Compound mid-channel bar

Position: In-channel

 

Form

A mid-channel bar that comprises an array of smaller-scale geomorphic units. Variable morphology reflects material texture, flow energy, and the history of flood events that induce formation and subsequent reworking, producing chute channels, ramps or dissection features. Further deposition may form ridges and lobes. If vegetation colonises parts of the bar, additional depositional features result, producing an island.

 

Process description

The assemblage of geomorphic units is dependent largely on channel alignment (and associated distribution of flow energy over the bar surface at different flow stages) and patterns of reworking by flood events. Formed initially from the lag deposition of coarser sediments (a unit bar). At high flow stage the bar may be reworked or material may be deposited around obstructions. At low flow stage, the bar may have finer depositional features deposited on top of the bar platform. The range of bedforms reflects sediment transport across the surface.