GW Water Supply Department seeks water consent variation

Greater Wellington’s Water Supply Department has applied to vary its resource consent for taking water from the Hutt River at Kaitoke as a contingency measure while the Stuart Macaskill water storage lakes are upgraded.

The 2-3-year project to increase the lakes’ seismic strength and storage capacity will require lake 2 to be empty in the summer of 2011/12 and lake 1 in summer 2012/13 – there’s also the possibility that one of the lakes may be out of service in summer 2013/14 if construction is delayed.

“The strengthening is needed to ensure the lakes are very secure following a major earthquake – and it’s also essential if we are to meet national dam safety guidelines. Increasing the lakes’ capacity will boost overall water supply capability during a dry year. The seismic strengthening is needed whether or not the storage is increased,” says Greater Wellington’s Utilities and Services General Manager Murray Kennedy.

“However, draining a lake will effectively halve the stored water capacity for 2-3 years and reduce our ability to provide enough water, particularly in a dry summer. We may need additional water, depending on public demand so having a bit more water available from the Hutt River will help us to stave off a serious water shortage.”

The consent application seeks to reduce the minimum permitted flow in the Hutt River below the Kaitoke Weir from 600 litres per second (L/s) to 400 L/s. The application also proposes new conditions for an enhanced long-term monitoring programme and formal low flow management plan for the Hutt River.

Mr Kennedy says that change to the minimum flow would be for three years – the duration of the upgrade project. “We’ve had independent scientists look at a range of potential effects on the river habitat. Their reports say any effects will be no more than minor. We’ve provided the reports with our application.”

Greater Wellington will work with Lower Hutt, Porirua, Upper Hutt and Wellington city councils to manage water consumption and encourage responsible water use. Its summer water demand management plan and water conservation advice will reflect the reduced level of stored water during the upgrade project.

The public will have an opportunity to have a say on the consent application when it is publicly notified.

The consent application, including scientific information, is available from Greater Wellington’s website www.gw.govt.nz/kaitoke-consent and will also be available at some local libraries. Any queries on the consent process should be directed to Greater Wellington’s Environmental Regulation helpdesk at (04) 830 4255.

Kaitoke Weir resource consent application – Q&As

Why do you need to increase the seismic strength and capacity of the Stuart Macaskill lakes?
A feasibility study for increasing lake capacity in 2009 found that in a Wellington Fault earthquake (using the latest GNS energy estimate) significant cracking in the lakes’ lining could occur, ultimately resulting in the loss of stored water and erosion of the lakes’ embankments. In order to comply with NZSOLD Dam Safety Guidelines, we are required to reduce this possibility by increasing the lakes’ seismic strength.

Increasing the lakes’ capacity is an important short-term measure to boost our overall water supply capability in a dry year. The lakes’ embankments need to be reinforced regardless of whether we increase the storage capacity.

Why do you need to change the current Kaitoke Weir resource consent for three years?
This lakes upgrade project will require lake 2 to be empty in summer 2011/12 and lake 1 in 2012/13. There is a possibility of lake 1 also being out of service in summer 2013/14, if there are any construction delays.

Taking a lake out of service will approximately halve the available water storage capacity and therefore affect the ability of the bulk water supply system to provide adequate water, particularly in a warm, dry summer.

In order to reduce the potential for, and severity of, a summer water shortage, Greater Wellington’s water supply department has applied for a change to the consent for taking water from the Hutt River at Kaitoke. The change would reduce the minimum flow over the Kaitoke weir from 600 litres per second (L/s) to 400 L/s.

Why do you need to do this work over summer?
The upgrade of each lake involves removal of the clay lining from the embankment’s internal face and installation of a plastic liner, followed by replacement of the clay lining. The clay lining needs to be relatively dry to make handling easier. The plastic liner is welded in place, which also needs dry conditions. This means the work needs to be carried out over summer. Depending on the weather, it may be possible to start work in November.

Why not delay the upgrade until you have built more storage?
As a responsible large dam owner (the Stuart Macaskill Lakes are classified as dams) and legislative regulator, Greater Wellington has decided that the upgrade work should be carried out within an acceptable timeframe. Our assessment of an acceptable timeframe is up to five years, and the programme for the work meets that criterion. Investigations into a new storage lake are at an early stage, and, if built, could take around eight years. A dam may take longer. It would not be responsible to delay for that length of time.

