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    Saturday, 30-Oct-2004 04:15:17 EDT

USGS Tethered ADCP Platforms become a Worldwide Trend

By Scott E. Morlock and Michael S. Rehmel

When the idea of a tethered boat for an Acoustic Doppler Current Profiler (ADCP) entered Jim Stewart's mind in 1998, it never occurred to him that it would one day be accepted worldwide. Jim's idea has increased the ability of USGS hydrographers to measure streamflow while eliminating some of the risk they face and has had such utility that it has spread from Indiana to countries across the globe.

Streamflow information is a vital national asset. Understanding and monitoring the flow of the Nation's rivers helps to protect lives and property and to ensure adequate water resources for a healthy environment and economy. The USGS currently operates and maintains 7,000 streamgaging stations, collecting data for a variety of uses including forecasting floods; establishing flood plains; designing dams, highways, bridges, and water treatment facilities; tracking reservoir inflow and outflow; and assessing river conditions for recreation.

The USGS has been using ADCPs in making streamflow measurements since 1985. Simply stated, ADCPs use sound energy to measure water velocity and depth and thereby compute streamflow. By the late 1990's, USGS use of ADCPs with manned boats was commonplace on large rivers. For Stewart and his staff, combining the ADCP with unmanned boats, radio communication, and ropes was an obvious step forward -- advancing the speed, accuracy, and safety of streamflow measurements and extending their use to small streams by removing the need for a boat. Crews could operate the tethered boat from bridges or cableways instead of being in or on the water.

Stewart, with the help of his Indiana staff, designed a prototype ADCP boat -- a tethered, lightweight catamaran. The catamaran hulls were made of polystyrene planks glued together, and a plywood platform secured the ADCP, batteries, modems, and transmitters. The boat was built in Stewart's garage over a weekend. The prototype was so successful that the Indiana District built several similar tethered boats for other USGS districts.

The original tethered boat built in Jim Stewart's garage in Indiana. The original tethered boat built in Jim Stewart's garage in Indiana.

The USGS Kentucky District Office also developed a remote-controlled boat for conducting bridge-scour investigations. Recognizing the potential of these technologies, the USGS initiated a project to refine the tethered and remote-controlled ADCP boats.

A search for possible off-the-shelf products did not yield any hulls that met the project specifications. Private vendors were commissioned to construct prototype hulls specifically designed for making ADCP streamflow measurements. The resulting hulls included two catamaran, two mono-hull, and three trimaran designs, which were tested in a tow-tank at the USGS Hydraulics Laboratory at Stennis Space Center and in the field during ADCP streamflow measurements under various flow conditions. The results of the testing indicated that, although any of the designs could be used under certain conditions, trimaran designs provided the best all-around performance under a range of conditions.

The manufacturer of the three trimarans tested now offers a fiberglass trimaran. This product is based upon the trimaran prototypes tested and is designed specifically for use as a tethered boat with an ADCP.

Today 158 tethered boats have been sold worldwide -- to at least 18 countries on every continent except Antarctica and Australia. The Swedish Meteorological and Hydrological Institute, for example, owns two tethered boats. The United Nations Food and Agricultural Organization has tested the tethered boats and has at least four boats in the Nile Basin.

Tethered boat being evaluated by the United Nations Food and Agriculture Organization. Tethered boat being evaluated by the United Nations Food and Agriculture Organization, which has at least four tethered boats in use in the Nile Basin. (Photo courtesy of RD Instruments.)

A USGS Open-File Report, Tethered Acoustic Doppler Current Profiler Platforms for Measuring Streamflow, is available on the web at http://in.water.usgs.gov/newreports/rehmel_teth_dop.pdf (493 kilobytes PDF)

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