Millions at stake in floodworks

Two $4 million stopbank options have been put out for public consultation following predictions a 100-year flood in Greytown could cause $54 million in damage to private property.

A Greater Wellington Regional Council advisory committee has been examining options to prevent significant damage in the event of a major flood of the Waiohine and Mangatarere Rivers, narrowing it down to two - Option 4 and Option 7.

Option 4 would see a new stopbank built alongside the river from the end of Wood St to SH2 and a second stopbank built around Greytown, creating a channel for water to flow around the town.

Option 7 focuses on upgrading and filling in the gaps in existing stopbanks, and the creation of spillway at The Wire Shed.

Flood protection manager Graeme Campbell said options, narrowed down from seven to two, were assessed on practicality, cost and future impacts of issues like climate change and earthquake risk. Making Greytown a safer place was the core aim of the project, he said.

"A balance is going to have to be struck. The flood waters are there, and if you push them away from one place someone else is going to get them in the end. You have to make a decision for the whole community."

No residents would be displaced by the proposed works in either option, but a balance would have to be struck in the land and property that could be saved in a major flood.

Option 4 is estimated to cost about $4 million, saving about $1.3 million a year in average annual damage, and Option 4 would cost about $4.5 million, saving about $1.4 million a year in average annual damage.

Mr Campbell said community consultation was an important part of the process. "They are two quite different options and they do achieve some different outcomes for the river. We want to know which one people prefer. But we do ask the community to be patient. We need to make a fully informed decision. There's no really easy way."

Management options

Option 4

• 
  New stopbank built close to the river channel, from the end of Wood St to SH2, and upgraded stopbanks from there to the Waiohine Bridge.
• 
  A new stopbank built around the Greytown township from the middle of Wood St around the town running parallel to North St and Hupenui Rd.
• 
  Upgraded stopbanks along the other side of the river, and around the urupa at the end of Swamp Rd.

Option 7

• 
  New stopbanks from the downstream end of the existing Greytown stopbank to The Wire Shed, and from The Wire Shed to the Waiohine Bridge.
• 
  Existing stopbanks running parallel to SH2 from Ahikouka Rd to Hupenui Rd raised in height, three points on the stopbank on the other side of the river, running parallel to Matarawa Rd, raised.
• 
  Two overflow spill sections of the stopbank built near North and Mole St, and retaining the existing overflow spill section opposite Ahikouka Rd.
• 
  Upgraded stopbank around the Urupa at the end of Swamp Rd.