Storage lakes upgrade

http://www.gw.govt.nz/storage-lakes-upgrade

Storage lakes upgrade

We've completed the work to upgrade the Stuart Macaskill water storage lakes in Te Marua to improve their strength in an earthquake and increase their capacity. 

Project update - October 2013

The northern lake has been refilled and was put back in service on Monday 21 October.

We began refilling the northern lake on 14 August and it was full on 19 September 2013.  Filling was followed by a month of careful monitoring before it was put back into service. The northern lake now holds 1607 million litres of water.

 

Lake one ready for refilling

The refilling process for the northern lake begins

Lake refilling 

Project history

In 2009, a feasibility study for increasing the Stuart Macaskill lake capacity was carried out. It found that in a Wellington Fault earthquake (using the latest GNS energy estimate), significant cracking in the lakes’ lining could occur, possibly resulting in the loss of stored water and internal erosion of the lakes’ embankments. In order to comply with NZSOLD Dam Safety Guidelines and to retain stored water for use following an earthquake, GWRC decided to reduce this possibility by increasing the lakes’ seismic strength.

Increasing the lakes’ capacity by 13% is an important short-term measure to boost our overall water supply capability in a dry year. However, the lakes’ embankments needed to be reinforced regardless of whether the storage capacity was increased.

The project required that the northern lake (closest to the water treatment plant) was empty in summer 2012/13 and the southern lake (closest to Upper Hutt) was empty during summer 2011/12.

Having one lake empty during summer, halved the stored water available to Lower Hutt, Porirua, Upper Hutt and Wellington. We were granted a variation to our consent to take water from the Kaitoke Weir, to reduce the risk of a summer water shortage while the lakes were upgraded.

The upgrade project began in January 2011 with construction work to strengthen the outer embankment walls of both lakes.  This strengthening work was completed in December 2011.

In 2012, the southern lake was upgraded while in 2013 it was the northern lakes turn.  The upgrade work consisted of draining the lake so that a plastic liner could be laid underneath the rip-rap (the rocks that protect the embankments of the lake). The storage capacity of the lake was increased at the same time.

The liner is made of plastic that can stretch to seven times its original length without breaking and is designed to stop leakage of stored water and erosion of the lakes' earth embankments after an earthquake.

 

A sheet of the lining is pulled into place