Lake and pond construction

Building a pond or lake

Building a pond close to a house can create a useful transition between the formality of the building and the informality of the garden beyond. Alternatively, the pond may be sited some distance away, still in full view of the house, creating a beautiful focal point. You might even choose to swim in the pond. It is important that wherever a large informal pond is sited, it appears to be a naturally occurring body of water.

Beneath the water, the pond needs to have a profile that will allow water plants to thrive, but only where you want them to thrive. If the pond margins are too shallow, too wide or too deep you might have a problem. The profile also needs to allow for pond maintenance and easy access into the water. If the sides of the pond are steep and slippery at the waterline, access will be difficult and getting out of the water may be problematic, and potentially quite dangerous.

Planning consent for building a pond

If you are building a pond within the boundaries of the garden then consent is rarely needed. If the site is outside the curtilage of the garden on, for example, agricultural land then change of use consent may be required. In these situations we employ a planning consultant. The planning process may take several weeks but we have never had planning refused. Local planning departments and the Environmental Agency tend to look favourably on new pond construction so long as you don’t alter a watercourse, flood plain or interfere with a protected habitat. and you adhere to wildlife-friendly principles.

The process of building a pond

The initial site survey will tell us the levels of the ground we will be excavating and how they will influence the design of the pond construction. Soil type will also be ascertained. We will iron out any access issues for machines and lorry deliveries and determine how we re-landscape the excavated spoil as removal from site is expensive and to be avoided.

Along with costings, a written specification will be produced together with concept plans and pond construction drawings should they be needed.

Once the details of the project and terms have been agreed, work on the project can begin. Firstly, the outline of the pond can be marked out. This is often done well in advance of construction so that the client has a clear idea of the scale and shape of the pond. This outline can often appear very large but as the pond matures the visible water’s surface will be significantly diminished when planting in and around the water becomes established. It is important to build a pond as big as the site and budget will allow.

The pond is then excavated to the agreed depths and profile. If under liner drainage is deemed necessary it will be installed at this point, together with any overflow pipework and footings for decking legs.

If the excavation is very stony we will spread a layer of sand over the bottom of the pond in addition to protective underlay. The next stage is to install the protective underlay followed by the installation of the pond liner. Our preferred liner for large ponds is Greenseal EPDM which is a synthetic rubber membrane. A protective overlay is then installed in the pond margins where the planting beds are built and where the planting media will sit on top of the pond liner.

Pond edging

It is important that the pond liner is not visible above water or in the shallow pond margins. The excavated profile must be such that the grass turf at the waterline does not dry out. The grass must also not be allowed to get too wet or boggy. For this reason we often install an overflow so that we can create a fixed maximum water level. This then ensures that excess water doesn’t overflow the liner and create a boggy area.

Building a clay lined pond

This section refers to importing clay to use as a lining material and not the construction of a pond into indigenous clay. However, we recommend rubber lined ponds rather than any form of clay.

Clay is rarely a good choice as a liner. It might seem good in theory and a clay pond usually holds water initially but the chances are it will leak before too long.

We find a common cause of leakage is in clay ponds that have been built using imported clay to cover a porous substrate. Often an insufficient thickness of clay is used or the pond is not kept brim-full, allowing the exposed clay to dry out and crack. Water then seeps through these cracks and the water flow causes erosion.

If clay is to be used, good quality engineering clay should be put down in layers, using a sheep’s foot roller vibrating compactor to compress each layer. The finished clay lining should amount to a minimum thickness of 400mm. Obviously, the excavation will need to be overdug by the same amount to accommodate the clay. The clay should be kept wet throughout the construction process.

Clay ponds are also more likely to suffer from the growth of invasive pond weeds which can take root in the bottom of the pond. This rarely happens in a rubber lined pond.

Ideally, the finished clay pond should have a permanent natural supply of water (not mains) keeping it topped up. The process of building a clay pond is laborious and expensive and a perfectly installed clay liner will still be inferior to a well-installed rubber liner.

Pond decking and water plants etc

Finally, the wooden decking can be installed. We generally build pond decking on top of the liner and not through it. Planting is then carried out when the water level is near the marginal beds.

A new pond might take as long as a year to settle down, though it is usually quicker than this. If a pond is built during the winter or spring then there is a good chance of it looking reasonably mature by mid-summer.

New ponds are usually planted when they are built and we find that two or three years after construction, and sometimes sooner, plant growth will have progressed to a stage that requires a small amount of annual pond maintenance. Even on a large pond this need not be a major task if done on a little and often basis.

Follow this link for an overview of formal pond construction.