GPS drifter data from near-field river plume in Doubtful Sound, New Zealand

Date 2016-03-04
Temporal extent 2016-03-04 -2016-03-13
Author(s) McPherson RebeccaORCID1, Stevens CraigORCID1, 2, O'Callaghan JoanneORCID2, Lucas AndrewORCID3, Nash JonathanORCID4
Affiliation(s) 1 : University of Auckland, Department of Physics, Auckland, New Zealand
2 : NIWA, National Insitute of Water and Atmospheric Research, Wellington, New Zealand
3 : Scripps Institution of Oceanography and Department of Mechanical and Aerospace Engineering, University of California San Diego, San Diego, CA, USA
4 : College of Earth, Oceans and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA
DOI 10.17882/79574
Publisher SEANOE
Keyword(s) river plume, plume spreading, drifters, dispersion, stratified flows

Here we provide GPS drifter data from the near-field region, Deep Cove, in Doubtful Sound, New Zealand. A controlled freshwater discharge is carried from alpine lakes (Manapouri and Te Anau) through the Manapouri hydroelectric power station and, via a constructed channel, into the head of Doubtful Sound, located on the southwest coast of New Zealand (45.3 S, 167 E). The freshwater tailrace is discharged into the head of the inner fjord, Deep Cove. Deep Cove is 3.6 km long and, flanked by steep topography, has a maximum depth of 126m that occurs within 50m of the shoreline. A 2-week field campaign was conducted in March 2016.

Lagrangian measurements of near-surface currents were made during six GPS drifter experiments. The plume discharge rate and wind speeds for each experiment are detailed below, and wind direction was consistently up-fjord due to the surrounding steep topography.

The drifters each had a cylindrical drogue of height 0.5 m and diameter 0.2 m, and were ballasted to measure the upper 0.5 m of the water column by a small spherical float. Wind slippage was minimal as the float had little exposure to wind above the surface water level. Each drifter was equipped with a GPS receiver (Columbia V-900 GPS data logger) which recorded every 1 second. The GPS devices have a position accuracy up to 1.5 m, depending on satellite coverage. The drifters were released approximately 10 m apart across the width of the tailrace discharge point and were recovered after $\sim 1$ hour. A total of 8 drifters were deployed in the first two experiments then, due to the loss of a GPS receiver, 7 drifters were deployed and retrieved in the subsequent four experiments

Licence CC-BY
Acknowledgments This research was funded by the New Zealand Royal Society Marsden Fund, the Sustainable Seas National Science Challenge and the National Institute of Water and Atmospheric Research Strategic Science Investment Fund, and supported by the National Institute ofWater and Atmospheric Research (NIWA). The authors would like to thank Brett Grant, Mike Brewer, Tyler Hughen and June Marion, who helped with the 2016 field experiments, and Meridian Energy for providing the tail-race flow data. Bill Dickson and Sean Heseltine from the University of Otago skippered the vessels for the duration of the field campaign.
Sensor metadata

GPS Drifter deployment conditions for each experiment

Day (March 2016)    Wind Speed (m/s)         Discharge Rate (m3/s)    Total Drifters Retrieved
        04                         5.6 - 6.8                              515                                8
        06                         0.8 - 2.4                              527                                8
        07                         1.5 - 1.8                              501                                7
        08                         4.8 - 6.0                              530                                7
        09                         2.3 - 2.6                              532                                7
        13                         4.1 - 5.3                              536                                7

File Size Format Processing Access
GPS Drifter Data 2 MB KMZ/KML Raw data Open access
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How to cite 

McPherson Rebecca, Stevens Craig, O'Callaghan Joanne, Lucas Andrew, Nash Jonathan (2016). GPS drifter data from near-field river plume in Doubtful Sound, New Zealand. SEANOE.