Wash load in the Paraná River, Argentina.

KOSTASCHUCK, R,; ORFEO, O.

S. M. de Tucumán - Argentina

Congreso; 9th International Conference on Fluvial Sedimentology; 2009

Univ. Nac. de Tucumán - Fundación Miguel Lillo

The Paraná River has one of the largest watersheds in the world, draining significant portions of Argentina and Brazil. The main tributary of the Paraná is the Paraguay River. Virtually the entire wash load, defined as fine sediment (usually <64 ìm) in permanent suspension, present in the middle and lower reaches of the Paraná originates in the Bermejo River, which is a tributary of the Paraguay. Surveys in May 2008 were undertaken to determine the discharge and wash load concentrations at three sites in the middle reach of the Paraná: Bermejo River 50 m upstream of the confluence with the Paraguay River, Paraguay River 50 m upstream of the confluence with the Paraná River, and Paraná River 300 m upstream of Corrientes Bridge. Velocity and discharge at each site was determined with an acoustic Doppler current profiler. Surface samples of wash load were taken at each site and analysed for concentration and particle size using a portable laser system. Discharge increased downstream from about 500 m3s-1 in the Bermejo to nearly 20,000 m3s-1 at Corrientes, due to the increase in watershed area and addition of flow from tributaries. Wash load samples were composed entirely of silt and clay and particle size increased slightly downstream. Wash load concentrations decreased downstream from nearly 8000 mgL-1 in the Bermejo to around 140 mgL-1 at Corrientes. Wash load flux decreased by 50% between the Bermejo and Paraguay and then remained  constant downstream to Corrientes. These preliminary results suggest that wash load is being diluted downstream in response to increasing discharge, but is also being deposited in the Paraguay River between the Bermejo and Paraná3s-1 in the Bermejo to nearly 20,000 m3s-1 at Corrientes, due to the increase in watershed area and addition of flow from tributaries. Wash load samples were composed entirely of silt and clay and particle size increased slightly downstream. Wash load concentrations decreased downstream from nearly 8000 mgL-1 in the Bermejo to around 140 mgL-1 at Corrientes. Wash load flux decreased by 50% between the Bermejo and Paraguay and then remained  constant downstream to Corrientes. These preliminary results suggest that wash load is being diluted downstream in response to increasing discharge, but is also being deposited in the Paraguay River between the Bermejo and Paraná