Design considerations

Design Considerations

Dew ponds versus lined ponds

It's important to decide what kind of pond you want, and whether you want to keep it brim full or whether you're happy to see some flux in water level.

• A dew pond is a natural dip that was made by farmers in the past for watering livestock. The water in a dew pond will go up and down with the seasons.
• These can be useful because you'll have water when it's needed at the end of the winter, and then the margins will gradually get bigger, so there's an interesting change in ecology too.
• This flux does mean, though, that the pond will not always look great, so you need to decide what's important to you.

The use of marginal plants

One of the great things about marginal plants is that they help if there's a flux in water levels.

• If the water levels drop, the plants will stop us seeing the exposed muddy margins as much as we would if we just had grass growing down to the water's edge.

Designing the Water Flow for Hillside

Siting the pond

I wanted to create a pond at Hillside from the very beginning, and this site at the bottom of the slope had always seemed like a natural place: the field dips into a hollow, which stays very wet throughout winter and is sometimes even gently flooded.

Ascertaining whether a liner is needed

To check whether you need a liner for your pond, simply dig a hole and test whether it will hold water like a dew pond. Mine didn't – the clay is marbled with other silts, which let water drain away quickly.

• From that experiment, I knew I wouldn't be able to just puddle the pond using the native clays, as they weren't consistent enough. It was clear it would need some sort of liner.

Creating a flow of water to and from the pond

Luckily, we did have an ideal water source: a spring that emerges at the top of the garden and runs down the garden along a hedge line. By harnessing this, I knew we could feed the pond. There would then also be an exit point where water could pass out down to the stream once the pond was full.

Deciding how big to make your pond

I initially staked out a rough oval that was around 30 m long and 18 m wide.

• You should always consider making your pond bigger than you think it should be, because around a third will become covered with vegetation as the marginal plants grow in.
• I wanted to keep an uninterrupted watery surface at the centre for the reflections. For this, you need a central depth of at least 75 cm, so that the plants can't grow the whole way across.

I knew I wanted to make a wildlife pond down here, rather than something overly ornamental.

• I therefore made sure to create plenty of marginal spaces and damp habitat for the wildlife to inhabit and for native plants to grow.

Lining the Pond

Contouring the pond

When designing a pond that needs a liner, you need to think about how it's going to work when you build it. A good idea is to draw a cross-sectional diagram of your pond across its longest length, showing the original ground level, the feeder spring – if there is one – and the excavation.

• My pit went down to 1.5 m in the middle – I wanted it to be 2 m, but we hit the water table.
• I then drew on the marginal shelves that bracket each end of the pond. These go to a depth of about 45 cm, and then shelve steeply downwards so that vegetation can no longer grow there.

I didn't create marginal shelves around the whole pond because I only wanted vegetation at the two ends, mainly in order to preserve the sight line across the open water to and from the rest of the garden.

The process of creating and lining our pond

1. The first step was to get the contouring of the pond right in terms of the marginal shelves and central depth of 1.5 m.
2. The soil was then dug away with a digger and taken up the hill and used to extend the vegetable garden.
3. A layer of fine sand was then dressed over the base of the pit to stop any sharp stones coming through.
4. A bentonite liner was next laid down over the top of that sand layer.

• Bentonite liners are composed of bentonite clay sandwiched between two fabric layers, so you can roll them out in big sheets. They are a good alternative to plastic liners.

1. Importantly, the liner was then folded over and keyed into a trench we'd dug around the outside of the pond, so that it couldn't be pulled back in again.
2. Finally, we put a 30 cm-deep layer of clean subsoil over the Bentonite liner to protect it.

The headwall and splash stone

Where the spring meets the pond, we made a feature consisting of a headwall and a splash stone that the water falls onto. This provides a focal point, sound, movement, and facilities for wildlife.

I positioned the wall so that it faces due south. This provides a habitat that's always warm for bees, which will want to nest in here, and other insects that like to bask in the warmth.

Surrounding Trees

It's best to keep a pond in an open area

It's important with any pond that it's not too close to trees.

• The shade from too-close trees can inhibit growth, but also you may get leaf litter falling into the pond.
• This litter will often build up as sludge at the bottom of the pond, which can become anaerobic and cause the water to sour and eventually become inhabitable for wildlife.

Influencing an Existing Pond

Awareness of protected species

If you're working with a pre-existing pond, especially if it's a large pond, you need to be very careful when going in and adjusting the balance (e.g. dealing with congestion) – there may be great crested newts that use the pond, which need consideration as these are a protected species in Britain and Europe.

• If you have great crested newts, you need a strategy for any making any changes to the pond.
• You may need to get an ecological survey done to find out whether you've got these creatures.

If you do have great crested newts, you need to think about this being their domain, and ensure that anything you do to make the overgrown pond into a healthier environment is something that will work with their lifecycles and give them the opportunities they need for good living.

Pond congestion and maintaining a balanced ecosystem

Congested ponds are often the result of a feeder spring silting up, or perhaps an accumulation of leaf litter.

• When organic matter builds up in a pond, the nutrient levels rise and the vegetation grows twice as fast as it should.
• Keeping nutrient levels down, and maintaining the right balance, is thus important.

Ponds do have a life of their own, and every pond is different. But there are certain things you can do to set your pond off on the right course, and then try and keep it on that course with the right maintenance.

Creating the Right Sense of Place

The wildlife nature of this pond was really key to me. It was very important that the pond sat well in the landscape, here in this hollow, and that there were soft edges.

• I deliberately didn't do too much hard landscaping around it.

I could have made this pond feel like a more distinct place to be – by having a jetty for instance – but I wanted to keep this area very quiet so that it felt part of the hollow. All I've used is a fallen tree trunk to provide a focal point and a place to perch on.