COMPARISON OF SSC MEASUREMENTS WITH ACOUSTIC BACKSCATTER DATA: WEST BAY SEDIMENT DIVERSION, MISSISSIPPI RIVER.

In recent years the use of acoustic backscatter (ABS) intensity from commercially available instruments, such as Acoustic Doppler Current Profilers (ADCP), has become a more widely used means of estimating suspended solids. To obtain accurate estimations of suspended sediment concentrations (SSC) from ABS the instrument must be calibrated to the conditions at the time of the survey. By plotting the distribution of measured SSC from water samples against the distribution of ABS intensity, a calibration equation was obtained that allowed for such a specified calibration. Calibrated SSC from ABS showed strong correlation to measured concentrations (r 2 =0.97) from six separate surveys conducted at different stages of the Mississippi River's hydrograph. Because this method of calibration requires a unique equation that is tied to water samples collected in unison with the ABS data, hysteresis effects are accounted for that otherwise might be missed by performing a calibration based on conditions set in a lab or from previous surveys at similar discharge and stage levels.