An experimental study of turbulence in a heterogeneous channel

This paper examines the velocity field in an idealised heterogeneous open channel during normal flow conditions, corresponding to two different subcritical flow conditions (discharges of 0·040 m³/s and 0·056 m³/s, with corresponding Froude numbers 0·51 and 0·57). The bed of the channel is formed of two full-length, longitudinal strips of equal width, a smooth section constructed from polyvinyl chloride and a rough section constructed from gravel (d₇₂ = 10 mm). The results indicate that the turbulence appears to propagate vertically from the rough bed and horizontally over the rough–smooth boundary. There is also evidence to suggest that the turbulent momentum transfer is maximised at the rough–smooth boundary. Secondary flow structures are seen to exist due to the rough–smooth boundary and provide another mechanism for momentum transfer. These transfer mechanisms are important in understanding the effect of a heterogeneous channel bed on open-channel flow.