'High risk' parts of the Historic Village to close during heavy rain

Parts of the Historic Village will close during and after severe rain because of slip risks.

Tauranga City Council put a Trigger Action Response Plan (Tarp) in place for the Historic Village in February after identifying multiple geotechnical hazard zones.

The Tarp was developed based on a site walkover by geotechnical engineers Engeo and its observations on the ground conditions.

The Historic Village is a 5.5ha site with about 50 buildings and it hosts outdoor events with up to 4000 people.

The Tarp report said the village has moderate to steep escarpments on its northern and eastern boundaries. Its soils are "highly sensitive" and potentially unstable when waterlogged.

The Tarp will be triggered during orange and red rain warnings.

The lack of a Tarp to manage Mauao landslide risks, despite experts recommending this, was a key criticism of the council in a review into the January 22 Mount Maunganui landslide tragedy.

Six holidaymakers died when a landslide hit the Mount Maunganui Beachside Holiday Park after heavy rain and a red warning.

While the campground remains closed, a Tarp has been created for it.

Risk zones

The Historic Village area has been split into three zones – high risk, conditional use and low risk.

The high-risk zone covers areas with steep slopes, evidence of instability, uncontrolled fill, seepage, and/or structural retaining elements showing movement.

The public is banned from these areas.

The conditional use zone may be used during fine weather and stable ground conditions, but will be restricted following heavy or prolonged rainfall.

The low-risk zone may remain open during weather events unless otherwise advised.

The procedure

The Historic Village's management has a list of actions to complete when MetService forecasts an orange or red rainfall event.

These include monitoring forecasts and identifying activities, events and buildings in the high-risk and conditional use zones.

Site management, event organisers and security will be briefed on current zoning and controls.

Signage and cordons will be erected to prevent public access to high-risk areas, and barriers prepared in case cordons need to be extended.

Buildings in the high-risk and conditional-use zones will be closed.

Events in those zones will be cancelled, postponed or relocated during red-level events, and during orange-level events if risks cannot be managed.

Stand-down period

After the rain stops, there will be a minimum stand-down period of five days.

During this time, village management will inspect escarpments, slope toes, drainage outlets, and retaining structures and gabion walls daily for signs of instability.

If no instability signs are observed and fine weather is forecast, the conditional-use zone can reopen after the stand-down.

If instability is observed, the zone will remain cordoned off until a geotechnical professional can confirm it is safe to reopen.

Historic Village manager Blair Graham said the village was surrounded on two sides by slopes and the Tarp would help manage risk and public safety.

He said there had not been any slip-related incidents at the village for many years.

"While activation of the Tarp can be disruptive for some tenants, it has been well supported by those affected to date.

"We work directly with any affected tenants to find alternative spaces where possible so they can continue their business-as-usual activities."

He said other precautionary measures included drainage improvements and installing a weather station.

An earth bund was built next to the village's western boundary to protect the village and 17th Avenue business park from flooding.

In May, 4500 native plants were planted on the slopes, with further planting planned this season.

Businesses

The Incubator Creative Hub director Simone Anderson said she thought the plan was "excellent".

"Having clear procedures in place helps ensure the safety of tenants, visitors, and staff."

The Incubator has been based in Historic Village for 13 years.

Anderson said there had been two flooding events in that time. The village was built on low-lying land and flooding was "a significant concern".

She said the bund had been highly effective in preventing the flooding, which had been a "fairly regular occurrence".

"Our concern about flood damage itself is relatively low. The stability of embankments during extreme weather events remains an important consideration."

Several artists had been affected by building access restrictions since the Tarp was initiated.

Anderson said the Tarp provided reassurance that potential natural hazards were being planned for.

"While some measures may appear cautious, they are entirely understandable when the risk of injury or worse is a factor."

The Kollective general manager Caitriona Anderson said having a clear and precautionary response plan in place was a "sensible approach" given the risks associated with severe rainfall across Tauranga.

She said the Tarp had been activated a handful of times this year.

"In our experience, it has provided a clear and reassuring framework for responding to these situations, with minimal disruption to our operations."