Quantifying Channel Mobility and Floodplain Reworking Timescales Across River Planform Morphologies

Source-to-sink transfer of sediment and organic carbon (OC) is regulated by river mobility. Quantifying trends in river mobility is, however, challenging due to diverse planform morphologies (e.g., meandering, braided) and measurement methods. Here, we utilize a remote-sensing method applicable to all planform morphologies to quantify the mobility timescales of 80 rivers worldwide. Results show that, across the continuum from meandering to braided rivers, there is a systematic reduction in the timescales of channel mobility and-to a lesser extent-floodplain reworking. This leads to a decrease in the efficiency with which braided rivers rework old floodplain material compared to their meandering counterparts. Reduced floodplain reworking efficiency of braided rivers leads to smaller channel-belt areas relative to their size. Results suggest that river-mobility timescales derived from remote sensing can aid in the characterization of sediment and OC storage and transit times at a global scale. Rivers transport sediment and organic carbon (OC) from the mountains to the sea, and river movement affects sediment and OC transit times in landscapes. Understanding the controls on timescales of river movement is critical for assessing how fluvial processes influence the terrestrial carbon cycle. While previous work has quantified different river planform shapes on the Earth's surface (e.g., meandering, wandering, and braided), little is known about how the pace and nature of river movement is different between river planform shapes. This is because we lack methods to measure and compare river movement across different river planform shapes. Here, we leverage a tool to quantify river movement from time series of satellite imagery that is equally applicable to all river planform shapes. We apply this method to calculate the timescales of river movement of 80 rivers worldwide for the last 37 years. We show that (a) braided rivers migrate faster than meandering rivers, and (b) braided rivers move over a smaller area relative to their size. Comparing results with geochemical observations from the R & iacute;o Bermejo-a well-studied river for sediment-OC cycling-we show that our mobility framework may provide a new way to assess sediment and OC storage timescales in floodplains. We quantify timescales of floodplain reworking and channel-overlap decay from satellite imagery of 80 rivers worldwide From meandering to braided planform morphology, there is a reduction in the overlap timescale and the reworking timescale Mobility timescales provide a means for remotely quantifying terrestrial-sediment and organic-carbon storage and transit