Ashley Rakahuri flood resilience project

Over the next several years, we’re planning to create new flood resilience measures along the 22km section of the Ashley Rakahuri that runs between the Ōkūkū River and Waikuku Beach.

Our goal is to strengthen flood resilience for Rangiora, Kaiapoi, Waikuku, and surrounding areas.

We want your input on the initial options we're considering. Please give your feedback by 5pm on 31 July 2026. We’ll be considering your feedback as it comes in, and there will be further opportunities to have your say as the project progresses.

Why we’re doing this work now

Early flood protection works on the Ashley Rakahuri started in the 1930s. The existing stopbank scheme has protected the district for around 70 years, but over that time, the flood risk has increased.

  • Recent events, such as the Auckland Anniversary floods and Cyclone Gabrielle, have demonstrated that extreme rainfall and flooding are happening more often and causing greater damage than in the past. Scientific evidence shows these types of events are becoming more frequent and intense.

  • There are now more people, homes, businesses and infrastructure located within the Ashley Rakahuri floodplains. This means the consequences of flooding are higher than they were when the scheme was first built. View our flood modelling maps to see the areas that could be affected during a 1‑in‑500‑year flood event.

  • Our modelling shows there is a risk of floods breaking out at different points along the river. We want to ensure our flood protection reflects today’s risks and that they are fit for the future.

Our approach

As we follow the Ashley Rakahuri from its confluence with the Ōkūkū River to the coast, the river changes. Flood breakouts can travel in different directions and have different impacts in different places. That's why we're looking at the river in three reaches, each requiring different ways to manage breakout flooding risk.

Reaches:

  • Ōkūkū confluence → Rangiora Railway Bridge

  • Railway Bridge → SH1 Bridge

  • SH1 → the ocean


What options we're considering

We’re considering a range of possible solutions that may be combined. Different approaches may be needed for different parts of the river. These include:

  • Upgrading or modifying the existing primary stopbank
  • One or more secondary stopbanks
  • Managed floodways
  • Stopbank retreat
  • Berm vegetation management
  • Wetland creation / room-for-the-river approaches
  • Gravel management

At this early, investigative stage of the project, we have no preferred option/s. Your feedback will help select a preferred option by correcting our assumptions and highlighting unintended consequences. This will be balanced with other criteria such as safety, practicality for land use, environmental and cultural outcomes, feasibility and cost.

Have your say on flood resilience options

Over the next several years, we’re planning to create new flood resilience measures along the 22km section of the Ashley Rakahuri that runs between the Ōkūkū River and Waikuku Beach.

Our goal is to strengthen flood resilience for Rangiora, Kaiapoi, Waikuku, and surrounding areas.

We want your input on the initial options we're considering. Please give your feedback by 5pm on 31 July 2026. We’ll be considering your feedback as it comes in, and there will be further opportunities to have your say as the project progresses.

Why we’re doing this work now

Early flood protection works on the Ashley Rakahuri started in the 1930s. The existing stopbank scheme has protected the district for around 70 years, but over that time, the flood risk has increased.

  • Recent events, such as the Auckland Anniversary floods and Cyclone Gabrielle, have demonstrated that extreme rainfall and flooding are happening more often and causing greater damage than in the past. Scientific evidence shows these types of events are becoming more frequent and intense.

  • There are now more people, homes, businesses and infrastructure located within the Ashley Rakahuri floodplains. This means the consequences of flooding are higher than they were when the scheme was first built. View our flood modelling maps to see the areas that could be affected during a 1‑in‑500‑year flood event.

  • Our modelling shows there is a risk of floods breaking out at different points along the river. We want to ensure our flood protection reflects today’s risks and that they are fit for the future.

Our approach

As we follow the Ashley Rakahuri from its confluence with the Ōkūkū River to the coast, the river changes. Flood breakouts can travel in different directions and have different impacts in different places. That's why we're looking at the river in three reaches, each requiring different ways to manage breakout flooding risk.

