Echoes of Bola, with more rain to come

DEBRIS: Beach Road at Tokomaru Bay was littered this morning with rocks, washed up in the overnight storm. Picture by LilyBeth Houia-Raroa

MetService this morning upgraded its “orange warning” to “red” and says the weather has “the potential of an extreme event”.

It warned the district could expect a further 150 to 200 millimetres of rain on top of what had already fallen.

The deluge that has already hit the East Coast will have brought memories of 1988's Cyclone Bola flooding back for many residents, especially those at Tolaga Bay.

As in 1988, there is a sub-tropical low sitting off the North Island, hosing a stream of dense moisture on to the district from the northeast.

At Tolaga, heavy downpours over the past 48 hours swamped the Uawa-Hikuwai River catchment, dumping especially hard on the coast-facing river valleys.

Large rainfall totals were recorded from the top of East Cape and Waikura Valley, through Ruatoria, Te Puia Springs, Tokomaru Bay and Tolaga Bay.

While the downpours were nowhere near the peak of Cyclone Bola — over 900mm recorded in the hill country between Gisborne and Tolaga — that was a full three-day event.

Even so, Te Puia Springs township recorded 314.5mm over the 24 hours up to 7am today and 423mm for the past seven days, virtually all of which fell over 48 hours.

Ruatoria township had 154mm in the 24 hours to 7am today, with just over 238mm over the rain event.

The two gauges on the Hikuwai River recorded 220-230mm over the 24 hours to 7am and over 300mm in the rain period.

Over most of the Raukumara hill country, stations generally recorded 170 to 180mm.

The rain reached lesser, normal autumn amounts around Gisborne and further south, ranging from 30mm to some over 100mm.

The rivers of the top part of the district all came up rapidly with big hourly totals in the early part of this morning.

At Te Puia, over 57mm fell in just one hour between midnight and 1am this morning.

On the Hikuwai River, 130mm fell in six hours from 9pm last night to 2am this morning, with almost half of that between 1am and 2am.

As a result the river rose alarmingly, from around 10.5 metres just after 1am, to a near-record peak of 12.84m at Willowflat at 5.15am this morning.

The highest the Hikuwai has been seems to have been on March 7, 1988, during Cyclone Bola, when a peak of 14.37m was recorded.

Other 12m-plus events have occurred, mostly in the past 10 or so years, although there was one big flood event in 1916 which swept a span of the Uawa River bridge away.

In the north, the Waiapu River peaked at 6.7m at 3.30am while the Waimata River at the Monowai Bridge hit 4.2m and the Waingaromia River at Terrace Station peaked at almost 4.8m.