Maitai Flooding

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The most important thing

Please don’t be alarmed by this new information. Council has received new information regarding Maitai River flood models, and it’s our responsibility to share it with you so we are all aware of the latest information and can all make informed decisions in the future.

Latest information on possible Maitai River flood paths

Most Nelson residents are aware that the Maitai River is prone to flooding, especially when heavy rain coincides with a big tide. The latest research has been done to update the previous flood models that were based on flooding information from 1986. This new report uses updated data from NIWA and was checked against river levels during the December 2011 storm event. It gives us a model based on current rainfall predictions and current sea level in 2013, and also makes some initial predictions about how sea level rise and increased rainfall (as a result of climate change) might affect the flood path of the Maitai River over the next century.

The report is called Maitai River Flood Hazard Mapping Modelling report, August 2013. It’s available to read at the Nelson Public libraries, the Customer Service Centre or you can download copy below.

  • The model was developed by Tonkin and Taylor and has been peer reviewed by Aurecon. 
  • The flood hazard maps show peak river flows in the urban area coinciding with the peak level of the annual storm tide. 
  • Compared to the existing Flood Path Overlay this new modelling shows more of the residential and commercial area potentially affected by flooding during a 1 in 100 year storm event in 2013.
  • The research shows that the extent of urban flooding is sensitive to tidal influences and peak flow volumes. The model will need to be reviewed after future recorded significant rainfall events to check its accuracy. 
  • The effects of climate change are shown in the flood hazard maps. This includes sea level rise scenarios of 0.3, 0.5, 0.8, and 1.0m over time, and also an increase of 8% rainfall intensity by 2060 and a 16% increase by 2110. These predicted changes are based on guidance from Ministry for the Environment.
  • In the report Tonkin and Taylor have also provided an assessment of the impact of a Maitai dam failure, as required by the Building (Dam Safety) Regulations 2008. However there is an extremely low probability of a dam failure.

What next?

The flood modelling contained in this latest report is intended to be used to update Council planning documents and future Council projects, with the aim of reducing the risk to people and their properties when new building and development is done in the affected areas. However there is more work to be done first. We will be writing to property owners about this in more detail next year.

Land Information Memorandum (LIM) and Project Information Memorandum (PIM) interim note

Because we’ve received this new information, we will add an interim note to the property files that we hold. The interim LIM notation reads:

Other Information pursuant to s44A(3) of the Local Government Official Information and Meetings Act 1987

“The Council holds new and updated modelling information showing that this property is in an area that may be at risk of flooding in the event of a Maitai River flood. That information is in a report entitled “Maitai River Flood Hazard Mapping Modelling Report, August 2013” and is publicly available at Nelson libraries, Civic House and online at nel.so/n/maitai. The Modelling Report was not done to a property specific level of detail and further site specific investigation may be required should this property be further developed or have a change in use.

Feedback is being sought from landowners before that new information is able to be confirmed as identifying/further identifying a special feature or characteristic of the land within this area under section s44A(2)(a) of the Local Government Official Information and Meetings Act 1987, or s35 of the Building Act 2004. Note: This is an interim LIM notification only, and may change once all new information has been evaluated.
For more information please contact Customer Services at Nelson City Council specifying the address of the property concerned.”

Download the report

Map

You can search on this map for a closer view of your property to see how it is affected. You’ll need to search on your full road name, e.g. “110 trafalgar” or “50a grove” to bring up your property.