Design solutions: Ponds & Pools

Ponds are becoming ever more popular in gardens. They are a calming influence and, at their best, look entirely natural, but nothing could be further from the truth. As most gardens do not contain water naturally, the junction between artificially retained pools and dry land is one of the most difficult to design well.

Traditionally, ponds were lined with ‘puddles’, a mixture of clay and sand formed into bricks, to create a satisfyingly natural look. Once damp, the puddles were moulded to form a continuous watertight lining or layer. This was time-consuming and the practice has fallen out of fashion and is expensive if attempted.

How to line your pond

There are three alternatives for the modern garden. Firstly, every garden and water garden centre stocks pre-formed fibreglass liners, mostly in a ‘naturalistic’ kidney shape. They are cheap but almost always too small, too complex in form to allow for aquatic planting, and mass-produced. The second option is to line the pond with butyl rubber, available in large sizes, and the best way of making your pond look natural.

In both examples, the liners have to be disguised above the water line. That’s easier to achieve with paving than, for example, planting and loose soil. Some people try a ‘necklace’ effect, using paving slabs or broken stone to create an edge around the pond. This looks anything but naturalistic and is potentially dangerous, as there is little space for mortar to hold the paving together, creating a weak surface.

Any rigid paving used alongside the water should overhang slightly to create a ‘shadow line’ to disguise the liner or edge detail. Try to use larger slabs or units, where possible, with flexible liners, to maximise the area of slab to be fixed on dry land. Use dense or marginal planting to disguise the emerging liner alongside borders and remember that once the liner ends, the soil alongside is very dry. This can create difficulties with plant associations as, in nature, the move from wet to dry conditions is much more gradual. Avoid this by creating artificially boggy or damp conditions next to the pool. Butyl liners can be used to create these conditions: perforate the material before back-filling with compost and soil. It is best not to attach the bog to the pond as this can lead to water loss.

The third alternative is to use concrete – either pre-cast blocks or poured into formwork on site. The resulting rigid framework suits gardens designed in an ‘architectural’ style, although it is possible to achieve an interesting contrast between the clear geometry of ponds like this and bold, textured water planting. Poured concrete will retain water, but it is still essential to waterproof it using butyl, applied fibreglass, gelcoat or ‘bitumastic’ paint.

Waterproofing materials are usually black, green or dark blue. Once the pool is full of water the dark base creates both an illusion of depth and an attractive mirror effect on the surface.

Shallow or smaller pools will heat quickly in sunlight – perfect conditions for the growth of algae, which will quickly make the water murky and the liner slimy. Keeping your pool clear of algae can be hard work. The best way of discouraging these tiny plants is to make your pool as large and deep as you can. Pools in which water does not circulate should be at least 70cm deep, which allows the deeper water to keep cool. Algae live off the nutrients in the water, so avoid topping up the pond as this provides a fresh food supply.

Planting in ponds

Plants look attractive in a pond, but they also counteract the warming effect of sunlight. Water lilies in particular create rafts of shade. Some plants, however, prefer deeper water than others. Water lilies may prefer 10cm of water or 150cm, depending on the cultivar. With this in mind, a pool intended for a range of water planting types needs to include several changes of depth. It is often useful and less time-consuming to excavate a hole, line it and then add changes of depth.

In concrete pools, the creation of these planting shelves, or pockets, is relatively easy – simply build up blocks on the solid pool base.

If you are using butyl as your lining, make a concrete ‘pad’ or footing, lay the liner over it and add your block-work on top. As a precaution, lay a geotextile (a protective fabric) over the footing, before the butyl liner, to prevent stones from puncturing the liner. An additional layer of geotextile used over the liner allows walls to be constructed on top without damaging the butyl.

Try to create a sudden change of level between reed beds or marginal planting and the pool base. As the plants die back, a layer of detritus builds each year. A shallow bank profile allows the plants to colonise this layer and spread into open water, a process prevented or at least slowed if the shallow part of your pool suddenly drops to the base. Planting baskets will restrict the spread of more aggressive growers.

Pools without planting

If you don’t want plants, you may have to add chemicals to prevent algal growth. You can also refresh water by using cascades or fountains that oxygenate and cool the water. The pumps used to move water contain filters. Ceramic ones are fine enough to catch algae, and ultra violet ones will kill them. Pumps should be concealed, whether fitted under the water or housed separately. Underwater pumps are easier to install, but finding a way to run cables unseen into the pond can be awkward. One good place to conceal a pump is beneath a deck overhanging the pond.

All planted pools require regular upkeep – think of them as wet borders – including dredging the water and clearing excessive growth. The intention is to achieve a balanced system with oxygenating plants helping to keep water clear. With all ponds, consider the need for an overflow to regulate the level of the water and prevent flooding. This should lead to a soak-away – at its simplest level, a rubble-filled hole to allow water to seep back into the ground in a controlled manner. This needs to be located away from the house or paving to ensure that excess water will not cause damage.

A pond in a garden can be a beautiful attraction, but it is a serious commitment and careful planning prior to its installation is vital but will pay dividends in the long run.

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It is important to disguise and cover the liners as they emerge from ponds and pools. Firstly, this is unsightly and, secondly, exposure to sunlight can weaken and damage the material, which becomes more prone to leakage.
Keep pond shapes simple so that excavation is easier. Introduce planting to create visual interest and a naturalistic quality. Complex shapes often produce shallower and narrower water, which will silt up and warm quickly in sunlight.
Butyl rubber is available in sheet form but can be glued or welded to create large-scale pools. With larger ponds, be aware of the local water table. If this varies dramatically, pressure from a rising water table can force water out of a lined pond. Liners can then be vented to allow pressures to be equalised.
Don’t install lighting within a pool. This will reveal the lining, wiring, pump and detritus within the pool. Instead, light objects or planting on the far bank. Their reflection will be seen on the surface of the water after dark creating a more dramatic result.
Existing streams and rivers cannot be dammed or altered. The Environment Agency is responsible for all watercourses and must be contacted before any work is considered. In general, create separate, self-contained ponds that do not overflow into nearby watercourses.
Sunlight can create problems in ponds and water features in terms of solar gain, but it would be more problematic to site water in heavy shade. Sunlight brings life to water but does need to be controlled with careful planting allied with a good pool size and depth.