Equivalent velocity profile for turbulent flows over gravel riverbeds

Practitioners need simple estimates of the mean velocity distribution dependent on easy-measurable river characteristics. A simple formulation of the 2D mean velocity profile is thus essential. Recent field measurements obtained with the Acoustic Doppler Velocity Profiler (ADVP) in gravel-bed rivers showed that above the roughness layer the logarithmic law describes the mean velocity distribution fairly well. However, roughness parameters representing local flow conditions differ. It is assumed that the turbulence structure above the roughness layer may be described by the log-law, scaled with height, friction velocity, absolute size of the elements forming the equivalent bed roughness (k) and a coefficient designated by the letter "B". The authors present here a parameterization of the log-law, for turbulent rough flows over gravel riverbeds, where the equivalent roughness is physically based on the bottom roughness protuberances and the coefficient B should represent the bottom geometry.