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

In this paper, the sediment budget at the confluence of the Parana-Paraguay Rivers is updated on the basis of new suspended sediment concentration data, obtained during the 1990s at carefully 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 Parana River had decreased by 60% due to the influence of the dams. This decrease occurred in spite of the influence of climate change across the Upper Parana 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 Parana River. The Parana River currently transports about 120 x 10(6) t year(-1) of wash load, with nearly 90% of this being supplied by the Bermejo. The contribution from the Bermejo is now about 35% larger than its contribution during the 1970s, when it accounted for approximately 60% of the sediment load of the Parana River. These changes that have occurred over the last 30 years have enhanced the natural asymmetrical distribution of solid and water discharges in the Parana River basin. Copyright (C) 2009 John Wiley & Sons, Ltd.