The role of vortex shedding in the scour of pools

Flume experiments were conducted in a 6-m flume to determine the role of turbulence in the scour of pools. Paired results from constricted-flow experiments with and without a wake zone formed behind obstructions to flow show that pools are deeper and shorter when vertical free-shear layers are present. Although non-streamlined obstructions initially present more resistance to flow, channel-bed scour develops a pool morphology that lowers mechanical energy losses to levels below those in pools with streamlined obstructions. Scour primarily enlarges the cross-sectional area in the constricted section. Feedback between pool geometry and localized turbulence production play a secondary role in total scour but still exert a major influence on final energy slopes. The experiment shows that pools with wake zones evolve to reduce longitudinal energy expenditure with an associated reduction in total turbulence production associated with the obstruction.