The method of construction of a new pond will depend chiefly on the landform, substrate and water supply. Other factors which must be considered include the existing habitat, safety, access and underground services (see below).
The basic types of created pond, determined by landform, substrate and water supply, are shown in the following diagram.
Substrates
Impermeable substrates of clay are naturally wet unless drained, and shallow ponds can be created by excavation. Water levels will fluctuate according to the weather and season, unless the pond is topped up from a stream or other supply.
Permeable substrates will need an artificial lining in order to hold water. Artificial linings are described fully in Chapter 7 – Artificial linings.
Water supply
Where the water table is high, any hole dug in the ground will fill with water. The level of the water table varies with the season, and from year to year according to rainfall.
Water flowing from springs or in streams can be impounded or diverted into ponds. Such ponds can be described as ‘on-stream’ or ‘off-stream’. Any abstraction from watercourses, water bodies or underground sources in England requires an abstraction licence from the Environment Agency, and from equivalent agencies in other parts of the United Kingdom.
Ponds with artificial linings constructed for amenity and educational use are usually filled and topped up from the mains supply. The local fire brigade will often fill school ponds initially. Tap water used to top up existing ponds should be left in open containers for 48 hours to allow the chlorine to evaporate.
Rainwater can be diverted from roofs to fill and top up small ponds.
Run-off from roads and other surfaces in urban areas can be held in balancing ponds. Waste water of many types including sewage, from residential buildings and agricultural and industrial processes can be filtered through reed beds, and then into ponds or lakes.
See here for further information on water supply.
Landform
On a sloping site, the obvious place for a pond may be at the base of the slope or in a depression. However, these sites may already be damp or waterlogged, and valuable for wildlife as they are. Locating a pond at the lowest point may also cause problems due to excess run-off or silt- laden water running into the pond, and causing flooding or silting. Overflows are more difficult to construct if the pond is sited at a low point on the site. A site part way up the slope may be easier to manage.
Existing habitat
The existing habitat should be of lesser wildlife value than the pond habitat with which it would be replaced. In particular, avoid destroying wet grassland or marsh which is likely to be of high wildlife value. The wetland habitat will be complemented by a nearby pond.
A ‘buffer zone’ of rough grass, shrubs, hedgerow or woodland close to the pond is important in providing seasonal habitat for amphibians and invertebrates and in effect greatly extends the pond’s area of influence. Dry stone walls, piles of stones, timber and other debris provide hibernating sites for amphibians and habitats for other animals.
Existing trees should not normally be felled in order to prevent shading of a new pond. Shaded ponds develop their own particular community of invertebrates and other organisms. It may be appropriate to coppice or pollard existing trees, or to lay overgrown hedges, in order to increase sunlight to a pool, but mature or decaying native trees should be retained, along with standing deadwood that does not present a hazard.
Access
Most ponds are dug by machine, so initial access is needed for an excavator of some type. Where the water table is high, a tracked machine working from supporting mats may be needed to prevent ground damage. The contractor will advise on the most suitable machine for the site and the job.
Artificial linings for all but the smallest ponds will need transporting by vehicle as near as possible to the pond site.
Access for maintenance will depend on what is planned. Small-scale annual maintenance, as carried out on most school or village ponds is not dependent on vehicle access. Pedestrian access is considered below.
Underground services
The location of gas, electricity, telecommunications and water supply and drainage services should be checked for any sites where ponds are planned. Urban sites may have many different services crossing them, including redundant ones, and farmed areas often have old drainage systems which the landowner may not know about. Initially check with the landowner, and with the relevant companies for the services concerned. However, underground services’ plans are not always reliable, as cables and pipes may ‘snake’ between points, or may have been moved during subsequent work. If problems are indicated, request that the utilities trace the services accurately with cable and pipe locating devices. Tracing devices can also be hired that trace live electricity cables, metal pipes and plastic pipes with a metal tracer laid with them, and water pipes to which you have access at either end.
Land drains in farmland may cause a problem if the excavation cuts through an old ‘dry’ drain which results in the pond mysteriously refusing to hold water. Cutting through a working drain may be an advantage in creating a water supply, but silt traps and overflows may then be needed. The digger driver needs to watch carefully for any signs of clay or tile drains during excavation, and for the more modern perforated plastic pipes. If found, either block off or make good use of any existing system.
Where land drains are still required to function, it may be necessary to put in a new drain to intercept the flow, and to prevent pond water backing up into the system and creating an unwanted wetland area in drained land.
Safety
It is possible to drown in only a few centimetres of water, so all water bodies are potentially dangerous. Safety is a priority for ponds in school grounds and community areas. Most education authorities will insist on school ponds being fenced, not only to control access for children attending the school, but also for younger siblings who may have access to the school grounds at the beginning and end of the school day or during special events, and against people trespassing on the site.
Points to consider
- For school or community ponds, an open site which is within view of rooms which are in frequent use will give some degree of supervision, as well as discouraging vandals and other unwanted visitors.
- The following guidelines are recommended for school ponds in Surrey (Surrey County Council, 1993), aimed at ensuring that no pond is too deep for a child of the relevant age to stand up in.
Secondary schools – one metre maximum.
Junior and middle schools – 750mm maximum.
Infant and first schools – 600mm maximum.
Alternatively very shallow seasonal pools or scrapes can be created. - Paving or other surfacing around school ponds should be even and non-slip. Boardwalks and dipping platforms should have toeboards to clearly define the edge, and to aid safe wheelchair use.
- Raised pools may be appreciated by the elderly or disabled, as pond life can be easily observed. However, any low raised wall is an invitation to small children to climb. Raised pools should have sloping banks within the pool, and access for amphibians to the pool area.
- Lighting may be needed in some situations, for schools that are used in the evening.
- Any fencing should be ‘see through’, so that a child who gets into the pool area can be seen. Stock netting, chain- link, chestnut paling or picket fencing are suitable. None are proof against a determined invader, but will prevent access by small children. Gates should be lockable. In certain situations handrails may be useful.
