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The Orange–Fish Tunnel, constructed between 1966 and 1975, is an long irrigation
tunnel A tunnel is an underground or undersea passageway. It is dug through surrounding soil, earth or rock, or laid under water, and is usually completely enclosed except for the two portals common at each end, though there may be access and ve ...
in central
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
, built to divert water from the
Orange River The Orange River (from Afrikaans/Dutch language, Dutch: ''Oranjerivier'') is a river in Southern Africa. It is the longest river in South Africa. With a total length of , the Orange River Basin extends from Lesotho into South Africa and Namibi ...
to the Fish River valley. It is the longest continuous enclosed aqueduct in the southern hemisphere.


Purpose

For many years, large areas in the
Eastern Cape The Eastern Cape ( ; ) is one of the nine provinces of South Africa. Its capital is Bhisho, and its largest city is Gqeberha (Port Elizabeth). Due to its climate and nineteenth-century towns, it is a common location for tourists. It is also kno ...
experienced severe water shortages because of little
rainfall Rain is a form of precipitation where water droplets that have condensed from atmospheric water vapor fall under gravity. Rain is a major component of the water cycle and is responsible for depositing most of the fresh water on the Earth. ...
in the arid
Karoo The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe Khoemana (also known as !Orakobab or Korana) word is a semidesert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its extent is ...
. The situation was aggravated by the reduction in capacity of many of the existing
dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, aqua ...
s due to heavy silt deposits. The project to alleviate this situation comprised two interdependent engineering schemes — neither of which was of any use without the other. First, a dam had to be built across the Orange River, then a tunnel had to be driven to take the water across the watershed into a further river system. The Orange–Fish Tunnel, together with its network of canals, weirs and balancing dams, has enabled these areas to be restored and has made the irrigation of thousands of hectares of additional land possible. The main purpose of the tunnel is to divert water from the
Gariep Dam The Gariep Dam is located in South Africa, near the town of Norvalspont, bordering the Free State and Eastern Cape provinces. Its primary purpose is for irrigation, domestic and industrial use as well as for power generation. It the largest dam ...
to the
Eastern Cape The Eastern Cape ( ; ) is one of the nine provinces of South Africa. Its capital is Bhisho, and its largest city is Gqeberha (Port Elizabeth). Due to its climate and nineteenth-century towns, it is a common location for tourists. It is also kno ...
Karoo for irrigation, household, and industrial use.


Route

The tunnel forms part of the Orange–Fish Water Scheme where it diverts water from the
Orange River The Orange River (from Afrikaans/Dutch language, Dutch: ''Oranjerivier'') is a river in Southern Africa. It is the longest river in South Africa. With a total length of , the Orange River Basin extends from Lesotho into South Africa and Namibi ...
to the
Great Fish River The Great Fish River (called ''great'' to distinguish it from the Namibian Fish River) () is a river running through the South African province of the Eastern Cape. The coastal area between Port Elizabeth and the Fish River mouth is known as ...
and the semi-arid areas of
Eastern Cape The Eastern Cape ( ; ) is one of the nine provinces of South Africa. Its capital is Bhisho, and its largest city is Gqeberha (Port Elizabeth). Due to its climate and nineteenth-century towns, it is a common location for tourists. It is also kno ...
province. The Orange River is the largest river in South Africa by volume, and the longest. It rises in the Drakensberg Mountains of
Lesotho Lesotho, formally the Kingdom of Lesotho and formerly known as Basutoland, is a landlocked country in Southern Africa. Entirely surrounded by South Africa, it is the largest of only three sovereign enclave and exclave, enclaves in the world, t ...
and flows Westwards through increasingly drier country to discharge into the South Atlantic at Oranjemund, where, through evaporation and abstraction, the volume was far less than it was at the location of the
Gariep Dam The Gariep Dam is located in South Africa, near the town of Norvalspont, bordering the Free State and Eastern Cape provinces. Its primary purpose is for irrigation, domestic and industrial use as well as for power generation. It the largest dam ...
. The inlet tower at takes water from the Gariep Dam at
Oviston Oviston is a settlement in Walter Sisulu Local Municipality in Joe Gqabi District Municipality in the Eastern Cape province of South Africa. Township 8 km north of Venterstad, on the southern bank of the Gariep Dam The Gariep Dam is lo ...
; the name ''Oviston'' is an acronym based on the
Afrikaans Afrikaans is a West Germanic languages, West Germanic language spoken in South Africa, Namibia and to a lesser extent Botswana, Zambia, Zimbabwe and also Argentina where there is a group in Sarmiento, Chubut, Sarmiento that speaks the Pat ...
''Oranje-VISrivier TONnel''. After traversing due south under the
Suurberg The Suurberg (also Zuurberg or Suurberge) is a mountain range near the Addo Elephant National Park in the southern Sarah Baartman District Municipality of the Eastern Cape, South Africa. The range of some 70 kilometres long (west to east) i ...
mountain plateau, it releases the water to the Teebus Spruit (tunnel outlet at ), to the Groot Brak River and onwards to the valleys of the
Great Fish River The Great Fish River (called ''great'' to distinguish it from the Namibian Fish River) () is a river running through the South African province of the Eastern Cape. The coastal area between Port Elizabeth and the Fish River mouth is known as ...
and the Sundays River. The tunnel is on what is called a "self-cleansing" gradient of 2% from north to south. During construction, South Africa changed over from Imperial measurement to the
metric system The metric system is a system of measurement that standardization, standardizes a set of base units and a nomenclature for describing relatively large and small quantities via decimal-based multiplicative unit prefixes. Though the rules gover ...
, but special dispensation was made for this project to use Imperial measure throughout, which was half-built at the time.


