Rivers in reverse: Upstream-migrating dechannelization and flooding cause avulsions on fluvial fans

Abstract The process of river avulsion builds floodplains and fills alluvial basins. We report on a new style identified in the Landsat satellite record. found 69 examples retrogradational avulsions rivers densely forested fluvial fans Andean New Guinean Retrogradational are initiated by channel blockage, e.g., logjam, that with sediment forces water overbank (dechannelization), which creates chevron-shaped flooding pattern. Dechannelization waves travel upstream at median rate 387 m/yr last average for 13 yr; many show multiple dechannelizing events same reach. ends is complete when finds flow path. simulate upstream-migrating dechannelization one-dimensional morphodynamic model open flow. Observations consistent results blockages can cause steep (10−2 to 10−3), low-discharge (~101 m3 s−1) rivers. This illustrates floodplain sedimentation unaccounted ecologic stratigraphic models.