The Water for a Growing West (WGW) project was instigated to improve the reliability of water supplies in the rapidly developing outer western suburbs – one of the fastest growing areas in Melbourne. The project required installing a 17 km long water main from the St Albans Reservoir to Cowies Hill Reservoir in Tarneit, in order to deliver drinking water to 40,000 homes and runs. The new main is designed to transfer a maximum of 200 megalitres of water per day, the equivalent of 80 Olympic-sized swimming pools.

The water main was constructed largely under existing power lines and within current and future road reserves to minimise disturbance to landowners in the area. John Holland was contracted for the project given the company’s experience in delivering similar projects, including the recent Sugarloaf Pipeline Alliance and on a number of projects as part of the Barwon Water Alliance.

While the majority of the installation utilised open trenching, given the constraints of working in close proximity and under live rail, the project team chose to utilise microtunnelling as part of the installation. This technique was chosen as it minimises impacts and disruptions to rail services. Bothar Boring & Tunnelling was subcontracted for this portion of the works.

Challenges
The WGW Project spans three Council jurisdictions: Brimbank, Melton and Wyndham. A Planning Scheme Amendment (PSA) was pursued and approved for the project, which required extensive consultation with councils and state departments to ensure each stakeholder’s considerations were included in the WGW Project requirements.

With a mandate to have water supply up and running by November 2015, John Holland had to work hard to meet stakeholder requirements and balance relationships with a number of councils.

Due to the growth of the outer western suburbs, planning and construction of other infrastructure upgrades was also taking place during the construction timeframe. Route selection, coordination of surveys and land tenure was undertaken in conjunction with road upgrades (in association with VicRoads and councils), the Regional Rail Link, planned transport terminals and other essential services infrastructure including water, sewerage, electricity and gas.

The WGW Project crosses a wide variety of terrain, including urban, rural and farmland, each with its own complexities. Melbourne Water put strict environmental and heritage controls and management plans in place due to the location of the project.

Located in grasslands that are home to several threatened fauna species, including the Golden Sun Moth, Growling Grass Frog and Striped Legless Lizard, John Holland took extensive measures to ensure the delicate environmental and cultural surrounds were not negatively impacted upon.

The grasslands also contain the Spiny Rice Flower, a threatened flora species. Management plans were developed to avoid, minimise or mitigate impacts to the threatened flora and fauna species through construction.

Cultural considerations particularly came to the fore when planning to cross Kororoit Creek, an area of known sensitivity. Cultural Heritage surveys were carried out and a Cultural Heritage Management Plan was developed and approved for the project, and an archaeological salvage in proximity to Kororoit Creek was completed prior to construction.

Dry stone walls were located along the alignment, where their former (and in some cases current) use was for holding livestock. These dry stone walls are heritage-listed, so a Dry Stone Wall Management Plan was developed for the protection and reinstatement of the walls and fences.

The geology of the area and existing infrastructure provided the key engineering challenges for the project. The WGW Project area is predominantly located within basalt plains, and large basalt boulders or ‘floaters’ are scattered along the watermain alignment.

Where drilling was required, it was necessary to conduct this work in the deeper consistent rock rather than the variable ground conditions.

The majority of the alignment is within a high voltage electricity transmission line easement; due to the induced voltage issues and complex corrosion control equipment associated with the use of welded steel pipe near high voltage lines, FRP with rubber joints has been adopted instead.

Future outlook
As at October 2015, 96 per cent of the water main has been constructed, with reinstatement works being carried out through October and November.