Concave‐bank benches on Barwon River, N.S.W.

Abstract

Concave‐bank benches, similar to ‘concave or eddy accretions’ on the lower Mississippi River, are found along the Barwon River (N.S.W.). In contrast to the lower Mississippi the slow downstream migration of the Barwon channel does not allow space for these benches to form. They can form only on hairpin bends where cut‐offs or ancient channels result in expansion of the present channel. They consist of muddy sediments deposited adjacent to the outside bank, upstream of the apex of the bend, in gentle reverse flows. The pattern of deposition suggests an association between turbulence, at the interface between upstream and downstream flow, and rate of deposition presumably following flocculation. Rates of deposition as high as 60 mm per year have been observed.