LAUSR

An experiment was conducted in the St. Anthony Falls Lab main channel flume, involving sand sediment (d50 = 0.4 mm) in unidirectional flow. The flow conditions were 1 m/s flow rate and 1 m depth, and the bed state consisted of quasi-linear sand dunes with ~1 m wavelength and 10-20 cm height. A pulse-coherent acoustic Doppler instrument (MFDop) measured high-resolution near-bed vertical profiles of velocity and backscatter amplitude at various positions spanning the dune profile. These measurements are used to obtain probability distributions of instantaneous suspended sediment concentration and flux, which are compared to predictions from two stochastic theories. While the stochastic theories were previously developed and validated for low transport rates over a flat bed, the acoustic measurements enabled measurements at a much higher transport rate; despite this, the new measurements remain in remarkably good agreement with the theories.