Building Ponds in Unlevel Ground Using Flexible Liners
When things are not so simple: When part of the pool edge emerges above the level of the surrounding landscape, or if the pool is in loose soil or made up ground.
1. Establish a datum peg at some point that will mark the water level of the pool. Normally this will be a piece of 2x2 driven into where the pool will be deepest. There will also be an indelible mark on it at the bottom end that will mark the final depth of the excavation.
2. Excavate the pool area as much as necessary to make a level space in which you can drive in several more pegs to the same level as your datum peg. These can roughly mark the deeper area inside the marginal shelf.
3. Several more can be driven in to mark the level of the marginal shelf area and the rough shape of the pool. If you are intending to face the inside of the pool with stone work or brickwork ensure your marginal shelf area is wide enough to support this whilst leaving enough room for plants to sit in baskets
4. Use the datum peg and several intermediary ones level with it around the excavation as reference in laying a blockwork framework. In loose soil or made up ground, this blockwork will need a footing into consolidated soil.
The shape of the pool must be marked on the ground. From this line outwards by at least 4 inches (10cm), a small 4 inch (10cm) deep trench for a footing must be excavated and filled with a semi-dry concrete 5:1 mix of 'All-in' ballast and cement powder. The width of this footing depends ultimately on the thickness of the facing stone or brick that the water feature is intended to have on the inside of the pool or the outside.
3. If the pool emerges from the ground to its full depth, the marginal shelf needs to be constructed from blockwork too and backfilled with sub soil. This will be the skeletal structure for your pool, which will be lined with sand and underlay (particularly on the upright blockwork) and can be faced outside and inside with your choice of materials.
ANOTHER TIP OR TRICK: To have a pool brimming with water
This simple pool has a skeleton of blockwork laid onto a thick mortar mix straight onto soil.
A granite set edge is supported by the blockwork whilst the liner comes up behind the sets. In this way, the water level in the pool can be maintained almost flush with the top of the edging stones.
