AbstractChannel change induced by tributary sediment injection to a regulated, gravel‐bed river is described for the River Rheidol, U.K., eighteen years after dam closure. Morphological and sedimentological data are presented for an aggrading reach. A primary lobate bar appears to have initiated flow separation and the subsequent construction of channel‐side berms. Hydraulic sorting has operated to produce both longitudinal and lateral particle‐size reduction, and selective particle‐size dispersal appears to be an important process influencing channel change. The channel is adjusting to a lower width‐depth ratio form, of smaller capacity, and with a steeper slope.