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Unsteady ground . . . A landslip above the Cromwell-Clyde Rd was cause for concern on Tuesday. PHOTO: SIMON HENDERSON

A landslip at Deadman’s Point above the Cromwell Bridge on Tuesday is causing ongoing delays on the Cromwell-Clyde Rd.

SH8 was reduced to a single lane for about 100m in both directions from the junction with SH8B, and drivers were directed to move swiftly but steadily under the landslip.

NZ Transport agency maintenance contract manager Mark Stewart said the slip was around 30m above the highway.

It was estimated at about 30m top to bottom, 20m wide and 15m deep, he said.

Police were advised of the slip at 9.54am on Tuesday as it was seen moving relatively slowly but steadily.

Helicopters were called to the site with monsoon buckets to sluice the slip, but were hampered for some time due to fog.

Once it was safe to start more than 150,000 litres of water was used to flush the slip.

Mr Stewart said crew and two helicopters were used to flush the earth, schist and vegetation.

‘‘They [the helicopters] use that water to drop on to the unstable slope . . .the weight of the water and the movement of the water washes down all the loose material up there.’’

He described it as a ‘‘substantial’’ slip which was capable of causing significant damage.

‘‘I have calculated approximately 150,000 litres of water have been put on the slope.’’

Mr Stewart said road user safety was the ‘‘primary concern’’.

‘‘If we were not able to get up there to do the sluicing because of fog — we would have closed the road.

‘‘Rocks and small amounts of material were continuing to fall. That sluicing brings down all that material that is likely to fall into the line of traffic.’’

Helicopter crews resumed sluicing work yesterday, starting at 9.30am, and work progressed throughout the day.

The sluicing work was likely to continue for several days ‘‘at least until we are sure the hillside is again stable’’, Mr Stewart said.

‘‘The highway is likely to remain at single lane while this work is under way and we thank all road users for building in the extra time and being patient.”

Traffic would be stopped for up to 30 minutes and controlled by stop-go and manual traffic management while work to loosen the schist rock was under way, so Mr Stewart advised people to plan their trips to include delays.