99mTc vs Rhodamine WT for tracing coastal hydrodynamics

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Rhodamine WT is a tracer commonly used to quantitatively and visibly trace currents and contaminant plumes. Radioactive tracer 99mTc can also be used for these applications. Both of these tracers were injected simultaneously in a study of currents in a nearshore area of Darwin Harbour, Australia. Five subsurface drifters were released at one minute intervals during the tracer releases as an additional method of determining dispersive processes. Aerial photography was used to observe the Rhodamine WT plume. These methodologies provided data on dispersion and advection for calibration of a 2D hydrodynamic model of the harbour, which was in turn used to design the extension of a sewage outfall. Using this case study we contrast and compare the independent analysis of the two tracer methods. Some differences in the initial tracer plume are expected due to different deployment methods. Differences in detection systems may lead to time lags between datasets. The methods used to quantify tracer concentration will also be discussed. Once these technical aspects are accounted for it should be possible to directly compare the behaviour of the two tracers and their suitability for determining dispersion. Logistical aspects relating to tracer availability, detection systems, human safety, environmental impact and cost will also be addressed. Unexpected regulatory obstacles existed for Rhodamine WT – a tracer specifically designed for surface water and 99mTc was the favoured tracer out of the two for regulators in the Northern Territory of Australia on the basis of environmental impact.
Technetium 99, Rhodamines, Tracer techniques, Hydrodynamics, Coastal regions, Northern Territory, Australia, Plumes, Environmental impacts
Hughes, C. E., & Patterson, R. G. (2014). 99mTc vs Rhodamine WT for tracing coastal hydrodynamics. Paper presented at the Seventh International Conference on Tracers and Tracking Methods, "Tracer technologies to the benefit of better future", Tracer 7, 13-15 October 2014, Marrakech.