Reaches:

  • Ōkūkū confluence → Rangiora Railway Bridge

  • Railway Bridge → SH1 Bridge

  • SH1 → the ocean


What options we're considering

We’re considering a range of possible solutions that may be combined. Different approaches may be needed for different parts of the river. These include:

  • Upgrading or modifying the existing primary stopbank
  • One or more secondary stopbanks
  • Managed floodways
  • Stopbank retreat
  • Berm vegetation management
  • Wetland creation / room-for-the-river approaches
  • Gravel management

At this early, investigative stage of the project, we have no preferred option/s. Your feedback will help select a preferred option by correcting our assumptions and highlighting unintended consequences. This will be balanced with other criteria such as safety, practicality for land use, environmental and cultural outcomes, feasibility and cost.

Have your say on flood resilience options

  • Flood modelling maps

    These maps show the potential extent and depth of flooding if the Ashley Rakahuri were to breach the primary stopbank at the Ōkūkū confluence and near Smarts Road during a 1-in-500 -year flood event. The Ōkūkū confluence is one of the most likely breakout locations along the primary stopbank, but a flood could break out at any point in the stopbank, as braided rivers are highly dynamic. A breakout could also occur in a smaller flood event, such as a 1-in-100 year event, as erosion rather than overtopping is the cause of breakouts.


    The coloured areas on the map indicate where floodwater could travel across the floodplain and how deep the water could become. The different colours on the map represent different estimated water depths in metres. See the colour key on the side of the map.

    Flood modelling - Upstream of Rangiora


    Flood modelling - Ōkūkū confluence to coast


    How our flood modelling is developed

    We use a combination of the following:

    • Historic breakout data

    • Updated LiDAR ground levels (remote sensing technology that uses laser lights to determine ground levels)

    • Recent hydrology and climate information

    • Different flow scenarios, including rare but high-impact events

    • Sensitivity testing to understand how water behaves when it breaches stopbanks

    Models are peer reviewed internally and will continue to be refined using information from site visits, landowner feedback, and iwi knowledge. The depth ranges shown in the key are estimates based on modelling, not precise measurements at individual properties.

    These maps show the potential extent and depth of flooding if the Ashley Rakahuri were to breach the primary stopbank at the Ōkūkū confluence and near Smarts Road during a 1-in-500 -year flood event. The Ōkūkū confluence is one of the most likely breakout locations along the primary stopbank, but a flood could break out at any point in the stopbank, as braided rivers are highly dynamic. A breakout could also occur in a smaller flood event, such as a 1-in-100 year event, as erosion rather than overtopping is the cause of breakouts.


    The coloured areas on the map indicate where floodwater could travel across the floodplain and how deep the water could become. The different colours on the map represent different estimated water depths in metres. See the colour key on the side of the map.

    Flood modelling - Upstream of Rangiora


    Flood modelling - Ōkūkū confluence to coast


    How our flood modelling is developed

    We use a combination of the following:

    • Historic breakout data

    • Updated LiDAR ground levels (remote sensing technology that uses laser lights to determine ground levels)

    • Recent hydrology and climate information

    • Different flow scenarios, including rare but high-impact events

    • Sensitivity testing to understand how water behaves when it breaches stopbanks

    Models are peer reviewed internally and will continue to be refined using information from site visits, landowner feedback, and iwi knowledge. The depth ranges shown in the key are estimates based on modelling, not precise measurements at individual properties.

  • Decision making and next steps

    How decisions on flood resilience options will be made

    Our next step is to do a comparative analysis of the design options, balancing:

    • Protection of life and property
    • Feasibility and cost
    • Environmental and cultural outcomes
    • Equity across communities
    • Practicality for farming / land use

    Councillors from Canterbury Regional Council (Environment Canterbury) will make the final decision on the preferred option/s after public and iwi input. This will be consulted on within the Long-Term Plan in 2027.

    Project timeline

    We’re in the early stages of this project, so the feedback and information you provide will help us select one of the options we’re considering.

    Indicative timeframes are:

    • 2026: Engagement with landowners, iwi, community, and Waimakariri District Council. Options refined into a shortlist.
    • 2027: Preferred options selected, resource consent process begins, land compensation / purchase process begins (if required). Project details are updated in Environment Canterbury’s Long-Term Plan.
    • 2027–2032: Work begins (depending on Council decisions)


    Once an option has been selected, we will complete the work in stages:

    1. Ōkūkū confluence → Rangiora Railway Bridge
    2. Railway Bridge → SH1 Bridge
    3. SH1 → the ocean

    How this work is funded

    This project was socialised in the Long-Term Plan 2024-34 with an indicative eight-year cost of $15 million. This funding will come from a mix of local targeted rates (for directly benefitting communities) and regional general rates, with potential for central government co-investment too.

