Arrrgh! It looks like we've got a hippo in our pond!

FAQ: Our pond liner has lifted to the surface of the pond. Because of heavy rain the water table has pushed up from underneath.

Question: I have been looking at your website and found it very informative, in fact, I wish we had found it a year ago, before we embarked on our pond project.

I wont take up your time relaying the whole series of unfortunate events that we have encountered, but will just say that, due to our lack of initial research into the aspects of pond building, we have more than a few problems with our pond.

We are constructing a large (12m x 9m x nearly 2m deep) wildlife pond; the liner is in, it is full of water and the edges are just being laid. Pump and UV's are not yet installed. We are not having a filtration system.

The latest problem we have is that due to heavy rain and standing water in our garden (we are in a low water table area) we have water beneath the liner which has lifted it to the surface of the pond in one area.

We are unsure whether we can solve this problem or whether it will happen every time we have prolonged heavy rain. Hence we are considering abandoning the project and turning the pond into a large soak away!

We now realise that being sited in an area with a low water table, in a garden that periodically has a lot of standing water, is not an ideal site for a pond. We have spent considerable time and money on the pond but dont want to spend more money finishing it if we are left with ongoing problems. We have had enough pond stress already!

Have you experienced problems like this and, if so, can there be rectified? I would greatly appreciate it if you would give us the benefit of your experience and offer some advice on what the best course of action would be.

Answer: Hi Carolyn
This is a problem that I have come across many times and it is something you must always bear in mind when planning a pond. I have built many water gardens near my home down on the Somerset Levels, which are inundated with water every year now. I live on the side of Mendips by the way - a lot of rain but it doesn't hang around for long. I've been building water gardens since 1981 and am at present overseeing a big project in the Caribbean in a bay and has a very similar potential problem to you, but on a massive scale. You can see some articles about it on my magazine website. You may also find there some beginners guide articles on building ponds, and I think that one of the main Commandments to abide by in planning your water garden is to not build your water garden in the lowest part of the garden. If I dont say it on the website I've said it somewhere in the half a dozen books I've written on the subject.

Anyway, you garden with your problem may be completely flat and it may not apply to you. Also that Commandment does not necessarily apply in a garden like mine, which although it is on a slope, I've happliy put the watergarden at the lowest point because we are still 500ft above sea level and there is plenty of lower land for ground water to drain away to.
So what should you have considered if your ground is likely to become water logged?
It certainly helps if there is lower ground outside the garden. In which case you build a 'French Drain' in the base of the pool that takes the water away to lower ground.
If there is no lower ground and your garden is flat, you must maintain the water level as high as you can in order to displace the water underneath. But if there is a hill or a slope nearby then the water comes in under pressure. I have had this problem on a gigantic scale when I lined a pond for Leslie Crowther near Bath. He lived on the side of a hill and the last you expect is ground-water problems on a hill. Unfortunately it turned out that the pond was on the site of an old stream that still carried water underground when there was a lot of rain. I should have built a French drain under it then , but he said leave it. He thought was funny,because the liner ballooned up like a giant hippo was in the pool. I'd had to leave off my work on the project halfway through because of an enormous abscess on my neck. It was so bad I couldn't move my neck. After I had finished and the hippo would appear this balloon was named "Pete May's abscess" and he would take great delight in showing it to his many friends and visitors from stage and screen. Some claim to fame!

On a couple of occasions we have tunneled under ponds to drain them from underneath and build a sump on the edge of the pond with a submersible pump fitted with a float switch. This was very mucky work indeed and it has worked well when there was a ditch to pump the water too. One pond was in a natural basin, which mean that pumping the water away was fine but it immediately drained back again, and so the pump was working away full time. A big waterfall meant that there was inevitable water loss in the throughout the day and so the liner was still constantly being pushed up from underneath.

So the name of the game is simple displacement. If there is no pressure from the surrounding area, a full pond will help. Something heavier than water in the bottom may help, like a layer of heavy pebbles and ornaments. But dont bank on this - Leslie Crowther's "Pete May's abscess" could tip over a 3cwt ornament stand and statue.
If possible raise the water level above the level of the lawn. That may be a stupid suggestion if you already cut the liner and begun the edging.

Next and last option. Render the inside with cement. Use chicken wire to support the 'muck' on the sides. Use a strong mix of water cement with fibre reinforcement. It should be as much as an inch deep, if not more on the bottom. Render it in 2 layers. Then tank it with a Vandex water proofing slurry that they use for waterproofing water tanks, obtainable from v. good builders merchants.
Hope this is of some help. Rest assured you are not alone.

At very last resort, make the pond into a bog garden. Make hole in the bottom of the liner and put in 8ins of clean inert gravel. Top off with sacking and fill with humus rich soil. Mulch with composted bark.