Quantitative Meso-Scale Mass-Flux Routing Across a Large Tropical Foreland Basin

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9903157David R. Montgomery We will study and model the role of foreland basins in modulating the transport of sediment from mountain ranges to lowland rivers and estuaries, developing a quantitative, process-based model of sediment transport and storage, including fine-grained 'washload', by sinuous, mobile rivers. We will develop insights from earlier investigations of floodplain sedimentation processes along the Amazon River by studyingAndean tributaries of the Amazon as they cross the foreland basin of eastern Bolivia. We have initiated field observations and satellite-image interpretation of these Bolivian rivers as an outgrowth of our prior study of the flux of sediment out of the Andes into the foreland basin. The field study will include longitudinal transects along the river to measure channel characteristics required for flow and sediment routing along thechannel and into the floodplain, as well as transects across floodplains to collect sediment cores for 210Pb and 137Cs that will facilitate the testing of calculations and other hypotheses concerning processes that exchange sediment between floodplain and channel. The field sampling will be conducted in the context of a mathematical model of sediment transport and storage (of spatial 'reach-scale' 1-10 km and temporal scale 1 year) in a set of sinuous river channels crossing a broad floodplain. The results ofour study will contribute to theories of the relationship between tectonism, fluvial geomorphology, and sedimentation in basins and along rivers. The study will also address the fluvial geomorphic relationships between sediment transport and channel and floodplain characteristics, and will develop methods for sediment routing through mountain-front reaches of mobile channels and dynamic floodplains which are of interest to scientists, engineers, and resource planners concerned with the habitability of large alluvial valleys.