Maungatua Contracting

Still waters run deep

in Central Otago irrigation scheme

A best-of-breed irrigation scheme completed in November 2014 means there’s now more than enough water to go around for client shareholders in the small central Otago farming settlement of Tarras.

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PROJECT: Tarras Irrigation Scheme, Otago CONTRACTOR: Maungatua Contracting T he Tarras Irrigation Scheme takes water from the Clutha River at a rate of 830 litres a second and pumps it through a network of pipes to supply a number of agricultural demand points.

Valued at $3.66 million, the contract for the scheme was awarded to Wanaka-based Maungatua Contracting – a family business with over 50 years’ experience in civil construction and earthworks.

Maungatua Contracting was tasked with completing the whole kit and caboodle – covering design, planning, consents, supply and construction, earthworks and commissioning. This was no small task, but the firm approached things with relish and enthusiasm.

The scale of the newly minted Tarras Irrigation Scheme can best be described as immense. Involving the construction of a 74,200 cubic metre reservoir, the project saw kilometres of piping installed across five privately owned farms and four public road crossings. Eight and a half kilometres of power cabling was also installed.

Split into eight stages, construction of the vast earthen reservoir was first cab off the rank. Shortly after, the scheme’s

bore field was constructed and four separate pipeline builds began. Rounding out the work saw the construction of sidelines and air valves; after which rigorous pressure testing and pumping was undertaken.

The objective was to produce an irrigation scheme that was simple and easy for the client shareholders to operate and maintain. To help achieve this Maungatua Contracting teamed up with South Island firms McNeill’s Pumping and ElectraServe.

Key to success was open and honest lines of communication. Point person was Maungatua Contracting project manager Kane Duncan, who was responsible for overall project delivery. Kane maintained close contact with stakeholders and suppliers throughout, notably Hynds Pipe Systems and Humes for pipe materials supply.

Client spokesperson Simon Maling from Terraces Irrigation says they’re very satisfied with the scheme.

Simon was especially impressed with Maungatua Construction’s professional approach in the face of some unique challenges, including the need for the build to cross farmland at different stages of cropping and for construction to be completed in a limited timeframe during an unusually wet winter.

A key consideration was meticulous planning to minimise disruption to the public. There wasn’t a single instance where the public were unduly affected by construction, says Kane, and local farmers were kept fully informed at all times.

Work needed to happen within a kind of Goldilocks Zone. Unfortunately, because of farmers’ grazing plans it couldn’t happen too early; nor could it happen too late. This put a complete twist on the entire construction project, says Kane.

From May through to August, Maungatua Contracting was unable to cross any farmers’ paddocks while winter feed was being grazed. However, following a meeting with neighbouring farmers and affected property owners, work was programmed to work in with farming activities.

To speed things up, a system that could lay up to 230 metres of pipe each day was adopted. This was based around a group of six workers all with specific tasks and responsibilities. Delegation of duties also sped up progress where excavation was concerned, and Maungatua Contracting smartly modified its excavator for ramming and boring purposes.

Because of the time constraints, Fulton Hogan was subcontracted for seven weeks to install some sections of pipe. This too helped put Maungatua Contracting well ahead of the eight ball.

The build saw Maungatua Contracting flex some considerable innovative muscle. Features that were improvised during the course of the project included having bore service lines able to isolate in the event of power failure.

From a cost saving and resiliency perspective, the reservoir was also designed to be able to pump water at night power rates and have 24 hours’ capacity in the event of a power cut at the river.

The upshot of this fascinating and innovative project is a first-rate irrigation scheme that will see the client shareholders’ land well-watered for years to come. l