The design details of a pond will be determined by the natural features of the site, and the purpose of the pond. For most situations, the design will also be closely dependent on the funds available, especially where artificial linings are needed. There are no hard and fast rules. A series of linked ponds and wetlands of different size, shape and depth, and with varying degrees of disturbance and management, is the optimum where the resources are available.
Size
Ponds which are intended to be fairly ‘static’ features, maintained for amenity and education, need to be of sufficient size to support a stable but diverse plant and animal community. The Conservation Volunteers in Hampshire worked with the County Council in advising on the construction of school ponds. They suggest 40 m2 as the minimum, and usually aim at a size of about 60 m2. Their preferred method of construction, which uses concrete, needs to be completed by voluntary labour in one day. They have found that 140 m2 is the absolute maximum for completing comfortably within one day.
Smaller ponds, of between 20 and 40 m2 can still be maintained as a useful amenity and teaching resource, and ponds smaller than this can, with or without management, provide a valuable habitat with seasonal interest for educational use.
Depth
The guidelines on depth given above for safety are also a reasonable guide for wildlife. Few pond organisms need depths greater than one metre, and ponds dug for general conservation and amenity purposes need be no deeper than this. Make the deepest point off-centre to provide a range of slope profiles and encourage water movement within the pond.
Ponds with fluctuating water levels may need to be made deeper, if the aim is to retain some water during the summer.
A shallow area, merging into marsh, or a separate but nearby marsh area will provide valuable habitat.
Ponds dug for other purposes, such as water supply or quarrying, will often be much deeper than one metre, but their main wildlife value will be found at their shallow margins.
Shape
Where artificial linings are needed, the type of lining will strongly influence the shape and edge treatment of the pond. Simple oval shapes are the easiest and cheapest to construct, but keep the valuable edge zone to a minimum. Convoluted shapes with a longer edge develop a more varied community. Within a simple oval or squarish shape, a variety of edge treatments will increase the length of edge, and effectively disguise the original shape. Some gently sloping banks are essential for amphibians, with ‘shelves’ for marginal plants. The spread of marginal plants can be restricted by a drop down to deeper water. A muddy or shingly beach is useful for invertebrates and birds. Normally, these variations are built in at the construction stage, and the liner then laid over the ‘preformed’ shape. However, some variation can be built in afterwards, for example by building up marginal shelves, spits or reefs of bricks or small boulders. On butyl-lined pools, use a thick geotextile liner over the butyl to protect it from damage, and use stones with a rounded shape.
Edge treatment and access
The edge treatment of school ponds is strongly influenced by the need to accommodate groups of children with sufficient room for pond dipping and other investigation. This will normally need paving, boardwalk, bridge or dipping platforms adjacent to mainly open water.
Access for people all around a pond is not normally recommended. An untrampled buffer zone of marsh, long grass, shrubs or trees on at least a third of the edge will allow undisturbed access for amphibians and other organisms. Fence this as necessary to keep people out, or include it within the area of safety fencing.
A fenced pond area should be as large as possible, to include enough room for a class to gather, as well as plenty of buffer zone. For a pond approximately 10 x 8 metres, an area of at least 50 x 20 metres should be enclosed.
School ponds or those designed for educational use need a generous amount of space not only for dipping at the pond edge, but also for gathering groups of children together for teaching and discussion. Paving, stone aggregate surfacing or wood chip surfacing may be needed to prevent the area becoming muddy and unusable. Benches and tables are also useful.
Boardwalk, dipping platform and path construction for damp ground are described in Chapter 10 – Banks, revetments and access. For further information see Footpaths – Boardwalks and bridges.
