Constructing a pond

Although there are a number of approaches to installing lined ponds, there are a few general points to follow in order to ensure that it all goes well.

Planning
The most important part of installing a pond. Start well here and the rest will be easy.

Using a liner to build your pond means that you have a great deal of flexibility in its design. It is therefore worth taking the time to carefully think about what the pond is going to look like when it is finished. It is also important to determine the optimum position for it, both for its aesthetic appeal and also for practical considerations.
You should bear the following points in mind, even though you may not be able to implement them all.

• Proportion: The pond shouldn’t be disproportionate to the size of the garden.

• Position: The pond should be in a position where it can be easily viewed.

• Electricity: It is important that an electricity supply can be run down to it.

• Aspect: The pond should be in the sun for about 6 hours a day in order to promote good plant growth, without encouraging excessive algae problems.

• Trees: Over-hanging trees can present a problem as they drop blossom and leaves, which pollute the water. Strong root growth can also threaten the structure of the pond, and therefore it should not be situated next to large trees. Certain trees, such as willows, are also poisonous and should be kept well clear of the pond. It is also advisable to keep the pond away from cherry and plum trees, as they provide over-wintering sites for the eggs of water lily aphids.

• Style: The style of the pond must suit its surroundings. For example, a wildlife pond will look out of place in a formal patio.

• Access: The pond should be accessible for occasionalmaintenance.

Materials
It is very important to select the correct material to construct your pond from, as you do not want it to cause problems once installed.Although ponds can be constructed from brickwork and fibreglass, or installed as rigid units, liner is the easiest option, and gives the greatest scope for flexibility and design.There are three main types of liner:

• PVC: Thin and lightweight, and the cheapest type of liner. However, it is therefore more vulnerable to natural degradation and tearing.

• Butyl: Made from thick rubber, and therefore much stronger than PVC. However, this can be very heavy and quite difficult to handle. It is also vulnerable to UV degradation over time.

• Pondtex: TetraPond Pondtex liner is a unique material, that gets its strength from a special, fibrous material, called Xavan. It is as lightweight and easy to handle as PVC, but is far stronger, more tear-resistant, and more resistant to degradation, than Butyl. Pondtex also comes with a 25 year guarantee, and is more environmentally friendly than traditional liners.

Sizing Liner
It is important to have an appreciation of how much liner you are going to need, before you dig the hole for it.The size of liner that you need can be determined using the following equation:
Length + twice the depth + overlap = Total Length
Width + twice the depth + overlap = Total Width
For example, assuming that we allow 40cm (16in) for overlap (20cm on each side), a 3m x 2m x 0.6m (9ft x 6ft x 1.5ft) deep pond would require a liner of:
3 + 1.2 + 0.4 = 4.6m Long
2 + 1.2 + 0.4 = 3.6m Wide

Sizing the liner in this way will give you an idea of how much you will need, and what it is going to cost, before you go ahead and dig the pond. Once the hole is dug, a more accurate measurement can be taken with a flexible measure. Be sure to always oversize the liner, so as to leave plenty of room for error, as it is easy to cut it down to the required size.

Digging the Pond
It is important to carefully plan the shape of your pond before you start digging.This can be done by marking the outline of the pond with pegs and a hosepipe (or rope). Once you have determined the shape you want, the pegs should be levelled using a spirit level.The ground should also be levelled, unless the pond is being built on a slope and you are happy to have a raised edge.

Starting from the centre you should then dig down to the level of the first shelf (the marginal shelf).The outline of the shelf should then be marked out with pegs and the ground levelled.The soil should then be well firmed.The main purpose of the shelf is to provide a planting area for marginal plants, and it also creates a shallow area in which fish may spawn.The shelf should be around 30 – 45cm (12 – 18in) wide , and 15 – 30cm (6 – 12in) deep depending on the size of plants you want to grow. If the soil you are working with is particularly crumbly then you may need to make the shelves slightly wider.

Once the shelf has been levelled and marked out you can continue to dig down, excavating the remainder of the pond. For most fish a depth of 45 – 60cm (1.5 – 2ft) will be adequate, but if you plan to keep koi and other large fish you should have a minimum of 0.9 – 1.2m (3 – 4ft).The soil should be well compacted around the base and sides, and any weeds, roots and stones should be removed.When the hole is finished, all the levels should be checked with a spirit level, and the sides and base covered with 3 – 5cm (1.5 – 2in) of damp sand.

Installing the Liner
If you are using ordinary liner, like PVC and Butyl, then you will need to put down a layer of pond underlay to protect it. This does not rot down like carpet or old newspaper, and therefore provides longer-term protection against punctures. TetraPond Pondtex, on the other hand, does not need an underlay due to its enhanced strength.You might wish to smooth the excavation with a layer of sand.
The liner should be placed in the middle of the pond and unfolded out towards the edge, positioning it as you go. Once in position it should be weighted down with stones.The pond should then be filled slowly, removing the weights as you go, so as not to put too much pressure on the liner. If possible, fill the pond using a water meter so you accurately know its volume, this will be very useful should you ever need to add treatments or remedies.

Once the pond is full, check that it is level again (you can drain some water and add or take away soil if necessary). Ideally, the liner should be fastened in place above ground level, so as to ensure that water does not drain into the pond from the garden.Alternatively you could dig a drainage trench around the pond in order to take away any run-off. For most situations, an overlap of 20 – 30cm (8 – 12in) will be sufficient for securing the liner.

Waterfalls
A waterfall makes an attractive addition to the pond, not only providing the effect of running water, but also adding much needed oxygen to the system.

The soil that has been excavated from the site of the pond can be used to build up the base for the waterfall, taking care to firm it down well. Rocks and logs can be added as needed if you want to create a more interesting effect. Any rocks which are likely to come into contact with the pond water should be treated with a suitable sealant to prevent them leaching substances into the water. If you are creating a number of cascade pools then these should slope back slightly to create a natural effect.

When lining the waterfall you should start at the bottom and work up to the top, making sure that the bottom liner is well overlapped by the top one.With Tetra Pondtex, the two liners can be stuck together for extra security, using Pondtex liner tape. Securing the liners in this way will reduce the chance of water loss through leakage or capillary action.

Once you have the waterfall lined, run it to see how it looks before you secure rocks into the watercourse.This will allow you to make sure that it flows properly, and that it is level.

Before you construct the waterfall it is worth considering how much water will be required to run it, as this will affect how large a pump you will need to buy. As a rough rule of thumb you will need 90 – 180 litres (50 – 100 gallons) per hour for every cm width (1/2 inch), depending on how strong a current you want.Therefore for a 30cm (12in) wide waterfall you will need a pump that can deliver around 4000 litres (900 gallons) per hour.