Eyes on big slip as more rain due

City engineers will keep a close eye on the Matua properties affected by a large slip as more rain is expected in the Bay.

"A staff member will visit two to three times a week for the next few weeks," said Paul Baunton, the council's manager of city development. "We will be keeping a watching brief ... we've still got a couple of weeks of intermittent rain."

Slip-face cordons were removed from three of the seven Rewarewa Place properties on Tuesday afternoon, after being inspected by a Geotech engineer. All of the properties were deemed safe "at this point in time", Mr Baunton said.

Three of the property owners had already lodged claims with the Earthquake Commission.

Four homes were left precariously close to the sheer cliff face after the slip about 4am Tuesday uprooted heavy trees and spanned about 40 metres. A slip was also reported in the area two weeks ago.

Council staff inspecting the properties would check for additional erosion and signs of undercutting. Water flowing out of the cliff face was a good sign, as it indicated water pressure in the soil was being released, Mr Baunton said.

"Sometimes it gets blocked by rubbish or vegetation in the slope and builds up. If it's draining there's not a lot of built-up water pressure in the soil. It will stop once the water is no longer there.

"We will also check areas back from the slipface for cracks in the ground. At the moment there are none."

In addition, fences, landscaping kerbs and other garden structures would be monitored for cracking and distress.

Mr Baunton said there was no general rule on how close an existing building could be to the edge of a cliff.

However, under the Building Act, new houses would be built "quite a bit further" back.

"The distance back from a slope relates to what's underneath it," he said.

The upper 4-5m of Tauranga soil was a mix of ashfall materials that was prone to superficial slipping on steep slopes.

The Matua slip was only about 1-2m deep, but looked dramatic because it had gone the full height of the cliff, Mr Baunton said.

It was typical of slips in the Bay resulting from heavy and persistent rainfall.

"It's an aspect of life for the geology of Tauranga."

People living near cliffs could protect their properties by making sure stormwater did not run directly over the edge.

"Keep surface water off them. That's the best they can do," Mr Baunton advised.

Water could be channelled into the stormwater system or piped clear of the cliff edge, on the advice of an engineer, he said.

If people thought there was immediate risk they should contact the council.

"We can come and have a look and assess it. We put public safety first."

A severe thunderstorm outlook for the Bay of Plenty was yesterday issued by the MetService, warning of heavy rainfall of 15mm to 25mm/h, small hail, wind gusts of 90km/h and possibly small tornadoes.

Spokesman Dan Corbett said the weather would slowly settle and dry out today through to Saturday.

Meanwhile, State Highway 29 through the Kaimai Ranges will open for night travellers at 6pm on Saturday.

The New Zealand Transport Agency closed SH29 at Ruahihi Bluffs on Sunday to remove overhanging rocks and to assess the stability of the bluffs.

Bay of Plenty state highway manager Brett Gliddon said while the section of road would remain closed during the day, measures would be put in place so drivers were able to use it safely outside those hours.

The road would be open to one lane, with an earth bund in place to protect road users from rock falls while more permanent works to stabilise the bluff were completed.

It would be closed between 7am and 6pm on Saturday and Sunday, during which time a detour would be in place via Poripori Rd.

"It is not ideal to have a busy state highway such as this one closed for this length of time and we appreciate that this will cause some travellers inconvenience. However, this is essential work to protect road users from further possible rock falls and it does need to be undertaken immediately," Mr Gliddon said.

Before starting their journeys people should check with the NZTA's freephone 0800 4 HIGHWAYS or 0800 444449, or its website www.highwayinfo.govt.nz, he advised.