The Site Even the cat was interested An inch from infinity The Pond'

An Infinity Pool

Discussing the design of fountains and waterfalls with Catharine, an Internet friend, she commented
"Do you think you could make an "infinity" pool? I also adore those."
I didn't know what an "infinity pool" was. She explained it was a pool which ends in a weir, so has no wall at one end and has a clear view to the horizon.

I thought about it. I liked the idea of a pond, I had always dreamed of attracting dragonflies to my garden, but no, I couldn't see how. You need to get a sightline from behind the pool to see the horizon over the weir, but whatever I build on street level backs up against the hillside. Now if I were on the other side of the road I would be looking out over the pool downhill and that might work. On the other hand, what has the road got to do with it, I need to think about building at the top of my land. That won't work either, the garden is topped by a line of hawthorn trees ( I suppose it once was a hedge but now they are 10m high) and the only way to get a long enough sightline would have to be along the hillside.

Well I'll be dammed

My imagination The reality Then I saw it! The top half of the garden is 6m above the back yard, separated by a cliff and dry-stone wall. I have been terracing this into level strips about 2m wide. The lowest terrace ends abruptly in a drop of about 1.5m, and if I dammed the end the view along the terrace would look over the pool, out down the main road and across the valley.

Of course it was not as simple as it looked, on land which slopes every which way it is remarkably hard to visualise a horizontal surface. In the end I made a water-level out of a roll of pvc tubing and used it to mark out points of equal level around the area. This revealed some remarkable facts, firstly the main issue of the spring was actually a full metre above the proposed water level, and secondly that if I removed the turf and levelled an area 2m wide and 3m long just by redistributing the soil it would be 20cm below the water line.

The uphill boundary was defined by a land drain I dug ten years ago, which had been smothered by silt. This made a foundation for a small dry-stone wall to hold back the mud. I defined the inner end arbitrarily as the line where the prospective water level intersected the existing ground. The downhill boundary was the inner side of the cliff wall. This I noticed for the first time sloped downward quite sharply, so its end capstone marked the maximum available water level. This stone weighs about 100kg, I know because one evening a large drunken man attempted to throw it from its normal position on top of the wall at a comrade below. That he managed to lift it at all was remarkable, I needed ropes to shift it from where it landed. He was lucky that it missed his toes as it fell almost vertically, gouging a path down the hillside.

Materials for dry-stone walling were conveniently to hand. Fifteen years ago I demolished a neighbour's derelict barn to use the stone for my terracing, The remains of my main stone dump was only a few metres uphill from my new project, and while all the heavy stuff was used up, there were plenty of bits left for these tiny walls

Dry-stone-walling continued around the open end to build a dam. The weir itself is two lengths of plastic guttering screwed together along their length to make an S section. The inverted section is inwards to form the lip of the weir, the outer section is a normal gutter and leads the run off water into a drainpipe, onwards and downwards. To get an even run-off this weir has to be extremely level, I used the water-level to get the top of the wall within a centimetre or two and finished off with packed earth.

Now came the heavy work. Picking dry weekends between the spring showers I stripped off the vegetation, broke up and levelled the ground beneath, leaving until last the channels which captured the run off from the muddy bank. The final preparatory job was to rake out all the stones from the now well ploughed earth, to stamp it down and have Natasha go around with the water-level looking for high spots.

I had been reading up on pond design and soon realised that I had already strayed extensively from 'received wisdom'. It is not recommended to make ponds or waterfalls out of natural water flow at all. Ponds are supposed to be topped up by rainwater or tapwater, tightly sealed, pumped and filtered and if they are of any size, about 1m deep. Liners are made of strong expensive materials to ensure that leakage is kept to a minimum. This sort of pond is deep enough and warm enough to keep decorative Koi carp, which are glorified goldfish, and for lake-edge vegetation to thrive. Well I had no aim to keep fish or grow water-lilies, so that rather seemed to rule me out of the pond-building fraternity. However I did have an idea for a use for a 20cm deep cold pond, beyond silt interceptor for the spring water. I could sail on it! Not personally you understand, but by proxy, with a small radio controlled yacht.

But back to the construction. Next I needed a water supply. I channelled the spring into the defunct drain which although covered over with mud still passed water happily, then dammed the channel with stone and mud to make a collection pool to feed into a hosepipe, which for now went straight back into the drain.

