Good data needed to plan for sea-level rise

Kāpiti Coast District Council has commissioned a report to help our community prepare for the impacts of sea-level rise due to climate change.

Planning for our future requires robust information about how our coast will change due to sea-level rise and the coastal hazards this will cause over the next 30, 50, and 100 years. That’s why Council asked coastal engineering and environmental experts Jacobs New Zealand Ltd to do a ‘coastal hazard susceptibility and vulnerability assessment’ for the Kāpiti Coast District coastline.  

The report is being developed using scientific best practice, the most up-to-date technical data currently available, and meets central government requirements. 

Read the methodology on the Council website www.kapiticoast.govt.nz/coastal-science. 

Looking at the likelihood and degree of change over time 

It’s likely coastal erosion and inundation (flooding from the sea) will impact upon community assets like roads, pipes, and parks within the next 100 years. Some will become too vulnerable to make repairs a cost-effective option. Private property will also be impacted. 

The technical report will detail where and when coastal erosion and inundation may happen and the amount of change over three timeframes:

• 30 years for long-term council asset planning
• 50 years is the expected lifetime of a building for consent applications
• 100 years is how far out government requires councils to plan for climate change. 

For each timeframe, the report will look at two or three sea-level rise scenarios. Each reflects degrees of certainty, as in it is:

• ‘likely to occur’
• ‘will probably occur’
• ‘unlikely but possible it will occur’.

Using the past to understand the future

Predicting the future is only as good as the information we know today, but scientists are able to develop models of expected change over time based on historical and current data.

The Jacobs team is using a range of scenarios and certainties for projecting future changes to our coastline due to sea-level rise. 

As we look further out, projections usually become less certain, but they are still valuable in giving greater certainty of what we might have to plan for.

Like a road map, we can use this information to plan our journey, but also to work out a different route or destination if conditions change along the way. We will have a greater range and probably cheaper options the earlier we identify the need to switch direction.

Our coastal planning

We were one of the first councils in New Zealand to recognise the need to plan for the impacts of sea-level rise.

In 2009 we commissioned a comprehensive assessment of hazards for our district. Aspects of the technical information were challenged by property owners worried it would reduce the value of their properties. As a result, some of the technical information was withdrawn, so coastal hazards aren’t fully covered in our District Plan. This means Council can’t stop people building homes in areas that could be at risk of coastal hazards. 

In 2019 the Council reset to put the community at the heart of working out how we should adapt to sea-level rise. This is the Takutai Kāpiti coastal adaptation project: www.takutaikapiti.nz. 

We envisage coastal hazard provisions will be included in a future District Plan, but not until the Takutai Kāpiti community-led Coastal Advisory Panel completes its work, and more consultation occurs.