TDC accepts the stopbank refurbishment option

September 28th, 2011

The Tasman District Council unanimously accepted the engineer's recommendation to solve Motueka's flood control problem by refurbishing the existing stopbanks.

The project, which has been conservatively costed at $13.3 million, will now go forward to the Draft Long Term Plan 2012–2022 for further consultation, while further work is undertaken on the rating impact of this decision

The decision, taken at last week's full council meeting, follows the latest round of public discussion on the issue (see our report here), and included opinions from 42 written submissions which showed that for the small sample 31% wanted the status quo (do nothing), 50% wanted the refurbishment option and 12% voted for rebuilding the stopbanks from scratch.

The main issue that came out of the public meetings was the affordability of the project to the Motueka ratepayers. This was also linked to the potential upgrade of the water reticulation scheme. Considerable discussion took place on how much the whole district should pay towards the cost of new stopbanks.

It was proposed the required loan would be spread over 40 years and repaid by ratepayers depending on the benefit they received. The rating funding split would see 60 per cent of the cost fall on those for who the risk of flooding would be removed by the refurbishment, 30 per cent to those who would have been inconvenienced by flooding and 10 per cent across the rest of the district.

There were also some few comments about gravel extraction but council engineers felt there was now a greater acceptance that while gravel extraction is essential it is not a standalone option. Gravel extraction has an estimated cost of $2 million and has been included in the total project cost.

Council engineers noted that gravel extraction provides some benefits including the reduction of overtopping, reducing the need to quarry outside the stopbanks, and it could be undertaken in conjunction with sourcing materials (e.g. silt) for the stopbank upgrades.

Disadvantages of gravel extraction are:

The natural protection to the foundations of the stopbanks buffer zone would be reduced.
It will increase the risk of under seepage.
Does not address the problem that areas of the stopbanks are weak.
Gravel should not be extracted from the active channel as this will affect groundwater.
Trees lining the banks of the river will not be able to be moved as they shade the river and provide some bank protection in flood events.
Gravel extraction below the bridge at SH60 would be ineffective in reducing the flood effects at high tide when the peak creates the greatest risk.
It will be an ongoing project as more gravel will be moved downstream in flush events. This means ongoing river works will be required which is costly.

In addition to the $11.6m refurbishment proposal (including gravel extraction), the council plans to spend about $200,000 to provide additional freeboard for flood wave action and about $1.5m to upgrade the stopbanks protecting Brooklyn Stream, making the total project cost $13.3m.

The work will see the banks widened on the river side of the existing stopbanks and their height increased by about 700mm to cater for a 1:100 flood. The current banks only protect Motueka in a 1:50 year flood.

Including the Brooklyn Stream stopbanks will add to the number of ratepayers in the direct benefit zone, spreading the income base. But engineers said that hydrology reports also indicate that if there was to be an event in the Motueka river catchment, there is a high possibility of it also happening in the Brooklyn. In 1976, the Brooklyn had a flood event, which was caused by a tree trunk being washed down the stream by the floodwaters. It then got stuck and caused the water to dam up and overtop the stopbanks. The effect was felt over the Riwaka Township.

It was noted that there are land ownership issues associated with the stopbank project. The Iwi owns approximately 80% of the riverside land and therefore will be directly impacted by any decision made. It was seen as imperative that the Iwi are consulted with separately. A cultural impact assessment will be required.

Council's next steps will be:

A newsletter will be sent out to the community informing them of Council's decision on the preferred option.
Consultation with Iwi.
The preferred option will be reviewed and placed in the Long Term Plan, which will go out for public consultation in December 2011.
Further work on the rating impacts will need to be carried out, on which Council will need to make a decision.

Comment by Philip Grimmett:
[Posted 2 October 2011]

Is this Bob Cooke and KMB's next project? Ensuring that the stopbank upgrade is useable by walkers and cyclists? How amazing would that be!

Comment by John Westall:
[Posted 2 October 2011]

Agencies working together to combat rising hardship & unemployment in Motueka, NZ's credit rating downgraded by two agencies, the government and the T.D.C. already overloaded with current debt, and now this pack of clowns want to push us in even deeper?

Get off the grass Noddies, as Jim Butler points out, the present banks have held for 50 years. and as for so called "climate change" this is a cult belief that ranks right up there with witchcraft & voodoo, and suits the less than truthful agendas of the Al Gores and Nick Smiths of this world, who see it as a great scam to make more money and cause even more hardship.

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