Calibrating the Geomorphic Clock: Remote Sensing of Sediment Storage and Transit Timescales in Alluvial River Corridors

Constraining sediment and organic carbon storage duration in river corridors is essential for understanding terrestrial carbon cycling and interpreting the sedimentary record. However, existing methods rely on geochemical dating or theoretical models tailored to idealized meandering rivers, limiting their broader application. Here, we present a remote sensing framework using four decades of Landsat imagery and an area‐based mobility metric to quantify decadal‐scale channel mobility across diverse river planforms. We extrapolate these observations to millennial‐scale sediment storage and transit times using a bounded random‐walk model informed by remotely derived channel‐belt widths. Modeled storage and transit times reproduce independent geochemical benchmarks within a factor of three across four morphologically diverse rivers. River planform and channel mobility timescales independently govern sediment transit: multithreaded reaches transmit stored sediment faster than meandering reaches, and slower floodplain reworking prolongs transit. Our results provide a scalable foundation for quantifying fluvial sediment and carbon dynamics globally.