Influence of bed roughness on near-bed flow characteristics is of considerable importance,
especially in turbulent flows over rough beds. This experimental study is devoted to insight
various turbulent flow characteristics such as velocity distributions, Reynolds shear stresses
(RSS) and velocity power spectra at the groove, lee and crest level of carrier fluid in an immobile
gravel bed stream. Uniform round shape gravels were used in five layers in a laboratory flume.
Nortek’s Vectrino four-receiver Acoustic Doppler velocimeter (ADV) probe was used to capture
the instantaneous three-dimensional velocity components at groove. The interference between
incident and reflected pulses in the ADV data measured in the near-bed flow zone produced
spikes. Spikes were detected and filtered with a spike removal algorithm based on the
acceleration threshold method (Goring and Nikora, 2002). The velocity power spectra provided a satisfactory fit with the Kolmogorov “–5/3 scaling-law” in the inertial subrange. Velocity
distributions below the roughness crest level fairly follows a third-degree polynomial series
Keywords: Roughness, gravel-bed stream, turbulence, Reynolds shear stresses, inertial sub- range.