Significant rain event Nelson August 2022


On August 16 2022 the north of the South Island was warned about an impending severe weather event, with the greatest impact predicted to occur on the West Coast. Residents in the Buller district and particularly Westport were on standby for flooding – which would be the third severe flood in a year. By the next morning, however, it was apparent that the rain was not as heavy as predicted. Insteadthe heavy rain predicted for the Nelson region became a deluge and this area became the focus of an emergency. 

On Wednesday August 17, water levels around Golden Bay started rising rapidly, with paddocks turning to rivers and road closures cutting off Collingwood. The story was the same in the Rai Valley, which was only just drying out after flooding in February. In Nelson, people living near the Mahitahi/ Maitai River watched as the water level rose fast. At 3pm the river burst its banks. It became apparent that Nelson was suffering the worst of the weather. The tropical low which had been forecast had become a stuck weather pattern, as the atmospheric river became blocked by a “mountain” of warm air to the east of the country. 

Flood event Aug 2022

Flood event August 2022. NCC photo.

By Thursday, hundreds of homes along the Mahitahi/ Maitai were evacuated and water entered a number of houses. Meanwhile, the hills started sliding. The first report was of a slip in Enner Glynn, where a hillside became mobile and residents bravely attempted to shovel earth away from their properties. 

Maitai flood

Maitai flood. NCC photo.

Similar scenes were occurring in Atawhai and the Brook and the rain continued. By Saturday a state of emergency was declared in Nelson and Marlborough, and there were evacuations in Richmond. Roads across the region - Nelson, Tasman, Rai, and Marlborough - were severely damaged. Many roads in the Marlborough Sounds were still closed following the July deluge. After five days of relentless rain it was reported that more than 500 properties had been evacuated in Te Tau Ihu. 


Weather stations across the region recorded heavy rainfall between 10pm Friday and 9am Saturday, with the bulk of the rain falling between 11pm to 4am. One metre of rain fell in four days in some areas. 

Nelson Airport topped its entire August average for rainfall on Wednesday August 17 alone  - monthly average for all of August is 80mm. On Saturday morning the monthly total was already sitting at 296mm, with 89.2mm falling on Wednesday alone. 

The heaviest falls were recorded at the top of the Rai Valley, where 158.7mm fell, 144.9mm on the Nelson side of the Bryant Range and 144mm in Abel Tasman National Park. 

River flows were significant: 

Maitai in flood

Maitai in flood. NCC photo

  • Wairoa River - 158 cubic metres at 8pm Friday, but had reached 1290 cumecs by 7am on Saturday. 

  • The Takaka River went from 557 cumecs to 1286 cumecs  at Kotinga. 

    Maitai River in flood. NCC photo

Weather records from John Matheson's climatological data show that the total August Rainfall in 2022 was 349.8 mm which is 351% above average. The heaviest rain day was recorded at 111.6mm on the 19 of August.

The after-effects 

The impact continued to be felt well after the event. Properties were immediately assessed and either red or yellow-stickered – red meaning no entry, yellow, managed entry but no overnight stays. White meant they needed work but could be occupied. On 31 August, 91 properties in the region remained red stickered, 103 yellow stickered, and 572 white stickered. Even four months later, others had problems with utilities, like water and sewage connections. Remediation of land and insurance claims continued to dominate the lives of those affected. 

While August's rain event affected a wider area of the South Island, in Nelson alone there were 1200 insurance claims amounting to $22 million - and this figure was expected to increase as more damage was assessed. NCC estimated the overall repair bill would come to between $40 and$ 60 million dollars and even more taking in the large road repair work required on State Highway 6.

A Mayoral Relief fund was established to support affected homeowners. There was additional emergency support from Work & Income and other organisations, and coordinated information from Nelson City Council, which established new "navigator" roles in October 2022 to assist people whose homes and businesses remained affected by the rain event.   By December, $700,000 had been paid out in grants to 200 households.

Nelson’s water supply was severely compromised, when it was revealed that the City’s main pipeline was damaged 1.3km downstream from the dam and was to take weeks to fix. A 12m gap had been created by a landslide and the City had to rely on a secondary water supply. This was finally fixed in November 2022. 

maitai and pipe

Maitai pipe. NCC photo

 Roads were severely affected. SH6 between Nelson and Blenheim remained closed until August 31. There were multiple slips on the road, the worst section being the Whangamoa Saddle between Hira and Rai Valley. The road was then closed again in mid October for seven weeks to allow permanent remedial work to be carried out, only reopening to allow traffic to flow over the busy summer season.  SH63 was also closed for a time because of a washed out bridge at Branch River. When both these roads were closed the only route between Nelson and Blenheim was over the Lewis Pass.

In Tasman all roads reopened by October 5, apart from Stafford Drive at Ruby Bay – closed by a massive slip from the cliffs. Work to repair the road started in December 2022. A significant amount of work had been required to fix roads across the region, notably McCallum Road, the main access road for the Rainbow Valley Community, and Dry River Bridge on Glenview Road in Golden Bay. 

Many roads in the Marlborough Sounds remained closed for months and a number of properties were only accessible by boat. 

Flooding Rai Valley

Flooding. NCC photo

Many mountainbike and walking tracks in the Nelson area were closed for some time but by December 2022, 95% of the walking tracks had reopened and swimming holes in the Mahitahi/Maitai had been cleared of debris and gravel and were again open for recreational use.

The rain event of 2022 was significant.  An analysis by NIWA confirmed this, indicating that it was "the strongest August atmospheric river on record since at least 1959, resulting in a 1-in-120 year rain event in Nelson." However, it is only one of the many such events that have hit the region, and with climate change a real and growing concern, it will certainly not be the last of its kind. 


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