Sources and temporal dynamics of suspended sediment transport along the middle Parana River

The Paran acute accent a River is one of the world's largest fluvial systems due to its discharge. During the last 30 years, water discharge has averaged 18,389 m3 s-1 downstream of the Paraguay-Paran acute accent a confluence, where its most important tributaries, the Paraguay and the upper Paran acute accent a rivers contribute 22% and 78% of its total discharge, respectively. However, the sedimentological dynamics of this system behaves peculiarly due to the influence of the Bermejo River, a tributary of the Paraguay River. Even though the contribution of the Bermejo River discharge represents only 2% of the Paran acute accent a River discharge, its input of suspended sediments is significant due to the erosive processes in the upper Bermejo basin. Most earlier studies have primarily focused on the contributions and dynamics of the wash load (silt and clay) from the Bermejo River through the Paraguay River to the Paran acute accent a River, and neglected the relevance of fine and very fine sands (coarser than 63 mu m). These sediment fractions play a key role in bed sediment composition, roughness, and bed forms, ultimately modifying the flow resistance and the morphodynamic processes, among other environmental and biological parameters. This study seeks to quantify the suspended sediment contribution of the main tributaries of the middle Parana acute accent River during the last three decades. In particular, water discharge, sediment transport and grain size data measured at gage stations located at the Paraguay River upper reach, the Bermejo River, and the upper and middle reaches of the Paran acute accent a River are analyzed. Focus is placed on the coarse suspended sediment fraction. Additionally, the authors collected sediment samples at different river cross-sections and water discharges. The temporal analysis revealed the dynamic behavior of the sediments along the system. The results show different behaviors of the wash load and suspended sand transport provided by the Bermejo River. Along the middle Paran acute accent a reach, results suggest a significant suspended coarse fraction deposition during the highest sediment input period. Bed sediments, in turn, are re-suspended during the months with low contributions from the Bermejo and/or during the high water levels stages of the Paran acute accent a. This sediment dynamics produces a complex pattern of coarse sediment transport in the Paran acute accent a River at its middle reach, also modifying the sedi-mentological characteristics of the river bed.