A jointly commissioned report by Hastings District and Napier City Council, as well as Hawke’s Bay Regional Council will be vital in planning for the future of coastal communities from Clifton to Tangoio.

Coastal inundation maps have been prepared as part of the report, Clifton to Tangoio Coastal Inundation, and they show the potential impacts of seawater flooding in the year 2100.

About 2000 properties are currently in the coastal inundation zone in Napier City Council area. In Hastings, 843 properties had no change to their status, while just over 200 of the previously affected had a reduced risk. Two hundred properties are newly affected.

Coastal inundation is the flooding of low-lying coastal land with seawater during tidal storms. This can happen when extreme weather events lead to storm surges, causing elevated wave crest height. Coastal inundation is likely to increase through future sea level rise caused by climate change.

The coastal inundation maps were developed by environmental and engineering consultants at Tonkin + Taylor Ltd and peer reviewed by NIWA.

They do not account for current mechanical mitigations such as pumps, and do not account for any future work council might undertake like raising beach crest heights. Napier , for example, has already put in place some mitigation measures such as raised gravel barriers, stormwater networks, gravel bunds and pumps.

The goal of the mapping exercise is to help inform decision making such as setting minimum floor heights and planning future infrastructure. There is also a legislated requirement from central government to map coastal hazard risks.

Having information that far into the future is essential for helping the community build resilience, explained Napier Mayor Kirsten Wise.

“We welcome this modelling and mapping because the more information we have about natural hazards, the better we can plan. This information will help us make sound decisions about future infrastructure investment,” Wise said.

“This work shows scenarios up to 75 years into the future, so we can help our community be prepared. “The report is a reminder that all coastal communities in New Zealand must continue to adapt and challenge the status quo. What works today may not work in years to come.”

Since 2016, Hastings District Council had relied on available hazard information for assessing the coastal inundation risk, namely the Hawke’s Bay Regional Council Coastal Inundation Study. 

The hazard information is noted on a property’s Land Information Memorandum and used when assessing Building Consent applications – particularly floor heights for properties at risk of inundation.

HDC’s group manager of planning and regulatory services John O’Shaughnessy, echoing Mayor Wise, said every property would be different depending on land contour and the siting and extent of any proposed building work.

“Very broadly, it means that applications for Building Consent must, under the Building Act and the Building Code, be considered taking into account the natural hazard,” he said. “There are a number of considerations and potential solutions, so we strongly recommend property owners talk to their design professional or a Council building officer before starting on building plans.”

By legislation (Building Act 2004), properties within coastal inundation zones must have notes on their property files, which will be accessible through the Land Information Memorandum process.

New builds and renovations will benefit from having the modelling in place as floor levels will be set to account for potential inundation impacts.

For councils, the modelling will be considered during building consent and subdivision consent processes, and in land use and infrastructure planning.

The maps are available to view here.

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