Riverbed research aids resilience

New research into how riverbeds move has far-reaching implications, with the potential to save energy companies and councils money, warn people when bridges are at risk of collapse, and preserve fish populations.

Andrew Neverman has been doing the research as part of his PHD at Massey University, looking at how riverbeds move in gravelly rivers – something there are plenty of in Manawatu¯ .

He presented some of his findings in Palmerston North on Wednesday as part of a series of workshops organised by the New Zealand Hydrological Society.

Accurately monitoring how riverbeds moved was important, as the movement had far-reaching consequences.

Dammed rivers often needed to be flushed a few times a year to ensure algae washes out to sea, but the amount of water needed was a a mystery.

Riverbed movement could harm bridges and fish habitats, and make it difficult for councils to get reliable data about river flow and height.

Neverman said most measurement systems were either crude, such as planting coloured rocks and trying to find them downstream later, or expensive, like creating specialist systems to catch rocks pushed downstream and measuring them with laser sensors.

So he created his own system – a plate that measures riverbed debris as it bounces across – and made some fascinating discoveries.

His data, collected from the Pohangina River at Mais Reach, showed water being sucked into the riverbed caused the bed to move.

It also showed certain parameters usually touted as important in models were not – something Neverman said was slightly awkward with undergraduate students helping him collect data.

‘‘We had to explain to the students why the textbooks were wrong.’’

The plate system showed it could give reliable data in quick fashion, enabling councils to have advanced warning about large volumes of riverbed moving down rivers, he said.

Horizons Regional Council catchment data manager Jeff Watson said the council could see how changes they made to rivers affect riverbed movement.

Figuring out how to minimise riverbed movement near bridges and riverbanks would make them stronger, he said.

It would also require less work for the council to ensure measurement points for river flow and height were accurate.

‘‘We could save thousands of dollars in labour costs over the years.’’

Power companies could also get a better idea of how much water was needed to flush algae, potentially saving them money in the long run.