The Orange River is a river in southern Africa that is one of the continent’s longest and one of the world’s longest rivers south of the Tropic of Capricorn. The river rises in the Lesotho Highlands, less than 125 miles (200 kilometres) from the Indian Ocean, and runs in a generally westerly direction for 1,300 miles to the Atlantic Ocean. After traversing South Africa’s veld area, the Orange defines the southern edge of the Kalahari and bisects the southern Namib before flowing into the Atlantic near Alexander Bay, South Africa. The river defines the eastern border of the South African province of Free State, as well as the border between Namibia and South Africa, as it flows through it.

Join us in learning more about Namibia’s longest river that stretches throughout the country for 1,300 miles (2,100 kilometres). The river runs into Namibia and constitutes a substantial portion of the boundary between the two countries.

Physical features

The Orange River rises 10,800 feet (3,300 metres) above sea level in Lesotho’s highlands, on a plateau, or elevated, flat terrain. The plateau is located between the Drakensberg and Maloti mountain ranges. The Orange River is known in Lesotho as the Sinqu (or Senqu) River. The annual rainfall in the area where the river rises is around 800 millimetres. The yearly rainfall in Alexander Bay, where the river runs into the sea, is less than 50 millimetres.

The Orange River travels across South Africa from east to west. It runs across the provinces of Eastern Cape, Free State, and Northern Cape. At Alexander Bay in the Northern Cape, the river empties into the Atlantic Ocean. The Orange River has two major tributaries: the Vaal and the Caledon.

Climate and hydrology

The rate of flow of the river is directly affected by rainfall patterns in the Orange basin. The rainfall in Lesotho, above the Caledon’s confluence, averages 28 to 32 inches (700 to 800 mm) per year, and this little area supplies about 60% of the Orange River’s total annual flow when coupled with the melted winter snows of the highland highlands. Annual rainfall declines from around 11 to 16 inches a year from the Caledon to the Vaal, and from 9 inches to less than 2 inches in the Namib beyond the Vaal confluence.

In the lower Orange watershed, the quantity of rainfall reaching the river as runoff drops from over 16 percent in Lesotho to less than half a percent. Summer maximum temperatures, on the other hand, rise from east to west, with the high topping 86° F (30° C) on an average of 5 days in Lesotho and 150 days in the west. As a result of these events, the rate of evaporation from east to west has increased dramatically. In the lower course of the Orange, water loss to evaporation might amount to 12 times the entire precipitation, and reservoir storage capacity in the drier parts could be decreased by up to 60%.

Economy

Both Lesotho and South Africa rely heavily on the Orange River for their economies. Fresh water from the river is used for agriculture irrigation and drinking. Power is also generated by the Orange River.

Many dams and tunnels are used in the Orange River Project and the Lesotho Highlands Water Project to assist store and convey water from the Orange River. The Gariep Dam is the river’s biggest dam. The Vanderkloof Dam and the Katse Dam are two more big dams. Lesotho is home to the Katse Dam. It is the Southern Hemisphere’s tallest dam above sea level.

The Orange River is not suitable for large boats or ships due to its numerous waterfalls and rapids. Augrabies Falls is a remarkable natural marvel consisting of a series of waterfalls and rapids on the Orange River. The falls are the principal tourist attraction of South Africa’s Augrabies Falls National Park.

Irrigation

The tremendous amount of waterborne sediment that clogs reservoirs and lowers storage capacity has impeded large irrigation and hydropower projects on most of the Orange. To counteract the problem, the Boegoeberg Dam (finished in 1931) was fitted with sluice gates, which enable much of the silt to pass through.

The Orange River Project was built farther upstream, between the Caledon and Vaal confluences, in order to gain complete control of the river. The plan includes a variety of dam and canal projects, with construction beginning in 1962. The Gariep Dam (1972), which created the Gariep Reservoir; the Van der Kloof (formerly P.K. le Roux) Dam (1977), about 90 miles downstream from the Gariep Dam; a 50-mile-long tunnel (1975) that carries water from the Gariep Dam to the Great Fish River; and an irrigation canal between the Great Fish and Sundays rivers are among the completed projects. The Van der Kloof irrigation canals below the Van der Kloof Dam were still under construction in the 1990s.

Exploration 

Jacobus Coetsee, an Afrikaner elephant hunter, was the first white man known to cross the river to the north bank, fording the Groot River at the river mouth in 1760. Later trips over the river in the 18th century were conducted by Afrikaner explorer Hendrik Hop, a Dutch officer named Robert Jacob Gordon, an English traveller named William Paterson, and a French explorer named François Le Vaillant. They examined the river from its source to its mouth, and Gordon named it after the Orange family of the Netherlands. From the late 18th century, mission sites were founded north of the Orange. In 1813, the London Missionary Society’s John Campbell tracked the Harts River from its confluence with the Vaal to its confluence with the Orange, which he investigated as far as the Augrabies Falls. In 1836, French Protestant missionaries Thomas Arbousset and François Daumas discovered the source of the Orange.

— Bronwyn Reynolds, Fizzin