Horizontal ADCP for remote mapping of currents

Harbors throughout the world realize the importance of water flow information of the main waterways for ship guidance. The most ideal measurement would be real time depth averaged flow information through the water ways. Reliable estimates of discharge may also useful for a variety of organizations interested in monitoring rivers and channels. Both of these applications may be provided by a Horizontally mounted ADCP (HADCP). However, because each sound beam has a finite opening angle, this generally results in the reflection of sound against the bottom and the surface. These reflections may contaminate the measurements of the water column. A specially designed and modified 300 kHz RDI workhorse unit was used to take data at two different river locations: Jersey Point on the San Joaquin and Walnut Grove on the Sacramento river. The unit is unique in that two pairs of vertically stacked transducers are used to obtain narrower beamwidths than a standard unit. Additionally, special firmware was installed to allow the raw pressure time series from each transducer to be recorded. Algorithms to successfully detect contamination from the surface and the bottom were used to assess data quality. Provided care is used in site selection and installation, the unit works well and is capable of producing profiles to about 100 m as well as estimates of discharge. The effective range of the system varies, even in locations which are not thought to be highly stratified. This indicates the need for real-time algorithms to assess data quality to be included in the firmware of such an instrument.