The Manapouri tail race in Doubtful Sound will act as a natural laboratory for National Institute of Water and Atmosphere (Niwa) marine scientist Dr Craig Stevens, University of Auckland PhD student Rebecca McPherson, and scientists from Oregon State Uni› versity and Scripps Institution of Oceanography in the United States as they examine what’s going on as the two waters meet.
‘‘You fly around New Zealand and see these river plumes flowing into the ocean. They contain things like sediments and run›off from agricultural practices or roads, but when you look at it from the air you have no idea how thick it is or what is really going on,’’ Dr Stevens said.
‘‘In fact, the plumes are often only about a metre thick and dropping material at different rates depending on the speed it comes out and how mixed up it is.’’
He said they were looking at how energy and material were trans› formed as a plume flowed into the coastal ocean. The measurements were difficult to get because the water surface was constantly chang› ing.
‘‘In lots of ways it is much easier to measure something one kilo› metre down in the ocean than one metre down.’’
The team will use turbulence profilers that Dr Stevens described as ‘‘mini torpedoes’’, which shoot upwards taking measurements every couple of millimetres.
They will also use a two metre› long mini research vessel, designed to operate in this environment.
The research will improve under› standing about how material that flows off the land ends up in the ocean, resulting in better predictive tools to manage the ultimate fate of run›off.
‘‘Rivers drop sediment that will smother stuff that’s on the bottom or stop light penetrating the water column.
‘‘Also if there’s excess nutrients that can result in excess growth of algae and that also changes the light and the ecosystem. You want to know where they are going to end up and how concentrated they are.’’
Dr Stevens said for a predictive tool like a computer model to work properly, it needed to be based around reliable measurements. The fiords provided a perfect ‘‘natural laboratory’’.
‘‘At the same time we will learn more about the fiord systems which have not really been strongly explored from a physical perspec› tive.
‘‘These sorts of detailed measurements is what Niwa excels at. If you are going to build a tool or model, you need to do your best to understand if it’s even close to being right. We are making it possible for those tools to be better.’’
The work is funded by the Marsden Fund and the team will be in Doubtful Sound for two weeks.