Flood channel (back channel)

Position: Floodplain

 

Form

Low sinuosity subsidiary channel. Entrance height approximates bankfull stage. Commonly observed at valley margins. Floodchannel depth tends to increase down-pocket with the basal section of the floodchannel elevated above the low flow channel (i.e. it lies perched within the floodplain).

 

Process description

Flow alignment along the valley floor short-circuits the channel during high discharge events, steepening the down-valley flow trajectory and inducing scour. At lower flood magnitudes, when the entrance to the floodchannel is not breached, suspended load deposition may occur via backfilling. Flood channels do not necessarily lead to meander cutoffs, but may situate future (or past) avulsion channels.