Ponds, Pools and Lochans

5.5 Good pond design


By looking at semi-natural wetlands and considering the preferred habitats of pond dwelling species it is possible to improve some aspects of the detailed design of wildlife ponds. Some of the best ways of doing this are described below.

Make pond mosaics - creating new wetland complexes

Pond depth and permanence (and probably waterbody size) are major influences on pond community types. Varying these factors at a site, to create habitat mosaics with a mixture of permanent, semi-permanent and seasonal pools, makes it possible to provide habitats for a far greater variety of wildlife than could be accommodated in a single waterbody. Creating such mosaics is usually possible in all but the smallest pond creation sche mes.

Include extensive areas of shallow water, undulating microtopography and drawdown

In most ponds, water rises and falls between winter and summer creating a drawdown zone of variable wetness. This land-water transition zone is an area of potentially high biological diversity in any pond (see Figure 17).

Lack of information about the importance of the drawdown zone has meant that, in most new ponds, it is rarely considered during the design process and it is therefore usually restricted to a narrow strip at the waters edge. Extending the drawdown zone, to give an extensive area of marshy or muddy habitat in summer, will considerably improve a ponds potential particularly for marginal, shallow water and semi-terrestrial plants and invertebrates.

Drawdown zones do not need to slope evenly down to deeper water. Centimetre scale variations in water levels and waterlogging, caused by subtle irregularities in the ground surface, should lead to major variations in plant community type.

In pond construction, there is an opportunity to simulate this small scale topographic variation by careful physical shaping of the drawdown zone. By extending the drawdown zone and areas of shallow water to include a patchwork of hummocks and pools of varying water regimes we can create a rich mosaic of small-scale habitats for plants and animals.

Use deep water sparingly

Deep water (1 to 2 metres or more) provides a relatively specialised wildlife habitat that typically supports relatively few species. From a wildlife perspective there is, therefore, no imperative to incorporate deeper water areas into pond creation schemes. The commonest exceptions to this are (i) projects where fish or wetland birds are the primary objective of pond creation, (ii) in some of the more remote parts of Scotland, where unpolluted, clear, deep water, could be created providing valuable habitat for a diverse and interesting range of submerged plant species (and associated invertebrates) including some of the rarer stoneworts and pondweed (i.e. Potamogeton) species (Stewart 1996).

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Figure 35. When designing ponds focus on creating pond complexes rather than a single pond. If possible include deep, shallow and temporary pools. This will help to maximise the number of plant, amphibian and invertebrate species that the site can support.

 

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Figure 36. For individual ponds, create extensive undulating margins and complexes of sub-basins to maximise the diversity within each waterbody.
Introduce islands into large ponds

For plants and invertebrates, islands are most likely to be of value where the margin of the pond is shaded, grazed or trampled and the islands provide a different set of habitats.

For birds, islands are particularly important, providing safe areas for feeding, roosting and nesting in larger ponds. So, where wader or waterfowl conservation is the main purpose of pond creation, islands are certainly valuable. Specific advice on island design for birds is given by Andrews and Kinsman (1990). More general points are:

  • Height above water level will determine vegetation type: if islands are low they can also be a wetland habitat
  • Gentle slopes near water level, and banks that are partly submerged, will give muddy areas for summer/autumn feeding
  • Occasional islands with steep bank areas may provide additional habitat for water voles (Strachan 1998)
  • Locating islands at least 4 to 5 m away from the bank and maintaining deep water around them, at least a metre or so, will provide birds with some protection from predators, but greater distances are better
  • Islands near to the centre of water bodies will feel safest for most birds. Some wildfowl also prefer islands incorporated into reed beds.

 

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Figure 37. Low muddy islands can be valuable habitats and provide roosting, nesting and feeding sites for waterfowl and waders. Try to avoid high central islands which block the view for people and create terrestrial rather than wetland habitat.
Use wind direction

In larger ponds (i.e. waterbodies greater than about 30m x 30m), wind-blown waves can have quite a marked effect. A potentially beneficial wind effect is that it blows seeds, spores and animal eggs across the pond and concentrates them. The prevailing wind direction in Britain is broadly from the SW, so this means that the NE margins are usually the best provided. The disadvantage of exposed shorelines is that wind-blown waves erode the bank, giving it a sharp edge which is often relatively inhospitable to wildlife.

A way round problems caused by wave action is to create a very undulating and embayed NE margin to the pond which will colonise-up from the good supply of seeds, but is protected from wave erosion. Very narrow-necked pools work particularly well, especially where their entrances to the main waterbody are off-set so that they do not face the prevailing wind.

Similarly, the front edge of islands can be protected from waves by creating a submerged bar (or reef) with a lagoon behind along the islands SW margin.

Retaining bare mud

Bare pond edges may look dull and lifeless, but are valuable for wading birds, many annual wetland plant species and a range of aquatic and semi-terrestrial invertebrates. There are, therefore, times when muddy areas need to be created, and more problematically, to be retained. Grazing or trampling (by stock, wetland birds or people) are obvious means of constantly creating muddy zones. But where this is not possible, design can help to encourage the retention of bare open ground.

Muddy areas appear to remain bare for longest in areas of very low topography which lie at and below water early in the growing season (late spring to early summer). This inhibits germination and increases the water stress and disturbance caused by fluctuating water levels. In these areas even very low undulations, which allow plants to gain a foothold and spread out over the bare mud, should be avoided.

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