<P> In the dry winter, the volume of the water in the river is considerably reduced because of the rapid run - off and evaporation . At the source of the Orange, the rainfall is about 2,000 mm per annum, but precipitation decreases as the river flows westward; at its mouth, the rainfall is less than 50 mm per year . The factors that support evaporation, though, tend to increase in a westerly direction . In the wet season (summer), the Orange river becomes an impetuous, brown torrent . The huge mass of sediment carried constitutes a long - term threat to all engineering projects on the river . </P> <P> The total catchment of the Orange River (including the Vaal) extends over 973,000 km2, i.e. equivalent to about 77% of the land area of South Africa (1,268, 5358 km2). Around 366,000 km2 (38%), however, are situated outside the country in Lesotho, Botswana, and Namibia . </P> <P> The earliest precolonial inhabitants called the river Gariep' . An early Dutch name for the river was Groote Rivier meaning "Great River". The river was named the Orange River by Colonel Robert Gordon, commander of the Dutch East India Company garrison at Cape Town, on a trip to the interior in 1779 . Gordon named the river in honor of William V of Orange . A popular but incorrect belief is that the river was named after the supposedly orange color of its water, as opposed to the color its tributary, the Vaal River (vaal being Afrikaans for pale or grey). Since the end of apartheid, the name "Gariep" has had greater favour in official correspondence in South Africa, although the name "Orange" has greater international recognition . In Lesotho, where the river rises, it is known as the Senqu River . </P> <P> The Eastern Cape Geographical Names Committee has advertised its intention to consider a name change for that portion of the river that forms the border between the Eastern Cape and the Free State, with suggestions being IGqili or Senqu . The advertisement placed in the Aliwal Weekblad newspaper states that the "present name is perceived to have a strong association with the history of colonial subjugation and has therefore no place under the current democratic dispensation ." </P>

Where did the orange river get its name