Abstract

The Bio Bio river is located between 37°00? and 39°00? south. It is one of the largest rivers of Chile, about 380 km long, and with a drainage area of 24,260 km2. Rising at an elevation of 1,200 m from Icalma and Galletué lakes situated in the high Andes, the river flows into the Pacific Ocean. It is 2,000 m wide at its mouth. Due to changes in the slope (over 0.5% in the Andes; 0.05% at the mouth), the river changes from a meandering to a braided river pattern with high sedimentation rate (650.5 t km-2yr-1) for the last 100 km. Annual precipitation varies between 1,100 mm along the coast to more than 4,900 mm in parts of the Andes range. At its mouth, water discharge of the Bio Bio varies from 120 m 3 s-1 in summer to 13,500 m3 s-1 during the rainy season. The mean annual discharge is about 1,000 m 3S-1. Water and sediment discharges of the Bio Bio river are presented and analyzed in this paper against the geology and geomorphology of the basin. It is concluded that bed load transport is much higher than suspended load. This could be the situation for all rivers on the western side of the Andes with a geomorphologic system similar to that of the Bio Bio. For most of the worlds rivers, bed load constitutes a much smaller fraction of the total sediment transported. © 2002 Gebrüder Borntraeger.