Keeping an eye on river flow

Two stories on keeping an eye on river flow - helping fish to migrate back upstream, and development of a national river flow forecasting tool.

Fish friendly flow

For thousands of years several species of New Zealand's native freshwater fish have been making journeys from the rivers, down streams, to the ocean, and back upstream again, as part of their natural lifecycle. Until we started putting things in the way.

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Look out into the fields and ditches of New Zealand, along the roadside and down on the farms, and you'll see them - culverts. Structures designed to channel water past an obstacle or under structures, such as roads. Often made of steel, plastic or concrete in either a box or pipe design, many in Aotearoa have been designed with water flow considerations in mind, but not the needs of migratory fish.

Changing the bottom of a stream into a uniform flat piece of concrete can mean very fast and uniform water flow. But native juvenile fish, on their return from their ocean phase of their lifecycle, just can't swim upstream against these flows. They're too fast. Plus, many culverts have steep drop-offs that some fish can't climb up and over.

Different solutions to this problem have been proposed - including remediation of the existing culverts - that is, installing devices to make them more fish friendly. Because if these fish can't make it back upstream, we lose the next generation, and most of these migratory species are already classified by the Department of Conservation as threatened with extinction or at risk of becoming so.

Claire Concannon catches up with Stephanie Patchett, an engineering master's student from the University of Canterbury, as she begins her research testing some of these devices in real world settings. In collaboration with a team of scientists from the Department of Conservation, the study will look at fish numbers up and downstream of each culvert before and after the devices have been installed to figure out which devices work best in different situations.

Forecasting the flow

It rains a lot here in New Zealand. A lot.

Between 600-1600mm falls here every year. For context, Australia gets around 400mm annually, although a more apt comparison might be with the United Kingdom, which records around 900mm every year.

Westerly winds scream in from the roaring forties, hit our high mountain chain and then rain falls, in vast quantities, sometimes very quickly…

Go to this episode on rnz.co.nz for more details