Water Gardening – Building a Water Garden
As well as requiring sun and shelter from strong winds, when you are building a water garden or pond, it should be in an area that is free from the dangers of pollution and serious flooding. In districts of high rainfall, it should be raised above the surface of the surrounding land and given an overflow. At the very least, the coping of a formal pool should be given a slight upwards and inwards tilt so that surface waters do not swill into the pool, especially if there is no overflow device.
Overflows are quite easy to install, as are inlet pipes, into pools made of concrete. A length of narrow piping is set in the concrete, just below the coping and above the water line. This leads either to the garden, to a ditch or to a soak-away. An outlet for the water can also be constructed on the bottom of the pool, just above the level if there is any, by setting a pipe into the concrete, which will lead to the same system as the overflow. This can be fitted with a plug; alternatively a screw-top bottle (such as a cider bottle), with its bottom end cut or broken off, can be set through the wet concrete and into the drain-pipe.
With liner pools, things are a little more tricky. Theoutlet is not possible, but an inlet pipe and an overflow can be constructed in a makeshift fashion by using a wider gauge of pipe and flattening the pool end to a thin slit, so that this can lie on top of and be stuck to the liner’s overlap fitting under the coping or edging. Water will tend to ooze round it to some extent, but more will go down the pipes, with any luck. All overflow pipes should have some sort of grid over them to prevent them becoming blocked or being sucked into them. Nylon mesh or perforated metal will do the trick, and the same applies to any outlet pipes.
Before you start building a water garden, the availability of water to fill the pool and of a drainage system to remove surplus water from it, should be investigated and if possible installed before work on the pool itself begins. If there is natural water about, it might be possible to channel it to feed the pool and perhaps to make a series of water-courses before it returns to its natural path. Surplus rainwater from roofs and gullies could be led by pipes to some kind of ‘reservoir’ whose overflow could, least, top up the pool. Even a permanently dripping overflow Iron a water tank or lavatory cistern could be channelled in this way. Something of the sort is the ideal solution to prevent the water level dropping and the materials used in the pool’s construction deteriorating.
With all these decisions as to site, style and design of the pool out of the way, the excavation work for building a water garden can begin. Having marked out the outline of the pool on the ground, begin to dig, remembering to save the topsoil for use elsewhere. Remember, too, to make sure that the edges of the pool are absolutely level. If you wish to have fish and anything larger than the miniature Waterlilies in your pool, 45cm (18″) is about the minimum depth, while 90cm (3ft) should be enough for almost any artificial pool. Even N.alba, which is often found in quite deep water, should oblige at that depth (if, however, you do have a large and deep natural pond, it will probably be even happier).
Whatever depth you decide upon, remember to allow in your calculations for a base of 5cm (2″) of sand beneath a liner pool. For.a concrete pool, you will need to allow for 10cm (4″) of hardcore and a 15cm (6″) slab of concrete for the base of the pool. The walls, too, will be about 15cm (6″) thick, whether they be of poured concrete or of screeded bricks. If the pool is to have some kind of coping set flush with the ground, this must also be allowed for.
Whenever possible, allow for a planting ledge or trough, 20-25cm (8-10″) wide and deep, to accommodate marginal plants. This can be made during the construction of the pool, or afterwards with bricks, etc. Pre-formed plastic and fibreglass pools are usually provided with these ledges, so that you only have to excavate to accommodate them, whilst when making a pool with a flexible liner, you can make the ledge how and where you wish, even providing a central mound (to take a plant, a stepping-stone or a statue) in the earth, before moulding the liner round it. Any stepping stones should be set, dead-level and firmly fixed, just above the surface of the water, so that they appear to float on the water.
Alternatively, both waterlilies and marginals can be planted in containers and raised to the appropriate heights on blocks or bricks.