Protecting Hawke's Bay's coastline and the communities who live along it from rising sea levels could cost upward of $131 million.
This is the verdict of a Tonkin and Taylor report completed for the Clifton to Tangoio Coastal Hazard Strategy, which aims to make the region's coastline resilient ahead of an expected 1.5m sea level rise in the next century.
Preferred solutions for nine coastal areas have been developed by two Coastal Hazard Assessment Panels, with estimated costings over the next 100 years detailed in the Tonkin and Taylor report.
The low range estimate is about $131m, with the high estimate around $286m.
However Coastal Hazards Joint Committee chairman Peter Beaven said the economic cost of doing nothing would be "several times greater".
"Doing nothing is quite simply not an option," he said. "The people [of] those communities, they want to stay and fight, and they want to try and protect the beachfront and manage it best they can for as long as they can."
The report states the potential economic loss from coastal hazards could potentially run into the hundreds of millions. This does not factor in the social, or cultural losses posed by sea level rise.
It has not been decided how costs will be divided, but most is expected to come from Hastings and Napier ratepayers.
Possible solutions for coastal areas north of Napier - Ahuriri, Pandora, Westshore, Bayview, and Whirinaki - have been developed by the Northern panel, while the Southern Panel has suggested actions for Clifton, Te Awanga, Haumoana, and Clive.
Each path is split into three terms - short, 20 years, medium, 20-50 years, and long, 50-100 years. For each term, a course of action - managed retreat, coastal defence, or letting nature take its course - has been chosen.
Managed retreats, moving communities from affected areas, are not preferred for any location in the short, or medium term, but is suggested for Clive, Haumoana, and Clifton in the long term.
Choosing renourishment, or to create defence structures in the short to medium term was the better option, Mr Beaven said, as the "cost of retreat is incredibly expensive".
There are other problems: "In the case of Napier north of the Port there is actually no where to retreat to. You've got the motorway and the airport immediately on the other side of the houses".
"Retreat is not an option, it's basically an abandonment of suburbs along there if they don't stay and fight."
This plan will be presented to the Clifton to Tangoio Coastal Hazard Strategy joint committee meeting tomorrow.
Also discussed will be how funding roles, and responsibilities could be shared among the three partner councils - the Hastings District, Hawke's Bay Regional, and Napier City Councils.
Final recommendations are expected to be made to the councils in March.