What are you proposing to do to manage the flood risk to Masterton?

We are proposing a staged approach for the urban reach of the Waipoua River. At the end of each stage an assessment will be made of whether to proceed to the next stage and what the scope of that stage will be. The staged approach will first focus on today’s risk and then address the future risk of flooding that includes allowing for predicted climate change. The first stage includes gathering some more data, considering detailed alignments for potential stopbank improvements and raising community awareness and preparedness. Following that we will address the areas at immediate risk of a 1% AEP flood (Oxford Street), then the Akura Road area. There will then also be a stage in 10-20 years’ time to further review and understand the future flood risk and then a plan to manage that future risk. This staged approach will feed into the Te Kāuru Floodplain Management Plan. 

Why are you doing a staged approach?

To allow better information to be gathered and more detailed options to be considered. We want to ensure we engage with the community during the selection of the best option, to ensure a sustainable and affordable outcome. Future increases in flow and level caused by predicted climate change have been estimated. By using a staged approach, we can ensure that we have more long-term trends included in our data records. We are proposing to include an allowance in the early stages of the approach for raising stopbanks in the future as necessary. 

How much is it likely to cost?

Given we are looking at a staged approach, the costs of flood protection improvements will be spread over a long-term period. Initial costs over the next two years are likely to be approximately $350,000. This cost will be for Stage 1: planning, engagement and data collection. Costs for future stages will be reassessed during Stage 1. 

What are the timeframes?

Between years 2 and 5 years we will look at the high risk areas (Oxford St) and the design and construction of flood management measures such as, stopbanks and improved channel capacity. The costs for this stage are provisional only, however, may require investment in the vicinity of $8 million. The timeframes are also indicative only. They will be reassessed at the end of each stage and will be balanced with other council priorities. 

Why do we need to do this?

Mainly due to differences in the hydrology between the different studies, and in the use of new “flexible mesh” From the data we have available and the current information on climate change, it is predicted that there will be an increase in large flood events. There is potential for significant property damage and risk to life. We need to take a proactive approach to flood protection now, so that in the future we are less affected by large flood events.

What’s wrong with the current stopbanks?

The condition of the stopbanks within the urban area require further investigation, we might not be able to rely on them to protect Masterton from flood waters. Preliminary investigations have indicated that the stopbanks are in poor condition. Some of the stopbanks around the urban area were built back in the mid-1900’s using material that may not have been suitable for the long-term integrity of the stopbanks.

Did you consider other options such as storage dams?

A range of options have been considered including upstream storage and the purchase of properties at risk. Our assessments of these options indicated a much greater cost (more than $30 million) and were not considered further. Increasing channel capacity and stopbanks was the approach considered most viable. However, other forms of storage such as wetlands further up in the rural reaches of the Waipoua River are included in the proposed approach to help with the flood management.

Why don’t you have enough flood data to know what’s going to happen?

We have data from as far back as 1996 which gives us an indication of historical flooding, however, it is not quite enough for us to be certain of severity of the flood risk. The more data we can gather over the coming years, the better our estimates can be.

What can the community do to help?

Provide us with your feedback, suggestions, and comments. Anything you feel will be constructive in ensuring the protection of Masterton from a large flood event.

Who is most likely to be affected by a flood?

From a house flooding point of view, people who are in Oxford Street and Akura Road are more likely to be most affected. However, access to Masterton and its amenities may be difficult immediately after a flood, therefore the general public will also be affected.

What does it mean for insurance?

The current flood maps are still in use and we recommend that residents advise their insurance company if they are in a flood hazard area. However, the maps available on the online GIS viewer include an allowance for climate change. From our conversations with insurance companies we understand that they are usually more interested in flood hazard under today’s climate because it reflects the risk they are insuring. GWRC is happy to provide additional information (including maps without climate change included) to assist with any queries from insurance companies. The new maps will be available showing today’s hazard (no climate change) and future hazard (including climate change)

What does it mean for building consents and LIMs?

As the maps are in draft stage, the information will be provided to give context.

I am the owner of a house in an area that looks to be directly impacted, what does it mean for me?

Please talk to GWRC about any site specific advice you may need. Note that the regulatory implications (e.g. new building levels) will be confirmed prior to final flood maps being produced.