Keeping an eye on river flow

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.

Follow Our Changing World on Apple Podcasts, Spotify, Stitcher, iHeartRADIO, Google Podcasts, RadioPublic or wherever you listen to your podcasts.

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.

Often - too often - rain means floods. Flooding is the most frequent natural disaster in this country. In the last dozen years, insurers have paid out more than $1 billion to people whose property and lives have been affected by flooding. Our complex and extensive river system and geography means New Zealand is extremely vulnerable. The likelihood of more extreme weather events is rising due to climate change. Preparation, planning and foreknowledge are key.

Dr Celine Cattoën-Gilbert is a hydrological forecasting scientist at NIWA and she leads a team at work on a national river flow forecasting tool that hopes to ‘support and strengthen our planning for and response to extreme rainfall events.’

The project monitors relative flow values in many of our ungauged rivers and then compares them with more than four decades of climate records. The result is a series of video animations that it is hoped will make it possible to predict river levels on a national scale up to 48 hours into the future.

The goal is greater public safety and the animations will be available to anyone: farmers, city dwellers, trampers and fishers as well as local government.

The national river flow forecasting tool project is still at proof-of-concept stage and Dr Cattoën-Gilbert  and her team have lots of work to do before it can be used by the public. While you’re waiting, if you’re worried about the level of your nearby river, you can check weather sites like NIWA or Metservice, go to local government websites and listen to your radio for weather warnings.