Two-Dimensional Flow Patterns Observed at Threemile Slough Using Two RiverSondes

Two-dimensional river flow patterns were measured using a pair of RiverSondes in an experiment at Threemile Slough in the Sacramento-San Joaquin River Delta system of central California during October 2007. An earlier experiment at Walnut Grove in April 2007, on the migration path of juvenile fish, revealed complex flow patterns during periods of tidally-induced flow reversals, but data there were limited by low winds. Consequently, a follow-on experiment was conducted at Threemile Slough where wind conditions and surface turbulence historically have resulted in abundant data from a single RiverSonde. The experiment at Threemile Slough included ADCP near-surface velocity measurements from unmanned survey vessels. Quantitative comparisons between the RiverSondes and the ADCPs showed mean differences of 0.007 cm/s in the cross-channel component and 0.5 cm/s in the along-channel component, and RMS differences of 7.9 cm/s in the cross-channel component and 13.5 cm/s in the along-channel component after obvious outliers were removed. Interpolation and integration of the velocity vectors revealed complex trajectories of simulated particles during times of flow reversal and smooth trajectories during the remainder of the tidal cycle.