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Otira Gorge, on the West Coast side of Arthur's Pass, was closed earlier this month after slip material spilled over the rock shelter and onto State Highway 73.
Waka Kotahi said high-pressure sluicing is needed to clear the built-up material on the shelter roof.
Its spokesperson, Moira Whinham, said the gorge will be closed between 10 in the morning and 3 in the afternoon, from tomorrow until Friday.
She said the route will still be open outside those hours, and an alternative is the Lewis Pass.
When the initial damage occurred, Waka Kotahi used a helicopter to sluice loose stone from the slopes but a lot of rock continued to come down posing a threat.
Heavy rain at the time also made the job more challenging.
Scree and boulders from the steep slope above the shelter continued to fall with the rain, blocking the lower end of the road, Waka Kotahi said.