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Coastal flooding

Coastal Flooding is the inundation of normally dry land due to an increase in sea level on the coast generally driven by storms.

As sea level rises Coastal Flooding is anticipated to become more frequent and affect a greater area of land.

What is Coastal Flooding?

Coastal Flooding happens when an increase in sea level enables seawater to flood low lying land. Typically driven by storms where low air pressure and strong winds driving large waves combine creating a storm surge. This can be worsened by high or spring/king tides. Climate induced sea level rise will increase the extent and frequency of flooding. Eventually leading to sunny day flooding where flooding occurs with no storm. Find out more about predicted sea level rise around New Zealand.

Schematic figure of how Coastal Flooding will be impacted by rising sea level.

Schematic figure of how Coastal Flooding will be impacted by rising sea level.

Coastal Flooding in Tauranga   

Bay of Plenty has a long history of large storms originating from tropical regions. The most significant was ex-tropical Cyclone Giselle which crossed the North Island on 9 April 1968. Over the next seven days the storm travelled down the east coast of the country. The storm generated a 0.88m high storm surge in Tauranga Harbour, the second highest ever recorded in New Zealand, and caused widespread damage across the country as well as the Wahine disaster.

In the past 30 years, parts of Bay of Plenty have been affected by several cyclones, including Cyclone Fergus (1997), Cyclone Ivy (2008), Cyclone Pam (2015), and Cyclone Gabrielle (2023). Additionally, a storm in early January 2018 coincided with a king tide, resulting in flooding across the region.

The sea flooding on to normally dry land in Tauranga Harbour during rough seas at high tide.

The sea flooding on to normally dry land in Tauranga Harbour during rough seas at high tide.

Maps of Coastal Flooding

Coastal Flooding hazard maps identify land that is potentially at risk of flooding from the sea, especially during storms, both with and without sea level rise.

Coastal Flooding maps are not a prediction of flooding. Modelling dynamic events such as storms is complex and requires specific inputs for tide, wind, and shoreline shape. Instead, the maps are an estimate of areas susceptible to flooding during storms at current sea level and as sea level rises.

Maps of Coastal Flooding for Tauranga Harbour produced by NIWA were released in 2019. Bay of Plenty Regional Council have subsequently commissioned NIWA to produced maps of Coastal Flooding for the rest of the Bay of Plenty region, including the coastal strip of Tauranga. The Coastal Flooding maps for the Bay of Plenty are expected to be released in 2024.

The Coastal Flooding maps for the harbour and coast were produced using a dynamic model that calculates the flow of seawater on the coast, accounting for the effects of tide, atmospheric pressure, and wind as well as the flow of water as waves break on the shore.

For more information about the methods used to produce the maps, and their limitations, you can find the technical report for the inner harbour here:

NIWA Tauranga Harbour Inundation Modelling full report (10mb pdf) NIWA - Tauranga Harbour Inundation Modelling 2019 Executive summary (81kb pdf)

It’s expected the technical report for the Coastal Flooding maps will be released along with the maps in 2024.

This figure shows how different processes can combine to enable the sea to overtop coastal structures and flood the land behind.

This figure shows how different processes can combine to enable the sea to overtop coastal structures and flood the land behind.

Coastal Flooding for the harbour viewer

You can see and explore the maps produced by this study via an online viewer. This viewer allows you to select a specific property and find the current flooding from the sea area as well as see what the potential flooding could look like over time, for a range of sea level rise scenarios and storm event likelihoods.

To use the Coastal Flooding map viewer: 

  • Open the viewer using the link below
  • Click on the magnifying glass symbol at the top right
  • Enter the address for the property you would like to see details for

Inundation map viewer

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