Fig. 1. Hydrodynamic characteristics of the four unobstructed flow treatments. (A) Profiles of horizontal flow speed (U_z) at various heights (z) above the sediment. ADV measurements were recorded in the center of the flume at the location of stimulus release. Each data point represents a 4 min average (mean) of instantaneous velocities collected at a frequency of 10 Hz. Precise replication of measurements heights was not possible due to slight differences in signal resolution across treatments. (B) Vertical profiles of RMS turbulence intensity corresponding to each of the velocity records in the unobstructed flow treatments. Turbulence increased with velocity, such that the slowest flow was least turbulent and the fastest flow most turbulent. In all four unobstructed conditions, turbulence intensity was greatest from 1–2 cm above the sediment and decreased with height (z) until boundary effects were negligible.