Shows an outer bank cell of secondary circulation and how this protects the bank from erosion.

What is it about?

Observations from a bend of moderate curvature in the Clutha river show flattening and deformation of the vertical profile of the primary flow due to the advection of momentum by secondary circulation. The observations are on a much larger river than previous studies so the increase in scale makes these observations robust. A counterrotating outer-bank cell of secondary circulation is associated with this deformation. A visual explanation for this outer-bank cell is proposed based around the forces of plane equilibrium and the deformation of the vertical profile of the primary flow. A suggested requirement for a counterrotating outer-bank cell is that the depth average velocity must be found at two depth locations on the vertical profile of the primary flow. The width of this outer-bank cell is twice that of previous flume experiments, perhaps due to outer-bank roughness.

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Why is it important?

Helps build body of knowledge of curved open channel flow. Has engineering applications for river channel migration and flood protection.