Bottom-Tracking ADP Used in Poverty Bay Study

A SonTek/YSI bottom-tracking ADP was successfully used by the Centre of Excellence in Coastal Oceanography and Marine Geology at the University of Waikato in New Zealand. The ADP was the focus of measurements of complex circulation in highly-stratified Poverty Bay on the east coast of the North Island where a sewage outfall is being studied.

Researchers Scott Stephens and Kerry Black used the ADP to record a complex pattern of rotating currents in depths of 10-15 m over several days and confirmed predictions of a numerical hydrodynamic model of the region. In particular, the ADP confirmed the model predictions of a residual anticlockwise circulation in the bay (Figures 1 and 2). A strong wind-driven influence on surface currents was also measured including an associated up-welling bottom-return-flow when winds exceeded ~4 ms^-1 (Figure 3).

The ADP was mounted on a small vessel (5.7 m) and operated under conditions that often included small chop on the water; however, the results were very satisfactory, particularly in shallow water where a strong bottom-return signal was obtained using the 1.5-MHz ADP.

	Figure 1. Numerical model velocity predictions in model layer three (4-9 m) revealing an anticlockwise circulation in response to a north-east shelf current.
	Figure 2. Currents at depth of 5.4 m in Poverty Bay on 17 September 1998, 12:22-14:49, measured by boat-mounted, bottom-tracking ADP. Wind measured at Gisborne Aerodrome is 1 ms-1 from 20°.
	Figure 3. Currents at depth of 5.4 m in Poverty Bay on 15 September 1998, 14:08-15:54, measured by boat-mounted ADP. A strong (6 ms-1) offshore wind is inducing an associated bottom-return-flow.

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