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Proposed approach to flood management in Masterton

http://www.gwrc.govt.nz/proposed-approach-to-flood-management-in-masterton

Proposed approach to flood management in Masterton

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This Consultation is closed.

The open period ran from 5:00pm 22 February 2019 to 11:59pm 05 March 2019 (closed 3 months ago).

Rivers are the lifeblood of our community. In fact, the name Wairarapa means ‘glistening waters’. However, sometimes our greatest assets can cause our biggest risk. Masterton District Council and Greater Wellington Regional Council are currently looking at options for managing the current and future flood hazard to Masterton from the Waipoua River. This is being done through the Te Kāuru Floodplain Management Plan.

As part of the process, draft flood hazard maps have been jointly released by the Councils. The draft flood maps will be finalised following an independent audit, at which point they will replace the current flood hazard maps for Council.

We are proposing a staged approach to managing the flood and erosion risks over the next 30 years. This will allow better understanding of the current and future risks to Masterton, prior to a large financial investment. We will communicate and engage with the community during each stage of the process.

The flood management responses developed for the urban reach of the Waipoua River include a combination of non-structural measures, increased river channel capacity, and new and upgraded stopbanks. However, these will depend on the information collected during the first stage of the process.

Staged Approach

We are proposing a staged approach, which will first focus on gathering more information and then addressing today’s risk. The first stage includes gathering some more data, undertaking geotechnical investigations on the existing stopbanks and surrounding environment, considering detailed alignments for potential stopbank improvements, and raising community awareness and preparedness. The later stages will address the future risk of flooding that includes allowing for predicted climate change. A preferred option will be developed with the community and key stakeholders. Following that we will address the areas at immediate risk of a 1% annual chance flood (Oxford Street), then the Akura Road area. It should be acknowledged that all stages following Stage 1 will be dependent on the outcome of the previous stage.

Often this size of flood is referred to as a 1-in-100 year flood, we call it a 1% annual chance flood; it means there is a 1% chance of this sized flood occurring in any given year. It does not mean that there is exactly one of these floods every 100 years. It is also important to remember that several big floods could happen in quick succession.

One of the following stages, in 10-20 years’ time, will look to further review and understand the future flood risk and then a plan to manage that future risk.

The staged approach is to ensure we are not doing unnecessary work and spending money if it is not needed.

The approach of increased channel capacity and stopbanks was agreed as the most viable, supported by non-structural responses such as encouragement of wetland establishment upstream. The increased channel capacity is being considered in order to minimise stopbank heights, but it will have medium term impact on the look and feel of the river channel and berms. A staged approach has been developed to try to manage the affordability.

Increased Channel Capacity

The majority of vegetation would need to be removed to achieve the greater channel capacity so the river area would change significantly in the medium term until new trees are established. In doing this, it also creates the opportunity to enhance the recreational and amenity values of the river corridor, including improved spaces for walking, running, cycling and other leisure activities.

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River Corridor Proposal

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Alternative Approaches

A range of approaches have been considered including upstream storage and the removal of at risk property. Both of these approaches had significantly higher costs (greater than $30 million) and were not considered further. The approach of increased channel capacity and stopbanks was agreed as the 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.

What does this mean for you?

This proposed approach aims to provide flood hazard and erosion protection for the Masterton urban community, while enhancing environmental and cultural values of the river. During Stage 1, we will ensure we are doing this in a sustainable and economical way. Stage 2 may require a flood protection investment in the vicinity of $8 million, however this will be assessed and confirmed during Stage 1, funding will be loan based as these projects are long term and have a long-term benefit. Repayment of the loan (borrowed money) will be via a rates increase, similar to how ratepayers in the Carterton area are paying for their new Wastewater Treatment Plant.

The cost estimates and timeframes of the plan are indicative only. They will be reassessed at the end of each stage and will be balanced with other council priorities.

Reading the Volumes:

Te Kāuru is currently in three volumes. Each of the three volumes are still in draft format.

Once feedback has been received on all three volumes, they will be combined into a single proposed Floodplain Management Plan for the Upper Ruamāhanga Catchment.

Volume 1:

Why we need this plan – This volume describes why we need Te Kāuru, the vision, the aims, the suite of responses and common methods that will be used, how they plan will be implemented.

We have made some changes to Volume 1 as a result of talking to the community last year. A new draft version of Volume 1 is available for your feedback.

Volume 2:

Outcomes for the rural areas – This volume looks at the different location specific management options to be delivered across the rural areas of the Te Kāuru catchment.

Some minor changes are being made to Volume 2 and updates will be included in the proposed FMP later in the year.

Volume 3:

Outcomes for Masterton urban area – This volume outlines the proposed management of the Waipoua River through the Masterton Urban area.

This has been recently developed and we are seeking your feedback on the proposed approach.

Next Steps

Community Feedback

Please 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. Have Your Say by Tuesday 5 March 2019.

The consultation is now closed and no further submissions can be accepted.
Thank you for your interest in this process

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