Abstract
Turbulent open-channel flows over a backward-facing step with smooth and rough beds were investigated experimentally by using a straight open-channel flume. Measurements were conducted by a PIV system with a high-speed video camera capable of capturing images at the maximum sampling rate of about 900fps. The rough bed was composed of sand grains with a mean diameter of 3.5mm. The measurements were made under a condition in which no appreciable water surface variation was observed. The results show that increase of turbulent mixing by the roughness apparently shortens the reattachment length. However, the influential region by the roughness was relatively small in the present hydraulic condition.
