Work on Anzac Cliffs for flood protection

David Unwin/

Update on the progress at Anzac Cliffs, as heavy machinery works to divert the Manawatu river back to its 1992 realignment.

Crews working to create a new bank and hill foundation on the Anzac Cliffs side of the Manawatu River are making use of every hour of daylight to complete the Palmerston North flood protection project before winter.

The $3.4 million river realignment project is running behind schedule, but Horizons Regional Council project engineer Derek McKee is optimistic the work will be done before river levels are expected to rise around the end of May.

The project returns the river close to its 1992 course, away from the base of the cliffs, protecting the city-side stopbanks from the angle of the flow.

Once work at the base of the cliffs has been completed, the cliffs will be reshaped into a hill.

That part of the project would not start until next summer, and would resolve the problem of erosion that has been sending about 20,000 cubic metres of soil tumbling into the river each year.

There have been ongoing cliff falls even with the river diverted away from the base.

Reshaping the cliffs into a hill will also make the land at the top safe for subdivision and building, and for public access.

So far this summer the river has been diverted closer to the city stopbank, and more than half of the 28,200 tonnes of rock has been carried across the ford that is a critical link to the worksite.

McKee said low river flows had created ideal conditions for working in the dry on the cliff side of the flow, stopping sediment loss from the site.

More than 660 holes had been drilled and filled to overcome liquefaction risks, the rocks have been placed for more than half of the 460-metre long new bank, and shingle from the former city-side beach is being shifted and compacted to form the base behind the rock wall.

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McKee said the key challenge for the project now would be rising river levels. Although the site could be quickly protected to withstand a flood, it would be a problem if the river level remained too high for trucks and machinery to get across to the site.

There was a contingency plan to stop the rock wall rather than extend it the full length of the downstream design if contractors ran out of time.

The realignment is the last major part of the eight-year City Reach project designed to protect the city from a one-in-500-year flood.

The remaining works for next year are on the Mangaone Stream at the Flygers Line spillway, at Palmerston North Airport and Benmore Ave.

 - Manawatu Standard

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