ADCP Hull Dynamics during Floor Gauging

Paul Hannah - Otago Regional Council , 22 August, 2012


Since the advent of Acoustic Current Doppler profilers, the search has been on for the perfect platform in which to carry the ADCP. To date the performance of factory platforms on the market has been disappointing when deployed in challenging flood conditions across the Otago Region (NZ). This has led to an array of prototype platforms being developed by the end users throughout New Zealand. The New Zealand topography provides an abundance of challenging flood gauging sites. These challenges include steep bed slope, rapid velocities, poor access, turbulent water, standing waves and high debris loading. Over the past two years Otago Regional Council (ORC) Field Hydrologists have been trialling various platforms as well as new methods of ADCP deployment in an attempt to improve data capture during flood events. ADCP’s are powerful tools, but to date the platforms have proved to be the Achilles heel when it came to gauging Otago Rivers in flood. The first part of this report describes hull characteristics that have proven problematic in Otago Rivers, as well as designs that work well. The second section outlines the results of recent heli-gauging trials conducted by ORC, and how this new technique will benefit ORC’s data capture during flood events. ADCP Platform design, and heli-gauging go hand in hand as the platform performance becomes critical when direct control of the ADCP is reduced by towing the platform from a long-line below a helicopter. The potential risk when gauging from the air is increased to both to the operators and equipment if a platform is used that is not suited to the conditions. Good platform design allows better operator safety.