looked at your Waterbug site. Thanks for the tips.

 

[j.w]

You will learn we are all a rowdy bunch of jokers at times GardenStreet! We like to add a little fun and games into the pondering now and then

 

[Waterbug]

We're talking about reducing the chance of liner floating. Just because there was enough gas under someone's liner somewhere doesn't mean rock doesn't help greatly reduce the risk. Without rock and just reshaping the bottom and adding vent pipe I'd have to bet the liner will float again. Just a small little indent to collect gas pushes up a bit, allowing more gas, etc. Same way they get a hot air ball off the ground.

 

[GardenStreet]

OK, so you are saying big rocks and/or rock & mortar is the way to go??? I gotta tell you, it was heart breaking to see all my 12" wide rocks floating right along side my rubber and fishes! That is why I just stayed with a felt bottom after removing the rubber... nothing was floating! Maybe a combination of hoses, non'flat bottom, strategically placed boulders....??

 

[Becky]

Hello from another Becky!

 

[j.w]

Garden if you try it as a natural pond w/ using no liner you could have an automatic water filling system that senses when your water level is low and automatically fills it up to the set level so if you were away or just don't want to have to mess w/ dragging the hose out all the time this would work.