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Planning for regional growth

Planning for regional growth

Updated 9 June 2009 4:11pm
Water Supply - Te Marua lakes

As part of the process of maintaining an adequate water supply for Hutt, Porirua, Upper Hutt and Wellington city councils, Greater Wellington is moving to develop several short-term water storage and supply projects, and a regional water strategy with a longer-term focus. The measures we are proposing are set out in the Bulk Water Supply Development Strategy paper. For detailed information, read the Wellington Metropolitan Water Supply Development report.

Questions and answers about our development proposals are set out below.

Why do we need to make decisions now?

Our aim is to have a water supply system that results in a very low risk of water shortage (less than a two percent annual probability). As recently as 2000, modelling of water use showed our system would achieve this standard for up to 377,000 people; a level of population not then forecast as likely until at least 2020.

However, since 2001 and particularly following the 2006 Census, Statistics NZ has increased its population projections for the Wellington region. Higher than expected growth has seen the latest estimate of urban population in the four cities reach 379,100.

Also, in 2007, NIWA supplied us with updated climate data for our water use model, which reduced the maximum supply population for the existing system (and water shortage risk standard) to 368,000 people. As a result, the annual risk of a water shortage for our current supply population is now almost three percent, and will increase gradually over the coming years unless we act. These developments have brought forward the region’s need to plan for provision of more water and more efficient ways of using it.

How will the short-term options affect ratepayers?

Increasing the water take from Kaitoke Weir, building a new reservoir in Wellington (in conjunction with Wellington City Council and Capital & Coast District Health Board) and raising the Te Marua lakes’ levels have already been budgeted in Greater Wellington's annual plan so will have no significant additional rates impact.

Developing the Upper Hutt Aquifer has been estimated at $15-19 million.

Why are we considering building a dam?

Although our current focus is on short-term requirements and developing a regional water strategy, we still need to plan for how to meet our water supply commitment to the region's cities in the long term.

If the short-term measures are implemented and we reduce demand for water by 15 percent, an additional water source is still forecast to be required when the population reaches 460,000. Based on the latest population projections, that’s likely for 2040. However, if one or more short-term options are unavailable, or per-capita water savings are not achieved, the need for more storage to retain a low risk of shortages will come sooner.

How much will a new dam cost?

Our preferred dam site is on the Whakatikei River in the Akatarawa Forest. The 2007 estimated cost for a dam and the associated water treatment plant is $142 million.

Have we considered other sites?

We’ve also investigated Skull Gully in the Wainuiomata Catchment Area, and Pakuratahi Forest. Multi-criteria analysis was used to assess the three sites on a range of attributes. The Whakatikei site has considerable advantages over the other two sites:

  • It’s located on the western side of the Wellington Fault, making distribution pipelines to Porirua and Wellington much less vulnerable to a fault movement
  • The dam capacity could be increased by 50% at a relatively low cost
  • The dam could potentially be supplied from the Akatarawa River in the future
  • There is greater likelihood of getting a resource consent to build the dam on this site
  • It’s closer to areas of projected population growth in the western side of the region.

Why don’t we build the dam now?

By introducing the short-term options, particularly the development of the Upper Hutt Aquifer, we can delay the need for a dam by possibly 18 years. The short-term measures carry a much lower capital cost. This approach also means that if population growth is less than our planning projections or water savings more in the intervening years, we can continue to defer the development of a dam.

Will conserving water help?

Reducing demand for water 'per person' (by methods such as increased use of water-efficient appliances and fittings or household water metering and associated conservation education) at a rate equivalent to population growth would help to defer the need to build a new dam.

We will be working with the region's city and district councils over the next year to develop a regional water strategy proposal, including elements of water demand management, for public consultation. However, our projections show that continued population growth will eventually outstrip acceptable water saving measures, requiring a dam to be built.

When will I have my say?

Greater Wellington will be talking to the four city councils in 2008 about the short-term supply options. We’ll be asking the public to have their say on these options and the Council's preference for the Whakatikei River dam site through the Long Term Council Community Plan consultation period in March-May 2009.

As part of the development of a regional water strategy, we will be working in close consultation with the region's territorial authorities. The public will be asked to have their say on water management options at an appropriate stage of the development process.