Analysis of floodplain storage and sedimentation in the middle Araguaia River, an anabranching system of central Brazil

The Araguaia River is the largest river that drains the Cerrado, or savanna ecosystem, in central Brazil. With a drainage area of about 377,000 km2 and a mean annual discharge of 6,420 m3s-1, the Araguaia River is an anabranching system with a tendency to braid. The study area is a middle section of the river, which maintains a well-developed alluvial floodplain. We use a water budget approach to analyze discharge data from 1976-2006 from four gauging stations along the study area, demonstrating that up to 30% of the river discharge is lost to floodplain storage during flooding periods in some river reaches. We link floodplain storage of discharge to the morphology of the channel and alluvial floodplain, emphasizing the role of morphological features such as paleomeander and oxbow lakes. Floodplain storage also displays a temporal pattern. In addition, we present initial results of floodplain sedimentation rates obtained through Pb-210 geochronology in a reach of the study area near the Aruanã gauging station. Channel and floodplain morphology is linked to floodplain sedimentation patterns. This research contributes to knowledge of water and sediment fluxes between tropical anabranching rivers and their floodplains.