Field Evaluation Of ADCP Refinements For Profiling Shallower Waters

Paul Devine, Peter Spain, Steve Maier, Mark Vogt

During recent years, RD Instruments has received increasing requests for ADCPs to be able to operate in shallower water. Providing this capability required several engineering developments with a twofold purpose (1) to reduce the unmeasured regions at the surface and bottom boundaries and (2) to control the variance in the velocity measurement as the sizes of the depth cells shrink.

Solving these issues involved several refinements of prior ADCP capabilities. These included creating an ADCP transducer (ZedHed TM) that has reduced ringing, bottom tracking at lower altitudes, increasing the pinging rate, and operating with smaller cell sizes in both slower and faster flows.

This presentation describes results from field data collected by co-located ADCPs during a variety of flow conditions. We deployed a bottom-mounted ADCP and a float-mounted ZedHed ADCP in a shallow tidal estuary during one flood / ebb cycle. Water levels ranged from 0.1 to 1.8 meters and velocities ranged from 0.0 to 0.9 m/sec. Comparison between measurements and theoretical expectations will be made.