A group of twenty-seven drifters was constructed from inverted plastic 19 L (5-gallon) buckets with a height of
37 cm and a 30 cm diameter, ballasted to float at the surface. Each drifter was equipped with two GPS receivers:
a Garmin Etrex (accuracy < 3 m) unit and a GPS satellite tracking communication system provided by Comtech
Mobile Datacom (horizontal position accuracy < 5 m). The Garmin unit stored location information internally
every 3 minutes, while the Comtech unit relayed location information every 30 minutes, via satellite, to a web-based
system for real-time tracking. Engineering experiments conducted in both the plume region and in Buzzards Bay, MA
indicate a low degree of wind induced slippage associated with the drifters.
The drifters were released in river discharge of approximately 159 m3/s (source: USGS gauging station at Lowell, 42.633° N 71.283° W, approximately 60 km upstream of the river mouth) and subjected to light (3 m/s) to high wind conditions (up to 8 m/s). Three waves of drifters were released on each ebb tide sampled at approximately 2 hours (WAVE I, green color), 4 hours (WAVE II, magenta color) and 6 hours (WAVE III, yellow color) after high tide. In each wave a total of nine drifters were released at three stations (North, Central, South), approximately 100 m apart, on the seaward side of the bar.