But hasn’t water use dropped? Why do you need more water when use is going down?
Actual water use has reduced over recent years and if our summer weather and water usage remain moderate, river flows may not fall below 600 L/s. Weather conditions are a key influence on the demand for water and the water supply available. We don’t know in advance the level of rainfall or demand for water that we will get each summer and with one storage lake out of service, we want to ensure we have options available to maintain an adequate water supply. It’s all about managing risk.

How much more water will there be if the lakes’ capacity is increased?
When complete, the storage capacity upgrade will provide some 400 million litres (ML) more storage (13%).

In early 2008 (the most recent year when we used the lakes extensively to supplement river flows), we supplied an average of 32 ML/day from the lakes on the days that we used them. The increased capacity would allow us to supply 32 ML/d for an extra 12 days. A drought management plan, in place since 2008, is likely to improve that situation further.

Isn’t there a conflict, given that consent application will be processed by Greater Wellington?
To maintain separation within Greater Wellington, the application will be considered by an independent hearing committee. The regulatory and operational arms of the council are separate. A consent application from the Water Supply Department is treated the same as one from an external applicant. We will go through the same process as an external applicant for a fully notified consent, which will provide an opportunity for the public to make submissions.

What will the effect be on the Hutt River from decreasing the minimum low flow at Kaitoke Weir?
The effects have been assessed as no more than minor by independent scientists. The scientists studied fish passage in the gorge immediately below the weir, the availability of suitable habitat downstream of Birchville, the number of small creatures in and around the river (this is an indicator of river health), and factors affecting algal growth. In the lower reaches of the river the reduction in flow at Kaitoke will not be noticeable due to flows from major tributaries joining the Hutt River between Kaitoke and Upper Hutt.

Does this consent change mean you’ll be taking more water from the river all the time that the consent for additional water is operative?
No it doesn’t. The proposed change would be used only when existing consent limits could not provide enough water to meet the demand from water users. This is most likely to be in January, February and March, when there is a higher risk of extended periods of dry weather and increased water consumption, particularly for gardening and outdoor use.
Greater Wellington and the four city councils that receive their water supply from us will manage water consumption and encourage responsible water use by running water conservation communications and introducing more stringent restrictions if required.

We have to go through a strict process to get consent and people will have an opportunity to be heard. Even if consent is granted we will only take extra water if it’s needed to meet public demand for water and maintain lake storage. We are not seeking to take more water per day than allowed under our existing consent.

Once the two storage lakes are full and have the extra capacity, will you still take more water from the Hutt River?
No, the proposed consent change is only for three years while we work on upgrading the two storage lakes.

Will taking more water increase the risk of toxic blue-green algae?
Algal blooms can occur in rivers across the region during periods of warm weather and consistently low flows and the absence of flushing from heavy rainfall. We commissioned independent scientists to investigate the potential environmental effects of lower river levels. This information is included in our consent application and will be assessed by the independent hearing committee. The scientific research is available on our website.

Will you go ahead with the upgrade project if you don’t get consent?
Yes, the project will still go ahead to reduce the lakes’ vulnerability and ensure water is retained in a significant earthquake. The raising of the lakes’ capacity is also an important short-term measure to increase the four cities’ water supply while Greater Wellington, the four cities and the community decide which longer-term measures to take.

What happens if you don’t get the consent?
If we aren’t granted the consent there is a greater probability of longer lasting and tougher water use restrictions being needed in an extended period of warm, dry weather while one of the storage lakes is empty. The four city councils may need to put in place strict measures to reduce water use to ensure water use doesn’t exceed supply. These could include banning non-emergency use of water for “outdoors” purposes (watering, washing cars, houses and yards etc).

Why do you need the consent now if the works don’t start until late next year?
The process of gaining consent is quite involved. We have lodged the application now to have the consent, should it be granted, in place before we drain lake 2 in preparation for the works. Lake 2 will be drained in the second half of 2011. We also need to know the outcome of the consent process so we can prepare appropriate public communications, to help manage the increased risk of water shortage while our storage capacity is reduced over the summers of 2011/12, 2012/13 and possibly 2013/14.

ENDS

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