    As we develop the design to a preferred option, the cost estimate and funding model will be refined. It is our intent to update the funding in the 2027-37 Long Term Plan.

    You can find out more about how we fund river management work on our River Rating District webpage.

    How decisions on flood resilience options will be made

    Our next step is to do a comparative analysis of the design options, balancing:

    • Protection of life and property
    • Feasibility and cost
    • Environmental and cultural outcomes
    • Equity across communities
    • Practicality for farming / land use

    Councillors from Canterbury Regional Council (Environment Canterbury) will make the final decision on the preferred option/s after public and iwi input. This will be consulted on within the Long-Term Plan in 2027.

    Project timeline

    We’re in the early stages of this project, so the feedback and information you provide will help us select one of the options we’re considering.

    Indicative timeframes are:

    • 2026: Engagement with landowners, iwi, community, and Waimakariri District Council. Options refined into a shortlist.
    • 2027: Preferred options selected, resource consent process begins, land compensation / purchase process begins (if required). Project details are updated in Environment Canterbury’s Long-Term Plan.
    • 2027–2032: Work begins (depending on Council decisions)


    Once an option has been selected, we will complete the work in stages:

    1. Ōkūkū confluence → Rangiora Railway Bridge
    2. Railway Bridge → SH1 Bridge
    3. SH1 → the ocean

    How this work is funded

    This project was socialised in the Long-Term Plan 2024-34 with an indicative eight-year cost of $15 million. This funding will come from a mix of local targeted rates (for directly benefitting communities) and regional general rates, with potential for central government co-investment too.

    As we develop the design to a preferred option, the cost estimate and funding model will be refined. It is our intent to update the funding in the 2027-37 Long Term Plan.

    You can find out more about how we fund river management work on our River Rating District webpage.

  • Detailed project information

    What level of flood protection this work may provide

    No flood protection system can remove all risk. This project aims to reduce risk to people, property and farmland, not eliminate it. Visit Waimakariri District Council's website for more information about natural hazards in your area.

    A 1-in-500 year flood (up to 3,900 cumecs - factoring in climate change) has been used as the design basis for these options so far, and the exact level of service (design flood) used in the upgraded stopbanks is to be confirmed through consultation with the community and councils.

    Ashley Rakahuri flood history

    The last significant breakout near the Ōkūkū confluence was in the 1930s, which was estimated to be around a 1,700 cumec flood. There were a series of breakouts in the 1950s between the Cones Road and railway bridge, which was the last time we had a flood that was above 2,000 cumecs.

    In the May 2021 flood, the peak flow was approximately 1,600 cumecs at Rangiora. Flood levels were one metre from the top of the stopbank at locations upstream of Rangiora (near Groyne 8) and some properties were evacuated on a precautionary basis.


    Secondary stopbank height

    The height of any secondary stopbank above the existing ground level depends on where it is located in relation to terrain features, such as terraces or channels. The height also depends on the expected water depth within the stopbanks, which varies for each alignment option.


    The role of gravel extraction

    Gravel extraction is an important part of how rivers are managed across Waitaha Canterbury, and more than one million cubic metres of gravel is removed from riverbeds across the region each year. However, there are limits to how much gravel can safely be taken out.

    Over the long term, gravel is carried downstream each year and settles in our rivers. Because of this natural process, lowering the riverbed in one place does not provide a permanent solution, as gravel will gradually build up again over time.

    Gravel extraction is carefully managed through permissions under the Resource Management Act to ensure we balance gravel supply with negative effects such as undermining flood protection assets, infrastructure, riverbank planting, private land, and important habitats.

    To manage these risks:

    • Minimum riverbed levels are set in some areas
    • Gravel can only be extracted when the riverbed is above those levels, and extraction must stop if those thresholds are reached.
    • Riverbed levels are regularly surveyed to make sure extraction remains sustainable.


