A dolos (plural: dolosse) is a

wave-dissipating concrete block A wave-dissipating concrete block is a naturally or manually interlocking concrete structure designed and employed to minimize the effects of wave action upon shores and shoreline structures, such as quays and jettys. Examples include such propr ...

used in great numbers as a form of

coastal management Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands. Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates due to climate change. Changes in s ...

. It is a type of

tetrapod Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids ( pelycosaurs, extinct t ...

. Weighing up to , dolosse are used to build revetments for protection against the erosive force of

waves Waves most often refers to: *Waves, oscillations accompanied by a transfer of energy that travel through space or mass. *Wind waves, surface waves that occur on the free surface of bodies of water. Waves may also refer to: Music *Waves (band) ...

from a body of water. The dolos was invented in 1963, and was first deployed in 1964 on the

breakwater Breakwater may refer to: * Breakwater (structure), a structure for protecting a beach or harbour Places * Breakwater, Victoria, a suburb of Geelong, Victoria, Australia * Breakwater Island Breakwater Island () is a small island in the Palme ...

of East London, a South African port city.

Construction

Dolosse are normally made from un-reinforced concrete, poured into a steel mould. The concrete will sometimes be mixed with small steel fibers to strengthen it in the absence of reinforcement. They are used to protect harbour walls,

breakwaters A breakwater is a permanent structure constructed at a coastal area to protect against tides, currents, waves, and storm surges. Part of a coastal management system, breakwaters are installed to minimize erosion, and to protect anchorages, h ...

and shore earthworks. In

Dania Beach, Florida Dania Beach (Dania until 1998) is a city in Broward County, Florida, United States. As of the 2020 census, the city's population was 31,723. It is part of the South Florida metropolitan area, which was home to 5,564,635 people at the 2010 census ...

, dolosse are used as an artificial reef known as the Dania Beach Erojacks. They are also used to trap sea-sand to prevent erosion. An order of 10,000 dolosse are required for a kilometre of coastline. They work by dissipating, rather than blocking, the energy of waves. 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. Though they are placed into position on top of each other by cranes, over time they tend to get further entangled as the waves shift them. Their design ensures that they form an interlocking but porous and slightly flexible wall. The individual units are often numbered so that their movements can be tracked. This helps engineers gauge whether they need to add more dolosse to the pile. Dolosse are also being used in rivers in the

Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Tho ...

of the

United States of America The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territo ...

, to control erosion, prevent channel migration and to create and restore salmon habitat. Examples are engineered

log jam A log jam is a naturally occurring phenomenon characterized by a dense accumulation of tree trunks and pieces of large wood across a vast section of a river, stream, or lake. ("Large wood" is commonly defined as pieces of wood more than in diame ...

s, or ELJs, that may aid in efforts to save stocks of salmon. Local, county, state, federal and private industry experts in

engineering design The engineering design process is a common series of steps that engineers use in creating functional products and processes. The process is highly iterative - parts of the process often need to be repeated many times before another can be entere ...

fluvial geomorphology In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

and fisheries conservation are working together to protect important public infrastructure such as roads and commercial and residential developments, while maintaining, improving, restoring, or creating aquatic 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. Such ELJs represent an innovative design aiding the recovery of Pacific Northwest (particularly Endangered Species Act-listed)

salmonids Salmonidae is a family of ray-finned fish that constitutes the only currently extant family in the order Salmoniformes . It includes salmon (both Atlantic and Pacific species), trout (both ocean-going and landlocked), chars, freshwater whit ...

, while protecting important public and private works and thus helping to balance the needs of

man A man is an adult male human. Prior to adulthood, a male human is referred to as a boy (a male child or adolescent). Like most other male mammals, a man's genome usually inherits an X chromosome from the mother and a Y chromo ...

and

nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are ...

Credit for invention

The design of the dolos is usually credited to the South African Eric Mowbray Merrifield, one-time East London Harbour Engineer (from 1961–1976). In the late 1990s the claim of Aubrey Kruger gained more prominence. 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. He said in later years that he wanted a block designed in such a way that it could be ''"sprinkled like children's jacks"''. 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. Merrifield was intrigued by the object and had Kruger draw a plan. Kruger never formally received credit for the invention. Merrifield won the Shell Design Award and the Associated Science and Technology Societies of South Africa's Gold Medal. The death of Merrifield (in 1982) has put this controversy beyond proof either way. Aubrey Kruger died in East London on 19 July 2016.

Design protection

The design of the dolos is not protected by any form of patent. Merrifield did not take the necessary steps to protect the concept. The reason for this is uncertain. Two reasons for this have been put forward: one by Merrifield; the other by Kruger. Merrifield stated that he did not protect them as he wished them to benefit humanity. Kruger alleges that Merrifield received incorrect legal advice: to wit, that as the blocks had been designed during office hours while he was employed by the State (

South African Railways and Harbours Administration The South African Railways and Harbours Administration (SAR&H) was established on 31 May 1910 with formation of the Union of South Africa by the amalgamation of the four colonial railways and all harbours in South Africa - about 11,000 kilometres of ...

), he was unable by law to protect their design.

Origin of name

The name is derived from the

Afrikaans Afrikaans (, ) is a West Germanic language that evolved in the Dutch Cape Colony from the Dutch vernacular of Holland proper (i.e., the Hollandic dialect) used by Dutch, French, and German settlers and their enslaved people. Afrikaans gra ...

word ''dolos''- plural dolosse. This word has two given derivations. states it to be a contraction of 'dobbel osse', or 'gambling' (Afrikaans) 'bones' (from Latin). Boshof and Nienaber state it to be a contraction of 'dollen os', or 'play' (old Dutch) 'oxen' (Afrikaans). The first is a meaning-shifted reference to ox knuckle-joint bones used in divination practices by ''

sangomas Traditional healers of Southern Africa are practitioners of traditional African medicine in Southern Africa. They fulfill different social and political roles in the community, including divination, healing physical, emotional and spiritua ...

'', Southern African traditional healers. They somewhat resemble these bones. The second is a reference to ox or lamb knuckle bones used by African children at play. The name was attached to the objects when Kruger's father, Joe Kruger, who also worked in the harbour, came upon his son and others playing with small models of the objects and asked him ''Wat speel julle met die dolos?'' (English: ''What are you playing at with the dolos?''). There is a very ancient game called

knucklebones Knucklebones, also known as scatter jacks, snobs, astragalus, tali, dibs, fivestones, jacks, or jackstones, among many other names, is a game of dexterity played with a number of small objects that are thrown up, caught, and manipulated in va ...

, a modern version of which uses playing pieces as shown in the adjacent photograph. The similarity between these and dolos is beyond question.

Notes and references

*''Eastern Cape Dispatch'', 28 June 1999 *''Martin Creamer's Engineering News'', 16 February 2001 *''South African Financial Mail'', 3 December 2004 * *

External links