Uniform flow in open channels with movable gravel bed

Abstract

Mean flow properties and turbulent characteristics of uniform open-channel flow were experimentally studied in a reasonably steep channel with an erodible gravel bed. A recently developed Acoustic Doppler Velocity Profiler (ADVP) was used to obtain instantaneously the information on the flow profiles. From these measurements, the mean velocities, the turbulence-intensities as well as the Reynolds-stress profiles were obtained. The experimental results show that: i) the mean velocity profile can be expressed by the log-law with Br ≃ 8.42 in the inner region; Coles' law can be used to explain the velocity profiles in the entire region with Π ≃ 0.08; ii) the flow resistance coefficient,f, is explained with a theoretical relation; iii) the horizontal turbulence- intensity distribution agrees well with the exponential relation; iv) the vertical turbulence-intensity distribution agrees with the exponential relation only in the outer region; in the inner region, it curves backwards; v) the Reynolds stress are linearly distributed over the depth; vi) the friction velocities calculated with three different methods agree reasonably well with each other, this is considered as a proof that the flow is nearly two-dimensional; vii) the measured bed-load transport rates compare favorable with a bed-load relation; viii) all the above conclusions are in general valid for flows without and with bed-load transport; only small differences are noticed.