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Drainage below pond liner

RekusuRekusu Posts: 125
in Garden design
What ho one and all,

There is a very wet area at the bottom of the garden, so when we bought, we decided to make a small pond with liner.  For the past 15 years, there has been no problems, but recently and given all the rain in the past 24 hours, the hydro-static pressure has caused the liner to balloon and now, there is no water within the liner.

Certainly a job for the spring/summer, but I don't fully understand how to drain ground water so the liner does not balloon.

Grateful for any suggestions or links to good site, that I have been unable to find.

Thanks and toodle pip

Posts

  • thevictorianthevictorian Posts: 1,279
    Do you know if it's just temporary flooding in the area or a higher water table? If it's temporary and just a drainage problem then you can fix it but if it's the water table then you would still run into the same problem because the water has nowhere to go.

    I've seen this problem solved by French drains under the pond connected to a soak away but it takes more digging if under a pond and you have to have somewhere to drain it to. 
    It may be easier to build a raised pond so the base is higher up. If it's for wildlife then you can build up to the edges for access. 
  • DovefromaboveDovefromabove Posts: 88,147
    🤔 I suppose it’s too much to hope that the pond might not need a liner?

    Gardening in Central Norfolk on improved gritty moraine over chalk ... free-draining.





  • RekusuRekusu Posts: 125
    I'm in surrey and the ground is very much London Clay. Slope, from the road to the back of the garden has a drop of around 3 meters and the pond is near the rear boundary.  The area of the lined pond was always wet/boggy, so a pond seemed the way to go.
    My wife's current thinking is to remove the liner and just allow it to be natural.  It would then be  full (ish) in the winter and more or less, a dry boggy hole in the summer!!!
    But since we have had it lined, it does attract considerable newts and dragonflies which I guess would suffer if natural and dry in the summer.

  • FairygirlFairygirl Posts: 55,117
    edited 3 March
    Have you got a couple of photos of the site @Rekusu?
    The ideal situation would be a channel or a lowered end of the pond so that any excess water can drain away. 
    I've never had the problem of the liner lifting, but our ground is always wet, and at most - it would only be the top couple of inches that would dry out in summer. All my ponds have had beached ends or similar to allow any excess to be filtered off, but they also have plants in pots, or seeded into the base layer, so perhaps that's a factor too- the weight of those?
    Is there anything else that could cause the liner to lift like that though - a burst pipe in an adjacent plot or something?
    If you can't easily sort it - you could also consider a bog garden as an alternative/extra. That way, you can have a good area that will drain well enough in very wet spells, but wouldn't dry ot completely in those hot dry ones, and your wildlife will have a better chance of thriving. Many dragonflies often just use wet, boggy land - they don't really need a pond as such.  :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • Joyce GoldenlilyJoyce Goldenlily Posts: 2,933
    I am wondering if your pond is fairly shallow. That would mean the excessive rainfall and the build-up of pressure from the high water table in clay soil is causing your pond liner to bulge.
    This would mean either deepening your pond or digging a couple of sloping trenches close to the pond and back filling with gravel or stone to relieve the pressure by providing drainage.
    I have a small pond but it is 3ft deep, the water table is very high at the moment, and the pond level is almost lapping over the edging paving slabs but no bulging. 
  • RekusuRekusu Posts: 125
    edited 3 March
    Thanks for the thoughts.  I think the idea now will be to kinda fill the 30 cms deep pond to be around150 cms deep and install some kind of drainage from below the liner.

    The alternative is do more or less do as above but remove the liner altogether.  The downside of a natural pond is that we do get a considerable amount of algae growing which when dry in the summer, will just be an awful looking dried green cover, and a lot of autumnal leaves, which I regularly rake out.  Raking out with no liner will just disturb any bog-garden growth, which does not seem like a good idea.  And then there are the newts and dragonflies, which just appear somehow.

    The photo is the pond; the back-filled water has receded somewhat, yesterday, the little water sitting in the liner was level with the edge.  It is around 2.5 meter diameter and about 30 cms deep.  Not beautiful but it is where the natural water flows and the birds do like it.


  • FairygirlFairygirl Posts: 55,117
    It doesn't need to be anything like that depth! People always think ponds have to be really deep to prevent them freezing in winter, but in reality, that's nonsense. You'd have to be a lot further north than I am, and/or at really serious altitude for that to happen nowadays. 
    I've only had one pond that was more than around 18 inches at the deepest point, and that was a huge one which was fed by a natural spring, with a run off to a smaller pond, with yet another run off into the surrounding area. It was big enough to swim in - which my younger daughter did now and again. None of those ponds have ever frozen to more than about the top 4 - 6 inches for any amount of time, and they've varied in size from around 3 feet diameter to 7 or 8 feet.   :)

    What I would suggest though, is to have some proper planting around it, which will give wildlife cover, and provide bits for those lovely dragonflies to lay eggs etc. There are plenty of plants which wil manage, but you can also create areas that can cope with the conditions you have - ie some of that soil drying out in summer.   :)
    It's a place where beautiful isn't enough of a word....



    I live in west central Scotland - not where that photo is...
  • KT53KT53 Posts: 9,016
    If you are on clay you can almost certainly create a pond without a liner by 'puddling'.  This explains the process http://www.gardeningmasterclass.co.uk/how-to-garden-ponds/puddled-clay-ponds/

  • LoxleyLoxley Posts: 5,698
    The answer is to install drainage below the liner, carrying the water away to a spot which is lower than the bottom of the pond. This is another reason not to dig the pond excessively deep. 60cm would be more than enough I think.
    "What is hateful to you, do not do to your neighbour". 
  • McRazzMcRazz Posts: 440
    Left field POV here - (Remove liner, puddle the clay - as above). Dig drainage IN to the pond from the surrounding area. Your pond is down hill, catch the water that naturally flows down and direct it in to the pond area. Add depth to increase volume and drought resistance.

    If you choose to stick with the liner then you really need to finish off your pond by adding some material into the pond such as an aquatic topsoil. This will not only greatly help plants and wildlife establish but it will also help counter the hydraulic pressure of the water table. The liner should almost never be the finish.
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