Bío-Bío

Course

The Biobío River originates at the east shore of Galletué Lake, in the northeastern part of the Araucanía Region near the international border with Argentina. The river flows east for a few kilometers to the point where it receives the waters of the nearby Icalma Lake, through a short stream. It then turns its course northwestward, meandering through a broad Andean valley and merging with some minor tributaries, such as the Lonquimay and the Rahue. The Lonquimay is fed by some glaciers of Sierra Nevada and passes close to the town of the same name. Just downstream from the confluence with the Rahue, the upper course of the river—locally known as Alto Bío Bío—begins to run rapidly through a narrow valley surrounded by mountains, the path becoming increasingly steep.

Hydrology

The Biobío basin can be divided into five hydrological sectors, each with a distinct flow regime. The upper sub-basin, extending from the river's source to its confluence with the Lirquén River and including the Lonquimay River, has a mixed rain-and-snowmelt regime, with major floods in July and November driven respectively by rainfall and thaw; low water occurs from January to March, when precipitation drops and irrigation demand rises. The middle sub-basin, between the Lirquén confluence and the mouth of the Vergara River—including the Bureo, Mulchén, Lirquén, and Duqueco tributaries—is predominantly rain-fed, though the main channel retains a mixed regime, with the same January–March low-water period.

History

The name "Biobío" comes from Mapudungun, the Mapuche language. For centuries the river marked the northern boundary of the Mapuche territories in south-central Chile, separating them from the Picunche peoples to the north. Juan Bautista Pastene is credited with sighting the river in 1544. During the Conquest of Chile, Pedro de Valdivia and his successors founded a number of forts and cities in the Biobío basin, including Concepción and Angol (originally known as Los Confines), in an effort to push Spanish control further south.

The Biobío subsequently became the traditional borderline, or "La Frontera," during the later part of the War of Arauco between La Araucanía, the southern Mapuche self-ruled areas, and northern Spanish-ruled Captaincy General of Chile.