Scroll bar

Position: In-channel

 

Form

Elongate ridge form developed along the convex bank of a bend. Commonly develop on point bars with an arcuate morphology.

 

Process description

Formed by two dimensional flow paths on the inside of a bend. Adjacent to the thalweg, sand or gravel bedload material is moved by traction towards the inner sides of channel bends via helicoidal flow. This is accompanied by a separation zone adjacent to the bank formed at near-bankfull stage, which shifts flow alignment adjacent to the bank. Convergence of these flow paths leads to the deposition of a ridge-like feature on the point bar surface. Associated with laterally migrating channels, scroll bars reflect the former position of the convex bank. With progressive channel shift and stabilisation by vegetation, scrolls develop into ridge and swale topography.