On unsteady velocity measurements and profiling in compression waves in an asymmetrical trapezoidal channel

A compression wave is a highly-unsteady rapidly-varied free-surface flow associated with a sudden rise in water surface elevation and may travel over very long distances along flat prismatic canals. New experiments were conducted to investigate the unsteady turbulent characteristics of compression waves, in a large-size channel. The focus was on the effects of the asymmetrical trapezoidal shape of the channel cross-section on the transient turbulence characteristics of the three-dimensional compression wave. The measurements showed a complicated unsteady motion down the transverse slope, underneath the leading edge of the compression wave. A marked increase in free-surface elevation was observed during the surge passage. A three-dimensional transient motion was observed. An intense transient recirculation was seen next to the invert at the base of the transverse slope and in the shallow flow zones. Visual observations and velocity measurements showed some recirculation primarily in the shallow water region. The results highlighted strong secondary currents on the transverse slope, albeit for short, transient periods