Sediment characteristics and sedimentations rates of a small river in Western Central Brazil

The purpose of this study is to characterise the alluvial sediments and to quantify sedimentation rates of a small river system, the Ribeirão do Torto in Central Western Brazil. The study area provides an excellent opportunity to examine the effect of land use on sedimentation rates in the region for the first time and thus contributes to understanding sediment transport processes into water reservoirs (silting). ¹³⁷Cs, ²¹⁰Pb and ¹⁴C dating techniques were used to estimate natural sedimentation rates and those associated with land use development. Complementary use of physical and chemical analyses of the sediments and contained anthropogenic materials revealed that sedimentation dynamics had varied over time. Natural sedimentation rates are more than ten times lower than in the period since the mid-1950s for the alluvial system of the Ribeirão do Torto. The results indicated that human impact had accelerated the sedimentation dynamics, which resulted in higher sediment quantities and sand content and changes of sediment sources. The variation of sedimentation rates may reflect also several other factors, e.g. natural fluctuation in flow energy or geomorphologic changes within the alluvial system. However, the multiple dating techniques and supplementary interpretation employed in this study show the potential use of radionuclides and soil/sediment parameters to identify changes in sedimentation rate, stream energy and sediment characteristics in floodplains.