Longitudinal bar (median bar)
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.
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.