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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). 137 Cs, 210 Pb and 14 C 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.

The management of water and land resources in the Distrito Federal (DF), Western Central Brazil is characterized by very dynamic changes of land use/land cover driven by economic development, population growth and climate change. This problem is addressed by the project IWAS-ÁGUA DF which aims at creating a scientific base for the sustainable management of water and land resources in scope of an IWRM approach for the Distrito Federal. Land use change and climate change are affecting water resources in the Distrito Federal already substantially. Major effects identified during the project phase are (1) decreasing base flow during the dry season, partially caused by the expansion of agriculture and urbanization and (2) sediment generation and siltation of reservoirs mostly caused by urbanization. The general objective of the project is to contribute to an IWRM approach for the Distrito Federal, identifying causes of problems and possible solutions to maintain sustainable water supply for the region. The objective of the selected five case studies was to develop approaches with focus on all river basins of DF (1) to assess effects of land use on water resources in the past and with focus on the Pipiripau river basin (2) to predict the efficiency of measures (environmental services) and C. Lorz