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Flood Hazard Frequently Asked Questions

http://www.gw.govt.nz/flood-hazard-frequently-asked-questions

Flood Hazard Frequently Asked Questions

Updated 24 March 2017 2:18pm

2014 Upper Ruamāhanga Flood Hazard Map

We understand that you might be concerned about potential risk to yourself, family, community and property.  Please find below some frequently asked questions about the flood hazard information that was shared with Upper Wairarapa Valley residents in late August 2014.

For clarification or specific information call the Greater Wellington Regional Council Flood Protection Department on 06 378 2484 or email info@gw.govt.nz.


1. I’ve lived at the same address for a long time, there’s never been any flooding here before. Why am I now in a flood hazard area? 
Even if you do not remember flooding at your property, flooding is a reality in and around Masterton. The town is built on a floodplain between three rivers. Works have been done in the past to reduce the risk of flooding however floods of greater size than these works may occur.

2. What do you mean by a very large flood/1-in-100 year flood

Floodplain Management professionals in New Zealand, and around the world, use measurements for large floods such as a ‘one-hundred-year flood’.  These measurements are based on probability supported by historic flood records. A 1-in-100 year flood means that a very large flood is statistically likely to happen once every 100 years; in everyday terms it means that there is a 1% chance of such a flood happening in any given year.  Of course floods can occur which are greater and lesser than this size, smaller floods occur more frequently, whereas larger floods are statistically more rare.

3. How deep could the flooding be at my property?  

Flooding depth will always vary depending on where you are located and may also vary across your property. Contact us to talk about possible flood levels at your property.   To find out specific details for your property contact GWRC Flood Protection Officers on 06 378 2484 or email info@gw.govt.nz.

4. How much warning of a flood will I have? 

Times of very high rainfall can be followed by flooding.  Listening to weather warnings on TV and radio can alert you to any unusually high rainfall.   The MetService updates its web page on the internet and offers an alert service: http://www.metservice.com/warnings/home, as well as information on FaceBook and Twitter.

Severe weather watch or warnings can usually be found on GWRC and WREMO websites.

5. What is happening right now to provide flood protection?

Greater Wellington Regional Council currently manages the risks of flood and erosion for major rivers and streams in the Wellington Region. In the Wairarapa this is currently carried out through river management schemes which maintain stable river channels, a range stopbanks and erosion protection structures and the gravel which affects river bed levels.

 For Masterton the current stop-bank provides protection from smaller more frequent floods. However a small number of areas are still vulnerable. Greater Wellington Regional Council monitors storm warnings and flood levels, and provides warnings to some at risk communities. 

6. What is being done to improve flood risk management in the Ruamahanga Valley?

GWRC has established the Te Kauru Upper Ruamahanga River Sub-committee to develop how the flood risk should be managed.  This is called floodplain management planning and is a process that happens across the region.

This sub-committee is currently gathering information and looking at options for a floodplain management plan (FMP) that they will share widely with the Upper Ruamahanga River Valley community for their input by mid-2015.  The FMP will consider community views on affordability and flood protection levels.

7. What do I do before the next flood? 

It is important to be personally prepared for a flood.  GWRC and the Wellington Regional Emergency Management Office (WREMO) support this with up-to-date information on: current flood risk and being prepared at home and in your community.  The WREMO website offers a range of information on how you can develop home emergency plans, mitigate your flood risk and what to do in a flood. http://www.getprepared.org.nz/.

8. How do I know you are right about the flood risk to my property?

We have been very thorough in our work to assess flood risk before sharing this information with you.   The new Upper Ruamahanga Flood Hazard map was completed in July 2014.  The Greater Wellington Regional Council Flood Protection Department have gathered high-quality information from ground and aerial surveys and used a range of well-established analysis techniques to improve on flood risk estimates made in 1995. Improvements to the technology we have available and the additional twenty years of data, have allowed us to draw a more accurate picture of where flooding may happen.

The flood risk estimate has been checked and reviewed by independent experts DHI (local New Zealand employees of the Danish Hydrology Institute) who have nationwide and worldwide experience in this work.

9. What if I have information about past floods?
If you think you have additional technical information or observations/photos to help us improve our flood maps please share this with us.  We will take information we receive into consideration during future model updates and reviews.

10. Will my house insurance premiums rise?
Insurance premiums take into account a range of risk factors.  The level of flood risk at your property may change your insurance premium if your insurer believes your property is at a greater risk of damage.  Talk to us about the depth of possible flooding at your property and discuss this with your insurer.  Your insurer may decide not to change your premiums, charge more, offer you a higher excess or require policy exclusions. Click here to read our Flood Hazard and Insurance factsheet.

11. Why is this information being made public?
GWRC is responsible for identifying flood risk for the region.  We are legally required to identify and share this information with district councils and the affected community to help them make informed decisions about flood risk management.

This information is public and available to anyone who has an interest in the property.  It will be included on LIM (Land Information Memorandum) reports held by district councils. Insurers can request it. 

12. If this information goes on a Land Information Management (LIM) Report will it lower the value of properties?  

It is not possible to categorically say that published information on risks to property won’t influence buyers. However we have been advised that there is no evidence that data on flood risk has any long term bearing on property values. This is based on work they carried out in a similar situation in the Mangaroa Valley, near Upper Hutt.

Insurance companies regularly ask district councils for updates to Land Information Memorandum data and for current hazard information.  Councils have a duty to the community to use the most accurate information available. This new information will be attached to your property LIM reports.

An outcome of the floodplain management plan may be reduced risk to your property, if this happened this would then change the information on your LIM report. You should convey this information to your insurer.  

13. How much of Masterton will be affected by flooding? 

For an overview of the new Upper Ruamahanga Flood Hazard map go to: http://mapping.gw.govt.nz/GW/URFMP/; or contact GWRC Flood Protection Officers on 06 378 2484 email info@gw.govt.nz.  Approximately 2000 properties (homes and businesses) are now included in the Upper Ruamahanga Flood Hazard area. 

14. How many other areas have you got flood hazard information on that people haven’t heard about?
Most of the floodplains in the Greater Wellington region that have heavily populated areas at risk of flooding have already had a flood hazard assessment including:  the Waiohine, Hutt, Waikanae, Otaki, Mangaroa, and Wainuiomata rivers, and the Waiwhetu, Pinehaven, Porirua and Waitohu streams.

In the future GWRC intends to develop and refine new or existing flood hazard models including updating the Hutt River flood model, and review the flood risks for the Lower Wairarapa Valley.