Floods, slips and road closures expected in Nelson and Tasman

The developing weather situation in Nelson and Tasman has prompted the activation of the region’s Emergency Operations Centre (EOC), to be set up in a monitoring mode, late today Tuesday 16 August.

The Buller Region has been issued a red heavy rain warning and have activated their Emergency Operations Centre earlier in the day.

The Emergency Operations Centre is fully operational, while a state of emergency has been declared for the whole of the West Coast region.

This area is expecting periods of heavy rain up to 550 mm of rain to accumulate about the ranges south of Little Wanganui, and up to 280 mm elsewhere. Dangerous river conditions are expected with significant flooding with slips and floodwaters which are likely to disrupt travel, making some roads impassable.

The Tasman and Nelson areas have a heavy rain warning orange for west of Motueka and there is the same for Richmond and Bryant ranges, Rai Valley, Nelson Region and the Marlborough Sounds.

There is a heavy rain watch yellow for the Tasman District east of Motueka excluding Richmond and Bryant ranges, Rai Valley, Nelson Region and the Marlborough Sounds and the same for Marlborough northwest of the Inland Kaikoura Range and south of the Richmond Range.

There is quite a complex area of warnings and watches. If in any doubt check with MetService and see their maps of areas with warnings and watches.

Finally there is a strong wind watch yellow from 8am Wed, 17 Aug to 6am Thu, 18 Aug. The areas effected are Nelson, Tasman and Buller with Northeast winds which may approach severe gale at times.

Heavy rain may cause streams and rivers to rise rapidly with surface flooding and slips also possible and driving conditions may be hazardous.

In Tasman there is an expectation that rain in large amounts will accumulate about the ranges in the west. Some models indicate 650 to 750 mm about the ranges during a period from 9am Tue - 6pm Thu, 18 August. To a lesser extent rainfall will accumulate in the rangers to the east and in Nelson itself.

NIWA weather Tweet

A long-lived atmospheric river (AR) will make landfall in the South Island on Tuesday, intensify Wednesday-Thursday & last into the weekend.

This will lead to flooding, slips & washouts with well over a month's worth of rain, especially in the northern & western South Island.

The Nelson and Tasman Emergency Operations Centre advise “at this stage it is important that residents note that now is the time to prepare for heavy rainfall and associated hazards. Clear drains and gutters, move stock to higher ground and consider your travel plans.”

The highest rainfall accumulations remain in Golden Bay and in the hills behind Richmond. Less rain is predicted in the Upper Motueka and Nelson Lakes areas.

“Widespread surface flooding is expected on low-lying ground, as well as areas in the vicinity of rivers, particularly the lower Aorere Valley, Waitapu splash as well as the mid and lower Tākaka Valley.”

“In addition, there is also the potential for moderate flooding in the Aorere, Takaka, Riuwaka, and lesser flows in the Motueka, Waimea and Maitai Rivers. Council staff are monitoring this closely and if the information changes updates will follow.”

The ECO advise that even a small increase in rainfall could increase peak flows significantly so they recommend residents be prepared especially where assets or animals are at risk. While they are only expecting moderate flooding, they need to make sure the community is prepared for the situation to change.

There is potential for landslips, disruption with road closures, tree falls with wet ground and high winds and the wastewater treatment systems could be put under strain.

Local controller Rob Smith says “Nelson Tasman Civil Defence Emergency Management (NT-CDEM) will be operating in the monitoring mode overnight with increased presence from 7am on Wednesday morning to monitor and manage the response to the event.”

He went on “it is also important that people delay or avoid unnecessary travel, particularly those travelling to or from Golden Bay/ Mōhua in the next 72 hours and that people need to be prepared and take necessary precautions to protect themselves and their property.