SAO FRANCISCO RIVER

Portuguese Rio So Francisco, river of South America, the largest wholly within Brazil, rising in the Serra da Canastra in southwestern Minas Gerais state, and flowing north and east across the great central plateau for about 1,811 mi (2,914 km) to its mouth on the Atlantic Ocean about 60 mi (100 km) north of Aracaju. Paulo Afonso Falls on the So Francisco River, Alagoas, Brazil. The river flows more than 1,000 mi northward across Bahia state, receiving several tributaries along both banks. About 100 mi above Petrolina, the river begins a great curve to the northeast and enters a 300-mi-long stretch of rapids and falls. Below the falls, the river flows about 150 mi to its one-mile-wide mouth on the Atlantic Ocean. The upper river valley is an area of thorny forest vegetation and includes plants such as the caro (used for its fibres), the mamona (which yields castor oil), the date palm, the caj (cashew), and the rubber tree. The upper middle valley, extending to the falls zone, is less dry and is covered with grassland and forests of semideciduous trees. The falls zone passes through the dry Brazilian interior leading to the lower So Francisco, which flows through a floodplain of fine silt soils. The fish of the river are an important food source and include sardines. The climate of the river basin is dry and hot. Rainfall is deficient over most of the area and drought is frequent. Precipitation occurs during the summer months and the rest of the year is dry. The average annual discharge of the river is about 102,000 cu ft per sec (2,900 cu m per sec) but varies seasonally four to five times. The upper river valley is an agricultural region, while the lower river valley is dry and suitable for pastoral activities. Along the coast near the mouth of the So Francisco, wetland rice is grown. The river is subject to seasonal changes of water level of up to 30 ft (10 m), and all of its tributaries run dry during the winter. Its drainage basin has an area of 243,681 sq mi (631,133 sq km). The river is navigable for more than 1,000 mi upstream of Petrolina. Its hydroelectric potential, estimated at 520,000,000 kilowatts, is its most important resource; major hydroelectric dams on the river include the Trs Marias (Paulo Alfonso), Itaparica, Sobradinho, and Moxoto, which provide electric power to northeastern Brazil. The So Francisco River and its drainage network. Portuguese Rio So Francisco major river of South America. With a length of 1,811 miles (2,914 kilometres), it is the fourth largest river system of the continent and the largest river wholly within Brazil. The So Francisco has been called the river of national unity, for it long has served as a line of communication between Brazil's maritime and western regions and between the northeast and the south. The river is named for the 16th-century Jesuit leader St. Francis Borgia (So Francisco de Borja). It is an important source of hydroelectric power and irrigation for eastern and northeastern Brazil. The So Francisco basin occupies some 243,700 square miles (631,200 square kilometres). Additional reading The So Francisco River is addressed in Kempton E. Webb, The Changing Face of Northeast Brazil (1974); Manuel Correia de Oliveira Andrade, The Land and People of Northeast Brazil (1980; originally published in Portuguese, 1973); and Jos Amaury de Arago Arajo et al. (eds.), Dams in the Northeast of Brazil (1982; originally published in Portuguese, 1982). Kempton E. Webb