Work on flood control scheme to halt for winter

A109 Light Utility Helicopter flight with mayor Gisborne City from the air in November 2023.

WORK on the multi-million dollar Waipaoa River Flood Control Scheme upgrade is expected to stop for the winter this week, Gisborne District Council was told at its May meeting yesterday.

Council lifelines director David Wilson was speaking as councillors adopted a policy for removable pipelines over the stopbanks to the river.

Mr Wilson said the contractor had good weather through the start of May but that was ending, and ground conditions were getting a bit wet.

He understood the contractors were finishing this week and the site would be closed over winter.

They would start again in October.

Contractors were going well and the council was happy with the progress so far.

At the meeting, the council was considering a report from asset engineer Nick Gordon about the risk of physical failure of the council’s flood control schemes from private pipelines that crossed over or under stopbanks.

It was told there were 13 known pipelines intersecting the Waipaoa River Flood Control Scheme and seven horticultural properties interested in installing a private pipeline.

It was estimated that with full allocation of the surface water resource, the number could reach 40.

A pipeline through a stopbank increased the risk of a breach by creating a pathway which water might travel through, the report said.

This could cause erosion from within the land mass, called piping, which could result in a catastrophic collapse of the stopbank.

Piping erosion along a pipeline occurred in Cyclone Bola in 1988. A catastrophic failure was narrowly averted with significant emergency sandbanking.

The council adopted a recommendation that it approve the use of a suitably pressure- related removable pipeline over stopbanks as the required solution to take water for irrigation from within the council’s flood control schemes.

In reply to a question from Shannon Dowsing, Mr Wilson said the council would usually get two or three days notice of a heavy weather event and it would be a part of the consent that pipes would be removed.

In most events they would stay in place. They would only be removed for a heavy event.

Larry Foster said the council was trying to promote a cycleway on the stopbank and asked how the pipes would affect that.

Mr Wilson said the pipes lay flat when not in use.

“You’re talking about a speed bump if you rode over them,” he said.