“…The tests nominal flow rates were of 5, 5.5, 6, 6.5 and 7m 3 /h, corresponding to cross-section mean velocities in the range 0.19m/s ≤ U ≤ 0.29m/s and to Reynolds number Re = U 2H gap /ν in the range 16000 < Re < 27000, where H gap is the distance from the granular bed to the top wall. The flow rates' lower and upper bounds were fixed to, respectively, correspond to the bed-load threshold [1,3,18] and to avoid the formation of ripples on the granular bed within the time scale of the tests [19,20,21,22].…”