GW investigating new water storage options at Kaitoke

Greater Wellington has secured an option to buy land owned by AgResearch at Kaitoke, adjacent to State Highway 2, with the intention of investigating the land to find out if it’s suitable for a water storage lake.

“The size of the proposed lake will be determined during the investigations but it could have a capacity of around 5,000 million litres – making the volume around 50% larger than the two Stuart Macaskill water storage lakes combined,” says Greater Wellington’s Utilities and Services General Manager Murray Kennedy.

Water for the proposed lake would be piped from near the Te Marua Water Treatment Plant, using the existing Kaitoke weir resource consent. The lake would allow Greater Wellington to capture more of the water when there is high rainfall but would not affect river levels at times of low flow.

The investigations are likely to begin in November and could take up to 12 months. They will include investigations into geological/geotechnical and civil works as well as environmental, social and cultural issues.

Murray says that if the site is seen as being suitable for a storage lake, it will be evaluated along with other options that Greater Wellington has previously investigated for future water supply.

“If the proposed lake is built, a dam or another water storage lake probably won’t be needed for about 20 years. If a new storage lake isn’t built soon, it’s likely that a dam would need to be built within 10 years. However, timing will depend to some extent on household and commercial water usage, with Greater Wellington remaining committed to reducing per capita water consumption.”

Murray says that if a decision is made to proceed with the project, the public would have the opportunity to have their say on the project through Greater Wellington’s Long Term Plan process and the Resource Management Act’s resource consent process.

If the project proceeds, construction is likely to take two to three years to complete after the necessary consents and approvals are obtained. The cost of purchasing the land would be determined through Greater Wellington’s negotiations with AgResearch.

Greater Wellington is responsible for supplying bulk water to the Upper Hutt, Hutt, Wellington and Porirua city councils.

Investigation into a potential water storage lake – Questions & Answers

Why is Greater Wellington investigating another water storage lake? Isn’t the Whakatikei dam the preferred water supply development option?
Although Whakatikei was confirmed as a preferred dam site in 2009, Greater Wellington has continued to look at other options to ensure the region has a secure water supply at a cost effective price.

Preliminary indications are that a new water storage lake at Kaitoke may be cheaper to construct than the Whakatikei dam and may have a lower environmental impact. Following the investigations, a comparison would be made of the benefits and impacts of a water storage lake at Kaitoke with the Whakatikei site.

How big would the lake be?
The investigations will determine potential lake size, but we think a lake of 5,000 million litres could be possible. That is a volume about 50% larger than both of the Stuart Macaskill Lakes combined but smaller than the proposed storage volume of the Whakatikei dam.

If a lake is built, how long will the construction take?
If the investigation concluded that a water storage lake could be built here and it is confirmed as the preferred alternative to the Whakatikei Dam for water supply development, then we would expect that construction could take between two and three years to complete. Time to obtain the necessary consents would be additional to this.

Will investigations have an impact on properties near the site? And will there be an impact if Greater Wellington decides to proceed with construction?
Neighbouring occupants may notice minor drilling and excavation activities during the investigation stage of the project but this is only expected to take a few weeks in total. If we decide to proceed with the construction of the proposed lake there would be some impact from construction, such as earthworks and truck movements. We would consult those affected before any works start.

Who is doing the investigation work? What does it involve?
A major consulting company will be commissioned to carry out most of the investigation work, which will include geological/geotechnical and civil works as well as an investigation into any environmental, social, and cultural issues. Some of the work will be carried out by Greater Wellington. The geological/geotechnical investigation will require some sub-soil testing bores to be drilled and minor excavation work.



How much water will the proposed lake supply and for how many people?
A lake of 5,000 million litres would provide enough water to supply the average daily water needs (150 million litres per day) of residents in Porirua, Lower Hutt, Upper Hutt and Wellington for around 33 days.

Where will the water come from?
Water for the proposed lake would come from the existing pipeline near the Te Marua Water Treatment Plant, using water from Kaitoke weir. It is also possible that water could come from the Pakuratahi River in the future.

What will the environmental impact be?
We don’t know at this stage. The investigations over the next 12 months will help to determine all possible environment impacts.

Will a new lake mean more water is taken from the Hutt River?
The proposed lake would allow Greater Wellington to capture more of the water available when there are higher river levels, but would not affect river levels at low flow. Water taken from the Hutt River at the Kaitoke Weir would be in accordance with resource consents for that purpose.

Why didn’t you investigate this option earlier?
The opportunity to purchase this land has only recently become available. Other options in the general area have been considered but were not preferred options, including a dam on the Pakuratahi river.

If a new lake is built, does this mean that we won’t need to build the Whakatikei or another dam in the future?
No. But if the proposed lake is built, it will mean that a dam or another water storage lake won’t be needed for perhaps 20 years, or longer if there is reduced demand for water. When more water supply is needed the option of a dam on the Whakatikei would still be available. However if we don’t build a storage lake it is possible the Whakatikei dam will need to be built within 10 years.

Why is a water storage lake being considered when water meters could lower household consumption, therefore delaying the need for a lake or dam?
Any decision the City Councils may make on domestic water meters would benefit from considering both demand side and supply side options. The information that will be gained from the investigation into the storage lake, including its cost estimate, will assist in evaluating the supply side options.



Won’t further delay in building a dam have a severe impact on the security of the water supply?
Per person and total annual water consumption has dropped over the last couple of years. This is probably due to a number of factors including: city council efforts to fix leaks, repair and replacement of pipelines, the increasing use of more efficient domestic appliances, showers and dual flush toilets, water conservation by users, climate affecting water use and the recession. The effect of this reduction has been to improve our security of water supply, which gives us more time to further reduce demand and/or build more water supply.

How much will it cost Greater Wellington to buy the land?
If Greater Wellington decides to purchase the land it would be bought at the market rate. The value would be determined as part of our negotiations.

How big is the land that Greater Wellington is looking at purchasing?
The AgResearch Ltd land covers approximately 215 hectares over a number of titles on both sides of SH2 at Kaitoke. Not all of this land area would be needed for the proposed lake.

What will Greater Wellington do with the land it doesn’t need for the lake?
If Greater Wellington goes ahead with the lake, a part, or all, of the remaining land could be leased for farming purposes. There may an opportunity to use this land to improve public access from one end of Kaitoke Regional Park to the other.

Will the design of the proposed lake be similar to the existing Stuart Macaskill lakes?
In general terms – yes. The proposed lake would consist of natural and constructed earth embankments (most likely internally lined, as planned for the upgrade to the Stuart Macaskill lakes) and depending on the lake bed structure, the lake could be fully lined.

If the lake is built, will it be available for recreational purposes?
Greater Wellington believes that it is inappropriate to permit recreational access to the Stuart Macaskill lakes that store water meant for drinking. This principle is likely to apply to any new water storage lake.

When will Greater Wellington consult with the local community? When do I get to have a say?
If this option is found to be suitable for a storage lake, and is the preferred alternative to the Whakatikei Dam for water supply development, people will have the opportunity to have their say through Greater Wellington’s Long Term Plan process and also through the Resource Management Act’s resource consent process.

Why is the lake being built on/near the Wellington Fault? Doesn’t that compromise it as a secure source of water?
An important part of the feasibility study, which we’re about to begin, is to confirm the location and potential impact of the Wellington Fault on a lake structure. This information would allow the design of the lake embankments to provide secure containment of the water in the event of an earthquake.