    While gravel extraction can help manage flooding and erosion hazards in some situations, it cannot provide the same level of protection as flood protection infrastructure. Stopbanks are designed to provide a reliable and predictable level of protection during large flood events by helping keep floodwaters within the river corridor.

    Our engineers consider a range of tools, including gravel management. In many cases, however, stopbanks are needed to provide the level of protection required for communities.

    Insurance considerations

    New Zealand’s National Adaptation Framework is clear that there is a difference between sharing information about risk and changes to physical risk on the ground. This recognises that better information helps people, insurers and banks make informed decisions but does not itself change the level of risk landowners face.

    For this project, it means discussing options or providing updated information doesn’t alter existing flood behaviour, stopbank performance, or protection levels.

    But individual insurers may take different approaches. If you have concerns, we encourage you to speak directly with your insurer.

    You can find out more on the national adaptation framework webpage.

    Properties that may be impacted by this work

    We have attempted to contact all homeowners whose properties would be impacted by our current flood resilience designs. If you think your property may be affected and would like more information, please email us directly on rivers.delivery@ecan.govt.nz

    What level of flood protection this work may provide

    No flood protection system can remove all risk. This project aims to reduce risk to people, property and farmland, not eliminate it. Visit Waimakariri District Council's website for more information about natural hazards in your area.

    A 1-in-500 year flood (up to 3,900 cumecs - factoring in climate change) has been used as the design basis for these options so far, and the exact level of service (design flood) used in the upgraded stopbanks is to be confirmed through consultation with the community and councils.

    Ashley Rakahuri flood history

    The last significant breakout near the Ōkūkū confluence was in the 1930s, which was estimated to be around a 1,700 cumec flood. There were a series of breakouts in the 1950s between the Cones Road and railway bridge, which was the last time we had a flood that was above 2,000 cumecs.

    In the May 2021 flood, the peak flow was approximately 1,600 cumecs at Rangiora. Flood levels were one metre from the top of the stopbank at locations upstream of Rangiora (near Groyne 8) and some properties were evacuated on a precautionary basis.


    Secondary stopbank height

    The height of any secondary stopbank above the existing ground level depends on where it is located in relation to terrain features, such as terraces or channels. The height also depends on the expected water depth within the stopbanks, which varies for each alignment option.


    The role of gravel extraction

    Gravel extraction is an important part of how rivers are managed across Waitaha Canterbury, and more than one million cubic metres of gravel is removed from riverbeds across the region each year. However, there are limits to how much gravel can safely be taken out.

    Over the long term, gravel is carried downstream each year and settles in our rivers. Because of this natural process, lowering the riverbed in one place does not provide a permanent solution, as gravel will gradually build up again over time.

    Gravel extraction is carefully managed through permissions under the Resource Management Act to ensure we balance gravel supply with negative effects such as undermining flood protection assets, infrastructure, riverbank planting, private land, and important habitats.

    To manage these risks:

    • Minimum riverbed levels are set in some areas
    • Gravel can only be extracted when the riverbed is above those levels, and extraction must stop if those thresholds are reached.
    • Riverbed levels are regularly surveyed to make sure extraction remains sustainable.


    While gravel extraction can help manage flooding and erosion hazards in some situations, it cannot provide the same level of protection as flood protection infrastructure. Stopbanks are designed to provide a reliable and predictable level of protection during large flood events by helping keep floodwaters within the river corridor.

    Our engineers consider a range of tools, including gravel management. In many cases, however, stopbanks are needed to provide the level of protection required for communities.

    Insurance considerations

    New Zealand’s National Adaptation Framework is clear that there is a difference between sharing information about risk and changes to physical risk on the ground. This recognises that better information helps people, insurers and banks make informed decisions but does not itself change the level of risk landowners face.

    For this project, it means discussing options or providing updated information doesn’t alter existing flood behaviour, stopbank performance, or protection levels.

    But individual insurers may take different approaches. If you have concerns, we encourage you to speak directly with your insurer.

    You can find out more on the national adaptation framework webpage.

    Properties that may be impacted by this work

    We have attempted to contact all homeowners whose properties would be impacted by our current flood resilience designs. If you think your property may be affected and would like more information, please email us directly on rivers.delivery@ecan.govt.nz

Page last updated: 01 Apr 2026, 05:47 PM