It is important to measure carefully the proposed site of the pond, and take levels which mark out the predicted water level, together with positions of any inlets, outlets, islands or other features. Any assessment by eye is likely to be misleading. The work should also be planned so that movement of spoil is minimised, and where the spoil is suitable, good use is made of it for impoundment, landscaping or island creation.
Where a flexible liner is being used, and especially if features such as dipping platforms or bridges are planned, accurate scale plans should be drawn up. Where ponds are being created by making use of the existing landform or disused excavations, then measurement on site may be all that is needed.
A scale plan can be drawn up as shown in the example below. By measuring the contoured bottom along the two cross sections A-B and C-D, using a piece of string, the required dimension of any liner or other materials can be worked out. Allow a safety margin of at least 300mm width for flexible liners, or as advised by the manufacturer. When estimating volumes of clay for puddling, remember to allow about a third extra as the clay is supplied unconsolidated.
For very small ponds, up to about 5m diameter, levels can be simply marked out on site with a long piece of timber and a spirit level. Cut plenty of square wooden pegs to mark the perimeter of the excavation. Starting at the highest point of the proposed site, knock in a peg to the proposed water level. Then working around the perimeter of the site with the long piece of timber and spirit level, knock in more pegs to the same level. Check across the centre of the site as necessary. If the pegs show that a sizeable bank will be needed on the lower side to impound the water, a flatter site may prove more practical.
The sites of larger ponds, of 5-10m diameter, can be levelled using a length of hosepipe filled with water, with a section of transparent hose at either end. Knock the pegs in level with the water in the hose.
Ponds larger than about 10m diameter should be levelled using accurate surveying equipment.
