Introduction to hazards

This site illustrates and describes flooding and erosion threats faced by our region’s coasts and river catchments and will give you easy access to scientific information and climate data.

Scroll on through or use navigate with the headings tab at the top of the screen to explore the information and maps on sea-level rise, coastal and river flooding, as well as coastal erosion. There are also maps of future flooding scenarios based on numerical modelling.

Throughout this resource we have interwoven Kōrero shared by Māori voices, offering traditional knowledge and views about natural hazards.

•  Winiwini Kingi 
•  Nicki Wakefield 
•  Chantez Connor-Kingi 

Sea level rise and increased storm severity brought on by climate change is likely to have a growing, negative impact on our coastal communities over time. Understanding where, and how, communities could be affected is important.

Here you’ll find information about:

•  Sea level rise 
•  Coastal flooding 
•  Coastal erosion 

•  What is sea level rise? 
•  How is sea level projected to rise in Northland? 
•  What are the consequences of sea level rise? 

As the globe warms, we see a corresponding rise in sea levels. Burning fossil fuels is one of the main causes of global warming because it releases carbon dioxide and other heat-trapping gasses into the atmosphere. The oceans then absorb the majority of this heat and as water becomes warmer, it expands. When we combined this with increased volumes of water melting from land-based ice, the result is rising sea levels.

Factors such as El Niño / La Niña weather cycles can also increase sea levels around New Zealand in any month by up to 0.15 to 0.25 m.

Sea level rise is happening and needs to be factored into risk assessments and land-use planning for coastal inundation.

Over the past 100 years, around 20cm of sea level rise has occurred, at an average rate of 2.2mm per year in Northland. However, recent estimates predict these could accelerate to as much as 10cm per year in coming decades.

While rates of sea level rise are dependent on how quickly global greenhouse gas emissions are reduced, an amount is already ‘locked in’. This means our communities will increasingly be affected by high water levels over the coming decades.

Sea level rise projections in Northland were based on the  Ministry for the Environment (2017) Coastal hazards and climate change – a guide for local government .

Sea level rise projection scenarios were used to develop our coastal hazard assessments. These have been mapped and show areas of risk known as coastal flood hazard zones (CFHZ) and coastal erosion hazard zones (CEHZ).

Find out more information about the hazard zone assessment mapping here:

•  Coastal flood hazard zone maps 
•  Coastal erosion hazard zone maps 

As sea levels rise, we expect to see increased intensity of storm surges, flooding, and damage to coastal areas. This will threaten the viability of some coastal areas, and how we currently use or inhabit them. It may even affect inland areas as rising seas can contaminate soil and groundwater with salt. Accurately predicting how high sea levels will actually rise is difficult but using data to create models, and monitoring are the best tools currently available.

I currently live on the Horahora River and have been there for roughly 40 years. If you look at the topography of the land where I stay, you can see that most of it was once under water, operating as tidal flats.

I’m concerned about what’s going to happen in the future. We also have a lot of burial caves and other places with our koiwi in them. They would be greatly affected by a tsunami, most of them would probably be under water.

Currently, my house sits at about 32 metres above sea level. Any tsunami above that, I’ll have to move even higher. Unfortunately, many of my neighbours and others in my community who live closer to the sea level do not know about the potential threat a tsunami poses.

I think there is a lack of information and education around these issues. We’re not expecting it, a bit like Covid-19 - we’re not expecting a big earthquake, or a huge tsunami and we’re not prepared.

As a child, the only kōrero I heard about earthquakes was about Ruaumoko being angry with his siblings. In te ao Māori, everything has whakapapa. There’s all sorts of different names for the currents, the winds, the waves and there are also demigods too. There are stories about an octopus who is one of the protectors of those realms too. It’s all about the realms and their respective guardians.

•  What is coastal flooding? 
•  What causes coastal flooding? 
•  Coastal flood hazard zone (CFHZ) maps 

Coastal inundation (flooding) is particularly likely when stormconditions like surge and large waves combine and meet high tides. At these times, areas where rivers or creeks meet the sea are more vulnerable because high seas can cause the rivers to back up inland.

With inundation there is a risk of damage to infrastructure and stormwater networks becoming overwhelmed. Large waves can create many hazards besides overtopping and inundation including rip currents, beach erosion or hazardous driving conditions. Higher salinity water up rivers and streams can affect potable water supplies and pasture can be damaged for up to a year from salt burn.

•  What is coastal erosion? 
•  What causes coastal erosion? 
•  Coastal erosion hazard zone (CEHZ) maps 

Coastal erosion is a natural process that is part of normal beach behaviour. However, projected sea level rise, and an increase in storm events, is likely to worsen its effects long term.  Unfortunately, a substantial number of our coastal developments have occurred too close to the sea, potentially putting them at risk of coastal erosion. This growing hazard will need to be carefully managed.

