Longitudinal bar (median bar)

Position: In-channel

 

Form

Mid-channel, elongate, teardrop-shaped unit bar, formed in flow direction in gravel- and mixed-bed channels. Bar deposits typically decrease in size downstream, away from a coarser bar head. May contain distinct imbrication.

 

Process description

As flow diverges around the coarse bedload fraction it is no longer competent to transport sediment and materials are deposited in mid-channel. Finer materials are trapped in the wake. Alternatively, there is too much sediment for the channel to transport (i.e. exceedence of a capacity limit under highly sediment charged conditions) and material is deposited.