Reconnaissance of sediment transport and channel morphology in the Lower Rio Bermejo Basin, Argentina - with a section on reconnaissance of the lower Rio Pilcomayo Basin, Argentina and Paraguay

Sediment transport conditions are described for the Lower Rio Bermejo and the Rio Pilcomayo in the Gran Chaco region of northern Argentina and southern Paraguay. The Lower Rio Bermejo is in many ways atypical, as its channel narrows downstream. Also its flow decreases downstream even though average annual rainfall at its mouth is twice that at its head (1,200 mm vs. 600 mm) and its suspended-sediment at El Yacare was about 41 million metric tonnes per year during 1970-73 and 82 million metric tonnes per year at El Colorado. The Rio Pilcomayo ' Superior ' disappears near Laguna Escalante, owing to plugging of its channel by sediment, into a network of shallow lakes and marshes. Another stream known as the Rio Pilcomayo ' Inferior ' appears about 160 km to the southeast and meanders downstream to the Rio Paraguay. The Rio Pilcomayo ' Superior ' carries about 100 million metric tonnes of sediment per year. The average annual concentration of sediment is more than 6 kg per cubic meter of flow. (Woodard-USGS)