Creating an island in any lined pond is not difficult in most cases. Simply by excavating the shape and building the various levels and shelves the line may be cut to shape, leaving a hole to the area designated as the island. The liner may then be installed in the usual manner – I will not go into detail here to avoid confusion; in any event, Tricks of the Trade involved in working with ponds, pools and liners are subjects for more in depth articles at a later date!
The site shown in these photographs presented a different sort of problem. The land was almost pure sand, and the design called for a decent sized island to be constructed and planted.
There was no possibility of any automatic top up system, and the scale of the project rendered the use of hose pipes impractical (except for the initial fill up). Therefore the sides of the scheme were designed to slope gently into the water, allowing a water level rise and fall of around 90cm, between the lowest side shelf base and top of the liner, with sandy soil placed over the liner to provide a natural effect sloping side to the pool.
The difficulty came in constructing the island. The water could rise and fall – fed naturally by rainfall draining across the sloping field site into the pond, with any overflow simply draining into the area beyond the feature. However, as there was no opportunity for such an ebb and flow to the island, another solution was required.
The pond was sculpted, with laser level precision across the whole scheme, and an area of land was left as a mound, graded to shape, not re-graded afterwards, to give maximum stability to the island. The top was taken off the mound, almost resembling a hard boiled egg with the crown removed, and the resultant plateau left as a circular (could be any shape) area, the top of which was level with the lowest part of the internal side shelves.
The island was created using sand bags filled with soil concrete (see Tricks of The Trade / Hints and Tips) secured together as a necklace around the outer edged of the island, using strong galvanised wire threaded through the sacks. A second and third layer of sandbags was added to give greater depth. The hessian sacks would rot after a while, and the soil concrete remain to secure the soil/planting. The resultant ‘doughnut’ of the island was infilled with good quality topsoil, with an amount of light clay content but substantially stone free. (The quality of the soil was such that an additional membrane was not deemed necessary, but beware of sharp stones which may penetrate the liner). This soil level was slightly higher than the highest part of the main pond sides, so that the island would always be visible, even when the pond was at maximum water level.
The main reasoning behind the decision to create the island in this manner was the thought that the sandy island may ‘implode’, or collapse once it was the only dry area within the precints of the pond works, causing the whole project to lose water through the island. I realise that the likelihood was probably zero, but I did not want to take the risk!
The result was very successful, with the island being planted with a variety of native species. When the project was completed, part of the hand over package was a strict instruction NOT to use forks and spades when working the island soil!
