Bedform

A bedform is a repetitive relief feature on a sediment bed shaped by the flow that moves the grains, ripples, dunes, plane beds, and antidunes in order of increasing flow strength. Under steady flow over sand the sequence climbs through ripples, then dunes, to upper-stage plane bed and antidunes as Froude number rises, each producing a diagnostic internal cross-stratification. The Ashley (1990) SEPM scheme groups all large flow-transverse forms as dunes, deprecating megaripple and sandwave, and sizes them by spacing: small 0.6 to 5 m, medium 5 to 10 m, large 10 to 100 m, very large over 100 m. Bedforms set bed roughness and bottom stress and are tracked by repeat bathymetry in navigation channels.