Ponds, Pools and Lochans

5.7 Lining vs natural ponds

It is a very common misconception that most ponds in the countryside are lined - in fact, most ponds in the countryside are found in places where holes in the ground naturally hold water. Only in places where the underlying rocks are too permeable to hold water at the surface (e.g. in areas of limestone or chalk geology) are ponds likely to be lined.

Wherever possible, it is preferable to create ponds where they can be dug into substrates that naturally retain water (i.e. groundwater-bearing gravels or naturally impermeable substrates). Such ponds are generally much easier, cheaper and more flexible to create than those using artificial or natural liners. They are also likely to last longer and be easier to manage than lined ponds.

Most small garden ponds will, of course, need to be lined, since most gardens are too well drained to support ponds in natural soil. A wide range of flexible and pre-formed liners are available for this purpose. With larger ponds, however, (more than 100m2) only four main types of lining are available: butyl rubber, clay, bentonite and concrete. All can be tricky to install over large areas and large numbers of lined ponds fail within five years. Clay puddling, for example, though appealing in principle, is difficult to achieve successfully unless the lining is thick. Bentonite (either in the powdered form or as sheets of Rawmat) is fairly easy to work with but has often failed where it is installed over sandy soils or other substrates where minerals have interfered with the clay swelling process.

The best answer is to use skilled and fully experienced contractors.

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