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Floodplain processes are driven by water flows that seasonally change in direction and consist of a myriad of interacting streams of varying depth, velocity, source, sediment concentration and chemistry. Here we show, using spaceborne interferometric synthetic aperture radar (SAR) JERS-1 measurements, the first spatially dense hydraulic mapping of the passage of a flood wave through a large, topographically complex floodplain. We find that temporal changes in flood water heights(partial derivative h/partial derivative t) are more complex than typically assumed. During the passage of a flood wave, sharp variations in partial derivative h/partial derivative t are localized along some floodplain channels. These channels separate adjacent locations with different rates of infilling. Near the peak of the flood wave, some of the channels are no longer evident as controls on partial derivative h/partial derivative t. During the passage of the flood wave, flow paths change from bathymetrically influenced to hydraulically controlled ( and back again), thus it is difficult to know the flow path a-priori from bathymetry alone.

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