The 31 km Gascoyne Irrigation Pipeline was built under a design and construct contract to improve water supply and security for nearly 200 growers in the Carnarvon region. The new pipeline ranges in size from PN 900 to PN 250.

The high-density polyethylene (PE) pipeline currently delivers groundwater at a rate of 350 litres per second (L/s) but it has been sized to cater for three times the current demand in order to service the proposed 400 hectare expansion, and will be able to deliver up to 1,400 L/s when operating under future pumps.

Project planning: approval, funding and contracting

The project was initially conceived to replace the ageing asbestos cement pipeline, which Gascoyne Water Co-operative (GWC) inherited when it took over the scheme from the state approximately ten years ago.

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GWC has worked closely with the Western Australian and Federal governments over the course of nearly ten years to secure approval and funding for the project.

The $19.9 million project successfully received funding from the WA Government’s Royalties for Regions program ($7.4 million) and the Federal Government’s Water for the Future initiative ($6.6 million), with GWC contributing the remaining $5.9 million.

Project works in road reserves required environmental clearances from the WA Department of Environment and Conservation, Main Roads WA and Shire of Carnarvon. In addition, works within the Gascoyne River reserve required clearance from the WA Department of Water.

In January 2011, GWC advertised for expressions of interest and short-listed four of the 21 respondents to go to tender. On 23 March 2011, the design and construct contract was awarded to Pipe Fusions Australia and on 18 May 2011 works commenced onsite.

According to Mr Keane, when comparing design proposals for a PE solution to proposals for rubber ring joints, a significant attribute of the PE pipe was the fact that it is joined using thermal butt-welding equipment. This, according to Mr Keane, reduces the risk of damage to the pipe caused by tree roots and results in less maintenance overall.

The project team

Pipe Fusions is a Perth-based company which has extensive experience in steel and plastic pipe installation around Australia.

Pipe Fusions employed Iplex Water Design to provide hydraulic design and detailing, and Iplex Pipes Perth supplied the majority of pipes and fittings. In addition, Pipe Fusions employed a number of local subcontractors for the Gascoyne Irrigation Pipeline, including North West Solutions (excavation and backfilling), CMS (pipe fittings installation), and HTD Surveys (survey pick-up for design and survey set-out for construction).

At peak construction, Pipe Fusions Australia had approximately 40 employees and subcontractors working onsite.

Throughout the pipe-laying process, GWC acted as a liaison between Pipe Fusions and the growers, distributing regular newsletters and providing onsite clarification with regards to service connections.

Pipe-laying challenges

Transporting project materials from Perth to Carnarvon, a distance of over 900 km, was a major administrative challenge in the project. It required constant close co-ordination between Pipe Fusions and Iplex Pipes, with Iplex keeping a member of staff onsite at all times to quality assess all deliveries.

Additionally, complying with the Australian standard for traffic control for works on roads, AS1742.3, was a significant task. The standard stipulates the measures that the contractor has to implement to maintain safe work practices where work sites fall within road reserves open to vehicle and pedestrian traffic.

“Apart from routine occupational health and safety management, traffic management proved to be a significant consideration in the execution of the works, given the requirements of AS1742.3 for works in road reserves,” said Mr Keane.

Another challenge the team faced was the task of connecting the mains to an existing pipeline that was attached to the underside of a bridge on North West Coastal Highway (NWCH).

Mr Keane said “Main Roads WA showed great foresight when constructing the NWCH bridge in 2005 by including in the bridge works a steel water main fixed to the underside of the bridge for future use by others.

However, connecting the mains took a lot of consideration and planning, particularly in relation to assessing the impact of movement joints in the bridge on the relatively fixed water main.”

The 182 grower services installed totalled approximately 57 km and ranged in length from 5–500 m. The project schedule was extended due to the time-consuming task of locating all existing grower services from the original pipeline ahead of the excavator.

“Although Pipe Fusions went over schedule to complete the works, the project still came in within the GWC budget. Practical completion of the mains was granted on 19 February 2012, and the work required to complete grower connections was completed 18 May 2012,” said Mr Keane.

Operation of the Gascoyne Irrigation Pipeline

Since the pipeline was commissioned on 13 April 2012, GWC said that it has experienced some minor teething issues associated with poor installation procedures of electrofused saddle offtakes, which are used to take service connections off the main. According to Mr Keane, a number of faulty saddles have now been replaced and, as a standard practise, all failed electrofused saddles have been extrusion-welded instead in order to provide added integrity.

Electronic water metering and supervisory control and data acquisition equipment is being used to provide to-the-hour data on individual growers’ water usage back to base. Aside from being a more efficient way of gathering usage data, this will also allow for separate pricing for off-peak water usage in the future, facilitating more even water distribution.

Manual reading of meters will also be possible as a backup option, and this will be carried out periodically to verify the accuracy of electronic data.

GWC is currently working on the next stage of its water supply development plan, which is set to improve and expand the borefield supply.