Buller River flows during flood NZ's largest in a century

Flood flows measured on the West Coast's Buller River this month were the largest recorded in New Zealand in almost a century, according to the National Institute of Water and Atmospheric Research (NIWA).

A raging Buller River flows through Westport after a dumping of rain. Source: Anita Kay

NIWA environmental monitoring technician Mike O'Driscoll used a radar gun from the Westport and Orowaiti bridges to measure the speed of the Buller River - which has a mean flow of 454 cubic metres per second - at its surface on July 17.

As bridges were being closed two weeks ago, the measurements showed a much bigger flow of 7640 cubic metres per second - the largest direct measurement of river flow ever completed in New Zealand.

The previous record in New Zealand using the tools used today was 5870 cubic metres per second, taken in the Grey River in 1988. 

In a statement today, NIWA hydrodynamics scientist Richard Measures said Buller River wasn't New Zealand's largest river but that it did experience big flood flows.

"The flood levels through the Buller gorge are incredible," he said.

"We can confidently say that the recent flood flows in the Buller River are the highest of any river in New Zealand since 1926, when historic records and photographs of flooding show an even bigger flood on the Buller."

NIWA said data is used to model and map flood risk, design flood defences, provide flood forecasts and understand the effects of climate change.

Data collected during this event is being used as part of project that began in April to develop improved flood forecasts for Westport.