A review of the suspended sediment budget at the confluence of the Paraná and Paraguay Rivers

Abstract

Abstract. In this paper the sediment budget at the confluence of the Paraná-Paraguay rivers, is updated on the base of new suspended sediment concentrations data, measured during the nineties at carefullly located cross-sections after the construction of several large reservoirs. With these data, it was possible to estimate that the suspended sediment load transported by the Upper Paraná River had decreased by 60% due the influence of the dams. This decrease occurred in spite of the influence of climate change across the Upper Paraná and Paraguay basin, which increased the precipitation and surface runoff. As a consequence of these anthropogenic and natural processes, the Bermejo River (the main source of wash load to the system) accounts for an increasing proportion of the sediment transport along the middle and lower reaches of the Paraná River. The Paraná River currently transport about 120 x 106 t year-1 of wash load, with nearly 90% of this being supplied by the Bermejo. The contribution of the Bermejo is now about 35% larger than its contribution during 1970s, when it accounted for approximately 60% of the sediment load of the Paraná River. These changes that have occurred over the last 30 years have enhanced the natural asymmetrical distribution of solid and water discharges in the Paraná River basin.