“Future sea level rise, driven by climate change, may drive a long-term trend of coastal erosion. We need to manage this carefully so we can protect our coastline's future.”

Northland’s east and west coasts vary in their exposure to erosion. The sandy bays and beaches of the east coast have limited sediment supply but are generally well-protected from large swells. In contrast, the west coast has a large supply of sand flowing north but is exposed to heavy ocean swells.

Coming from a taiao or ao Māori perspective, it’s difficult to find a definition for natural hazard in te reo. We think of natural hazards as being connected to our taiao, which is connected to our wellbeing. Equally, our wellbeing is connected to the wellbeing of te taiao. Land use decisions have taken the land away from focussing on its function within te taiao and being an interconnected ecosystem and instead prioritised the economics over the whenua.

What was already a destructive period for te taiao is going to continue, because we are going to continue to protect those cities from sea level change. It’s resource intensive, developing these coastal areas, and it will only become more intensive. This furthers the economic disparities that stem from when the lands were stolen in the first place. Urban development is a much more costly exercise now.

To plan for floods, you need to understand the type – or types – of flood you may face. You might think all floods are the same but the reality is they can actually be caused by different factors and have different impacts in terms of how they occur, how they are forecast, the damage they cause, and the type of protection you need.

•  What is a fluvial (river) flood? 
•  What is a pluvial (flash and surface water) flood? 
•  River flood hazard zone (RFHZ) maps 

A fluvial, or river flood, occurs when a river, lake or stream overflows its banks due to excessive rain. The damage from a river flood can be widespread as the overflow affects smaller rivers downstream, which can cause dams and stop banks to break and swamp nearby areas.

The severity of a river flood is determined by the duration and intensity (volume) of rainfall in the catchment area of the river. Other factors include soil water saturation due to previous rainfall, and the terrain surrounding the river system. In flatter areas, floodwater tends to rise more slowly and be shallower, and it often remains for days. In hilly or mountainous areas, floods can occur within minutes after a heavy rain, drain very quickly, and cause damage due to debris flow.

To determine the probability of river flooding, models consider past precipitation, forecasted precipitation, current river levels, and well as soil and terrain conditions.

A pluvial flood occurs when an extreme rainfall event creates a flood independent of an overflowing water body. A common misconception about flood is that you must be located near a body of water to be at risk. Yet pluvial flooding can happen in any location, urban or rural, even in areas with no water bodies in the vicinity. There are two types of pluvial flooding, surface water floods and flash floods.

What are surface water floods? Surface water floods occur when an urban drainage system is overwhelmed, and water flows out into streets and nearby structures. It occurs gradually, which provides people time to move to safe locations, and the level of water is usually shallow (rarely more than 1 meter deep). It creates no immediate threat to lives but may cause significant economic damage.

What are flash floods?

Flash floods are characterized by an intense, high velocity torrent of water triggered by torrential rain falling within a short amount of time within the vicinity of, or on nearby elevated terrain. They can also occur via sudden release of water from an upstream dam. Flash floods are very dangerous and destructive not only because of the force of the water, but also the hurtling debris that is often swept up in the flow.

Our people knew that when the heavy rain and flooding was coming, so were the tuna. We would take one big catch from the first run of the tuna whakaheke, or migration of tuna upstream. From our point of view, the only hazard we currently see is the pumps coming on and the effects they have, specifically on tuna populations.

In a massive flood, the repo takes the brunt of the impact before the water travels on down to the Kaipara, through the Wairua River. The repo would remove much of the paru (sediment and build-up of nutrients) before it flowed to out sea. The repo was like a peacemaker, it would filter out the raruraru and flow with good out the other end.

From a Māori point of view, it doesn’t really worry us when the swamp floods, because we are seeing the swamp do what it’s meant to do. It affects the farmers, but Māori don’t own any farms in the repo. We live in the upper reaches, as we should. Māori people never built on lower ground and around swamps, because of floods.

Because of climate change, our seasons are shifting. The rains are coming later or are coming early and they’re more intense. What we would normally see across three days, we’re seeing in three hours. 

Northland Regional Council: P 0800 002 004 | E  info@nrc.govt.nz 

Starting in 2022, District Councils and Northland Regional Council will be working with communities on climate change adaptation options and actions. This is part of the developing regional adaptation strategy and part of District Council’s climate change work programme. We encourage you to become actively involved in the conversation about coastal hazards and the development of an adaptation approach for both the region and the district.