Vaal, a river of South Africa, chief affluent of the Orange (q.v.). It rises at an elevation of over 5000 ft. above the sea on the slopes of the Klipstapel, in the Drakensberg mountains, Ermelo district of the Transvaal, and about 170 m. in a direct line west of Delagoa Bay. It flows in a general S.W. direction, with a markedly winding course, across the plateau of inner South Africa, joining the Orange in 29° 3′ S., 23° 56′ E. The river valley is about 500 m. long, the length of the river being some 750 m.
The first considerable tributary is the Klip (80 m. long), which rises in the Draken's Berg (the hill which gives its name to the range) and flows N.W., its junction with the Vaal being in 27° S., 29° 6′ E., 12 m. S.W. of Standerton. From this point to the eastern frontier of the Cape the Vaal forms the boundary between the Orange Free State and the Transvaal. The river is usually shallow and is fordable at many places, known as drifts. But after the heavy summer rains the stream attains a depth of 30 or more feet. At such times the banks, which are lined with willows and in places very steep, are inundated. As a rule little water is added to the Vaal by its tributaries. Of these, the Wilge (190 m.), which also rises on the inner slopes of the Drakensberg, flows first S.W., then N .W. across the eastern part of Orange Free State and joins the Vaal 60 m. below the Klip confluence. Lower down the river receives from the south the Rhenoster, Valsch, Vet and other streams which drain the northern part of the Orange Free State. On the north the basin of the Vaal is contracted by the Witwatersrand and Magaliesberg range, and its tributaries are few and, save in the case of the Harts river, short. The Klip, not to be confounded with the southern Klip already described, rises on the south side of the Witwatersrand about 15 m. W. of Johannesburg, is joined by several small streams, and after a S.E. course of 70 m. reaches the Vaal 2 m. E. of Vereeniging. The Klip is of importance in the supply of water to many of the Black Reef gold mines. The Mooi rises in the Witwatersrand west of the Klip and, after running almost due S. 75 m., unites with the main stream about 90 m. below Vereeniging. It gets its name Mooi (Beautiful) on account of the picturesqueness of its banks. Some of its sources are at Wonderfontein, where the issue from stalactite caves. The Harts river (200 m.) rises on the S.W. slopes of the Witwatersrand and flowing S. by W. unites with the Vaal about 65 m. above the confidence of that stream with the Orange. The volume of water in the Harts is often very slight, but that part of the country, the eastern division of Griqualand West, in which the Vaal receives its last tributaries and itself joins the Orange, is the best watered of any of the inland districts of the Cape. The Vaal here flows in a wide rocky channel, with banks 30 ft. high, through an alluvial plain rendered famous in 1867–70 by the discovery of diamonds in the bed of the river and along its banks. The diamonds are washed out by the water and found amid debris of all kinds, frequently embedded in immense boulders. The last afiluent of the Vaal, the Riet river, rises in the Beyers Bergen S.E. of Reddersburg and flows N.W. 200 m. through Orange Free State, being joined, a mile or two within the Cape frontier, by the Modder river (175 m.), which rises in the same district as the Riet but takes a more northerly course. The united Riet-Modder joins the Vaal 18 m. above the Orange confluence.
The name Vaal is a partial translation by the Dutch settlers of the Hottentot name of the river—Kai Gariep, properly Garib (yellow water), in reference to the clayey colour of the stream. The Transvaal is so named because the first white immigrants reached the country from the south by crossing the Vaal.