Our Kāpiti coastline is changing

Sea Level Rise

NIWA and Greater Wellington Regional Council tide gauge records show the sea level in the Wellington region has risen 27cm over the past 120 years, and 17cm since 1960.

In other words, the tides are reaching almost 30% higher today than they were in 1900. We’re starting to see the impacts of this on our coast and in our coastal environment.

Accretion and erosion

Coastal erosion and accretion (sand accumulation) occurs in different places and at different times along our coast and these patterns may change in the future.

  • In areas such as Waikanae and Ōtaki there has been a history of coastal accretion.
  • In Paekākāriki and Raumati South there has been a sustained period of coastal erosion.

Coastal erosion can be a slow creeping thing that happens incrementally over a long period of time. Or, it can have dramatic effects with sand disappearing from the front of dunes and beaches after big storms, sometimes up to several metres.

Tectonic land movements

GPS measurements show the Greater Wellington region has been sinking at rates of around 2–5mm per year since 1995, with the Kāpiti Coast sinking 3.5–5mm per year.

To put this into context, the Kāpiti Coast has dropped 7cm since 2000.

What does this mean?

There is a cumulative effect of coastal erosion, sea-level rise and tectonic land movements on our coastline. While there is still some uncertainty about how significant these impacts will be, and how quickly they will happen, there is a need for us to start planning for our future.

Communities that plan together for change are more resilient.

THE TERMINOLOGY

Coastal Erosion

The loss of land due to coastal processes, such as waves and tidal currents, wearing away the land suddenly or overtime.

Coastal Accretion

Deposition of sediment (such as sand) at the immediate shoreline area, resulting in the beach profile elevating/ advancing seaward.

Coastal Inundation

Flooding of land or buildings from seawater.

Storm Surge

The rise in the level of the sea caused by a storm. This is due to low atmospheric pressure and onshore winds causing surge and extreme wave heights along the coast.

Sea Level Rise

The rise in the level of the sea. Relative (or local) sea level rise is measured by tidal gauges and includes both:

  • the change of the level of the sea (such as from global warming);
  • and movement of the land (such as from earthquake subsidence) for the area.

Tectonic Movement

Movement of the tectonic plates (earthquakes) that make up Earth’s crust.

Updated Coastal Hazard Susceptibility and Vulnerability Assessment

Council has commissioned Jacobs Ltd to undertake a Coastal Hazard Susceptibility and Vulnerability Assessment for the Kāpiti Coast District coastline, from Ōtaki in the north to Paekākāriki in the south. This assessment is subject to independent review by Beca Ltd.

The updated assessment will be independently peer reviewed and will identify areas susceptible to current and future coastal erosion hazards with various magnitudes of sea-level rise over a 30, 50 and 100-year period. It will also identify the vulnerability of critical council infrastructure and community services.

The methodology used to inform the development of the assessment reflects both national and international best practice, and meets the requirements of the New Zealand Coastal Policy Statement 2010 and Ministry for the Environment: Preparing for Coastal Change. Guidance for Local Government