A technique for accurate measurement of the average water velocity in
estuarine environments has been developed. The technique is based on
measuring the travel time of 200-kHz ultrasonic signals. A high degree
of precision has been obtained using a cross-correlation technique, and
long, detailed time series have been recorded. However, in some
geometries the precision is degraded by multipath interference.
Measurements of current speed in California's Sacramento-San Joaquin
River Delta system will be discussed, with particular reference to the
effects of multipath interference. Data were collected throughout a
large flood in Dec. 1996-Jan. 1997. An analysis of the variation of the
strength of the ultrasonic signal has been carried out to determine the
attenuation of the signal due to the load of suspended sediment, and the
results will be presented. The current-velocity time series recorded in
the San Francisco Bay also show wave trains from boat wakes. These
wakes will be discussed.