Canal upgrades complete

The excavation of the new canals showing the placement of new concrete drop structures.

The excavation of the new canals showing the placement of new concrete drop structures.

The large scale upgrade of the Ngāi Tahu Farming water canals at Te Whenua Hou has been completed and with water flow now tripled, Ngāi Tahu Farming now has the capability to supply peak flow water demand to over 5,800 hectares of irrigated farm land.

Glen Clayton, General Manager Farm Development says timing for the redevelopment was crucial so the project was split into two stages, beginning in May-June 2015.

“We always knew there would be a need to upgrade the canals, it was just a matter of timing it correctly to fit with our development,” he says.
“We wanted to avoid the worst of the winter weather but we also had to have the job completed by late September to fit in with our irrigation season. That was the biggest challenge.”

From the beginning of the development, water sourced from the Waimakariri River at the Browns Rock intake was gravity-fed to the farms via Waimakariri Irrigation Limited’s infrastructure.

“Ngāi Tahu had an agreement with Waimakariri Irrigation Limited to convey our water through their infrastructure but we always knew that their infrastructure didn’t have the capacity to carry all the water we would need for the total farm development,” says Glen.

“Prior to the upgrade, our existing canals provided a maximum flow rate of 1.5 cubic metres of water; we needed approximately 4 cubic metres.

The completed canal upgrade.

The completed canal upgrade.

The Farming team carried out in-depth investigations with surveyors, designers and engineers before going ahead with the upgrade of over 30 kilometres of new and of existing canals. They considered piping versus an open race system of delivery but after modelling cost of life analysis, they established that the open race system was a far more cost effective approach.

Ngāi Tahu Farmings’ own contracting team excavated the existing canals, working to the approved design, before compacting the earth to stop the leaching of water from the canal system. Thirty engineered, reinforced concrete drop structures were then installed in the system. These slow water flow and encourage it to move across the top of each drop structure while the water at the base remains relatively calm.

Glen Clayton is happy the canal upgrade has been completed on schedule and a reliable water supply for the farms has been secured.

“Breaking the upgrade into two stages proved to be a good decision. We learned a lot in the first stage so we knew what lay ahead for us in stage two,” he says.

The upgraded canal system now distributes all Ngāi Tahu Farming’s water requirements to on-farm storage ponds; from here the water is applied to each farm via centre pivot irrigators.

The completion of this project ensures that peak demand water flow can now be maintained in the canal. This, along with on-farm water storage, ensures greater irrigation and pasture efficiency, by de-risking the business against dry spells.

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