Informal pools and rigid structures
Unlined pools use the natural water level, or are made in impermeable ground (such as clay or rock). The main factors determining their design are the pool edge and the required depth.
The edge of the pool may be vertical, or may be shelved and form a beach. From the point of view of habitat diversity, it is good to have either a gently sloping “shelf” edge or a series of terraces because different plants grow at different depths of water. A beach permits ease of contact with the water: one can touch it, or indeed swim in it. A beach can be sandy or covered in cobbles. Vertical edges may be constructed like a retaining wall, and this is usual in canals which have to resist wave action. These edges ...