Preparing the pond area for lining.

Because butyl and other liners are damaged by sharp objects such as flints it is critical that during the building of a pond they are protected. Old carpet ( of a synthetic, non-rotting type ) can be used as an underlay, although modern geo-textiles are readily available and easier to work with in a secure way.

Consider the subsoil where the pond is to be. If it is naturally draining and is not affected by the local water table, no further action need be taken; however, if the subsoil may hold some water (such as clay or shale for example) or the natural water table may come up during the winter, you will need to create and escape for any water that might accumulate under the liner. Dig a trench 300 mm wide by 300 mm deep from the lowest point in the excavation, following the contours of the excavation towards the (downhill) lowest side of the site. End the trench 800 mm outside the excavated area. Place a 100 mm perforated land drain in the trench and fill with 10 mm gravel.