Preliminary works

Construction started in 1966; preliminary works included a tarred road running parallel to the route of the tunnel, and three towns, Oviston at the North end, one in the middle called "Mid-shaft", on the watershed plateau some 600 feet higher than on either side, and "Teebus" at the South end. These towns included such facilities as a clubhouse, tennis courts, a community hall, primary school, clinic, etc. At Oviston there was also a power station to provide electricity to the tunnels and to the towns, and also an transmission line. Other facilities included contractor's yards, a testing laboratory, and offices for the staff.


Construction

The tunnel is in finished diameter, with a thick mass concrete lining. The ground was excavated entirely by the drill-and-blast technique. The lining was done using a travelling shutter - concrete arrived first thing Monday morning, and continued unstopped until Saturday afternoon. The concrete mix was specially developed for the project, and the "cement" content was 50% Slagment a.k.a. PFA ( Pulverised Fuel Ash). The mix contained retarders to enable the concrete to be placed up to six hours after mixing, and it also contained accelerators, to enable the shutter to be moved after only eighteen hours. The speed of the shutter was about a week. The tunnel ranges in depth below the surface between and . It is on a gradient of 1:2000. It was engineered by the British firm of Consulting Engineers, Sir William Halcrow & Partners, in association with Messrs Keeve Steyn and Partners of Johannesburg. The Client was the South African
Department of Water Affairs The Department of Water and Sanitation is one of the departments of the South African government. It is responsible for the state of water and sanitation in South Africa. In May 2009, following the election of Jacob Zuma, the Department of ...
. Halcrow's senior partner, Sir Alan Muir-Wood, sometimes known as "the father of modern tunnelling", worked on many of the world's leading tunnel projects, including the Orange-Fish Tunnel; the senior Engineer in charge of the design & supervision was Barry Kidd, who died young, before construction was completed. The tunnel was opened in 1975. When completed the tunnel's length of was the longest continuous enclosed aqueduct in the southern hemisphere and the second-longest water supply tunnel in the world. Over 200 000 m3 of concrete was used to line the tunnel which has a maximum throughput of . Construction was not without incident, and was tested both by flood and by fire. - the Inlet tunnel drive South from Shaft 2 intersected a water-bearing fissure that within 24 hours filled a mile of tunnel with water; and one of the Plateau drives intersected methane, that burned for three months. The project was divided into three sections - Inlet, Plateau and Outlet, each of about . In the Contract Documents it was anticipated that there could be one construction fatality for every mile of tunnel. The tunnel was opened in 1976.


Inlet

The Contractor on the Inlet Section was Batignolles-Cogefar-African Batignolles, a consortium of French, Italian, and South African firms. There was an inlet drive and two inclined shafts. At each entry was a small alcove with a small statue of
Saint Barbara Saint Barbara (; ; ; ), known in the Eastern Orthodox Church as the Great Martyr Barbara, was an Early Christianity, early Christian Greek saint and martyr. There is no reference to her in the authentic early Christian writings nor in the origin ...
, the Patron Saint of those who use explosives - tunnellers, miners and artillerymen. By the time construction was complete, there had been 17 fatalities, all but one were related to railway operations rather than tunnelling per se.


Plateau

The mid-section had three deep vertical shafts. The contractors on the Plateau Section were Orange River Contractors (Orco), which was composed of firms from South Africa, France, and the United States. By the time construction was complete, there had been 34 fatalities.


Outlet

The Outlet section had two shafts and an outlet drive, to discharge the water into the existing Great Fish River watercourse. The Outlet Section was contracted to J. C. I. di Penta, a consortium that was formed by two firms - Johannesburg Consolidated Investment Company (JCI) from South Africa, and Impresa Ing. di Penta from Italy.


Intake at Oviston

The
intake tower An intake tower or outlet tower is a vertical tubular structure with one or more openings used for capturing water from reservoirs and conveying it further to a hydroelectric or water-treatment plant. Unlike spillways, intake towers are intended ...
is situated on the south bank of the Gariep Reservoir at
Oviston Oviston is a settlement in Walter Sisulu Local Municipality in Joe Gqabi District Municipality in the Eastern Cape province of South Africa. Township 8 km north of Venterstad, on the southern bank of the Gariep Dam The Gariep Dam is lo ...
, approximately upstream of the dam wall. Seen from above, the intake tower is shaped like a four-leaf clover with each leaf containing an inlet gate - all at different levels. In this manner, water can be drawn from different levels to help control the water quality. Each of the four inlets can be sealed off to allow complete de-watering of the tunnel for routine maintenance.


References

{{DEFAULTSORT:Orange-Fish River Tunnel Orange River Great Fish River Water tunnels Tunnels in South Africa Tunnels completed in 1975 Interbasin transfer af:Oranjerivierprojek#Oranje-Vistonnel