Turbulence Characteristics of New Zealand Gravel-Bed Rivers

Abstract

Gravel-bed river turbulence is investigated on the basis of field measurements in New Zealand rivers. The data include instant longitudinal velocities obtained by two methods: point measurements and vertical profile measurements. In both cases, fast-response electronic Pitot tubes were used. Analysis of vertical distribution of velocity, velocity pulsation skewness and kurtosis, structure functions, spectra, turbulence scales, and energy dissipation is presented. In most cases, the investigated velocity spectra and structure functions are characterized by the existence of the inertial subrange. The frequency spectra and structure functions satisfy the Kolmogorov “−5/3” and “2/3” laws in the range of the scales from the smallest up to (2–2.5) river depths. Using theoretical considerations and the field data, relationships for the vertical distribution of relative turbulence intensity, scale, and turbulent energy dissipation are derived. A new characteristic turbulence scale representing the upper bound of the inertial subrange is proposed and investigated. The influence of bottom roughness on relative turbulence characteristics is shown.