Dolos

Weighing up to 8 tonnes (8.8 short tons), dolosse are used to build revetments for protection against the erosive force of waves from a body of water.

Their design deflects most wave action energy to the side, making them more difficult to dislodge than objects of a similar weight presenting a flat surface.

[citation needed] Dolosse are also being used in rivers in the Pacific Northwest of the United States of America, to control erosion, prevent channel migration and to create and restore salmon habitat.

The sheer mass of the dolosse provides ballast for logs and slash ("wrack" or "rack" organic debris) to create a stable, complex habitat structure, all the while precluding the need for excessive, environmentally-invasive and costly excavation for their placement into substrate.

[citation needed] The design of the dolos is usually credited to the South African Eric Mowbray Merrifield, one-time East London Harbour Engineer (from 1961–1976).

[1]: 10  Eric Merrifield lead a team which included Piet Grobbelaar and Jack Badham-Thornhill who collaborated for many years perfecting the design.

Kruger's claim is that he and Merrifield had considered the shape of concrete blocks to be used to protect East London's extensive breakwaters for the City's non-natural harbour, following a major storm in 1963.

Merrifield wished to design a block that did not break up or shift when struck by the sea; that was cheap; and that did not require precise placement.

Kruger stated that he went home for lunch, cut three sections from a broomstick, and fastened them with nails into an H-shape with one leg turned through 90 degrees to create the distinctive dolos shape.