The worst hit waterway in the deluge of October 15-16 was the Turakina River, which had a 75-year flood.

Flooding of up to 57 houses in Wanganui's Anzac Pde was narrowly averted and the highest rainfall to a contributing waterway was recorded at Marco Rd near the Whangamomona River in Taranaki - 133mm over a 24-hour period.

A report for Horizons Regional Council's catchment committee meeting yesterday puts some statistics around the October flood event.

While that volume of water in the Turakina River could only be expected every 75 years, the Whanganui had a 23-year flood and the Whangaehu and Rangitikei had 22-year floods.


The largest amount of land to be flooded was on the lower Whangaehu River - 947ha. On the lower Turakina 835ha were flooded - with crops lost and damaged. There was a lot of bank slumping in both rivers, but the report said water drained readily because the council has been removing bank vegetation that used to slow it.

The highest rainfall over 24 hours was at Marco Rd near Whangamomona, 133mm. The Whangamomona River is one of the Whanganui's tributaries.

The next highest was 115mm in the upper Kawhatau Valley, up against the Ruahine Ranges. The Kawhatau River feeds into the Rangitikei.

Next highest after that were 84mm and 83mm at Pipiriki and in the upper Whangaehu valley respectively.

Horizons staff and the New Zealand Defence Force worked together over the night of October 15 to prevent houses flooding in Wanganui's Anzac Pde.

They were helped by the absolute peak of the flood happening six hours away from high tide. If they had coincided water would have been 250mm higher at Balgownie, in Wanganui's industrial area. Emergency gates were put up there, but were not needed.

The 12-hour peak of the flood severely tested the Anzac Pde stopbanks. At one place in the McGregor Arboretum a 300mm diameter hole under the stopbank on the river side admitted water to a sand layer that caused ground level to rise up to 400mm in places.

Emergency workers responded by building a bund around 32m of stopbank there.