Half a Metre of Rain Falls Over the Weekend

The western part of the Tasman District was soaked by over half a metre of rain last weekend. Despite the deluge the rainfall intensities did not reach the levels seen in December 2010, when the massive Aorere flood occurred or the December 2011 rain event which resulted in slips throughout the region.

The region did not escape unscathed though, with the Murchison area receiving a repeat of the flooding seen several weeks ago, and road closures in a number of places.

The heaviest falls were at the Paradise rainfall recorder in northern Golden Bay, situated on the boundary of the Anatoki and Aorere catchments. In the 48 hours beginning midday Friday, 508mm were measured, with the next greatest total in Golden Bay being 426mm at Salisbury Bridge, and 377mm at Perry Saddle on the Heaphy track. The last two raingauges were only installed last year.

Within the same time period, 273mm fell at Third House in the Upper Brook and 279 mm at the Caretakers residence in the Roding Valley. In Richmond however, only a modest 40mm were measured.

At Murchison, 155mm were collected at the Longford recorder, this being the greatest two-day fall since records began in 1994. The one day total of 113.5mm was also the biggest seen in that time.

The worst flooding occurred in the south west of our region. The Tadmor River reached its highest level since 1994, as did the Upper Buller River. The Tadmor was graded as a 16-year flood, and the Upper Buller an eight-year flood. The relatively warm rain contributed further by thawing snow lying at low levels adding to the magnitude of flooding.

Below Murchison, the Buller River flows into the Westland District. Rainfall occurred throughout that catchment resulting in a very large flood in the lower Buller at Westport. The Buller holds the record for the largest flood flow in all of New Zealand, and this flood, while not the largest, was one of the bigger flows on record for the river.

Many of our most northern rivers reached levels corresponding to around three- to five-year floods, but those to the south in lower rainfall areas such as the Wai-iti River were only moderately affected by the recent rain.

The weather pattern bearing the latest rain has now moved west and is slowly crossing the North Island.

Further Information

For the latest information on rainfall and river flow in the region see:

http://www.tasman.govt.nz/environment/water/rainfall/
http://www.tasman.govt.nz/environment/water/rivers/