By the end of May Wanganui's Balgownie industrial area will be protected from 200-year floods, Horizons Regional Council operations manager Allan Cook says.
Horizons councillors had a brief tour of the almost-completed Balgownie flood protection works last Wednesday. Wanganui representative Greg Cox was there but his fellow, Bob Walker, was not.
Mr Cook said Balgownie experienced a 30-year flood in 1990. It wasn't the riskiest part of the city for flooding - Anzac Parade and the Old Town area were worse - but it was the first area protected because its closure would hit the town hard economically.
Wanganui has escaped anything like a 200-year flood for the past century. Even a major flood in 1940 was only a 70-year one. In 2004, when the Whangaehu River had a 150-year flood, Wanganui had only a 10-year version.
"That's not to say Wanganui will not be flooded. The risk is significant, and loss of life cannot be discounted," Mr Cook said.
In a 100-year flood the 60ha Balgownie area would be flooded to a depth of .5m to 1m. A 200-year flood would add a further .2m to .3m of water.
Global warming was likely to make 200-year floods as common as 100-year ones in 30 years. Mr Cook said protecting to the 200-year level cost little more than protecting to the 100-year level and it made sense to do that now.
Designing and building the flood barrier had been challenging, because of nearby buildings, gas lines and the need for access to, through and across the river. Two accessways would have to be manually blocked when river levels at Pipiriki got to 12m. The one at Q-West Aluminium Boat Builders took two to three hours to put together, but there was time for that because it took 8-10 hours for floodwaters to flow downriver from Pipiriki to Wanganui.
All the Balgownie construction would be done for the $3.2million budgeted, plus inflation adjustment. The average ratepayer paid $25 a year towards it, and the average annual saving to the city - from damage averted - was $1.4million a year.
The total cost to protect the city from floods was estimated to be $10million.
Stage two of Horizons' Wanganui flood protection will be to protect 50ha and buildings at Putiki and 20ha and buildings in Anzac Parade. Consultation on that will begin later this year, with construction in 2012-13 at the earliest.
Many plants were removed for the Balgownie work, and "huge amounts of rubbish" were taken away. Mr Cook said the council would plant 3000 shrubs on both sides of the flood walls this winter.
A walking and cycle track topped the new flood walls, and he was pleased to see families out riding bicycles on it.