At the western point of the Free State, southwest of Kimberley, the Orange meets with its main tributary, the Vaal River, which itself forms much of the northern border of the province.Click to see full answer. Considering this, where does the Vaal River join the Orange River?Vaal River, northern tributary of the Orange River, South Africa. Rising at Sterkfontein Beacon near Breyten, in Mpumalanga province, it flows 750 miles (1,210 km) southwest to its confluence with the Orange near Douglas; the Vaal’s middle section forms most of the Free State’s northern provincial boundary.Furthermore, in which direction does the Orange River flow? The Orange River is the longest in South Africa, starting in the Drakensberg in Lesotho, it flows westward towards the Atlantic ocean where it spills out on the border of South Africa and Namibia. Correspondingly, where does the Orange River start? Drakensberg Lesotho How full is the Orange River? Orange River Dams The Gariep Dam (formerly known as the Hendrik Verwoerd Dam) forms the largest storage reservoir on South Africa with a total storage of approximately 5 500 million m3 and a surface area of more than 370 km2 when full.