Boegoebergdam, concrete irrigation dam, on the middle Orange River, Northern Cape province, South Africa. The Orange River flows through a hard quartzite outcrop at the dam site. Built in 1931, the Boegoebergdam irrigates about 42,000 acres (17,000 hectares) for about 150 miles (240 km) on both sides of the river, an area where about one-half of South Africa’s cotton crop is grown.