How often has the Waipoua River flooded?
The Waipoua River has a history of flooding in the Masterton township. In the 1930’s the river was deviated, removing the meandering form of the river by straightening it to a shorter, single channel, and adding stopbanks.
Flood protections measures, such as stopbanks, have helped to reduce the impacts of flooding to the town. However, there is still a risk from flooding from large events, and therefore further work is ongoing to reduce the current and future risk.
What is Greater Wellington doing to protect Masterton from flooding?
Greater Wellington has been working alongside community members and mana whenua to explore ways to best manage the current and future flood risks to Masterton. The project team has worked with experts and collected as much data as possible to propose concepts to improve protection for the community.
Greater Wellington and the project team are now at the stage of taking these concepts to the community to gather feedback on concepts to provide better levels of protection against flooding.
How does this relate to other the works currently happening in the Waipoua River?
Following Budget 2024, Greater Wellington and MBIE’s Regional Economic Development and Investment Unit, Kānoa, agreed to co-fund 16 flood resilience projects as part of a nationwide initiative. The programme spans 15 sites across Wairarapa and 1 in Ōtaki, which are critical in future-proofing community, infrastructure, cultural taonga and the economy following a major flooding event.
These areas have been chosen specifically due to flood vulnerability and broader outcomes for the local communities. The Waipoua River sites include:
- Waipoua SH2 bridge left bank protection
- Waipoua Industrial Site – Akura Road
What is Te Kāuru Upper Ruamāhanga Floodplain Management Plan?
The Te Kāuru Upper Ruamāhanga Floodplain Management Plan addresses the risks of flooding by providing a blueprint for ongoing and future flood and erosion works on both rural and urban land. It aims to protect, enhance and restore rivers natural and cultural values while supporting sustainable economic development and resilient communities. Within this plan, it was identified that further work was needed to understand the risk to the urban reach of Masterton and propose concepts to manage this risk.
The Te Kauru Floodplain management plan can be found on the GW website:
Te Kāuru Upper Ruamāhanga Floodplain Management Plan
Does this project cover the whole Waipoua River catchment area?
This project is focused on the urban reach of the Waipoua catchment, where the river passes through Masterton. The proposed concepts have been based on the effects of flooding in a 1% AEP flood, that is a flood which has a 1:100 chance of happening in any given year.
What areas of Masterton are most prone to flooding?
During an earlier phase of this project, the flood risk to Masterton in a 1% AEP flood was assessed and flood hazard maps were produced. These flood hazard maps indicate the areas which are at risk of flooding, which includes areas around Oxford Street and the central area of town.
What level of protection will the upgrades provide?
The concepts proposed have been designed to protect Masterton urban areas to a minimum level of service of a 1% AEP (annual exceedance probability) including climate change.
How does stormwater flooding impact this project?
This project focuses on the impacts of river (fluvial) flooding on Masterton’s urban areas from the Waipoua River. Protection of communities from river flooding is the responsibility of Greater Wellington Regional Council.
Stormwater is the runoff of rainwater from urban surfaces. The management of stormwater is the responsibility of the local authority, Masterton District Council. For any stormwater enquiries, please contact Masterton District Council or look at the information on their website.
What’s the process from here?
This project is currently in the initial stage of work, which is to investigate feasible concepts to protect Masterton from flooding. The final design for managing the flood risk to Masterton will likely involve a combination of aspects from each of the concepts. The opportunity to provide feedback will close on 16 March 2025. The feedback received will be used alongside other factors, such as environmental and economic considerations and Te Mana o Te Wai, to help determine a preferred flood management design for the Waipoua River through the urban reach. The preferred option will then be taken through an approval process so that more detailed design and ultimately construction can occur in the future.
Why do we need to invest in flood protection?
Masterton is built on a floodplain between three rivers. While work has been done in the past to reduce the risk of flooding, there is still a risk from larger events, including a 1% AEP flood (that is a flood that has a 1% chance of happening in any given year). This flooding is worse when considering the predicted effects of climate change.
A significant flood in Masterton could devastate the community by destroying people’s homes and livelihoods. Recent examples of the devastating effects from flooding are from the Auckland Anniversary weekend and Cyclone Gabrielle events in early 2023.
How much will this all cost me as a ratepayer?
Based on our current knowledge, high level estimates suggest that the cost to implement these concepts will be similar and are in the order of $30 million. Based on current rating classification this equates to an average total rate increase of $10 per $100,000 CV for local Masterton rate payers. For a property with a value of $540,000, this would be an additional $54 per year. For regional rate payers outside of the Masterton area, the rates increase would be less than $0.50 per $100,000 CV. These costs could be less if funding from central government is available.
Do any of the concepts affect people’s properties?
The project team has worked hard to develop feasible concepts that have minimal impact on people’s properties, community infrastructure or access to the river. However, there are some proposed concepts/works that could affect private property.
Concept three, which proposes a retreated stopbank on the northern side of the river, could mean that Mawley Park, the Sports Bowl or adjacent sports fields may experience flooding in a large flood event. There is opportunity through this engagement for feedback about this concept and different possible alignments for the stopbanks that would protect these locations in a large flood event.
One of the proposed areas of work, which complements the concepts, is for a floodwall, bund (stopbank) and swale to be constructed in the Akura Road area. The high-level design of these works indicates that they will need to be at least partially constructed on private property.
Do nature-based solutions mean planting lots of trees to protect the town?
There are many different types of nature-based solutions used to reduce the risks from flooding, such as planting in the river catchment, installing a network of swales (depressions that collects and redirects water) and giving the river more room to move. Depending on the scale of land needed for a nature-based solution, it could take time to integrate into a flood risk management design. Further to this, different nature-based solutions have different levels of effectiveness over time. For example, swales can provide immediate effect, while planting trees and waiting for them to establish can provide increasing benefit over time.
How can I protect myself and property in the meantime if there is a large flood?
Know your risk: Find your property on the flood and erosion hazard map and find out what the predicted depth of water will be. The Wellington Region Emergency Management Office (WREMO) provides information about how to reduce the effects of flooding. This information could cover evacuation plans, how to protect items in your home by raising them above floor level, and how you can reduce the risk of future flooding to your home.
Be prepared: You will need to have:
- A Household Emergency Plan that will help you and your household plan for what to do when disaster strikes.
- Well stocked emergency survival items such as food, water, clothing and medical supplies for you and your family. You will need enough for at least 3 days.
- A Getaway Kit of essential emergency and medical items you need to have if you’re evacuated.