Still straying from accepted practice I laid down a cheap polythene groundsheet as a liner. I did 'splash out' on the heavy duty version, I think it cost about a tenth of the price of standard pond liner. I glued one end to the weir gutter. It blew around like a sail until I weighted it down with stones, this mayhem turned out to be a cause of problems later. My theory was that if the water was managing to stay in a mud-bottomed stream then it should not need much encouragement to stay in a pond. The silt was annoyingly good at blocking up my deliberate attempts to drain it, so I hoped to turn this to my advantage and have it block up any leaks in the liner. So without ceremony, in went the hosepipe.

Seals like a Sieve

Natasha in the pond Wading I had measured the flow down the pipe at about 5 litres/minute, and calculated the pond held 1000 litres, a ton of water. So the pond should fill in 200 minutes, say about 4 hours allowing for a little leakage. Everything seemed to be on schedule as the level rose to within 5cm of the top, but the next day the level was still the same. There were small tears in the liner just below the guttering where it had chafed while being windblown, and the water was running into the earth bank lining the dam and washing it through the dam wall. The theory of silting up was all well and good for the long term, but right now there was no silt in the pond and clean water was flowing out fast. I slapped some patches on the worst tears; the level rose another 2cm then stopped again. I had made earth banks topped with stones to hold down the liner and aligned them with the water level, but I had absent-mindedly set the tops of the stones to the surface, so the liner, pinned under the stones, was beginning to overflow all around.

This called for wading around with a bucket of earth and building up the banks. That looked like fun so Natasha took time off digging her own mini-pond to have a go too.

An Inch from Infinity

The level was rising slowly again and we called it a day. With an inch to go it was struggling. The collection pipe blocked up so I made an intake filter out of an old sieve. The hawthorn trees were in blossom and the pond was beautifully speckled with petals. I could see there was still a lot of water leaking through small tears near the weir, washing away the earth packing under the guttering so I carefully lifted the guttering, complete with attached polythene sheet full of water (remembering that this flimsy membrane was holding back a ton of water), repacked it with mud it and used an offcut of liner to double it up over the dam bank. To try to get the second layer to seal against the first I weighted it down with gravel. The next day when I came home from work, as I drove in I could see hawthorn petals strewn down the front of the dam under the (as yet unconnected) downpipe. Water was at last flowing over the weir, skimming the petals off the surface. There was still a lot of leakage, it was several days before I got the second liner sealed on by dropping some mud under it to clog the leaks.

The Gas Drain

Over the winter, storms and vandals showed up weaknesses in my design. The ground under the pond was still waterlogged and marsh gas bubbles accumulated under the liner, lifting it to the surface. Storm force winds got under the weir guttering and tore it from the liner. The liner itself was shredded by dogs playing in the water.

Well it was cheap. Before laying another liner I dug a drain across the bottom of the pond to lower the water table and allow the gas to escape. The guttering I weighted down with stones. I gave up trying achieve an aesthetic finish by glueing the polythene under the gutter, and simply laid it, doubled under, atop the weir. This is much easier, it is inherently sealed and can easily be replaced if dislodged. The gas drain was a success too, in wet weather bubbles do begin to form, but they disappear again as soon as the next dry spell comes along. The intake sieve rusted away over the winter and has now been replaced with a heap of gravel - much more effective and reliable.

Dogs seem to be a rare hazard, I have not had any recurrence of that, but teenagers are less so. A lot of debris has been thrown in, and the liner was punctured with a steel spike. Leakage was immediately visible as an increased flow of water from the gas drain, but after cleaning up, the damage slowly sealed up as originally envisaged and flows returned to normal.

Dust to dust.

The summer showed the beginnings of an ecological cycle in the pond. Leaves, petals, dust and other debris landed in there forming a convincing layer of silt on the bottom. Algae grew apace on the surface, at first I dutifully removed it so that I could sail my model boat, but eventually it got the upper hand, covered the surface and began to rot. After a while it fell to the bottom and the cycle started again. With a lot of light and a lot of nutrients in the stream, constantly replenishing the pond, it grew fast throughout the summer and blocked the drains. I overcame the last problem by filling the gutter with limestone chipping, which acted as an effective strainer. It also probably reduced the acidity of the water, which discouraged the algae, but not much. It didn't look much like an infinity pool any more though.

The design was finally defeated by something as simple as a broken wineglass. Vandals simply dragged the sharp edge along the bottom, completely shredding the liner, and the pond was empty again. Now it waits for plans for a concrete liner. I'd like to see them attack that with a wineglass.